Production
Churkne
of epibenthic
salt marsh algae:
Light
and nutrient
limitation1
D. Van RaaZte2 and Ivan Valiela
Boston University
Marine
Program,
Marine
Biological
Laboratory,
Woods
Hole,
Massachusetts
02543
John M. Teal
Woods
Hole
Oceanographic
Institution,
Woods
Hole,
Massachusetts
02543
Abstract
Epibenthic
algal production
was measured in Great Sippewissett
Marsh, Falmouth, Massachusetts, in plots treated with two levels of a mixed fertilizer and with urea or phosphate.
Production,
which followed
a consistent seasonal pattern with short-lived
peaks in spring
and fall, was increased by the highest dosage of mixed fertilizer but not by the other treatments. Fertilization
also increased production
of the marsh grasses. Algal production
at
the marsh surface was limited due to shading by the grass canopy. The production
rate
decreased with increasing biomass of the grasses.
To separate the effects of light and nutrients in the treated areas, additional
small plots
were enriched with three levels of nitrogen
(suspected
as the limiting
nutrient)
and
provided with three levels of canopy cover cross-classified
to the nitrogen treatments.
Shading by the grasses reduced, while fertilization
with nitrogen significantly
increased,
production.
When the grasses were dormant, prediction
from a model of epibenthic
production based on limitation
by light compared well with observed measurements.
The
predicted production
rate was higher than that observed during the growing season of the
grasses. In the plots receiving the highest doses of mixed fertilizer
the added nutrients
comoensated for the light limitation.
since the discrepancy between predicted and observed
valuis was smaller than in the control plots.
In marshes the effects of light and nutrients in limiting algal production are probably mediated by the grasses, since these
plants shade the marsh surface and could
compete for nutrients. Many epibenthic algae grow beneath a canopy of sea grasses
or macroalgae but the interaction between
these two photosynthetic
components has
been little studied. Both light and nutrient
availability may be involved in the interaction. For example, Gargas (1970) suggested that Ruwiu
shaded the sediment
and competed with the benthic microflora
for nutrients.
Estrada et al. (1974) and
Sullivan and Daiber (1975) used measurements of chlorophyll to study similar interactions. A 14C technique is preferable since
chlorophyll may not reflect production under different light and nutrient regimes.
Here, we attempt to evaluate and sep-
arate the effects of light and nutrients on
epibenthic algal production.
Fertilization
and clipping of grasses was used to alter
the nutrient and light regimes to which
benthic algae were exposed in plots on
Great Sippewissett Marsh, Massachusetts.
We thank C. Remsen, E. Carpenter, B.
Schroeder, F. Valois, D. Shafer, and S.
Volkmann for their assistance. J. Hobbie
and B. Hargrave had helpful comments on
the manuscript.
Methods
The main fertilization
treatments were
carried out at low tide; a mixed or single
nutrient fertilizer was broadcast every 2
weeks from May to November onto salt
marsh plots 10 m in radius. The dry mixed
fertilizer
(lO%N, 6%P, 4%K) was made
from sludge from a secondary treatment
plant and used at two levels: a high ( HF)
’ This research was supported by a grant from
dose of 25.2 g m-2 wk-l and a low ( LF )
the Victoria
Foundation
and National
Science
dose of 8.4 g m-2 wk- l. Nitrogen alone was
Foundation
grants GA-28272, GA-28365 and GA39722.
Contribution
3672 of the Woods Hole
added in the form of urea ( U) , 46%N by
Oceanographic
Institution.
weight, at a rate of 5.6 g m-2 wk-l. Phos’ Present address: Department
of Biology, Dalphate granules, 2O%P by weight, were
housie University,
Halifax,
Nova Scotia.
LIMNOLOGY
AND
OCEANOGRAPHY
NOVEMBER
1976,
V. 21( 6)
862
Epibenthic
salt marsh algae
added at a rate of 6.5 g m-2 wk-l. Each
treatment was applied to two replicate
plots. Details of the fertilization
regime
and nutrient retention in the plots arc
given in Valiela et al. ( 1973).
To measure production of epibenthic algae, an intact shallow core (0.5 cm deep
X 2.5 cm in diameter)
of surface sediment
collected with a plastic corer was placed
in a clear or black jar, and incub,ated with
10 ml of filtered marsh water containing a
known concentration of 14C-NaHCOa. The
cores were slightly submerged within the
jars. These samples were incubated at the
sampling site for about 3 h between 1000
and 1500 hours. The uptake of 14C was
stopped with 3% Formalin, and 14CIuptake
was then determined as described by Van
Raalte et al. ( 1974).
Cores were obtained from within each
of the HF, LF, P, and U pIots. Since Spartina growth in parts of this marsh is spatially heterogeneous, cores were also collected 2-5 m outside each plot to act as
controls. Samples from within the fertilized plots are, referred to1 as “inside” samples and the controls as “outside” samples.
Monthly samples were obtained for two
replicate light and dark incubations from
within each plot and ,at its corresponding
control site from 1972 to, 1974. Sampling
was done mainly on sunny days so that
rates could be compared from month to
month. In 1973 and 1974, samples from
sites inside and outside the plots but not
covered by the grass canopy were obtained
to study the effects of shading by the grass
during summer; these samples are referred
to as “unshaded” as opposed to the normally “shaded” samples.
During the summers of 1973 and 1974, a
small-scale fertilization
experiment
was
performed with l-m2 plots enriched with
three doses of urea, Since the concentration of NH4 in the pore water of the urea
plots was quite high, lower levels of urea
were used to fertilize the m2 plots: 1.9 g
m2 (HU), 0.95 g m-2 (MU), and none
(LU), all applied every other week for
the duration of the experiment. This expcriment also involved three levels of can-
863
opy cover cross-classified
to the urea
treatments. These light treatments were
obtained by removing all (no shading,
NS ) , half (medium shading, MS), or none
(high shading, IIS) of the grass plants in
the plots, The treatment
combinations
wcrc randomly assigned to a row of adjacent replicate ma plots in a homogeneous
area of low marsh.
The standing crops of marsh grasses
were measured monthly by harvesting a
O.l-m2 quadrat in low marsh inside and
outside each plot. After sampling, plant
standing crop was dried overnight at 60°C
and weighed. Details of sampling of vegetation and discussion of the vegetational
data are given elsewhere (Valiela et al.
1975).
Light was recorded continuously
with
an Epplcy pyrheliometer.
A Cd-S light
meter was calibrated to the Eppley meter
and used to measure the intensity of light
filtering through the grass canopy at sclected sites where algal production
was
measured.
Results
Seasonal variation in hourly procluction
rates-Regardless
of fertilization treatment,
hourly algal production
followed a consistent seasonal pattern (Fig. 1). Production was low during summer and early
winter, with peaks in spring (FebruaryMay) of up to 115 mg C m-2 h-l and in
fall (September-October)
of up to 60 mg
C m-2 11-l. Th ese periods of high production were usually brief and their dates
somewhat variable.
During
1972, the
spring peak apparently occurred between
our monthly samplings and was not observed. The peaks were not missed in the
following years since they coincided with
blooms of green filamentous algae (CZudophora spp. and Sphongomorpha spp.)
which were so obvious that sampling was
adjusted.
Effect of fertilization on algal procluctivity-Algal
production in the I-IF plots was
usually slightly higher than the corrcsponding controls. The differences between the
LF and U plots and their controls were
864
Van Raalte et al.
--+--
OUTSIDE
INSIDE
iiF
-OUTSIDE
--a--
INSIDE
80
.
-DUTSlDE
---CT---
U
INSIDE
.
-OUTSIDE
--O--
P
INSIDE
801
Fig. 1. Seasonal fluctuation
side plots undergoing
the HF,
take of 14C.
( (x) & SE ) of low marsh epibenthic
algal production
inside and outLF, U, and P treatments in Great Sippewissett Marsh measured by up-
slight if any, while no effect at all was
seen in the P plots ( Fig. 1). The inside
vs. outside control production values are
plotted in Fig. 2. A Kolmogorov-Smirnov
one-sample test comparing the frequency
of points above and below the line of
equality showed no differences between
the production of algae after the phosphate, urea, and LF treatments and their
controls. However, the number of points
above the 1: 1 line in the HF plots was
significantly
( P = 0.01) greater than that
below, implying that algal production in
the HF plots was significantly
(P = 0.01)
greater than in the controls.
Effect of light on marsh algal productivity-The
more grass in a plot, the less light
reached the marsh surface (Fig. 3 ) . Some
observations of the amount of light reaching the sediment surface were made during routine measurements of carbon fixation (Fig. 4). The production of algae on
the marsh surface during summer increased
as the amount of light penetrating
the
canopy and reaching the surface increased.
The production from shaded sites under
grass was lower than in nearby naturally
unshaded areas in all treatments ( Fig. 5).
In the m2 plots where the grass was clipped
to create unshaded areas, production was
significantly
increased as shading by the
canopy decreased ( Table 1). Figures 4
and 5 and Table 1 show in different and
independent ways that light was important
in determining marsh algal production. An
additional indication is that epibenthic production in the marsh followed a diurnal
curve (Fig. 6) whose shape suggests that
the rate of production over a day is limited by the availability of sunlight. However, this diel variation may have an endogenous component since it is maintained
when marsh cores are held constantly in
the light ( Gallagher and Daiber 1974a).
To facilitate monthly comparisons, we took
all samples discussed in this study between
midmorning and midafternoon.
During 1 year ( 1973) dark fixation for
Epibenthic
J
80
t
-0
40
d)P
/
l
20
865
salt marsh algae
60
80
100
0
20
40
60
80
100
mg C mm2 h -I OUTSIDE
Fig. 2. Production
of epibenthic
algae, inside
each graph indicates points with a ratio of one.
treated and untreated samples was 14.3 *
0.9% (X * SE) of light fixation and did
not differ with treatment.
Combined effects of light and nutrients
-Production
was measured several times
in both 1973 and 1974 in nine replicated
plots subjected to three levels of shading
and three levels of fertilization
by urea.
Single degree of freedom comparisons
showed that the three levels of shading
(NS, MS, and HS) decreased production
rate, and that within each light level fertilization with urea increased the uptake of
vs. outside.
a-EIF;
b-LF;
c-U;
d-P.
Line
in
carbon (Table 1) ; HU did not differ from
MU.
Since light and nutrients do not interact in their limitation of production (Table l), samples from the fertilized plots
show nutrient effects which are independent of the light effects. The production of
algae in HF plots ( Fig. 7a) is higher than
that in control plots (Fig. 7d), Carbon uptake rates by the algae in the HF plots
are reduced to the level of the control
rates only when the amount of grass is
2-3 times higher than in the controls. Nu-
866
Van Raalte et al.
0
.
3
.
20 1
I’
/’
I
I
I
I
200
400
LIVE
.
/‘.
l
l
I
C-
0’
.
w
. /‘-*
,/-
600
GRASS
I
600
BIOMASS
1000
1200
(gm-2)
Fig. 3. Salt marsh live grass biomass vs. percent of light measured at sediment surface below
the grass. Equation for line is x/100-y
= 0.077x
+ 2.86; 95% confidence
interval
of the slope is
0.0057 - 0.0098; correlation
coefficient
is 0.924.
trients compensated to some extent for the
lack of light since algae photosynthesized
at low levels of light when an external
source of nutrients was provided.
The
scatter in all the data of Fig. 7 is probably
due to local spatial heterogeneity in the
grass canopy and in algal distributions. The
LF treatment (Fig. 7b) only offered a hint
of increasing production
and probably
demonstrates threshold effects of fertilization. There was little effect of fertilization
with urea (Fig. 7~).
Nutrient
and light effects could be
ov:
0
:
20
:
:
40
SHADED
;
;
:
:
:
60
80
(mg c m-2 h -1)
:
100
Fig. 5. Production
of surface cores taken beneath the grass canopy (shaded)
vs. those in
naturally
bare areas ( unshaded ) from all treatments during summers 19721974.
Since there
were no differences
among treatments,
all points
are shown with same symbol.
evaluated by predicting algal production
based on the effect of light alone and comparing the predictions to field measurements. Differences
between predictions
and observations must be due to other factors such as nutrient availability.
The re-
Table 1. Three-way
analysis of variance of effects of light, urea fertilization,
and time on production of algae in the ma plots.
Source
of Variation
Light
MS vs.
NS vs.
df
.
0
10
.
20
30
40
mgcm-2h
50
-1
60
70
Fig. 4. Epibenthic
algal production
vs. light
reaching surface of the marsh during
summer
months.
Equation
is mg C m-’ h-’ = 7.5324 +
0.1225 x cal cm-l d-l.
F
2
1
1
11,496.5
8.8*
9.5*
8.1*
2
1
1
3,035.l
6.6*
1.0
11.1*
Tine
FXL
LXT
FXT
FXLXT
3
4
6
6
12
8,377.6
2,776.4
1.306.4
500.2
664.5
2.8
4.2
0.4
0.2
0.2
Error
36
3,042.g
Total
71
HS
HS 61 MS
Fertilization
HU vs MU
LU vs MU & HU
0
MS
* Significant
at the 0.1
level,
Epibenthic
HIGH
LOW
ol
salt
MARSH
MARSH
,
, l--.-f-?4-,
,
,
,
,
,
,
1 0400
1 0800
\ 1200
1 1600
\ 2000
\ 0400
0200
0600
1000
1400
1800
2200
9
JULY
1974
Fig. 6. Diurnal
curve of production
((x> z!z
SE ) of epibenthic
algae in high and low marsh,
July 1974. Vertical bar indicates SE of the mean
and horizontal
bar hours of incubation,
marsh
867
algae
lationship between light reaching the surface of the marsh and algal production was
shown in Fig. 4. If the amount of light
which actually reached the marsh surface
on each day is known, then the rate of algal production for each day based on light
alone can also be predicted. The Eppley
pyrheliomcter records had to be converted
to light actually reaching the marsh surface. The standing crops of grass for each
day were calculated by interpolation from
the monthly samples of marsh vegetation.
We then determined the percentage of
light reaching the marsh surface for each
day, using the data in Fig. 3, Multiplication of this percentage by the amount of
light measured by the pyrheliomcter
on a
70
60
aHiF
t
b)LF
2
4
6
8
L I v E
IO
12
G R A5
14
S
2
0 I OM A S S
4
IlO2
6
I
I
I
IO
12
14
gmw2)
Fig. 7. Live grass biomass vs. production
of epibenthic
algae on scdimcnt
surface below grass.
a-HF;
b-LF;
c-U;
d-control.
Dotted line in each graph (y = 55.1-0.48~
-Jr 0.0012) is rcgression of control data and is incIuded to facilitate
comparisons with other treatments.
868
Van Raalte et al.
1000
LIGHT
N
INTENSITY
E1 ,“z:
1.0 -
o.8 _
CONTROL
‘E
0.6 -
LIVE
WI
x
0.4 -
cd
0.2
7
100
r
Y
60
E
0
g
GRASS
BIOMASS
GRASS
BIOMASS
-
00
40
20
0
1.0 -
cv
‘E
0,
Y
0.8.
HF
0.6.
LIVE
0.4 0.2 0-f
I
r
(u
i
v
I
100
I
1
I
I
I
I
I
I
1
I
I
PREDICTED
ALG’A
PRODUCTIVITY
80
60
40
I
J
‘F’M
‘A
Fig. 8. Light intensity (amount of light received per day), live grass biomass, and predicted algal production based on effect of light alone in control and HF areas.
given day yielded the approximate amount
reaching the marsh surface each day.
The predicted daily rate of algal production based on light availability was calculated using the relation of light and production rate in Fig. 4. Figure 8 shows the
solar radiation and the standing crops of
grass as well as the predicted production
during 1973 for the HF and control plots.
Light intensity fluctuated greatly from day
to day although there was an expected
seasonal trend, with an increase in March,
a peak in June, and a decline to a trough
in December. Grass growth started slowly
in March and April, with maximum biomass during June and August, before the
plants began to die in September. From
January through May predicted algal production duplicated the level of light intensity ( Fig. 8), with peaks from March
through May. By June the grass shaded
the algae and predicted production
decreased as grass standing crop increased.
With the senescence of the grass in fall,
Epibenthic
J
869
salt marsh algae
again mimicked
the
algal production
graph of light intensity. In the HF plots
the shading effect was greater than in the
controls since the grass biomass in the HF
plots was greater due to the fertilization.
In addition to a high rate of photosynthesis in the spring, a small fall peak is also
indicated in the HF algae.
During the nongrowing season for marsh
grasses ( October-March),
measured rates
of algal production
compared well with
rates predicted independently on the basis
of light alone (Fig. 9). However, during
the growing season ( April-September)
the
was consistently
observed
production
lower than it would be if it were controlled
only by light. The grasses deplete sediment nutrients during growth, perhaps to
the extent of limiting algal growth. Even
though the greater biomass of HF plots
intercepts
more light, the enrichments
seem to compensate, with the added nutrients leading to a closer approximation
to the production rates allowed by available light. This only happened at the highest dosage of fertilization;
similar comparisons from the LF and U plots showed no
clear effects.
Epibenthic algal production was highest
in spring and fall in Great Sippewissctt
Marsh ( Fig. 1). While several factors, including light intensity, temperature, nu tricnts and grazing, act in concert to produce
the rates we observed, light is of primary
importance.
Light intensity is greatest at
the sediment surface in spring and fall,
On sunny winter days, the production rates
can also bc high. Diminished intensity due
to shading by the grass canopy results in
low production rates in summer.
A linear increase in algal production
with light has also been found in a sandy
bay ( Gargas 1971)) a tidal flat (Taylor
1964)) and on intertidal sediment (Burkholder et al. 1965; Pamatmat 1968). The
production
of algae growing under tall
Spartina alterniflora in a Delaware marsh
was similar to that reported here and decreased from spring to summer with increased shading by the grass, but algal
production in short Spartina areas where
0
APR-SEP
0
OCT
-MAR
607
ii 1 c
)
a
60
W
VI
g
40
20
0
PREDICTED
(mg
c f-r-r2 h -I)
Fig. 9. Measured production
vs. predicted production on the basis of light alone for I-IF and C
plots.
the canopy is sparse was not decreased
during summer (Gallagher
and Daiber
1974b-).
Pomeroy (1959) measured production
of oxygen by salt marsh algae in Georgia
and found low tide values similar to ours.
Summer oxygen production in Georgia was
higher during high tide than during low
tide. Since less light reaches the marsh
surface at high tide, our results would suggest that algal production would dccrcase
with increasing tide. Pomeroy ( 1959)) by
analogy with phytoplankton
studies, ascribed the difference in production during
the tidal cycle to inhibition of the algae by
high light intensities during low tide. However, benthic microalgae are less inhibited
by light than phytoplankton
(Burkholder
870
Van Raalte et al.
et al. 1961; Pamatmat 1968; Gargas 1971;
Hunding 1971). Taylor ( 1964) found only
10% inhibition
of production when intertidal benthic diatoms were exposed to full
midday summer sunlight, a level surely in
excess of that under marsh grass. The rate
of production in Great Sippewissett Marsh
increased linearly with light to the highest light level measured at the marsh surface (Fig. 4) and was highest in areas
fully devoid of vegetation (Table 1). Algae growing under marsh grasses are unlikely to be inhibited by intense light. It
may be that Pomeroy’s (1959) results were
in part due to the use of different techniques for measuring algal production during low and high tide.
The ability of benthic microalgae to tolerate and use light at high intensities may
be an adaptation to high intensity sunflecks at the sediment surface on sunny
days. Sunflecks are important in forests
( Evans lm) . This may account for some
of the scatter in Fig. 7. Or, the majority of
algae may in fact not be exposed to high
light intensities, since sediment, detritus,
and surface algae will limit light penetration.
Increasing
epibenthic
production
was
related to increasing temperature in some
studies (e.g. Pomeroy 1959; Hargrave
1969). In Great Sippewissett Marsh, as in
other habitats (Pamatmat 1968), we found
no correlation
between production
and
sediment surface temperature
(data not
shown). This is not surprising since lightlimited photosynthesis is a photochemical
process independent of temperature at low
light intensities ( Hunding 1971) .
Fertilization
with sewage sludge at a
dosage of 25.2 g m-2 wk-l stimulated algal
productivity
in Great Sippewissett Marsh
(Fig. 2). The green microalgae, Enterommphxz and Ulva, respond particularly well to
similar enrichments (Sawyer 1965; Waite
and Mitchell 1972; Tewari 1972; Subbarmiah and Parekh 1966). Sewage effluent
also stimulates marine phytoplankton production (Ryther 1954; Ryther et al. 1972).
Estrada et al. (1974) found no increase in
sediment chlorophyll
on Great Sippewis-
sett Marsh in the same fertilized plots reported on here, probably because the grass
canopy was fully developed at the time of
sampling.
Dosages of 0.95-1.9 g rnb2 wk-l of urea
added to the m2 plots stimulated the production of algae in Great Sippewissett
Marsh. Most of the urea added to the
marsh was probably decomposed to ammonium by bacteria ( ZoBell 1935) and algae (Remsen et al. 1974). The ammonium
concentration in the pore waters of the
urea-fertilized
plots can reach high levels
( 10.%3,360 pg atoms liter-l, unpublished
data). Since urea can stimulate marsh algal production and additions of phosphate
have no effect, nitrogen is probably the
stimulating component of the sludge. The
lack of enhancement of production by urea
in the large plots is curious. Perhaps concentrations of ammonium in the pore waters bordered on levels toxic to the algae.
Various other enrichments with marine
algae have shown that nitrogen, particularly ammonium, is the primary limiting
nutrient to production (Ryther and Dunstan 1971; Vince and Valiela 1973; Goldman and Stanley 1974; Thomas et al. 1974).
Many algae use ammonium in preference
to nitrate and nitrite because it is already
reduced (Syrett 1962). Although nitrate and
nitrite are often used in enrichment experiments, we did not use these nutrients
as fertilizers in the marsh since they are
actively denitrified and may lead to equivocal results ( Valiela et al. 1975). Nitrogen
fertilization
increased algal chlorophyll in
a Delaware marsh in areas where grass was
clipped during summer, while phosphate
had no effect during any season (Sullivan
and Daiber 1975). The amount of shading
in fertilized unclipped areas in those experiments was greater than in control areas
due to the increase in grass growth, confounding the effects of fertilization
and
light.
We have measured chlorinated hydrocarbons
(Krebs et al. 1974) and heavy
metals (Banus et al. 1974) in our sludge
fertilizer : both classes may be inhibitory
to algae (MacFarlane et al. 1972; Moser
Epibenthic
salt marsh algae
et al. 1972; Rachlin and Farran 1974).
There was no evidence of any deleterious
effect of such compomlds on algal production since it was, in fact, stimulated by the
sludge. There were, however, changes in
the -taxonomic composition of the -algae
(Van Raalte et al. 1976).
Epibenthic
production in Great Sippewissett Marsh was as high as or higher
than that of the marsh phytoplankton. The
phytoplankton fixed about 5-50 mg C m-3
h-l (E. J. Carpenter personal communication) and the volume of marsh water is
approximately
5 X KY5 m3, giving a total
productivity
by marsh phytoplankton
of
2.5 X 106-2.5 X lo7 mg C h-l. The area of
low marsh ( covered by S. alterniflora)
is
about 9.8 x lo4 m2. This area, multiplied
by 1-115 mg C m-2 h-l gives a range of
9.8 X 104-1.13 X lo7 mg C h-l for epibenthic production,
Since low marsh is about
45% of the marsh area, this is an underestimation for the whole marsh.
During 1 year, production of algae in
Great Sippewissett
Marsh beneath the
grass canopy was 105.5 f 12.5 g m-2 ((xj 2
SE) in unshaded areas. This annual production is about a quarter of the aboveground seasonal grass production for Great
Sippewissett Marsh of 424 g dry weight
m-2 ( Valicl a et al. 1976). IIowever, algal
production occurs even when grasses are
dormant and may provide more easily assimilable food for coastal food webs than
that provided by the higher plants.
References
BANUS, M., I. VALIELA, AND J. M. TEAL.
1974.
Export of lead from salt marshes.
Mar. Pollut. Bull. 5: 6-9.
BURKIIOLDER, P. R., A. REPAK, AND J. SIBEHT.
1965.
Studies on some Long Island littoral
communities
of microorganisms
and
their
primary
productivity.
Bull.
Torrey
Bott. Club 92: 378-402.
EST~ADA, M., I. VALIELA, AND J. M. TEAL. 1974.
Concentration
and distribution
of chlorophyll in fertilized
plots in a Massachusetts
salt marsh.
J. Exp. M ar. Biol. Ecol. 14: 4756.
EVANS, G. C. 1966. Model and measurements
in the study of woodland
light climates, p.
53-76.
In R. Bainbridge et al. [eds.], Light
as an ecological factor. Blackwell.
871
GALLAGI-JJZR,J. L., AND F. C. DAIBER. 1974a.
Diel rhythms in edaphic community
metabolism in a Delaware salt marsh.
Ecology 45:
1160-l 163.
197427. Primary
producAND -.
tion of edaphic algal communities
in a Delaware salt marsh.
Limnol.
Oceanogr.
19:
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Submitted:
Accepted:
17 June 1975
16 April 1976