....
p
Laboratory experiments on the
~ effects of Ocean Dumping on benthic
in vertebrates .
I. Otoice tests with solid wastes.
,
.. ,
LIBRARY
DEF'l'. OF THE RNVIRON.U!N1
FISHRkm·· :;El< VieR
NFLD.
ST. JOHN'S -
[by B. D. Chang and C. D. Levings
FISHERIES AND MARINE SERVICE
SERVICE DES PECHES ET DES SCIENCES DE LA MER
TECHNICAL REPORT No.
RAPPORT TECHNIQUE N°
1976
.
637
1+
Environment
Canada
Enviro nnement
Canada
Fisheries
and Marine
Service
Service des peches
et des sciences
de la mer
Technical Reports
Technical Reports are research documents that are of sufficient importance to
be preserved, but which for some reason are not appropriate for primary scientific
publication. Inquiries concerning any particular Report should be directed to the
issuing establishment.
Rapports Techniques
Les rapports techniques sont des documents de recherche qui revetent une assez
grande importance pour etre conserves mais qui, pour une raison ou pour une autre,
ne conviennent pas a une publication scientifique prioritaire. Pour toute demande
de renseignements concernant un rapport particulier, il faut s'adresser au service
responsable.
Department of the Environment
Ministere de l'Environnement
Fisheries and Marine Service
Service des Peches et des Scienes de la mer
Research and Development Directorate
Direction du Recherche et
D~veloppement
RAPPORT TECHNIQUE NO. 637
TECHNICAL REPORT No. 637
(Les
(Numbers 1-456 in this series
num~ros
1-456 dans cette
s~riesfurent
were issued as Technical Reports
utilises comme Rapports Techniques de 1 'office
of the Fisheries Research Board of
des recherches sur les pecheries du Canada.
Canada.
The series name was changed
Le nom de la
with report number 457).
s~rie
fut
chang~
avec le
rapport numero 457)
Laboratory Experiments on the Effects of Ocean Dumping
on Benthic Invertebrates.
I. Choice Tests.with Solid Wastes
by
B.D. Chang and C.D. Levings
This is the twenty-third
Ceci est 1e vingt-troisieme
Technical Report from ,the
Rapport Technique de 1a Direction du
Research and Development Directorate
Pacific Environment Institute
Recherche et Developpement
Institut de 1 'environnement du Pacifique
West Vancouver, B.C.
Vancouver-Quest
1976
ii
TABLE OF CONTENTS
Page
Introduction
1
General Methods and Statistical Analyses ............ ....
2
Experimenta 1 Animals ....................................
3
Experime r,}.t al Substrates.................................
5
Substrate Preference Experiments ........................
7
Brisaster latifrons
7
Cancer magister
9
Chionocectes bairdi
11
Chiridota laevis
Corophium salmonis
14
16
Crangon alaskensis
Hemigrapsus oregonensis
18
Macoma inconspicua
21
23
Munida quadrispina
26
Pandalus danae
27
....... .....................
General Discussion ......................................
28
Conclusions
37
References
38
Tables
45
Figures
55
iii
LIST OF TABLES
Table 1.
Page
Burrow locations for Cancer magister· (Dungeness
crab) after twenty-four hours exposure to
experimental substrates:
Table 2.
45
Burrow locations for Chionoecetes bairdi ("tanner"
crab) after twenty-four hours exposure to
experimental substrates.
Table 3.
46
Burrow locations for Chiridota laevis (burrowing sea cucumber) after three days exposure to
experimental substrates.
Table 4.
47
Burrow locations for Corophiwn salmonis (amphipod)
after twenty-four hours exposure to expetimental
substrates.
Table 5.
Burrow locations for Crangon alaskensis (brown
shrimp) in preliminary mud vs sand preference tests.
Table 6.
49
Burrow locations for Crangon alaskensis (brown shrimp)
exposed to mud and sand substrates for up to five days.
Table 7.
48
49
Burrow locations for Crangon alaskensis (brown shrimp)
exposed to various experimental substrates for
twenty-four hours.
Table 8.
50
Burrow locations for Hemigrapsus oregonensis (hairy
shore crab) exposed to experimental substrates for
twenty-four hours.
Table 9.
51
Burrow locations for Macoma inconspicua (small clam)
exposed to experimental substrates for twentyfour hours.
52
iv
Table 10.
Locations of Munida quadrispina ("squat" lobster)
when exposed to experimental substrates.
Table 11.
53
Locations of PandaZus danae (coon strip shrimp)
when exposed to experimental substrates.
54
v
LIST OF FIGURES
Figure 1.
Brisaster latifrons (A. Agassiz) (Heart urchin).
Dorsal
Figure 2.
Page
view ~
Chiridota laevis (Fabr.)
Length 5 cm.
55
Length 3 cm.
(burrowing sea cucumber).
The animal is extended, with tentacles
55
visible at right.
Figure 3.
Munida quadrispina Benedict.
Dorsal view.
Figure 4.
Chionoecetes bairdi
57
Rathbun ("tanner" crab).
Carapace width 1.7 cm (immature specimen).
57
Body length 7.5 cm.
58
Hemigrapsus oregonensis (Dana). (hairy shore crab).
Dorsal view.
Figure 9.
Dorsal
Crangon alaskensis Lockington (brown shrimp).
Dorsal view.
Figure 8.
56
Carapace width 16 cm.
Dorsal vie\fJ.
Figure 7.
56
Body length 9 cm.
Cancer magister Dana (Dungeness crab).
view.
Figure 6.
Body length 2.5 cm.
PandaZus danae Stimpson (coon stripe shrimp).
Dorsal view.
Figure 5.
("squat lobster").
Carapace width 1.7 cm.
58
Macoma inconspicua (Broderip and Sowerby) (small
clam).
Shell length 1.2 cm.
Figure 10. Sand used in preference experiments.
59
60
Figure 11. Rocks used in experiments in small containers
(tests with C. bairdi and H. oregonensis)
Figure 12. Wood chips used in preference experiments.
60
61
Figure 13. Wood debris forming cover with few gaps used
in preference experiments.
61
Figure 14. Wood debris loosely arranged used in preference
experiments.
62
vi
Figure 15.
Sediment from Ocean Falls (Cousins Inlet)
62
used in preference experiments.
Figure 16.
Experimental apparatus used in preference tests
with B.
latifrons~
P. danae.
c.
laevis~
M. quadrispina and
A and B are two substrate types.
same tanks were used for c.
magister~
The
but with the
tank divided into right and left halves. with one
substrate type in each half.
Figure 17.
63
Experimental apparatus used in preference tests
with C. bairdi.
A and B are two substrate types.
The same set-up. without the partition. was used
for C. aZaskensis and H. oregonensis.
Figure 18.
Experimental apparatus used in preference tests
with C. saZmonis.
A and B are two substrate
types. (1 cm deep).
Figure 19.
63
64
Experimental apparatus used in preference tests
with M. conspicua.
types.
A and B are two substrate
65
viii
ABSTRACT
Chang,B,D. and C.D. Levings.
1976.
Laboratory experiments on the effects of
Ocean Dumping on benthic invertebrates.
wastes.
I.
Choice tests with solid
Fish. Mar. Servo Res. Dev. Tech. Rep. 637: 74 pp.
One of the important effects of ocean dumping is to change the physicochemical nature of substrates, and the effects of such changes on some benthic
invertebrates were examined in laboratory 2-choice preference tests.
lowing species were tested:
the heart urchin Brisaster
ing sea cucumber Chiridota
Zaevis~
the IIsquat lobster Munida
quadrispina~
ll
Zatifrons~
the Dungeness crab Hemigrapsus
The fol-
the burroworegonensis~
the shrimps PandaZus danae and Crangon
aZaskensis, the bivalve Macoma inconspicua, and the amphipod Copophium saZmonis.
The substrates tested represented natural substrates and substrates altered by
dumping of solid wastes, and included the following: mud, sand, rocks, wood
chips, wood debris, and polluted sediments from near pulp mills.
The unnatural
substrates were usually less preferred by burrowing animals, although in some
cases no preferences were shown between artificial and natural substrates.
Mobile epifauna were attracted toward hard surfaces (wood debris, rocks).
Be-
cause of the preferences and field distributions, the results of the study
indicated that large changes in the nature of a substrate as a result of dumping will affect the abundance and species composition of benthic communities.
ix
"
.;
RESUME
Chang, B.D. and C.D. Levings.
1976.
Laboratory experiments on the effects
of Ocean Dumping on benthic invertebrates.
wastes.
I.
Choice tests with solid
Fish. Mar. Servo Res. Dev. Tech. Rep. 637:
74 pp.
L'un des effets notables de 1 immersion de dechets en mer est de modifier
I
la nature physico-chimique des substrats.
Ce sont les
r~percussions
de ces
changements sur certaines especes d'invertebres benthlques qui ont ~te
a 1 'aide
examinees en laboratoire
deux types de substrats.
cordiforme Brisaster
d'epreuves ou on les mettait en presence de
Les especes suivantes furent
latifrons~
~tudiees:
1 'holothurie fouisseuse Chiridota
l'oursin
laevis~
le crabe stercoraire Cancer magister, le crabe Chionoecetes bairdi, le crabe
commun Hemigrapsus
oregonensis~
Pandalus danae et Crangon
le homard Munida
alaskensis~
l'amphipode Corophium salmonis.
quadrispina~
les crevettes
le bivalve Macoma inconspicua et
Les substrats etaient soit naturels, soit
modifies par les dechets et comprenaient de la boue, du sable, des pierres,
des
~clats
de bois, des
des moulins de pate
d~chets
a papier.
de bois et des
s~diments
pol lues provenant
Les substrats artificiels ont habituellement
ete evites par les fouisseurs, bien que dans certains cas, ils n'aient montre
aucune preference entre les uns et les autres.
L'~pifaune itin~rante ~tait
attiree par les depots solides (debris de bois, pierres).
pr§f~rences
Compte tenu des
et de la distribution naturelle des especes, les
r~sultats d~-
montrent que des changements importants dans la nature des substrats,
a la
suite des decharges, influera sur 1 'abondance et la composition des especes
des communautes benthiques.
INTRODUCTION
The purpose of this report is to assess, based on data obtained in
laboratory experiments, the effects on benthic animals of bottom substrate
changes resulting from ocean dumping.
Due to increased growth and consumption
in today's world, there has been and will be increased demand for the use of
t he ocean s f or waste disposal (Gross 1971; Andreluinas and Hard 1972; Reed
1975 ) .
At the same time, there has been increased awareness of the pollution
probl ems res ul t i ng from the uncontrolled ocean dumping of the past.
r esult of these
proble~s,
As a
many countries signed, in 1972, the London Conven-
t ion on the Prevention of Marine Pollution by Dumping of Wastes and other
ma tter under which the participants agreed to regulate ocean dumping.
In
Cana da, ocean dumping is now regulated through a permit system under the
Ocean Dumping Control Act (see Fisheries and Marine Service 1975).
One of the major effects of ocean dumping is to change the nature of
the bottom substrate.
Changes in the substrate will affect most directly
the benthic fauna, and it has been found in many field studies that particular
benthic species are associated with particular substrate types (e.g . Sanders
1958; McNu l t y et al . 1962; Johnson 1971).
The effects of changes in the bot-
tom su bstrate on benthos can be determined from in situ observations before
and after dumpi ng , or by comparing the benthos in the dump site with that of
simi l ar areas where no dumping has occurred (e.g. Wash. State Enforcement
Pro j. 1967; Flemer et al. 1968; Pac. NW Poll. Control Council 1971; Bacescu
1972; Pearson 1972; Pearce 1972; Leathem et a l. 1973; May 1973; McDaniel 1973;
Pea se 1974).
However, such data are only available after dumping has occurred.
In order to predict effects of dumping before it occurs, experiments must be
performed.
In some instances, experiments may be done
laboratory experiments are necessary.
~
.?itu, but usually
2
Laboratory preference tests are of value in assessing effects of habitat
changes.
Animals show preferences for certain habitats when given a choice
(see reviews by Meadows and Campbell 1972a; Bacescu 1972; Gray 1974).
These
preferences are likely to be associated with the survival potential of the
different habitats tested (Meadows and Campbell 1972a, b; Gannon and Beeton
1971) .
In this study, animals were given a choice of two substrates, one representing a natural substrate and one a substrate altered by dumping.
The
tests examined mainly the effects of physical alteration of the substrate.
The materials tested represented substrates with different particle sizes.
individual particle densities, stabilities, and hardnesses.
strate (Port Mellon sediment) was also tested.
duration and done with single species.
One toxic sub-
All experiments were of short
Biological effects such as changes
in the abundance and types of food organisms, competitors, and predators
resulting from substrate changes were not examined.
GENERAL METHODS AND STATISTICAL ANALYSES
All experiments were done at the Pacific Environment Institute, West
Vancouver, British Columbia, between December 1975 and March 1976.
Sea-
water was taken from an unfiltered open system drawing water from a depth of
60 ft (19 m) below lower low tide.
The temperature in the system ranged
from 8-l0°C and the salinity from 27-29%0.
water~essels
placed in running seawater
was usually 1-2°C higher.
In experiments done in static
table~.
the seawater in the vessels
Lower salinities for some experiments were obtained
by dilution of seawater with well water.
Lighting conditions were not strictly controlled.
lights were on from ca. 0800-1800 daily.
tween 0900 and 1200 hours.
Room fluorescent
All experiments were started be-
Daytime observations were made for up to five hours
3
after the start of tests, and for up to four hours before the end of tests.
No night observations were made.
Preferences were determined in a series of single species 2-choice
tests.
For burrowing animals, the numbers burrowed in each of the two sub-
strates at the end of each test were compared using the x2 -test (df=l) for
n> 25 and the binomial test for n
<
25 (Larkin 1974), with 0.:=0.05.
Animals
burrowed at the boundary between substrates and non-burrowed animals were not
included.
For non-burrowing animals, observations were made for each animal at 21,
22, 23 and24 hours after the start of tests.
All observations for all
animals were totalled, and the number of observations for each of the two
substrates were compared using the x2 -test as above.
Observations of animals
at the boundary between substrates were not included.
Results of statistical tests were
'.
l-tailed in favour of the substrate
most characteristic of the natural habitat of the species, as determined from
field observations and literature data.
Results were 2-tailed when the test
species was one commonly observed in the field on both of the substrates
tested.
EXPERIMENTAL ANIMALS
Ten species of benthic invertebrates were tested.
The choice of species
was partly determined by the availability of the species and the feasibility
of maintaining them in the laboratory.
The species were chosen to represent
the effects of dumping at various depths and were collected locally in
the Strait of Georgia.
The heart urchin BrisQster
ZQtifrons~
(A. Agassiz)(Fig. 1), the sea cucumber Chiridota Zaevis (Fabr. )(Fig. 2)
the squat lobster Munida quadrispina Benedict (Fig. 3) were the deepest-
and
4
living species.
They were collected by sieving mud taken by an epibenthic
sled at approximately 80 - 200 m depth in Howe Sound (Queen Charlotte Channel)
on 9 - 10 February 1976 (CSS PARIZEAU).
coon-stripe shrimp
Some Munida quadrispina and some
PandaZus danae Stimpson (Fig. 4) were collected by a
shrimp trawl at approximately 70 m depth near Point Atkinson, on 24 February
1976.
Several species were collected by otter trawling at 20-25 m depth
along the mud bottom of English Bay, on 22 December 1975 and 15 January 1976
(R/V ACTIVE LASS): the Dungeness (or Pacific edible) crab Cancer magister
Dana (Fig. 5); the "tanner crab" Chionoecetes bairdi Rathbun (Fig. 6); and
the shrimps Crangon aZaskensis Lockington (Fig. 7) and PandaZus danae
Stimpson.
The intertidal species used were: the amphipod Corophium saZmonis
Stimpson, collected from mud in the Squamish River estuary on 22 January 1976;
the hairy or yellow shore crab Hemigrapsus oregonensis (Dana)(Fig. 8), collected from under rocks lying on the mud-sand substrate at Figurehead Point,
Stanly Park, Vancouver, on 28 January 1976; and the small clam Macoma inconspicua (Broderip and Sowerby) (Fig. 9), collected from the Roberts Bank mud-
flats (Fraser River estuary) on 19 December 1975 and 13 January 1976.
These species also represented different lifestyles:
BY'1:saster ~, Chiridota~
and Macoma remain buried in soft substrates most of their lives;
Chionoecetes~
Crangon~
Cancer~
and Hemigrapsus bury themselves and also move about on
the substrate surface; Corophium builds tube-burrows in soft substrates and
also moves about on the substrate surface; Munida and PandaZus do not burrow
in soft substrates.
All species except Corophium were maintained in the laboratory in running seawater (8-10°C, 25 0/00). Corophium was maintained in aerated static
water cultures (10°C, 10o/00). The species taken from deep water in Howe
Sound were kept in a refrigerated (5°C) seawater tank on board ship before
they were transferred to the laboratory.
Many (>50%) of the Brisaster and
5
Chiridota were dead within a few days of being brought into the laboratory as
a result of the collecting operation and/or the transfer to laboratory conditions.
Mortality in other species appeared to be low «10%).
EXPERIMENTAL SUBSTRATES
1.
English Bay Mud
Gr ab samples of the top 15-20 cm of substrate were taken from 20-25 m
depth in English Bay (outer Burrard Inlet; 49°18'; 123°11 ') on 22 December
1975 and 15 Janu ary 1976 .
2.
Median grain size: 62 wm
~evings,
1973; stn. SB15).
Robe r ts Bank Mud
Samples of the top 10 -15 cm of mud were taken intertidaT1y from Roberts
Bank on 19 December 1975 and 13 January 1976, near Stn. FRAPER 20 of Levings
and Cous t alin (1975) (49° 3.3'; 123°8.6').
3.
Median grain size: 20 wm.
Howe Sound Mud
Samples wer e taken by an epibenthic sled at approximately 100-200 m
depth in Howe Sou nd (Queen Charlotte Channel; app. 49°48 ' ; 123°16') on 9-10
February 1976.
4.
Median grain size : <62 wm(Stewart, 1974).
Sq uamish Est uary Mud
Samples were taken intertida11y from mudflats in the Squamish estuary,
(Western sector; 49°41'; 123°10') on January 22 1976.
wm (Bell, 1975; unpublished data).
Median grain size: <62
The top few cm were of fairly loose
consistency, with high water content; below this, the sediment was very compacted (hard to penetrate) and firm.
5.
Sand
Sand was collected intertidal1y from between the lona Island and Fraser
River North Arm jetties (app. 49°13.1'; 123°12 .8') on 23 December 1975 and
17 January 1976.
This sand originates from the North Arm, and was pumped to
6
this sector using suction dredging (Mathews and Murray 1966).
cm was taken.
The top 5 - 10
Median grain size: ca. 400 wm (own data; Fig. 10).
The sand
formed a very stable substrate.
6.
Rocks
Rocks 3 - 10 cm diamter (Fig. 11) were used in tests done in small con-
tainers (Cktonoecetes and HemigY'apsus).
Larger rocks (15 - 20 cm across)
were used in tests done in larger tanks (Munida and Pandalus).
The rocks
were collected intertidally in front of the Pacific Environment Institute
on various dates in February 1976.
In the preference tests, the rocks
were loosely arranged, with small gaps between rocks (as in Fig. 11), and
placed on mud or sand.
7.
Wood chips
Fresh wood chips were collected from the beach at Iona Island on 23
December 1976 and 17 January 1976.
X 1 - 2 mm (Fig. 12).
Individual chips were ca. 5 - 10 X 2 - 5
They were soaked in seawater before use in tests.
Wood chips formed a highly porous, unstable (easily disrupted) substrate.
8.
Wood Debris
Weathered wood debris was collected from the beach at Iona Island on
23 December 1975 and 17 January 1976.
1 - 4 X 1 - 2 cm.
Individual pieces were
~.
51- 10 X
Wood debris was soaked in seawater before use in tests.
In tests with Corophium and Macoma, pieces were laid flat on the substrate,
close together, so that there were few gaps in the wood debris cover (Fig.
13).
In other tests, the wood debris formed a loosely arranged layer (2 - 4
cm. thick) of overlapping pieces (Fig. 14).
9.
Ocean Falls Sediment
Samples were collected from
~
70 m depth near Ocean Falls, B.C. (52
0
7
21.0 1 ; 127°41.6 1 ) on 20 June 1972 and stored frozen.
The
sedi~~nt
of blackish oblong pellet-shaped particles, mostly 500-1000
~m
diameter (Fig. 15)0
~m
was composed
long x 200-400
These pellets appeared to be entirely organic matter,
probably wood fibre material; the sediment was from near a pulp mill.
sediment was not toxic to animals and there was no odor of H2S.
This
The pellets
were light in density and formed an extremely unstable (easily disturbed) substrate.
10.
Port Mellon Sediment
Grab samples were taken (RjV ACTIVE LASS) at approximately 10 m depth
near the pulp mill effluent outfall at Port Mellon (49°31
Sound) on 22 December 1975.
1 ;
123°30
1 ;
Howe
The sediment was composed of fine fibrous mat-
erial mixed with silt and some small pieces of wood.
The color was dark grey
to black, and there was a strong odor of H2S. . The sediment had a high water
content and formed a muddy substrate that was held together to some extent
by the fibrous material.
When the water was aerated, the top few mm of the
sediment became a greyish color, but the sediment below remained black .
In
aerated vessels, a white bacterial or fungal growth developed on the surface
of the sediment if left undisturbed for a few days .
SUBSTRATE PREFERENCE EXPERIMENTS
1.
Erisas ter Zatifrons (A. Agassiz) (heart urchin)
a.
Methods
Specimens were 2-4 cm in length.
The animals were tested in oval fibre-
glass tanks, divided into four compartments without partitions.
ment of the two substrate types is shown in Figure 16.
The arrange-
Seawater (10 C, 25 0/00)
flowed slowly into the tank and left via the central drainpipe.
Animals were introduced along the boundary between the two substrate
9
due to the unnatural laboratory conditions.
Some .animals on the substrate
surface were observed to probe the stirface with their dorsal tube feet.
This
is probably a feeding mechanism (see Hyman 1955; Buchanan 1966).
Of the seventeen surviving animals. fourteen chose mud and three chose
sand (p = .006; 1 - tail).
Of the fourteen that chose mud, three were com-
pletely burrowed, eight were partially burrowed, and three were not burrowed;
none of the three on sand were bur rowed.
A su i table substrate for this species must allow burrowing, provide a
source of nutrition, and must allow communication with overlying waters.
The spines used in burrowing may not be able to move the large sand grains
easily. The mucous secretions may be less able to hold together burrow walls
made of sand than of mud.
Sand may also provide less nutrition.
The preference of mud agrees with field observations off the Washington
coast, where
B.
l atifr ons was common in most muddy areas in deep water, but
was uncommon in deepwater stations where the sand or gravel content was high.
and in sandy bottoms at intermediate and shallow depths (Lie and Kisker 1970).
In conclusion, a change in the top few cm of substrate from mud to sand
will be detrimental for this species, as will covering the substrate with any
impenetrable material.
2.
Cancer magister Dana (Dungeness crab).
a.
Methods
Specimens had carapace widths of 12 - 60 cm.
The experimental tank was
as described for BY'i sas ter (see Figure 16), except that it was divided in
half along its length (without a partition).
The left half received approxi-
mately 10 cm depth of one substrate type and the right half the same depth
of the other substrate.
One crab was introduced at the boundary between the substrates.
Upon
10
introduction, the crab became extremely active, and stirred up the sediments,
which clouded the water (especially when mud was tested).
This made observa-
tions of the crab's position impossible until the crab had been settled for
about one hour.
Experiments were terminated after twenty-four hours.
The two-choice tests compared English Bay mud with sand, wood chips,
and wood debris.
Some tests with wood debris on top of mud and sand were
also attempted.
b.
Results and Di scuss i on
The crabs were extremely active upon introduction, moving around the
edge of the tank several times before burrowing.
In addition to clouding
the water, this activity resulted in a thin (up to 1 cm) layer of mud covering
both substrates in tests with mud.
Despite this, the crabs showed definite
preferences; the two substrates remained distinct below this surface layer.
When burrowing,the chelipeds pushed substrate forward from below the
body, the legs pushed substrate off to the sides and back, and the carapace
was moved backwards and down under the surface (see McKay 1942).
When com-
pletely burrowed, only the eyes, antennae, and part of the anterior edge of
the carapace remained above the substrate for sensing and to allow oxygenated
water to reach the gills.
Complete burrowing in mud or sand could be accom-
plished in less than a minute.
Crabs remained stationary when burrowed.
They
could leave burrows and crawl on the substrate surface.
During daytime observations, crabs were burrowed most of the time, but
usually did not accupy one burrow for the entire period.
Burrows were inhab-
ited for from a few minutes to six hours or more; most were occupied one hour
or more.
strate.
All crabs changed positions overnight, sometimes to the other sub-
11
The substrate preferences at twenty-four hours are shown in Table 1.
Since c. magister burrows just below the substrate surface, only the top 10 15 cm of substrate are important for this species.
Sand was preferred over
mud, probably because sand formed a more firm substrate (Gray, 1974), sand
could be easily burrowed into by these large crabs, and burrowing activity
caused less turbidity i n sand than in mud.
Wood chips could be burrowed into
but were less preferred than mud, probably because of the larger particle
size and the instability of the wood chip substrate.
It was noticed when
removing burrowed crabs, that it was most difficult to remove crabs from
sand, easier from mud, and easiest from wood chips.
One crab was able to form
a depression in the wood debris, where it remained for at least one hour, but
after twenty four hours it was burrowed in mud.
When tested with wood debris
on mud or sand, the crabs scattered the wood debris over both sides of the
tank, making preferences impossible to determine.
The preferences agree with field observations.
c.
magister is reported
mostly in sand, frequently in mud, and usually not in rocky areas
1942, 1943;
~1cDanie1
1973).
(McKay
They are also sometimes found under the cover
of seaweeds, boards, and sheets of metal that they have crawled under
(Mc Kay 1943).
In conclusion, changing of the top ten cm or more of the substrate from
mud to sand could improve the habitat for this species, while changing from
mud to wood chips, wood debris, or rocky substrates would be detrimental.
Just a few cm thickness, or scattered covering of easily moved materials
should no t be detrimental.
3.
Chionocectes bairdi Rathbun ("Tanner" crab)
a.
Methods
Specimens were immature; carapace widths were 1 - 3 cm.
The experimental
12
vessels were rectangular plastic dishpans placed in a running seawater table.
The dishpans were divided into two equal chambers by a partition across its
width and each chamber was divided without partitions into two equal compartments, one for each substrate, as shown in Figure 17.
dishpans was 12°C, 25 0 /00.
The seawater in the
Vessels were aerated in tests with Port Mellon
sediment.
One crab was introduced at the boundary between the substrates in each
chamber.
Single crabs were used because preliminary experiments indicated
that aggression affected burrowing behavior and preferences when there was more
than one crab per chamber.
Tests were terminated after twenty-four hours.
The twa choice tests compared English Bay mud with: sand, rocks (3 - 10 cm
diameter) on mud; wood chips; a 1 - 5 mm layer of wood chips on mud; wood debris; Ocean Falls sediment; and Port Mellon sediment.
b.
Results and Discussion
C. bairdi stayed burrowed in the substrate during most of the daytime.
They did not move when burrowed, but left the substrate to change position.
When burrowing, the legs were spread out and anchored on the substrate.
ment below the body was pushed forward by the che1ipeds.
Sedi-
The body was then
moved backwards and downwards into the substrate in a few back-and-forth
movements (the carapace is inclined slightly toward the anterior).
ing legs were then moved below the surface.
The walk-
Burrowing could be accomplished
in less than ten seconds in mud.
Crabs burrowed in mud, sand, wood chips, and Ocean Falls sediment.
In
mud, burrowed crabs usually had only their eyes and rostrum exposed, with a
space in the substrate at the anterior edge of the carapace probably to allow
oxygenated water to reach the gills.
However, sometimes this space was not
13
visible, and the eyes and rostrum were coVered, thus making the crab virtually
impossible to detect.
Animals burrowed in sand usually had more of the cara-
pace and part of the legs exposed.
Crabs burrowed in wood chips and Ocean
Falls sediment were sometimes only partially burrowed, as in sand, and sometimes were compl etely hi dden under the substrate.
Some crabs did burrow in
Port Mellon sediment, for several hours, but none remained after twenty-four
hou rs.
Ne ither wood debr is nor rocks were moved to allow burrowing.
Crabs
were considered burrowed in these substrates if they were stationary between
pieces of wood or rocks.
When placed on the boundary between the substrates, some crabs burrowed
there, while others quickly crawled off to one side,
where they might burrow
even though they had not experienced the other substrate.
Therefore, the
first burrow locations did not necessarily indicate real preferences.
crabs burrowed soon after the start of tests.
In mud, vs
Most
sand tests, 15 of
24 burrowed wi th in t en mi nutes, and 20 of 25 in thirty minutes.
Of those
that burrowed i n thi s test, 22 of 24 remained in the first burrow for the
duratio n of t he dayti me observations of the first day.
night, and probably experienced both substrates.
All crabs moved over-
Therefore, the twenty-four
hour lo cati on s should rep r esent true preferences.
The twen ty-four hour locations are shown in Table II. Since C. baipdi
bur row j ust below the substrate surface, only the top one or two cm of substrate are important
for these animals.
Mud was preferred for burrowing;
the small particle size made burrowing easy and quick.
Sand was less pre-
ferred and appeared to be more difficult to burrow in (animals were only
partially burrowed i n the sand) due to the large, heavier grains and the firmness of the substrate.
Wood chips and Ocean Falls sediment were not preferred,
14
probably owing to their large particle size and the instability of the substrates.
Port Mellon sediment was probably toxic.
Thin (a few mm) layers of wood chips did not significantly affect burrowing in mud.
Thicker (2 cm or more) layers would probably have prevented
immature crabs from reaching the more preferred mud below.
Apparently bur-
rowing under wood debris and rocks was not possible, so that covering of mud
with these materials could be detrimental.
The laboratory preferences agree with field data in Howe Sound, adults
of this species appearing to be restricted to muddy substrates (McDaniel 1973).
In conclusion, changing the top one or two cm of substrate from mud could be
detrimental, although a few mm thickness of easily moved materials such as
wood chips should not be harmful.
4.
Chiridota laevis (Fabr.) (burrowing sea cucumber)
a.
Methods
The length and diameter of these animals varies considerably owing to
their ability to contract and extend their bodies.
The usual size of relaxed
animals was 3 - 4 cm long and 0.5 - 1.0 cm diameter.
The experimental set-up was identical to that used for Brisaster (see
Fig. 16).
Up to thirty-one animals were placed along the boundary between
the substrates.
Experiments were terminated after three days.
The two-choice tests compared Howe Sound mud with: sand, wood chips; a
loose covering of wood debris on mud; and Ocean Falls sediment.
b.
Results and Discussion
Although many C. laevis had died within a few days of being brought into
the laboratory, the survival of animals used in the experiments was high -
15
only four died in all experiments.
Two others eviscerated, which is a response
to unfavorable conditions (Hyman 1955) in ho10thurians.
In preliminary ex-
periments in static sea water, mortality was greater than 50%.
c. laevis burrowed head first into the substrate, through use of the
tentacles and body musculature.
An animal could be completely buried in less
than an hour, but could take much longer.
Buried animals moved through the
substrate probably feeding as they moved.
Occasionally they wqu1d expose
their tentac l es at the at the substrate surface probably to obtain oxygenated
water.
Holes were sometimes visible in the mud surface indicating where they
had recently come to the surface.
depth.
Animals could burrow at least to 5 cm
Because of the periodic exposure at the substrate surface, they pro-
bably remain close to the surface at all times.
Little movement was shown
on the substrate surface before burrowing.
Substrate prefer ences are shown in Table III.
out preferences, in a wide variety of substrates.
C. l aevis burrowed, with-
The worm-like, flexible
body allowed burrowing in both firm and unstable substrates.
A loose covering
of wood debris did not prevent burrowing, and the gaps in the covering allowed
the an i ma l to ob t ain oxygenated water when it exposed its tentacles out of the
mud.
The anima l s were not able to move the wood debris.
A non-porous im-
penetrable covering would be detrimental.
This species has been reported in a wide range of field habitats; it is
found in mud, sand and under rocks (Clark 1901).
In conclusion, this species
should be tolerant of many changes in substrate conditions, provided the
animals can burrow and obtain food from the substrate and are allowed to
reach the substrate surface.
16
5.
Corophium sa lmonis Stimpson (amphipod)
a.
Methods
Specimens were 4 - 8 mm in length.
Four petri dishes (9 cm diameter X
1 cm deep) were each filled with substrate, two dishes of each substrate type.
The four dishes were arranged in the centre of a rectangular plastic dishpan
as shown in Figure 18.
Water in dishpans was at 10
was placed in a running seawater table.
0
e,
10 0 /00.
The dishpan
In the tests with Port Mellon sedi-
ment the water in the dishpan was slowly aerated.
Thirty animals were added near the centre of the dishpan between the
petri dishes.
After twenty-four hours, the dishes were removed and the
number of animals burrowed in each substrate was determined.
The two-choice tests compared Squamish estuary mud with: sand; a 1 - 3 mm
layer of sand on mud; wood chips;
a 1 - 3 mm layer of wood chips on mud; a
1 cm layer of wood chips on 4 cm of mud; a close-fitting cover of wood debris
on mud; Ocean Falls sediment; Port Mellon sediment; and Roberts Banks mud.
In the tests with 1 cm of wood chips on 4 cm of mud, the other substrate
was 5 cm of Squamish mud.
The substrates were placed in glass dishes (10 cm
diameter X 5 cm deep) instead of petri dishes; otherwise, the methods were
identical to that described above.
b.
Results and Discussion
C. sa Zmonis builds U-shaped t ube burrows in the substrate.
animals were burrowed within one hour.
Almost all
After landing on a substrate, the
animal usually crawled about and then either started burrowing or swam off.
Animals that started burrowing often swam off before finishing; this occurred
on preferred and unpreferred substrates.
Burrowing appears to be similar to that described for other species of
17
Corophi um (see Ingle 1966; Clay 1967).
C. sa lmonis rapidly moves its legs
pushing substrate out behind and creating a longitudinal depression underneath.
The animal then moves forward into the substrate, digging with its large
antennae.
seconds.
C. salmonis could be completely buried in approximately thirty
The burrow walls of Corophium species are solidified with secretions;
the burrows are tu be-shaped, usually U-shaped, with openings at the substrate
surface (ibid.).
examined.
The actual shape and depth of C. salmonis
Burrow openings of C. sa lmonis
burrows was not
could be seen in the substrate sur-
face; the openings were approximately 1 mm or less in diameter.
C. salmonis
remained in burrows du r ing most of the observation period, but sometimes would
leave a burrow and start burrowing elsewhere.
Burrowing was observed in mud, sand, mud covered with 1 - 3 mm layers
of sand or wood chips, and Ocean Falls sediment.
In the test .of 1 cm of wood
chips on mud, some animals were found in the wood chip layer, but none had
built tube-burrows; no animals had reached the mud below the wood chips.
large particle size of wood chips prevented tube construction.
The
Some animals
did burrow in Port Mellon sediment, but none were found in it after twenty-four
hours proba bly due to its toxicity.
A solid covering of wood debris prevented
animals from reaching the mud, except at gaps between the debris since the
animals could not move the wood debris.
C. salmonis builds tubes that may be several cm deep into the substrate.
A suitable substrate must allow tube construction from the surface openings
down to the bottom of the tube.
However, these animals can adapt the tube
shape to the depth of suitable substrates; in petri dishes, only 1 cm depth
was possible, but when deeper substrate was available, the burrows were deeper.
Substrate preferences are shown in Table IV.
Fine mud was preferred,
with no preference between Squamish mud and similar grain size mud from
18
Roberts Bank.
Sand could also be burrowed in, but was less preferred,
probably because the larger grain size made tube-construction more difficult.
Ocean Falls sediment was not preferred, probably owing to the instability of
the substrate and the large particle size.
Thin layers of sand or wood
chips could be moved away to allow burrowing in the mud below.
(at least
Thicker layers
cm) would prevent animals from reaching the more preferable mud
below.
The field data support the laboratory preferences.
In the Fraser
River estuary, C. salmonis is most abundant in mud, but is also common in
some mud-sand and sand areas up to 272
Coustalin 1975; Otte and Levings 1975).
~m
median grain size (Levings and
In conclusion, C. salmonis requires
a fine-grain, unpolluted, relatively stable substrate, but can inhabit sand
up to at least 400
~m
grain size.
6.
Crangon alaskensis (brown shrimp)
a.
Methods
Specimens were 4 - 8 cm long.
The shrimp were tested in rectangular
plastic dishpans placed in a running-seawater table (see Fig. 17).
Seawater
in dishpans was at 12°C, 25 0 /00.
Four to six shrimp were introduced at the centre of the dishpan.
Experi-
ments were terminated after twenty-four hours; in some early tests, observations were continued past twenty-four hours.
The two-choice tests compared English Bay mud with: sand, wood chips, a
1 - 5 mm layer of wood chips on mud; wood debris; Ocean Falls sediment; and
Port Mellon sediment.
19
b.
Results and Discussion
c. alaskensis stayed burrowed near the surface of the substrate during
most of the daytime, but left the substrate to feed or change burrow locations.
Burrowing was observed in sand, mud, wood chips, mud covered by wood chips,
and Ocean Falls sediment.
When burrowed, the shrimp were in a horizontal position just below the
surface.
In sand or mud, only the eyes,
dorsal body surface were exposed.
antennae~
and sometimes parts of the
In mud, and sometimes in sand and Ocean
Falls sediment, a space was present in the substrate at the anterior edge and
below the head, probably to allow oxygenated water to reach the gills.
In
wood chips, the entire head was sometimes exposed, and in some cases the entire
head was covered with loose wood chips.
Wood debris could not be moved to
allow burial; shrimp were considered burrowed in wood debris if they were
stationary in spaces between or under pieces of wood.
Tests with Port Mellon sediment in unaerated water resulted in two deaths
and two comatose animals out of six tested after 100 minutes; none of the six
tested showed any burrowing behavior in either the polluted or control mud
substrates.
hours.
In a second test, six out of six animals died after twenty-four
When water was slowly aerated for twenty-four hours before and during
tests, no mortalities occurred, and normal burrowing behavior was seen in the
mud.
Only one animal was ever observed to burrow in Port Mellon sediment,
but it left seconds after burying itself.
c. alaskensis burrowed by pushing substrate off to the sides and back by
rapid movements of its legs, thus creating a longitudinal depression under the
body.
Covering of the dorsal surface was accomplished by body movements and
the action of the antennae sweeping material over the body.
Complete burrowing
could be accomplished in ten seconds, but some animals remained partially
burrowed for some time before completely covering themselves.
C. alaskensis
20
did not move within burrows, but had to leave the substrate to move.
About 80 - 90% of the shrimp burrowed within ten minutes of being introduced into test chambers with suitable substrates.
About 2/3 remained in the
first burrow until the end of observations on the first day (4 - 6 hours
after start).
The first burrow often was in the first substrate encountered,
whether or not it was the preferred of the two substrates (although animals
were introduced near the boundary between the substrates, they usually landed
on one substrate or the other).
This was especially noticeable in prelimin-
ary tests in which the experimental dishpans were divided into just two compartments, one containing mud and the other sand.
Of twelve shrimp tested,
nine burrowed in the first substrate encountered, and eight of twelve remained
in the first burrow for the duration of the observations of the first day.
Therefore the positions on the first day may not be indicative of the preferences.
In these and later tests, most or all animals changed positions over-
night, often to the other substrate type (see Table V).
The twenty-four hour
locations appear to have been chosen after experiencing both substrate types,
and therefore should indicate true preferences.
Some shrimp were observed for
up to five days and there was little change in the burrow locations after
twenty-four hours (Table VI).
The burrow locations after twenty-four hours are shown in Table VII.
Since C. aZaskensis burrows just below the substrate
s~rface .
the top 1 - 2 cm of substrate are important for this species.
only
Sand was pre-
ferred, probably because it provided a firm substrate that could be easily
burrowed into, it allowed water to pass through to the gills, and the shrimp's
color closely matched the sand color.
Mud was not as firm and a space was
required in the substrate to allow water to reach the gills; this made the
shrimp easier to detect.
Water could pass through the particles of Ocean Falls
sediment, but this substrate was extremely unstable.
Wood chips were not
21
preferred due to t he large parti cle size and the instability of the substrate.
Wood chips could be moved away to allow burrowing in underlying mud when
only a few mm covered the mud; larger amounts (a few cm) would prevent animals
from reaching the mud.
Port Mellon sediment was similar to mud in particle size, and its
physical charac ter i st ics al lowed burrowing.
However, the presence of noxious
gases in the sed iments (probably hydrogen sulfide; see Werner and Hyslop
1968 ) modified behavio r and may have caused mortalities.
In unaeratedcon-
tai ners, gases releas ed by the sediment spread throughout the whole tank,
and many animals died.
In ae rated containers, the gases in the water were
appa ren tl y oxidized and mor t alities were reduced.
However, below the sedi-
ment surface the toxic gases remained and prevented burrowing.
In conclusion, a sand substrate would be best for this species, although
mud can also be inhabited.
be detrimental.
Larger size particles and toxic materials will
A few mm of material than can be moved away will not affect
burrowing, but j ust 1 or 2 cm can be detrimental.
7.
Hemigrapsus oregonensis (hairy shore crab)
a.
Methods
Specimens had ca rapace widths of 1 - 3 cm.
Methods were identical to
that used for Crangon (see Figure 17) except that the test of uncovered mud
vs mud covered with wood debris was done in a tank divided into only two compartments, as in the pr eli mi nary Crangon experiments.
The two-choice tes ts compared Engli sh Bay mud with: sand; wood chips; a
1 - 5 mm layer of wood chips on mud; a loose covering of wood debris on mud;
rocks (3 - 10 cm diameter ) on mud; Ocean Falls sediment; and Port Mellon
sediment.
22
b.
Results and Discussion
H. oregonensis burrowed in soft sediments and under large objects.
crabs burrowed almost immediately after the start of experiments.
The
Burrowing
in soft sediments was accomplished by crawling sideways in to the substrate.
WAen burrowed, sometimes one
o~
both eyes and the anterior edge of the carapace
were exposed, with a space in the substrate at the anterior edge of the substrate to allow water to reach the gills.
In other cases the crab was com-
pletely hidden, just below the surface; a space in the substrate for respiratory currents was usually present, but was often difficult to detect.
This
type of burrowing was seen in mud, sand, wood chips, Ocean Falls sediment, and
Port Mellon sediment.
Large objects such as wood debris and rocks wereutil ized as cover by
crawling underneath them.
The activity of the crabs scattered wood debris
throughout the tank when the tank was divided into four chambers.
The scatter-
ing was reduced when the tank was divided into only two compartments.
Some
scattering still occurred, and crabs found under wood debris in the compartment that originally had uncovered mud were considered to have chosen wood
debris.
Rocks were burrowed under, but were not moved much by the crabs.
The burrowing locations after twenty-four hours are shown in Table VIII.
Unlike the "tanner" crab (Chionocetes
bairdi)~
H. oregonensis preferred the
cover of large objects such as wood debris and rocks.
The general body shape
(stouter, with short, stocky legs) of H. oregonensis was better adapted to
moving large objects than was C. bairdi (smaller body, long, thin legs).
When cover objects were not present, H. oregonensis burrowed in the substrate, just below the surface, showing preferences similar to that of C.
bairdi, with mud preferred (see Discussion for C. bairdi; see also Low
1970).
Although Port Mellon sediment was not preferred, H. oregonensis
showed a greater tolerance to it than C. bairdi.
23
The laboratory preferences agree with field data.
H. opegonensis is
found in mudflats and und er boards or rocks (Ricketts e t al. 1968; own observations).
In conclusion, this species prefers the cover of solid surfaces,
so dumping of this type of material would improve the habitat for this species.
Otherwise, mud is preferred, and dumping of other soft sediments would be
detrimental, although just a few mm thickness would not be harmful, unless
the material is toxic.
8.
Macoma inconspicua (Broder ip and Sowerby)
a.
Methods
Specimens were 5 - 10 mm in shell length.
The clams were tested in cir-
cular glass dishes placed in a running-seawater table (see Figure 19).
Each
dish was divided in half without a partition, each half receiving one subo
strate type. The seawater in the dishes was at 10°C, 25 /00. One to three
clams were placed on the boundary between substrates.
were determined after twenty-four hours.
Locations of the clams
Clams that had not burrowed in
twenty-four hours were retested.
The two-choice tes ts compared Roberts Bank mud with: sand, wood chips;
a 1 - 5 mm layer of wood chips on mud; a 1 cm layer of wood chips on mud; a
close-fitting cover of wood debris on mud; Ocean Falls sediment; and Port
Mellon
b.
Sedi~ent.
Results and Discussion
The time required for M. inconspicua to bury itself in suitable substrates
ranged from less than one minute to several hours; some were not buried after
twenty-four hours.
The depth of burrowed animals ranged from just below the
surface to the bottom of the experimental dishes (4 cm deep in the substrate).
24
In nature. this species can burrow down to 25 cm deep within the substrate
(Vassallo 1971).
Burrowing was observed i n all of the substrates tested.
Once buried, clams were never observed on t he surface again.
The clams did
move within the substrate, sometimes moving from one substrate to the other.
M. inconspicua burrows by extending the foot into the substrate, anchor-
ing it, pulling the shell up on its edge. and pu"11ing the shell into the substrate in a series of rocking movements by contracting the foot (see Tr ueman
et al. 1966).
Once buried, clams could sometimes be detected by the presence
of their siphons at or above the substrate surface, or by the presence of
small holes «1 mm diameter) made by the siphons at the surface (although
these holes may indicate a previous, not current, position of the clam).
It was also possible that a clam with its body in one substrate could have
had its siphons break the surface in the other substrate.
The inhalent siphon could be held vertically above the substrate (up to
4 or more cm high when given sufficient depth of water) in order to obtain
oxygen or food from the water.
The in ha1ent s ipho n sometimes bent dovin to
the substrate surface to pick up food particles (deposit-feeding: see
Brafie1d and Newell 1961).
The locations of burrowed clams after twenty-four hours are shown in
Table IX.
The data represent the location of the shell (body): as mentioned
above, the siphons could have been extended over the other substrate type.
M. i ncons pi cua showed no preference between mud and sand.
Other soft
substrates were less preferred probably due to their large particle size and/
or instability.
Port Mellon sediment was not preferred, but the presence of
some individuals in this sediment after twenty- f our hours in unaerated
conditions indicates a greater tolerance than in many of the other species
tested.
This may partly be due to the siphons which allow the clam to obtain
25
water from abo ve the substrate surface.
A layer of less preferred material such as wood chips did not affect
burrowing as long as the animals could burrow and extend their siphons.
How-
ever, a hard, impenetrable cover which prevents siphons from reaching the
surface would be detrimental.
In the tests with the cover of wood debris,
those under the cover must have had their siphons extended between pieces of
wood, or onto the uncovered mud.
The preferences agree with data on the field distribution of ft!. ~ncon­
sp~cua.
This species has been reported in natural substrates ranging from
mud to sand (Du nni ll and Ellis 1969; Vassallo 1969; Levings and Coustalin
1975; Otte and Levings 1975).
as M. inconspicua
M.
baZthi ca~
which may be the same species
(Quayle 1969; Kozloff 1973) has been reported in mud
and
sand (see Vassallo 1969) and in anoxic black muds containing sulfur bacteria
(Yonge 1949).
This ability to inhabit many types of penetrable substrates
is related to its feeding habits - it can feed on material growing on or
deposited on the substr ate surface (e.g. diatoms, phytoplankton, detritus)
and can also function as a suspension feeder, removing food from the water
col umn (Brafield and Newell 1961: own observations).
In conclusion, this species can inhabit a wide range of soft substrates,
preferring sand or finer materials.
Dumping of larger particles, unstable
substrates, to xi c materials, or impenetrable cover materials would be detrimenta 1 .
9.
Muni da quadrispina Be nedict ("squat lobster")
a.
Methods
Specimens were 1 - 4 cm in body length.
The experimental set-up was
identical to that used for Bri saster (see Fig. 16).
Five animals
were added
26
to the tank at 1200 hours.
On the next day, observations of their positions
were made at 0900, 1000, 1100 and 1200 hours (21 - 24 hours from the start of
the tests).
A total of ten animals were tested, giving a total of forty
observations.
The two-choice tests compared sand with: Howe Sound mud; sand covered by
<1 cm of wood chips; sand covered by loosely arranged wood debris; and sand
covered by loosely arranged wood debris; and sand covered by large (15 - 30
cm across) rocks arranged so that crevices were present between and under rocks.
b.
Results and Discussion
M. quadrispina did not bUrrow in soft sediments, although some individuals
did create slight depressions in the substrate.
These animals could crawl
or swim about, but spent most of the time resting, with their posterior ends
against the walls or drainpipe of the tank, when only soft sediments were
tested.
When wood debris was present, the animals frequently rested on or
under pieces of wood; the wood debris could be moved.
When rocks were present,
the animals rested on rocks or in crevices between or under rocks; the rocks
could not be moved.
The substrate preferences are shown in Table X.
were tested, some definite trends were seen.
Although only ten animals
When neither substrate offered
either a hard surface or cover, no preferences were shown.
Hard surfaces and
cover, as provided by wood debris and especially rocks, were significantly preferred to soft sediments.
The results agree with field observations by McDaniel (1973); he found
M. quadrispina frequently on or in crevices formed by large wood debris and
rocks in Howe Sound.
In conclusion, dumping of large, hard-surfaced materials
can improve the habitat for this species, especially if they provide cover.
28
GENERAL DISCUSSION
1.
Types of Effects of Ocean Dumping
Acute effects of ocean dumping include burial of fauna, increased tur-
bidity, introduction of pollutants, and reduction in oxygen levels in and
above the substrate.
Long-term effects result from altering the physical,
chemical and biological nature of the substrate.
Physical effects include
changes in the size, weight, and shape of particles and the porosity, permeability, and stability of the substrate.
Chemical effects include changes
in the levels of pollutants, organic matter, and oxygen.
Biological effects
include changes in the food availability and the numbers of competitor and
predator species.
Such long-term effects will have an impact on animals
surviving the acute effects as well as on new colonizers.
The magnitude of both types of effects depends on the type of material
dumped, the frequency of dumping, the amount dumped, the size of area over
which the material lands (which depends on the method of dumping and the
water circulation at the dump site), the type of substrate in the dump site,
the rate of natural sedimentation, and the type of benthic fauna.
2.
Acute Effects
The extent of burial of animals depends on the thickness of the deposit
and the size and lifestyle of the benthic fauna.
Sessile or slow-moving
epifauna will be most affected, since they will be unable to avoid the dumped
material, and so would probably be killed if covered by the dumping (e.g.
Sherk 1972; Slotta and Williamson 1974).
have limited ranges of movement.
the dumped material.
Infauna generally move slowly and
They are also unlikely to be able to avoid
However, since infauna are adapted to living buried in
sediments, the dumping of more materials on top of the substrate might not be
29
seriously harmf ul.
Some bivalves are able to survive burial by a 5 cm layer
of a slurry formed by eroded paper wastes - Pitar morrhauna and Mercenaria
mercenaria could extend their siphons above this layer, while the large siphon-
less Arctica islandica could "blow" away the waste with strong exhalent currents (Prat t et a l. 1973).
Some burrowing bivalves and polychaetes have been
found to survive burial by up to 21 cm of sediments (see Slotta and Williamson
1974).
However, dumpi ng would be harmful if it prevented some organisms (e.g.
Brisaster~ Chiridota~
Macoma) from obtaining oxygenated surface water.
This
would occu r if the dumped materials is impenetrable or if the deposit is too
thick for the animal to move away, burrow through or extend siphons through.
Mobile epifauna, especial ly those capable of swimming, such as shrimp,
should be able to avoid burial; crawling animals such as crabs mayor may not
avoid burial (see Bacescu 1972).
In areas where large-scale dumping is fre-
quently do ne, the frequent changes in the level of the substrate surface will
bury colonizing anima l s or prevent them from settling (Gross 1971).
Increased tu r bi dity due t o dumping of fine materials may also cause
mortalities by interfering with respiration and suspension-feeding of some
species (Bacesc u 1972).
Species adapted to life in naturally turbid condi-
tions may not be harmed by the turbidity caused by dumping (Slotta and
Williamson 1974).
Introduction of pollutants can cause immediate mortalities.
For example,
the wastes from pulp mills sometimes contain toxins., and also have a high
oxygen demand which leads to oxygen depletion and sometimes H2S formation in
sediments.
These effects can immediately kill animals, as happened in this
study (see also Wash. State 1967; Servizi et al. 1969; Slotta and Williamson
1974).
As with the effects of burial, the ability of species to avoid the
effects of turbidity and pollutants will vary with the species.
30
3.
Long-term Effects
The effects of changes in the physico-chemical nature of substrates were
examined in the laboratory preference tests.
Bacescu (1972, p. 1291) states
that the substrate " ., largely determines distribution and associations of
bottom-living (benthic)animals".
The distribution of a species is determined
by the species' preferences and/or tolerances to various interacting factors
(Meadows and Campbell 1972 a, b; Moo r e 1975).
In most cases, the preferences
of a species for a certain factor do correspond with the optimal conditions
for that factor (Meadows and Campbell 1972 a, b; Gannon and Beeton 1971).
However, in some cases, animals may prefer a suboptimal or even lethal level
of a certain factor such as substrate when that factor is tested alone,
because "As is the case in regard to other environmental factors, responses
to the substratum cannot be viewed completely independently of the responses
to other factors" (Bacescu 1972, p. 1291).
When the distribution of a species
is narrower than what its preferences indicate, then the environment must be
limiting the species through the animal's tolerances (Meadows and Campbell
1972 a, b; Moore 1975).
In most cases as in the present study, the preferences do agree with the
field distribution of the species.
This indicates that the preferences are
associated with the adaptive value of the different substrates.
This may not
necessarily mean that the preferences are determining distribution, since the
choice of habitats available to the animal are restricted by the range of
movement of the species and the variability of substrates within this range
(Moore 1975).
However, if the preferred substrates do correspond with the
optimal conditions, then it does mean that if the animal is forced to live
in a less preferred substrate, then its productivity will be suboptimal.
Benthic fauna use the substrate for protection from predators and (mainly
for intertidal animals) from extreme conditions, and as a source of food.
31
Animals such as
Can(!er~
Chi onoe e e t e s~
and Crango n are both infauna and epi-
fauna -- they burrow for protection and also move about on the substrate surface to obtain fo od fro m, on or just under the surface . . Other animals burrow
for protection and deposit-feed from the substrate surface near the burrows
(e.g.
Corop hi um~ Ma coma ~
possibly Bri sas t er).
Some animals burrow for pro-
tecti on and ingest sediment as they move through the substrate (e.g. Brisas ter' ..
Chiri dota).
Mos t bi va lv es us e the substrate for protection (burrowers) or
attachment (sessile epifauna), obtaining food from the overlying water.
Mobile
epifa una (e.g. Munida .. Pandalus) oft en hide in crevices of hard materials on
the surface, and obtai n food from
on or just under the substrate surface.
I n th is study , sa nd , mu d and rocks on sand or mud represented natural
(unalter ed) su bstrates.
They also represented the types of materials that
could be dumped in dredging operations.
These substrates differed mainly in
parti cle si ze and or ga nic ma tter content.
The phys i cal di ffe r ences between mud and sand substrates have been discussed by many authors (e.g. Webb 1969; Bacescu 1972; Gray 1974; Rhoads 1974).
Sand is usually more porous and more stable (Gray 1974).
greater permea bi li ty and greater aeration of the sediment.
This porosity allows
However, because
of the size and weight of the particles, and the stability of the substrate,
sand may be more difficult to burrow in for some species.
Fine mud may be
easier to burrow in, but may not provide enough support for larger, heavier
animals (Rhoads 1974).
The fine particles, low porosity, and the often high
turbidity near the surface of mud can make respiration and suspension-feeding
difficu l t.
Sus pens ion-feeders that do exist in mud (e.g. Macoma inconspicua)
require special adaptations to avoid clogging of the gills (Rhoads 1974).
The
higher organic matter content and fine particle size of mud favors depositfeeders, including tube-builders (Bacescu 1972; Rhoads 1974).
Changing from
a sand to a mud substrate, or vice versa, will therefore cause large changes
32
in the benthic fauna.
Rocks on mud or sand can offer protection to species that can burrow under
the rocks, or species that can utilize crevices between rocks.
Covering of rocky
areas with soft substrates will therefore be harmful to these species.
Covering
of a soft substrate with rocks can be detrimental to those that cannot burrow
under or between the rocks.
Stable rock surfaces will favor sessile and mobile
epifauna.
The other substrates tested in this study represented substrates altered by
dumping of materials from forest products industries.
Ocean Falls sediment
and wood chips were both large-particle-size substrates, but due to the light
weight of the particles, they formed unstable substrates.
could be burrowed in only by light-weight or small animals.
These substrates
Wood debris
contained much larger particles that could not be moved by many species; the
size and weight of the particles prevented burrowing.
For all of the above
substrates, the large particle size would hinder most deposit-feeders and
tube builders.
However, the hard surface provided by wood debris sometimes
favors sessile and other epifauna (McDaniel 1973; Pease 1974).
Port Mellon sediment was a fine sediment that was avoided by most or all individuals of all species tested even though its physical characteristics allowed
burrowing by these species.
Similar sediments with high organic matter content
(wood fibres) produce H2S and deplete oxygen as a result of the activity of
bacterial decompos Grs(see Wash. State 1967; Servizi et e Z. 1969). Few species can
survive such conditions, so that this type of substrate will be detrimental to the
species existing before dumping (ibid.).
Large amounts of wood materials may also
reduce oxygen levels and release toxic chemicals (Pac. NW.Poll. Control Council
1971), but this did not seem to occur in the present study except with Port Mellon
sediment.
So far, this discussion has examined the effect of completely changing
33
the orginal su bstrate to one composed entirely of the dumped material.
In
reality, the dumped material will form a layer on top of the natural substrate,
and the effects depend on the thickness of this layer.
If the deposit pre-
vents burrowing animals from reaching the natural substrate below, then the
effect would be as if the entire substrate was changed.
If the dumped mater-
ial can be burrowed in, and if the animal burrows just below the substrate
surface, then just a few
cm thickness of the dumped material would be suf-
f i cient for this effect.
If the animal lives deeper in the substrate, the
deposit would have to be at least as deep as the burrow.
Thin layers of such
material should not be detrimental.
If the dumped material inhibits or prevents burrowing, the deposit would
not have to be as thick to have a detrimental effect.
of wood chips on mud prevented burrowing by
Co~ophium
burrows of this species can go much deeper than this.
For example, only 1 cm
even though the tubeAny thin impenetrable
cover would prevent animals that frequently enter and leave the substrate
Cancer~ Chionoecetes~ Corophium~ Crangon~
(e.g.
Hemigrapsus) or those that
remain constontly burrowed but must maintain communication with the overlying
waters (e.g.
Brisaster~ Chiridota~
Macoma) from inhabiting the substrate.
Such a situation could occur with a densely packed cover of wood debris
(McDaniel 1973) or rocks.
However, if these materials are widely scattered
in a thin layer over an area, they should not seriously damage the benthic
habitat.
Since most sessile epifauna prefer hard surfaces for attachment, covering of such surfaces with soft sediments can prevent settlement by these
species.
Dumping of materials with hard surfaces can be beneficial for these
species, since surfaces for attachment appear to limit these animals (Reed
1975) .
34
Toxic materials are often harmful in low concentrations; thus
even small amounts of such materials will be detrimental to all types of fauna.
Since benthic fauna are associated with certain substrate types,
the least change would result when the dumped material is similar to the natural
substrate in the dump site (Andre1iunas and Hard 1972; Reed 1975).
The site
after dumping should then be similar to its state before dumping, and recolonization can start almost immediately.
When the dumped material is different
from the natural substrate, the effect is likely to be detrimental to the
species that were present before dumping.
In some cases, as with the construc-
tion of artificial reefs from waste materials, the dumping may improve the
habitat for some of the local species (Turner e t al. 1969; Reed 1975).
Once the substrate has been changed, the area cannot begin to recover to its original state until the substrate has returned to its pre-dumping
state.
If the frequency of dumping is high, there will be insufficient time
for the substrate to recover before the next dumping is done.
Once dumping
has ceased, the recovery of the substrate depends on the amount and type of
material dumped, the rate of resuspension of the dumped material, and the
rate of natural sedimentation.
In some cases, recolonization by the original
species can begin within a few weeks of dumping (F1emer et al. 1968; Leathem
et al. 1973; May 1973; Reed 1975).
longer periods.
In other cases, changes may persist for
For example, when a mud flow covered a sandy area in an
Alabama estuary with 45 cm of silt and clay, the substrate remained altered
for at least eight months after the disruption (Vittor 1974).
In Alaska,
bark debris was found covering an area where log dumping had not occurred for
over fifty years (Pac. NW Poll. Control Council 1971).
The result of these changes in the substrate will be to decrease or,
less often, increase the productivity of the original species, depending on the
35
extent and nature of the substrate change.
be changed.
The species composition can also
Species adapted to the new conditions can become established,
while some of the original species can be eliminated.
This is especially
noticeable when polluted substrates are formed --- most or all of the original
species will be eliminated and replaced by large numbers of a few pollutiontolerant (and usually less desirable) species (Wash. State 1967; Servizi
~~
at.
1969; Pearce 1972; IMCO et at. 1975).
4.
Reduction of Effects
The only way to completely eliminate the effects of dumping on
benthic fauna would be to cease dumping through recovery and reutilization of
wastes and allow uses of alternative methods of disposal (Booth and Saucier
1974; IMCO et at. 1975; Reed 1975).
However, in some cases, no economically
feasible alternatives are available, and so ocean dumping will continue
(Andreliunas and Hard 1972).
If it is assumed that ocean dumping must con-
tinue, then efforts should be directed toward minimization of its deleterious
effects.
The disposal site must be chosen to avoid feeding and nursery areas,
and migration routes of commercially important species must be protected
(IMCO et at. 1975; Servizi et al.1969).
Depending on the amount and type of
material and the location of dumping, it may be best to disperse, confine, or
containerize the wastes (Servizi et al. 1969; Andreliunas and Hard 1972; IMCO
et at. 1975). Dispersal of dumped materials can reduce the burial effect and
r ecovery time (ibid.).
Sediments polluted by high organic content and H2S
should be dispersed to allow oxidation of the organic matter and H2S without
large oxygen depletion in the disposal area.
This can be accomplished by
dumping in areas of high water circulation (Andreliunas and Hard 1972) or by
36
using di s posal techniques
that release the material over a wide area (if
feasible; Servizi et a Z. 1969).
It may be possible to bury polluted wastes
by dumping unpolluted wastes over them (IMCO et aZ. 1975; Thorslund 1975).
If high turbidity will result, dumping should be done where natural turbidity
is high, since the animals in such areas will be adapted to turbid conditions
and should survive the additional t urbidity caused by the dumping (Slotta
and Williamson 1974).
If possible materials should be dumped on substrates
composed of similar materials so that the alteration of the substrate is
minimized (Andrelinunas and Hard 1972; Reed 1975).
5.
Suggestions for Further Research
Further research is required in order to properly determine the best
disposal methods.
Physical and chemical oceanographic data must be obtained
for proposed dump sites so that the behavior of the dumped material can be
predicted.
Biological research should concentrate on the effects of dumping
on ecologically and commercially important species in the proposed disposal
areas.
This should include tolerances to effects of burial and increases in
turbidity .
Effects on benthos of substrate changes should be determined in
preference tests as in this study, combined with tolerance tests.
Longer-
term studies such as growth rates on different substrates would be useful.
The studies should examine the effects of dumping of various amounts of the
types of materi a 1s that are proposed to be dumped so that a 11 owab 1e "safe"
concentrations and/or thickness of dumped material in the sediments can be
determined.
37
CONCLUSIONS
Benthic animals show preferences for certain substrates . These preferences usually correspond with the field distributions of the species.
Because of this, alterations in the physico-chemical nature of the substrate caused by ocean dumping will affect the benthic fauna.
The effect
can lead to changes in the productivity of the original species or to changes
in the species composition in the disposal area .
The magnitude of the effect
depends on the amount of material that lands on the substrate, the type of
material dumped, the frequency of dumping, and the type of benthic fauna.
In most cases, the dumping will be detrimental to the original species, since
the dumped materials usually form substrates that are less preferred by these
species.
If the dumped material is similar to the natural substrate, then
there may be an initial burying effect, but recolonization can occur quickly.
In some cases, it may be possible to enhance substrates through ocean dumping, as with the construction of artificial reefs.
In order to minimize the
deleterious effects of ocean dumping, research is required to allow determination of the proper disposal techniques for an area.
38
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45
Table I .
Cancer magister:
burrow locations after twenty-four hours.
Two-choice tests.
Substrates*
No. Animals
2
2
mud
sand
2
12
mud
WC
10
3
mud
WD
7
0
boundary"
0
0
not burrowed
Probabi 1ity
tota 1 {o: = .05)
0
14
.012 t
0
14
.046
1
8
.008
* mud is from English Bay; WC, wood chips; WD, wood debris.
t 2-tail; all other tests l-tail in favor of substrate 1.
47
Table III.
Chiridota Zaevis:
burrow locations after three days.
Two-choice tests.
Substrates*
No. Animals
2
2
boundary
not burrowed
total
Probabil ity
(0: = .05)
mud
sand
11
18
0
2
31
>.lOt
mud
we
12
10
0
3
25
.42
mud
WD/M
13
10
0
24
.34
mud
OF
6
4
1
12
.38
* mud is from Howe Sound;
1
we,
wood chips; WD/M, loosely arranged cover of
wood debris on mud; OF, Ocean Falls sediment.
t 2-tail; all other tests l-tail in favor of substrate 1.
49
Table V.
burrow locations in preliminary mud vs.
sand tests. The experimental chambers were divided into two
compartments, one containing mud and one with sand.
Time from
start of
test
Crangon alaskensis:
No. Animals
mud
sand
1st burrow
( 4 hours)
6
5
0
12
4 hours
6
5
0
12
11
1
0
12
24 hours
Table VI.
Crangon alaskensis:
boundary
0
not burrowed
tota 1
burrow locations for up to five days in
mud vs. sand tests.
No. Animals
Time from
start of
test
mud
1 day
(24 hours)
0
2 days
5 days
0
sand
boundary
not burrowed
total
18
0
0
18
17
0
0
18
18
0
0
18
50
Table VII.
Crangon alaskensis: burrow locations after twenty-four hours.
Two-choice tests.
No. Animals
Substrates*
2
2
boundart
30
<.001
3
0
13
. 17
4
4
0
30
<.001
6
9
0
2
17
.30
27
0
0
·28
<.001
4
1
WCjM
3
7
mud
WD
22
mud
.oF
mud
PM
WC
mud
(0: = .05)
0
25
mud
total
<.OOlt
0
sand
not burrowed
30
28
mud
Probability
* mud is from English Bay; we, wood chips; WejM, a 1-5 mm layer of wood chips
on mud; WD, loosely arranged wood debris; OF, Ocean Falls sediment; PM,
Port Mellon sediment.
t 2-tail; all other tests l-tail in favor of substrate 1.
52
Table IX.
Macoma inconspicua: burrow locations after twenty-four hours.
Two-choice tests.
No. Animals
Substrates*
not burrowed +
Probabi 1ity
(0: + .05)
2
1
2
mud
sand
17
12
0
1
30
>.30 t
mud
WC
22
6
0
3
31
<.005
mud
WC1/M
14
9
0
0
23
.20
mud
WC2/M
12
9
0
0
21
.33
mud
WD/M
16
6
0
0
22
.026
mud
OF
21
4
0
0
25
<.001
mud
PM
19
7
1
28
<.01
bounda.!:l.
total
* mud is from Roberts Bank; WC, wood chips; WC1/M, a 1-5 mm layer of wood
chips on mud; WC2/M, a 1 cm layer of wood chips on mud; WD/M, close-fitting
cover of wood debris on mud; OF, Ocean Falls sediment; PM, Port Mellon
sediment.
t 2-tail; all other tests 1-tai1 in favor of substrate 1.
+ clams not burrowed after 2 trials
54
Table XI.
observations of locations. Each animal (n=lO)
was observed at 21,22,23 and 24 hours from the start of tests.
Two-choice tests.
Pandalus danae:
No observations
Substrates*
Probabil ity
(ex = .05)
2
1
2
boundari:
total
sand
mud
18
16
6
40
>.70 t
sand
WCjS
16
23
1
40
>.] 0
WDjS
sand
29
4
7
40
<.001
RjS
sand
40
0
0
40
<.001
* mud is from Howe Sound; WCjS, a 1-10 mm layer of wood chips on sand; WDjS,
wood debris loosely arranged on sand; RjS, rocks (15-30 cm across) on sand
t
2-tail; all other tests l-tail in favor of substrate 1.
55
Figure 1.
Brisas ter Zatiforns (A. Agassiz) (Heart urchin).
Dorsal view.
Figure 2.
Length 3 cm.
Chir idota laevis (Fabr.) (burrowing s~a cucumber).
Length 5 cm. The animal is extended, with tentacles
visibl e at r ight.
56
Figure 3.
Munida quadrispina Benedict.
Dorsal view.
("squat lobster").
Body length 2.5 cm.
/
/
/
/
Figure 4.
PandaZus danae Stimpson (coon stripe shrimp).
Dorsal view.
Body length 9 cm.
57
Figure 5.
Cancer magister Dana (Dungeness crab).
view.
Figure 6.
Dorsal
Capapace width 16 cm.
Rathbun (lltanner': crab).
Carapace width 1.7 cm (immature specimen)
Chionoecetes bairdi
Dorsal view.
58
Figure 7.
Crangon alaskensis Lockington (brown shrimp).
Dorsal view.
Figure 8.
Body length 7.5 cm.
Hemigrq)sus oregonens~s (Dana) (hairy shore crab).
Dorsal view .
Carapace width 1.7 cm.
60
Figure 10. Sand used in preference experiments.
Figure 11.
Rocks used in experiments in small containers
(tests with C. bairdi and H. oregonensis).
61
Figure 12.
Figure 13.
Wood chips used in preference experiments.
Wood debris forming cover with few gaps used
in preference experiments.
62
Figure 14.
Wood debris loosely arranged used in preference experiments.
Figure 15.
Sediment from Ocean Falls (Cousins Inlet)
used in preference experiments.
64
SCALE IN CENTIMETRES
~-+-i--PETRI
TOP VIEW
Figure 18.
DISHES---,..
SIDE VIEW
Experimental apparatus used in preference tests with
are two substrate types. (1 cm deep).
C. salmonis.
A and B
65
17
7
SCALE IN CENTIMETRES
A
II
TOP VIEW
Figure 19.
SIDE VIEW
Experimental apparatus used in preference tests with M.
are two substrate types.
COnB ~)1>·'<'C .
A and B