DISTRIBUTION
OF PHYTOPLANKTON
SPECIES WITH RESPECT TO
SALINITY BETWEEN THE COAST OF SOUTHERN
NEW ENGLAND
AND BERMUDA1
Edward
M. Hulburt
Woods
Hole
and Janet Rodman
Oceanographic
Institution
ABSTRACT
The distribution
of phytoplankton
species throughout
a range of salinities from 31.68%
to 36.53%, indicates that a considerable number arc favored by lower and a smaller number
by higher salinities.
Most of the former arc commonly
considered neritic, many of the
latter are thought of as oceanic. However, during blooms in the open ocean, neritic forms
may become abundant.
The appearance
of these as related to nutrients as well as salinity is
-discussed.
served at 10 or more stations are included.
A salinity between 34.0%0 and 34.5%0 was
not observed at any of the stations, the
only salinity range not included.
A majority of the species were found
more frcqucntly
at low salinities ( <34%0;
37 observations)
than at high salinities
( >34.5%0; 28 observations).
The most extreme forms, those with no record of occurrence in water of 34.5%0 or over, are
Skeletonema costatum, Coscinosira
oestrupi, and Prorocentrum
micans. Other
forms, primarily diatoms, had a high frequcncy of occurrence at low salinities but
were also found occasionally at salinities
RESULTS
over 34.5%~. The best example of these is
The salinity of the water from which
Rhixosolenia
alata, which was observed
phytoplankton
samples were taken varied
most frequently ( 16 times) at salinities befrom 31.68%0 to 36.53%0; the lowest being
low 33%0 but was also twice recorded at
close to the mouth of the IIudson and
salinities greater than 35%0.
Raritan rivers and the highest near BcrNitzschia closterium was found at all
muda. Over the continental shelf salinities
observed salinities.
Two other diatoms,
were less than 34.0%0. Seaward of the IOORhizosolenia
stolterfothii
and Nitzschia
fathom line the salinities were always
delicatissima, were found as frequently at
greater than 34.5%0. The frequency of the high as at low salinities. Katodinium rosalinity observations in ranges of 0.5%0 is tundatum, Oxytoxum variabile, and Syrapresented in Figure 1, which also shows cosphaera pulchra were also widely disthe number of times each species was ob- tributed throughout the salinity range.
served for each salinity range on the four
Only three species were clearly associcruises. All species (68) which were ob- ated with the higher salinities.
Syracosphaera mediterrunea was never observed
L Contribution
No. 1185 from the Woods Hole
at salinities less than 34.5%0, though obOceanographic
Institution.
This work was supserved 10 times at higher salinities. Cocported by the United States Atomic Energy Comcolithus
huxleyi and Discosphaera tubifer
mission under contract AT ( 30-l )-1918.
were each observed only at one station
2 Present address : Bryn Mawr Collcgc,
Bryn
Mawr, Pennsylvania.
where the salinity was less than 34%0,
263
INTRODUCTION
An investigation has been made of the
distribution of phytoplankton
species relative to the salinity between southern New
England
and Bermuda.
Samples were
taken at stations over the continental shelf
(<lOO fathoms) to the cast and south of
New York. Twenty-five
stations were occupied in February and 26 in July 1957.
Samples were also taken bctwcen the continental shelf and Bermuda, 9 stations being occupied in August and 8 in Dccembcr
1959.
264
EDWARD
M.
EIUL-BURT
AND
-JANET
RODMAN
I2
IO
8
6
4
2
’
32
33
34
35
36
37
KATODINIUM
ADTUNDATUM
-
itiiin’zE’An,
32
33
h
34
35
36
37
,F$!yyPmn (
32
33
34
35
36
37
SALINITY
FIG. 1. The frequency clistribution
as rclatccl to salinity.
of salinity
though they were observed 15 and 11
times respectively at higher salinities.
The relative abundance of some of the
more frequent species has been obtained
by dividing their counts by the total number of cells counted ( Fig. 2). A wide
range is illustrated by Skeletonema costatum, which made up as much as 40% of
whereas Prorocentrum
some populations;
micans never exceeded 10% of the population, though it was observed just as fre-
and the frequency
of observation
of various
species
quently as Skeletonema. Rhixosolenia n&a
had a maximum relative abundance of almost 90% at low salinities but only 1% at
high salinities. There was a wide range
for species that were ubiquitous and for
occurred at
species that predominantly
high salinities.
Neritic and oceanic species
A list of all species which were observed
only at salinities less than 34S is presented
PHYTOPLANKTON
05
NERITIC
I
I
.
0.4 -
I
SPECIES
I
I
06
Skeletonema
costatum
SPECIES
I
UBlQUlTOUS
I
I
AND
SPEClES
I
I
.IOT
.
.
OCEANIC SPECIES
I
r
,
Coccol~thus
huxleyl
Nltzschlo
closterium
-07-
.
SALINITY
.
.
-09’
.
0.3-
-06-
-06b
.
$j
0.2-
.
l
l
I
-07-
-05
.
i=
l*
SALINITY
FIG. 2.
The relation
of the relative
abundance
in Table 1 and of all species only observed
at salinities greater than 34.5%0 is given in
Table 2. Many of these species were observed less frequently than 10 times and
consequently are not included in Figure 1.
Among the 56 species observed only at
the lower salinities diatoms were more
numerous than dinoflagellates
or coccolithophores. Of the species in Table 1, 37
( 66% ) are described as neritic in standard
taxonomic works (i.e., Cupp 1943; Lebour
1925) and in distributional
studies (i.e.,
Graham and Bronikovsky 1944). Ten of
these species are listed as oceanic and the
remainder as either both or questionable.
Thirty-one species were observed only
at salinities greater than 34.5%0. Coccolithophores, characteristic of the tropical and
open ocean, are more numerous than dinoflagellates and just as numerous as diatoms
in the list given in Table 2. Twenty-four
(77%) of all species listed are generally
considered oceanic. Two of the diatoms
of various
species to salinity.
are frequently referred to as neritic; the
remainder of the species are referred to as
common to both environments or questionable.
Our observations bear out, in general,
the neritic and oceanic characterizations
that have been given to many species.
However,
during phytoplankton
blooms
many neritic diatoms may appear in the
open sea where salinities always exceed
34.5%0. At Bermuda these blooms are very
ephemeral, so that the appearance of a
neritic form in great abundance is not usual
( Hulburt,
Ryther, and Guillard
1960).
Blooms were observed on 15 April 1958
and on 14 April 1960. On both of these
dates a considerable proportion of the species was neritic ( Table 3). On 15 April
1958 when the greatest number of cells was
observed, neritic diatoms were more abundant than other forms (12 of a total of 19
species). On 14 April 1960 the total number of cells was less, and 7 of 15 species
266
EDWARD
TABLE 1.
--
M.
HULBURT
Species observed
N = neritic
AND
only
JANET
RODMAN
at salinities
0 = oceanic
lozuer than
___~ ~
Dinophyceac
___~
Diatomaceac
N
N
N
N
N
0
N
0
N
N
:
N
N
N
N
N
N
N
N
N
N
0
N
N
N
N
N
Actinoptychus
undulatus
Biddulphia
alternans
Chaetoceros affinis
Chaetoceros radicans
Chaetoceros compressus
Chaetoceros concavicornis
Chaetoceros debilis
Chaetoceros densus
Chaetoceros didymus
Chaetoceros laciniosus
Chaetoceros similis
Chaetoceros socialis
Coscinodiscus marginatus
Coscinosira polychorda
Ditylium brightmellii
Gyrosigma sp.
Licmophora
lyngbyei
Melosira moniliformis
Melosira sulcata
Rhixosolenia faeroense
Rhixosolenia fragilissima
Rhixosolenia imbricata v. shrubsolei
Rhixosolenia styliformis
Skeletonema costatum
Thalassiosira decipiens
Thalassiosira granida
Thalassiosira nordenskiiildii
Thalassiosira ro tula
DISCUSSION
The appearance of neritic diatoms in the
small blooms off Bermuda shows that the
____
.~
N+O
N+O
N+O
N + 0
N
N+O
N
N+O
N
N(2)
N(T)
N
N+O
N
?
N
0
N
Ceratium furca
Ceratium lineatum
Ceratium longipes
Ceratium macroceros
Ceratium minutum
Dinophysis acuminatn
Dinophysis fortii
Dinophysis noruegica
Exuviaelkz baltica
Peridinium depressum
Peridinium globulus
Peridinium trochoideum
Phalacroma rotundata
Prorocentrwm redfieldi
Prorocentrum
lebourae
Prorocentrum
micans
Prorocentrum
ob tusidens
Prorocentrum
scutellum
N
N + 0
N
N
Calycomonas gracilis
Carteria sp.
Distephanus speculum
E bria tripartita
.---_
___
--
Other Flagellates
Coccolithophoridaccac
- were neritic. Nevertheless, the abundance
of all neritic species together was less than
that of the ever-present species Coccolithus
huxleyi. The very small bloom on 24 March
1960 also included a number of neritic spetics. The most abundant of the neritic
species observed at Bermuda are Cerctaulina bergonii and Rhixosolenia stolterfothii,
but these diatoms are observed not only
near the coast but also in estuaries (Wolfe,
et al. 1926)) so that there can bc no doubt
they are well adjusted to inshore conditions. They appear to bc just as well
adapted to the conditions fostering the
small plankton blooms in semi-tropical
waters.
34%0
0
0
0
0
0
0
- -----
Acanthoica acanthos
Braarudosphaera
bigeloujii
Pontosphaera nigra
Rhabdosphaera hispicla
Rhabdosphaera
tubulosa
Syracosphaera heimii
.-
higher salinity at Bermuda is no bar to
these species’ growth. Most of the neritic
diatoms observed in mid-April in water of
36%0 at Bermuda extend along the east
coast of Denmark, down the Kattegat toward the Baltic Sea, in water of 20%0 or
less (Ostenfcld 1913). They can apparently
survive and grow over an extremely wide
range of salinity.
Several of the species we have found more
frequently at salinities between 31.68%0and
34.5%0than between 34.5%0and 36.53%0have
been studied in culture and found to have
optimal growth at still lower salinities.
Prorocentrum micans ( Braarud 1951) and
Ceratium fusus and C. tripos ( Nordli 1953)
grow best at salinities around 20%0. Nevertheless, they grow moderately well between
15%0 and 40%0. Although the high salinity
PHYTOPLANKTON
TABLE 2.
SPECIES
Species observed
only at salinities
higher than 34.5%
0 = oceanic
N = neritic
Diatomaceac
N
0
N
0
0
O+N
O+N
0
Asterionella
bleakleyi
Asteromphalus
heptactis
Bacteria&rum
hyalinum v. princeps
Chaetoceros pen&us
Climacodium
frauenfeldianum
Coscinodiscus lineatus
Hemiuulus hauckii
Hemiaulus membranaceus
Long pcnnate single species
k(P)
0
0
0
Nitzschia closterium v. recta
Planktoniella
sol
Stigmophora rostrata
Thalassiothrix
2ongissim
Dinophyccae
0
0
0
2
0
0
Ceratium arietinum f. detortum
Ceratium arietinum f. regulare
Ceratium teres
Exuuiaella marina
Prorocentrum
rostraturn
Pyrocystis fusiformis
0
0
0
0
Acanthoica acanthifera
Calciosolenia granii v. closterium
Calciosolenia murrayi
Umbellosphaera
irregularis
Michaelsarsia
elegans
Michaelsarsla falklandica
Op hiaster h ydroideus
Pontosphaera syracusana
Rhabdosphaera
stylifer
Syracosphaera apsteinii
Syracosphaera mediterranea
Umbilicosphaera
mirabilis
Coccolithophoridaceae
:
0
:
0
0
0
water of the semi-tropical ocean may not
be ideal for these species, they should
nevertheless thrive there if other conditions
were favorable for their growth.
In many samples of oceanic water a
neritic species will bc included at almost
any time of year ( Riley 1957). In the
water between Bermuda and New England
diatoms never disappear.
Rhixosolenia
alata is much more abundant near shore,
but it persists as a rarity far into the highly
saline water of the western Sargasso Sea
(Fig. 2). Conversely, close to shore and
under the best conditions for diatoms, a
coccolithophore or specimen of Oxytoxum
may be found now and then. In fact,
AND
SALINITY
267
Syracosphaera pulchra is about as abundant at both high and low salinities.
Ubiquitous
species are represented by
Nitzschia closterium and Katodinium rotundatum. Both are found in the Sargasso
Sea, the coastal water, and shallow embayments behind the New England coast
line. Katodinium ro tundatum ( synonymous
with Massartia rotundata) flourished at a
salinity of about 15%0 in Great Pond in
summer ( Hulburt 1956) and was abundant
in another estuary in winter.
We found only a few ubiquitous species,
about 6 out of a total of 29 species. The
majority of our species are either neritic
or oceanic and thus compose two distinct
floras. However, the neritic species appear
to be usually present as minor elements in
the oceanic flora north of Bermuda and in
spring, when conditions are favorable, occur in some abundance.
Neritic species appear to bc favored at
Bermuda by availability
of iron, silicate,
of water
and vitamin B12. Enrichment
samples indicates that iron is more critically
needed than nitrogen
and phosphorus
( Ryther and Guillard 1959)) and cultures
show that several coastal or neritic species
require far more iron than the oceanic
Coccolithus huxkyi
(Ryther and Kramer
1961). Enrichment
of water samples in
plastic flasks with silicate included produced a flora of diatoms, but enrichment
with silicate omitted produced a flora
dominated by C. huxleyi and other flagellates. Vitamin B12 has a maximum during
the diatom blooms at Bermuda (Spaeth
and Menzel 1961).
Although iron, silicate, and B12 may be
important
in fostering
coastal species,
Gran (1962) observed that neritic diatoms
usually have resting spores while oceanic
ones usually do not and that these species
are thereby well fitted to the environments
that they typify. Further, Smayda (1958)
points out that the concepts neritic and
oceanic do not signify specific and dcfinable biogeographical units; a species “may
be confined to cithcr the neritic or oceanic
province, . . , because of the absence or
presence of a resting spore . , . , a nutri-
268
EDWARD
3. Species composition
Species are arranged in order
TABLE
--____-__
--
M.
HULBURT
AND
JANET
RODMAN
of the phytoplankton
at Bermuda in the springs of 1958 and 1960.
of decreasing maximum abundance.
Species marked with an asterisk
are considered neritic.
Cells/L at surface
-~~-1958
Spccics
--.-
-__-
25
March
-~--
Ai%
Coccolithus
huxleyi
Rhixosolenia
stolterfothii
Racteriastrum
delicatulum
Cerataulina
bergonii
Leptocylindrus
danicus
Bacteriastrum
hyalinum
Eucampia xoodiacus
Thalassiosira rotula
Nitzschia. delicatissima
Chaetoceros luciniosus
Chaetoceros decipiens
Nitzschia seriata
Syracosphaera
mediterranea
Thalassiothrix
mediterranea
Cyclococcolithus
leptoporus
Syracosphaera
heimii
Thalassiothrix
frauenfeldii
Dinophysis
ovum
Rhixosolenia
alata
Thalassiosira
subtilis
Chaetoceros affinis
Chaetoceros didymus
Nitzschia closterium v. recta
Katodinium
rotundatum
Chaetoceros teres
Lauderia borealis ( 3 )
Syracosphaera
pulchra
Oxytoxum variabile
Rhizosolenia
calcar avis
Chaetoceros curvisetus
Discosphaera
tubifer
Calciosolenia
murrayi
Rhabdosphaera
hispida
Chaetoceros densus
Asterionella
bleakleyi
Umbilicosphaera
mirabilis
Stephanopyxis
palmeriana
Dinophysis f ortii
Gymnoclinium
punctatum ?
Calciosolenia
granii
Mesoporus perforatus
Braarudosphaera
bigelowii
Ceratium teres
Guinardia
flaccida
Ceratium pentagonum
Syracosphaera
robusta
Bxytoxum sphaeroideum
Rhahdosphaera
stylifer
Phalacroma parvulum
Coniodoma polyedricum
Rhizosolenia setigera
Undetermined
Unde tcrmincd dinoflagcllatcs
6,400
200
20" 6,500"
300 5,800
3,000*
2,300"
1,800"
1,500"
1,200"
1,000*
1,000"
1,000
700*
so
600
20
300
300
200"
200"
200"
120
20
100
40"
20
zoo
-
Total
7,180
I
--.---
-__
31,100
hi&
917 8,550 2,000 9,280
60"
260"
- 1,9Bo”
60"
ii*
460
102"
165*
220*
612
10s
40 380
374
15
60
20
2;
30
180
220
20
ii
1oZ
80
140"
102
102
20
40
34
ii*
-34
45
75
68
60"
ii*
60
20
34
34
34
34
30"
20
20
15
20"
140
20
105
306
3,260
~____~
9,465
2,480 13,540
320
20*
40
20
20
20
ii
ii*
40
20
20
60
740
2,200
PHYTOPLANKTON
SPECIES
tional reason or a physiological reason other
than nutrition.”
We feel, however, that the
concepts neritic and oceanic are useful in
detecting factors which do foster different
species and thus produce distinct floras.
ACKNOWLEDGMENTS
The best of thanks go to Dr Bostwick II.
Ketchum for suggesting and assisting in
this study.
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AND
SALINITY
269
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