RESEARCH NOTES
the brighter coloured, more contrasted and sunflecked background of foliage. Mangrove ellobiaceans may be worth further study with respect to
substrate and shell coloration. Pythia pLcata is
unusual both in being associated with leaves and in
its polymorphism.
1 am grateful to Professor M Shahadat All, University of Dhaka, for making the visit possible, to
Professor M Salai Khan for information on the
plants and to the Bntish Council for financial support Dr David Reid (Natural History Museum) very
kindly identified the species recorded and provided
helpful information on nomenclature and comments
on the paper
129
9 FORD, E B 1971. Ecological genetics Chapman
and Hall, London
10 GRONEBERC, H 1976. PhtL Trans. R. Soc Lond
fl.275 385-426.
11 GRONEBERC H. 1978 Proc R. Soc Lond. B,
200:419-440
12. GRONEBERC H. 1979 Proc R. Soc. Lond. B,
203. 379-386
13. GRONEBERG, H. 1980. Proc R. Soc Lond. B,
210:533-548
14. GRONEBERC H. 1981. Proc R, Soc Lond. B,
212. 53-63.
15. GRONEBERG, H. 1982 Proc R. Soc Lond. B,
216 147-157
16. CLARKE, B., ARTHUR, W , HORSLEY, D T. &
PARKIN, D T. 1978. In. Fretter, V. & Peake, J.
Pulmonates. VoL 2A Systematic^, Evolution and
Ecology Academic Press, New York.
REFERENCES
17. KORNERUP, A. & WANSCHER, J.H 1967 Methuen
1 ANON 1975. The Times atlas of the world
Bartholomew & Times Newspapers, London.
2. HUBENDICK, B. 1978. In: Fretter, V. & Peake J.
Pulmonates, VoL 2A. Systematic*, Evolution and
Ecology Academic Press, New York, pp 1-47
3 COOK, L.M. 1983 BioL J Linn. Soc , 20-167-173
4. HOUBRICK, R.S. 1988. MalacoL Rev 1988 Suppl,
4-88-128
5 HOUBRICK, R.S. 1991. Malacologia, 33 289-338.
6. ADAMS, H. & ADAMS, A. 1858. The genera of
Recent Mollusca. Van Voorst, London.
7 BRANDT, R.A.M. 1974. Arch, Molluskenkunde,
105 1-423
8 BERRY, AJ., LOONG, S.C. & THUM, H H. 1967
Proc Malac Soc LontL, 37. 325-337
handbook of colour. Methuen, London.
18 REID, D G 1986. The littonnid molluscs of mangrove forests in the Indo-Pactfic region British
Museum (Natural History), London. 228 pp.
19 ANNANDALE, N. & PRASHAD, B. 1919. Records
of the Indian Museum, 16.241-257.
20 ABU AHMED, A.T. 1990. Studies on the identity
and abundance of molluscan fauna of the Bay of
Bengal. Bangladesh Agricultural Research
Council, Dhaka.
21. CAIN, AJ. 1977. /. Conchol., 29:129-136.
22. COOK, L.M. 1986. BioL J. Linn. Soc, 29" 89-99.
23. REID, D G. 1987 BioL J. Linn. Soc., 30:1-24.
24. REIMCHEN, T.E. 1979. Canad. J. Zool, 57- 10701085
J Moll Stud. (1996), 62,129-133
Tidal movement pattern of crown conchs, Melongena corona Gmelin
Paul V. Hamilton
Department of Ecology and Evolutionary Biology, University of West Flonda, Pensacola,
FL 32514 USA
Most studies of onented movements in gastropods
have centred on small intertidal species' which normally move only short distances during activity periods, either because of their small size or because
their feeding strategies do not require a systematic
search for food. Relatively little is known of the
movement patterns of the larger gastropods, often
known as conchs, much less about the orientational
strategies they employ. Movements of the commercially valuable queen conch, Strombus gigas, have
been studied,2 but primarily in connection to life history and resource management rather than with
regard to the onentational mechanisms involved.
Bits of information on movements are available in
general reports on the ecology of various other
conchs, e.g. 3 .
The present report describes the tidal movement
patterns of the crown conch, Melongena corona
Gmelin Previous studies have examined how loyal
crown conchs are to a given area over tune, and have
documented movements between oyster bar and salt
marsh habitats. 0 Because of their intertidal distribution and distinctive movements, especially during
outgoing tides, M. corona would be an excellent candidate for experimental study of the orientational
guideposts and associated sensory mechanisms used
by a large gastropod.
The movement patterns and activities of crown
conchs were studied by tracking and observing them
during outgoing and incoming tides at two lowenergy barrier beaches along the shores of Goose
Creek Bay, a portion of the St Marks National
130
RESEARCH NOTES
25-1
251 B
OUTGOING TIDE
20-
INCOMING TIDE
20-
_E
UJ
u.
S
UJ
2
0-
0-
-5
-5
1
2
3
4
TIME SINCE HGH TOE (hours)
I
I
I
V
3
4
5
6
TIME SINCE LOW TIDE (hours)
Figure 1. A. Difference in distance offshore between the starting and ending positions of 19 crown conchs
tracked during outgoing tides. B. Difference in distance offshore between the starting and ending positions of
20 crown conchs tracked during incoming tides.
Wildlife Refuge in Wakulla County, Florida. USA.
This area experiences semi-diurnal tides with a mean
range of 73 cm. The Spartina altemiflora zone normally extends from the high tide line seaward for
10-15 m, to about mean sea level.' A sand flat 5-15
m wide is typically located offshore from the lower
edge of the Spartina zone, before a zone of narrow
bladed seagrass (Halodule) begins. All tracking was
done during August and September.
Conchs were tracked along relatively straight
stretches of shoreline by triangulation to three
benchmarks. Water depth was measured periodically
at the offshore-positioned benchmark to record
actual tidal phase. Conchs were randomly selected
for tracking and each was tagged temporarily with a
clip bearing a 1 x 3 cm piece of numbered plastic
tape, attached to spines on its shell. At varying time
intervals, as appropriate given the movements of a
tagged conch, the directions of the conch to the
benchmarks were recorded to the nearest 1 degree,
and the water depth at the conch's location was measured to the nearest 1 cm. Because of difficulties following conchs moving in the Spartina zone on
incoming tides. Sags were used to mark periodic
positions, and the directions of these marker flags to
the benchmarks were recorded after tracking period
was completed. During analysis, conch positions
were normally estimated based on the intersections
of three pairs of lines, one pair for each combination
of two benchmarks. When a conch's position was
close to being in line with two benchmarks, its position was sometimes estimated based on two pairs of
intersecting lines rather than three.
A total of 70 conchs were tagged with the intent of
tracking their movements during incoming or outgoing tides. Data for 13 of these conchs were not
retained for various reasons (e.g., animal loss due to
murky water, tag loss caused by foraging crabs, visitor interference). In addition, 15 conchs did not
move at all and 5 moved less than 0.5 m (the minimum movement detectable by triangulation to the
benchmarks used), so their data were omitted Thus,
data for 37 conchs formed the basis for this movements analysis. These 37 conchs were tracked for an
average of 5.9 positions/conch (range: 2-22) while
they travelled a mean path distance of 6.91 m (range:
0.55-49.92). Two of the 37 conchs were tracked
before and after a high tide; their total tracks were
divided into incoming and outgoing tidal segments,
thus yielding a total of 39 tracks for analysis. The
tracked conchs averaged 51 mm in shell height
(range: 26-90).
Figure 1A shows vectors summarizing the intertidal positions of 19 crown conchs tracked during
outgoing tides, based on their beginning and ending
positions. Of the 19 conchs tracked, 17 moved pro-
RESEARCH NOTES
2
4
6
8 10 12 14 16 18
DISTANCE ALONGSHORE (meters)
20
Figure 2. Paths taken by selected crown conchs. See
text for details [s = start; e = end; t = duration (hr); v
= velocity (m/hr); arrow = peak high tide ]
gressively offshore, one barely moved offshore, and
one moved onshore. Collectively, these conchs
moved an average distance of 2.84 m offshore (range
6.89 m offshore to 0.87 m onshore). For at least 15 of
these 19 conchs, the ending positions of their tracks
were locations where they buried at least partially
into the substrate, either shortly before or after
being exposed by the outgoing tide. Degree of bunal
was greater on the sand-mud flat than in the Spanina
zone, presumably due to differences in substrate
compactness and/or shading from solar exposure
Occasionally a conch was observed continuing to
move offshore (- 0.5 m) after already being exposed
to air by the outgoing tide. Figure IB shows vectors
summarizing the intertidal positions of 20 crown
conchs tracked during incoming tides, based on their
beginning and ending positions. Of the 20 conchs
tracked, 10 moved progressively onshore, two barely
moved onshore, and eight moved progressively offshore. Collectively, these conchs moved an average
distance of 1.65 m onshore (range: 21.24 m onshore
to 4.90 m offshore). Of the 20 conchs which moved
less than 0.5 m (or not at all) after being tagged, 16
(80%) were being observed on an incoming tide, and
were located at positions further from the high tide
line.
Selected examples of crown conch tracks are
shown in Figure 2 to illustrate the types of movement patterns observed. Conchs A and B travelled
about twice the average distance offshore during an
outgoing tide. Conch C reversed its direction shortly
after peak high tide. Conch D travelled about five
times the average distance onshore during an incoming tide. Conchs E and F were not well oriented with
respect to the onshore direction during incoming
tides. Conch F was among the fastest conchs tracked;
131
it exhibited an average velocity of 12.81 m/hr over a
67-minute period.
Further evidence of the tendency to move offshore on an outgoing tide was provided by analysis
of shell orientation in buned conchs. In a separate
survey, 58 conchs were encountered buried at low
tide an average of 6.9 m from the high tide line
(range: 4 3 to 12.2). The direction in which the shell
was oriented and the direction toward the shoreline
was recorded for each conch. A V-test7 found the
distribution of conch shell orientations to be significantly clumped in the offshore direction (u = 2.633,
P<0.005), with the average direction being only 21
degrees deviant from directly offshore. This pattern
reflects the directions conchs were going upon being
stranded by the outgoing tide. The 58 buried conchs
had a mean shell height of 34 mm (range: 21 to 66
mm). There was no significant correlation between
conch size and distance from the high tide line where
buried.
The movements of a crown conch over two tidal
changes are summarized in Figure 3 Conchs foraging in the upper intertidal zone begin moving offshore in apparent anticipation of the outgoing tide.
They bury, at least partially, either shortly before or
as soon as they become exposed by the outgoing
tide. After becoming resubmerged to a depth of
about 5 cm by the incoming tide, most conchs
emerge and begin moving again. Most of these
conchs move onshore following the incoming tide
and forage nearer to the high tide line, however, a
significant number of conchs remain at about the
same distance from the high tide line after emerging,
or even move further offshore
Tracking data also allowed analysis of the velocities travelled by crown conchs during their tidal
movement cycle. Based on overall paths taken,
conchs crawled at an average velocity of 5 05 m/hr
(range: 0.63-13.97). Conchs that travelled entirely
within the Spartwa zone travelled substantially
slower (2 08 m/hr ± 1.03) than conchs that travelled
entirely within the sand-mud flat zone just offshore
from the Spanina zone (7.57 m/hr ± 3 74), and this
difference was significant (Student's t = 6.29,
P<0.0001). There was no significant relationship
between conch shell size and overall velocity, even
within microhabitats (.Spanina versus sand-mud flat)
Based on consecutive position records for the 37
conchs tracked, 182 velocity estimates were
obtained, each based on an increment of a conch's
total path. The greatest velocity achieved by crown
conchs was about 25 m/hr.
Thi* study indicates that crown conchs were moreuniformly oriented offshore on the outgoing tide (18
of 19) than they were oriented onshore on the
incoming tide (12 of 20). This difference may reflect
a difference in selective pressure associated with
movements during the two tidal phases. On an outgoing tide, conchs failing to move offshore are
exposed longer to the air and have their total foraging time shortened. In contrast, conchs failing to
move onshore on an incoming tide can still forage at
their intertidal locations, or even further offshore.
132
RESEARCH NOTES
Low <
Tide\
Line i;
:vx|:|xjx|
If
;•
High :!
Tide >
Line _
m\
:•:•:•:•:•:•:•:
Ixjxv'i;::
:|:::jx;:;:::
•:j:jxjx|:j:
*Xjr
'
A=Moving offshore
B=Buried
C=Moving onshore
D=Foraging
ill
VV.v.1 SNAIL
^-WATERUNE
TIME
Figure 3. General model showing distance from high tide line of the waterline (shaded area = water) and
positions of crown conchs over two tidal periods. Conchs move offshore in anticipation of the outgoing tide
(A), but are eventually overcome, at which time they bury at a location exposed to air during low tide (B).
Shortly after resubmergence by the incoming tide, conchs move onshore (C), where they forage during high
tide (D).
Table 1. Average velocities reported for various
large gastropod molluscs.
Gastropod
Haliotis
kamtschatkana
Cassis (3 species)
Lambis (4 species)
Strombus (5 species)
Strombus gigas
Strombus gigas
Fasciolaria tulipa
Busycon contrarium
Melongena corona
VELOCITY
(m/hr)
9.6
4.7-6.8
6.5-11.0
0.7-4.7
4.1
24.2
25.0
6.0
5.1
Reference
Voltzow (1986)
Miller (1974)
Berg (1974)
Berg (1974)
Hesse (1979)
Miller (1974)
Miller (1974)
Voltzow (1986)
herein
without lengthening their exposure to air or having
less time for foraging. The advantage gained by
those conchs moving offshore on an outgoing tide
can be estimated from the available data. Since the
time and water depth were both recorded at each
position recorded for each conch, and since the
water depth was regularly recorded at the most offshore-positioned benchmark, the time could be computed when each conch would have become
stranded had it remained at the intertidal location of
its first position record. The difference between this
time and the time when each conch actually became
stranded (or buried) at the intertidal location of its
last position record provided the time advantage
experienced by that conch. The average time advan-
tage for the 19 conchs tracked on the outgoing tide
was 34 minutes. Of course, this time advantage
accrues again on the incoming tide; and since Goose
Creek Bay experiences semi-diurnal tides, this
advantage doubles again over a 24-hour day, for a
total of 227 hours/day in average advantage gained
from this movement strategy. (This assumes that
crown conchs are equally active at night; conchs
were observed actively foraging at night but tracking
data were not obtained.)
The adaptive value for conchs to forage in the
upper Spartina zone is amost certainly tied to the fact
that this area possesses the shortest Spartina stems
and the greatest concentrations of marsh periwinkles,
Littoraria irrorata6 and mussels, Geukensia
demissa,
two common prey species. Most prey are found on or
just beneath the sand surface. However, crown
conchs were sometimes found tilted up on short
stems of Spartina at low tide, and upon investigation
were found to be feeding on marsh periwinkles which
had ascended short stems prior to the previous high
tide. On one occasion, a small M. corona (2.6 cm
shell height) was encountered 18 cm up on a Spartina
stem, about 4 cm above the water line, feeding on an
adult L. irrorata (1.7 cm shell height).
The average velocity observed here for crown
conchs (5.05 m/hr) compares reasonably well with
average velocities reported for other large gastropods (Table 1). The average velocities reported
by Miller for Fasciolaria tulipa and Strombus gigas
seem high; indeed these values are more similar to
the maximum velocity for Melongena corona (25
m/hr). Miller's average velocity for & gigas differs
substantially from the value reported by Hesse,2 and
from the range of values reported by Berg* for nine
133
RESEARCH NOTES
strombids. The slower velocities exhibited by crown
conchs moving through Spanina could be due to
several factors. Occasionally, Spartuw stems seemed
to impede a conch's progress, but that did not seem
to be a major factor There are undoubtedly many
sources of food odour m the Spamna zone, given the
abundance of prey living there and the accumulation
of dead animals deposited there during previous
tides; this multiplicity of odour sources may lead to
inconsistent orientation and slower movement Also,
neogastropods tend to orient into the current in
response to prey and food odours, and current flow
is certainly slower and more directionally variable
amid the Spamna, which could make oriented movements less precise and slower.
I thank D. Mernll for assistance, C. N D'Asaro
for editorial comments, and staff of the St Marks
National Wildlife Refuge for their cooperation.
REFERENCES
1 UNDERWOOD, AJ 1979 AUv Mar. Biol Ecol.,
16: 111-210
2. HESSE, K O 1979 Bull Mar Set, 29- 303-311
3. MAGALHAES. H 1948. Ecol Monogr, 18 377409
4. HATHAWAY, R.R.
5
6.
7
8
9
10
& WOODBURN, K.D
1961
BulL Mar Sa , 11: 45-65
BOWLING, C. 1994. J Exp Mar Biol Ecol, 197
181-195
HAMILTON, P.V 1978. Mar Biol, 46. 49-58.
BATSCHELET, E 1981 Circular statistics in biology. Academic Press N Y.
MILLER, S L. 1974 J Exp Mar Biol Ecol, 14
99-156.
BERG, CJ. 1974 Behaviour, 51.274-322.
VOLTZOW.J 1986 Can.} Zool, 94- 2288-2293
] MolL Stud. (1996), 62,133-135
Biochemical composition of prosobranch egg capsules
Patricia Miloslavich
Umversidad Simdn Bolivar, Instituto de TecnologCa y Ciencias Mannas (INTECMAR),
Postal 89 000, Caracas 1080, Venezuela
The egg capsules of gastropods are structurally and
chemically complex and energetically costly."
Among their attributed functions are the protection
of the embryos against bacterial attack, predators
and physical stress. ^ Egg capsules can also enclose
extraembryonic yolk,' nurse eggs and mtracapsular
liquid with nutritive value for the embryos. The egg
capsule walls have also been suggested to be a
source of extraembryonic nutrition for the developing embryos of some prosobranchs (Thais haemastoma canaliculate Duclos, 1832 and Adelomelon
brasiliana Lamarck, 1811).1J Studies on the egg capsule walls of prosobranchs have indicated that they
are microstructurally complex and composed of
three or four layers.*101"12 Histochemical and biochemical studies have indicated that these capsules
are composed by proteins and carbohydrates and
lack Upids."113-14-^"^
A previous biochemical study earned out in eggs
and hatchlings of several prosobranch species which
feed on nurse eggs (Miloslavich, unpublished) indicated that fasciolanid species do not have enough
biochemical material (protein, glycogen and lipid) in
eggs and nurse eggs to account for the total material
in the hatchlings, proposing that some of the material comes from another source within the egg capsule. The objective of this work is to determine the
protein and glycogen biochemical value of the egg
capsules and to verify the absence of upids.
The species used m this study were the buccinids
Buccinum undatum Linnaeus, 1758 from the Saint
Apartado
Lawrence estuary, Canada, Buccinum cyaneum
Bruguiere, 1792 from the Saguenay fjord, Canada,
Engoruophos unicmctus (Say, 1825) from Isla
Canbe-Chacopata, Venezuela, the fasciolanids Fasciolana tulipa hollisten Weisbord, 1962, Fusmus
closter (Phihppi, 1850) both from Isla Canbe-Chacopata, Venezuela, and the muncid Murex brevifrons
Lamarck from Isla Canbe-Chacopata, Venezuela.
The spawn masses were obtained both in the field
and under laboratory conditions. Recently deposited
egg capsules were carefully opened and their contents emptied. The egg capsule walls were nnsed
with distilled water and capsules were placed
individually in 1.5 ml eppendorfs for biochemical
determinations.
The protein determination followed the Bio-Rad
protein rrucroassay procedure based on protein dye
binding." Bovine serum albumin was used as a standard. Samples were left overnight in 1.5 ml of NaOH
0.5 N and thoroughly homogenized with the help of
a mortar. For spectrophotometer readings, a subsample of 10 ul was used. For the egg capsules of E.
unicmctus only 600 ul of NaOH were used- to homogenize the egg capsule and 80 ul sub-sampled for the
readings.
The glycogen determination was made by a modification of the iodine binding method." The procedure consists of the extraction of glycogen with
perchlonc acid (PCA) 10% and iodine binding to
produce colour Mussel VII glycogen (SIGMA) was
used as a standard. Samples were left overnight with