SIGNIFICANCE OF ENVIRONMENTAL FACTORS

I

have shown

thatthe

number

^of foraminiferal species increases to the east

and

that the

number

of living

Foramini

fera in the Eggerella

advena

zone of traverse

2

(west) is greaterthan in traverse 3 (cen- tral). It

was

also observed that the

most

striking

change

in the foraminiferal fauna is with depth. Broadly speaking, the fauna can

52

SMITHSONIAN MISCELLANEOUS COLLECTIONS

VOL, I49 be divided into near-shore

(<20

^m.)

^and

^offshore

(>20

^m.)

assemblages. In terms of

numbers

ofHvingindividuals,thenear-shore areas (10-20 m.) average 177 per sample, while the offshore areas (20-40m.) average 62.

At

depths of less than 10

m.

the living

popu-

lation has

an

average of 335 individuals per sample.

Riley (1959) has

shown

that the western

end

of the

Sound

is usually about 3-5%o ^fresher than the eastern end.

The

increase in foraminiferalspecies to the eastis

most

likely

due

tothe

more

oceanic conditions

found

there

and

to the proximity of the

open

ocean

from which

migrationintothe

Sound

canoccur.

InL.I.S. the concentrationofnutrients

and

phytoplankton increases to the west (Riley, 1959).

The

significantly larger living popula- tion in the E.

advena

zone of traverse

2

^is probably related to the potentiallygreaterfood supplyinthewesternarea.

To

relate the foraminiferal zonation with depth to environmental factors is

more

difficult. Riley (1956, pp. 17, 18) has

shown

that the seasonal cycle

and

range of variation in temperature

and

salinity at near-shore (8-12 m.)

and

offshore (19-28 m.) stations in the central part of L.I.S. are about the same.

Moreover,

the seasonal cycles

and

range of variation in phosphate, nitrate,

and oxygen

at near-shore

and

offshore stations

do

not

show

significant differences (Riley

and

Conover, 1956, pp. 51, 52, 54). Since the Foraminifera are holozoic, the seasonal cycle

and amount

of nutrients should affect

them

only insofar as it affects the organisms

upon

wliich they feed.

Very

^little is

known

concerning the

oxygen

requirements of the

Foraminifera.

At

several stations a strong

odor

of

HgS emanated from

the black

muds

in the cores,

and

at

some

of these stations the living population

was

abundant. Riley (1959) has indicated that

minimum

values of

oxygen

for

bottom

waterare about

40

percent of saturation. It

would

appear, then, that although reducing conditions

may

be prevalent in the sediments

below

the surface, the sediments atornearthesurface (within1cm. orso) arenot

oxygen

deficient.

The pH and Eh

of thesedimentsha^^e notbeen investigated during the present study.

McCrone and

others (1961)

have shown

that the

pH

is usually about neutral,

whereas

the

Eh

is negative.

They

did not indicate

any

differences

between

near-shore

and

offshore stations.

I

have

already pointed out that in L.I.S. both the distribution of species

and

the

number

of living individuals bear

no

relation to the particle sizeof the sediment.

NO. I

FORAMINIFERA

IN

LONG ISLAND SOUND BUZAS

₅₃

Conover

(1956, p. 69) rqjorted that the concentration of phyto- plankton

under

aunitareaof seasurface is usuallygreaterinthe off-

shore areas.

Although

planktonic diatoms

were shown

to be

an

important source of food for

Elphidium

crispum,

Myers

(1943) indicated that this foraminifer fed for the

most

part

on

benthonic unicellularplants.

No

dataare available

on

the distribution or quan-

tity of benthonic microflora in L.I.S. Riley (personal

communica-

tion) has indicated that calculations

from

Secchi disc readings indi- cate that the lower limit of the benthonic microflora in L.I.S. is

about

11m. None

of the species in this study is restricted to depths of less than 11 m., but

Elphidium

clavatum is

most abundant

at depths of less than 10

m. and

is relatively rare at depths of greater than

20 m.

(fig.8).

Bradshaw

(1955)

found

that

one

of the species of foraminifers

which he was

culturing

would

feedonly

on

thelivingdiatomNitzchia,

whereas

another species

would

accept living

and dead

flagellates as well. In L.I.S., species of Nitzchia are

more

often

found

in near- shore areas (Conover, 1956, p. 94).

Lee and

others (1961)

found

that

an

algal flora of eight species of pennate diatoms

and

three of blue-green algae best supported the species they

were

culturing.

Myers

(1943, p.

442)

suggested that

below

the photic zone the

growth

of bacteria

on

fecal pellets

might

constitute

an

important source of food for the Foraminifera. Apparently the food require-

ments

of the Foraminifera are

complex and

vary

from

species to species.

Although

a given species

may

accept

many

kinds of food,

it is likely that certain types or associations are

more

beneficial to it

than others.

Perhaps

in this

way

niche diversification

among

ben- thonicforaminifersisachieved.

Because

temperature, salinity, nitrate, phosphate, oxygen,

pH, Eh,

particle size of the sediment,

and

con- centration of phytoplankton

do

not apparently control the observed depth zonation, I suggest that the foraminiferal species in L.I.S.

areselectivefeeders,

and

thattheirdepth zonationis,therefore, related to the distribution of the material

upon which

they feed.

The

environ- mental parameters

which might

control the distribution of such materialarenotreadilyapparent

from

thisstudy.