ABSTRAC
Some characteristics of suspended particulate matter over
two pocket sandy beaches were investigated.
The amount of suspended material varied with wave turbulence
but differences averaged out over time.
Most particulate matter (80%) was algal detritus. Fifty per¬
cent ranged from .45 microns to 500 microns in diameter.
A standing pool of littoral particuate matter seems to be
maintained, alternating between a suspended and settled state.
Availability to biota depends on balance between states.
INTRODUCTION
The sandy beach environment, though familiar to many,
remains a complex and bewildering ecosystem. Its trophic
structure is based on quantities of suspended particulate
organic matter, which "may serve as food directly or by con¬
tributing to the total carbon budget" (Fox, 1950).
The components of this suspended matter are phytoplank-
ton, zooplankton, bacteria, and detritus. Numerous studes
in various seas and coastal areas indicate that the major
portion of particulate matter is detritus (Odum & de la Cruz,
1967, Krey, 1967, Khailov & Finenko, 1970, Finenko & Zaika,
1970, Suschenya & Finenko, 1966, Ryther & Menzel, 1965,
Steele & Baird, 1961, Parsons & Strickland, 1962, Glynn,
1965). Detritus is here defined as "all types of biogenic
material in various stages of microbial decomposition which
represent a potential energy source for consumer species
(Darnell, 1967), and is recognized as the energy source at
the base of many ecosystems (Teal, 1962, Darnell, 1967, Heald,
1969, Odum & de la Cruz, 1963).
Most of the organisms of the sandy beach (e.g. echino¬
derms, sipunculid & annelid worms) depend either on "copious
supplies of finely divided and suspended, adsorbed, or preci¬
pitated organic detritus as a primary source of nutrition'
(Fox, 1950) or on the larger algal detritus washed up as
wrack. The concentration and composition of this organic
matter at any time and place is subject to an intricate array
of littoral factors, "an equilibrium between input rates and
removal rates, and we can do little more than guess at these
magnitudes" (Strickland, 1970).
Though some work has been done on the role and composi¬
tion of organic material in estuarine and rocky intertidal
environments (Glynn, 1965, McIntyre, 1970, Teal, 1962, Odum
& de la Cruz, 1967, Darnell, 1967, Heald, 1969), very little
research has been conducted on the energetics of the sandy
beach ecosystem. This study is an attempt to determine the
amount of suspended particulate matter (less than 1 cm in
diameter) available to the sandy beach ecosystem in terms of
organic carbon, the distribution of size and nature of the
particles, the protein content of the particles, and some of
the littoral factors affecting the availability of this material
to the benthic community of the sandy beach.
MATERIALS AND METHODS
Two beaches at Hopkins Marine Station, characterized by
vastly different physical parameters and ecological communi¬
ties, were chosen as sites for a comparative study. (Figure 1),
Boatworks Beach is a long, shallowly sloping beach, dominated
by fine sand grains (Md % -
and protected from heavy wave
action. Marinostat Beach is a shorter, steeply sloping beach
composed of coarser sand grains (Md % -) and exposed to
heavy wave action.
Four two-liter sea water samples were taken at each beach
just behind the roil line at approximately the same time,
Preliminary studies corroborated those of Glynn (1965) indica¬
ting that there was no appreciable difference in samples taken
during the light or dark periods of the day. Samples were
therefore taken in daylight hours during the first 3 weeks of
May at times subject to different tidal and other physical
conditions. Local wave turbulence was estimated visually as
the magnitude of water stirring at the roil line.
The sea water was filtered through a series of Tyler
screens with pores 1 cm, lmm, and 500 microns in diameter.
A 500 milliliter aliquot of filtrate was passed through a .45
micron HA Millipore Filter coated with a suspension of 1% Mgcoz.
The particulate matter remaining on the two smaller screens
and millipore filter was washed into separate tubes and collected
by centrifugation. Organic carbon was determined by a wet
oxidation method (Strickland & Parsons, 1965). Protein was
measured by the Lowry method. Chlorophyll a and phaeophytin
were determined by flourometric analysis. (Strickland & Parsons,
1965).
RESULTS
Different quantities of suspended particulate organic
matter were collected at Boatworks Beach and Marinostat Beach
at different times. This variation was strongly correlated
with the intensity of local wave stirring (Figure 2). Boat¬
works Beach was characterized by higher turbulence during
the sampling time, resulting in slightly higher amounts of
suspended carbon. Fluctuations in the abundance of sand
were also related to water turbulence.
When the amount of suspended material collected at each
beach was averaged over the period of study, remarkably simi¬
lar figures were obtained: 2879 micrograms/liter + 1207 micro¬
grams/liter as one standard deviation (Boatworks Beach) and
2115 micrograms/liter + 1057 micrograms/liter (Marinostat
Beach). This data is presented in Figure 3.
The amount of suspended material in each of the three
size classes considered: .45 microns - 500 microns; 500 microns¬
Imm; Imm - lcm; varied between the four sample sets taken at
any one time on a beach and between beaches sampled at the same
time. Thus, the relative proportion of material in each size
class (and the corresponding standard deviation) was different
each sample time (see data Appendix 1). Figure 4 gives some
indication of this fluctuation in the size distribution of
suspended organic carbon.
The average amount of organic carbon in each size class
was expressed as a percentage of the average total suspended
organic carbon. Both beaches had similar size distributions
(Figure 5). The smallest size fraction (.45-500 microns) con¬
tained the largest amount of organic carbon, the middle size
raction (500 microns - lmm) contained the least.
Microscopic examination of the suspended material pro¬
duced observations relatively consistent for the two beaches
over time and corresponding closely with those of other
studies (Glynn, 1965, Odum & de la Cruz, 1967). The pro¬
portions most commonly found were: Phytoplankton - 5%:
Zooplankton - 7%; inorganic debris (e.g. sand) - 5%; and
organic detritus - 80% (Figure 6). All but 2% or 3% of the
organic detritus appeared to be fragmentary remains of benthic
algal origin.
The amounts of chlorophyll a (micrograms/liter) obtained
for the smallest size class were converted to micrograms
phytoplanktonic carbon per liter after the method of
Finenko and Suschenya (1966). These values varied, both
absolutely and as the percentage of total suspended organic
carbon. A mean of 7% phytoplankton, correlating closely with
values discussed above, was obtained for both beaches (Figure
6).
Protein (percentage organic carbon) was determined for
two different size classes: .45 microns to 500 microns, and
500 microns to 1 cm. The smaller sized material on both
beaches contained much more protein than the larger particles,
(Figure 7).
DISCUSSION
The composition and concentration of suspended particu¬
late organic matter in the water column over a sandy beach
ecosystem vary constantly in time and space. These differences
appear to be averaged out over a periodof time well within the
lifespan of many sandy beach fauna. During the period of
study, remarkable similarities were found in the amount and
nature of material collected from two beaches characterized
by different physical and biological parameters. This suggests
that conditions other than the amount of suspended organic
matter available to the ecosystem are important in determining
the nature of some sandy beach communities.
The size distribution of particulate organic carbon was
virtually the same in both beaches. Approximately 53% of the
material was in the size range .45 to 500 microns; 11% in the
range of 500 microns to 1 mm; and 36% in the size class 1 mm to
1 cm in diameter. The predominant portion of suspended matter
in both beach ecosystems was organic plant detritus (80%),
followed by zooplankton (7%), phytoplankton (5%), and inorganic
debris (5%). The smallest particles (.45-500 microns) were the
richest in protein. A combination of several factors may be
responsible: 1) the smaller organisms are protein-rich (e.g.
phytoplankton, bacteria) and/or 2) the smaller detrital par-
ticles are older and have a greater surface area to volume
ratio, thus supporting a larger buildup of protein-rich micro¬
bial populations.
Over the brief time period studied, it has been shown
that Boatworks Beach and Marinostat Beach are exposed to
essentially the same quality and quantity of suspended par¬
ticulate material. Plausible explanations include: 1) the
source of input is the same and/or steady over time, 2) pro¬
cesses providing the material are similar, 3) the incoming
material has been sufficiently mixed to disguise source
variability.
Both study sites are surrounded by the same rocky inter¬
tidal algal communities. These biologically rich areas could
provide a substantial detrital contribution to the surrounding
sandy beach ecosystems in the same manner reef detritus pro¬
vides a base for trophic systems within a lagoon (Marshall,
1965).
The hydrodynamic forces which apparently cause extensive
variation in suspended particulate organic matter at any one
time and place are the same processes which would result in
its steady input over time. They include surface winds,
waves, currents, obstacles (e.g. rocks, larger algal drift),
small benthic irregularities causing local eddies or pockets
of calm, and the diminishing of littoral water forces with
depth (Smith, 1968). During periods of calm, plant detritus
usually settles with the fine-grained sediments. "But the
topmost layer of such sediments is often flocculent and so
easily stirred up that the detritus in it is continually re¬
exposed to decomposition in suspension" (Smith, 1968). Once
the detritus is stirred, irregularities in water cells, the
sheltering and filtering properties of floating wrack, and
the ability of detrital particles to interfere with settling,
all cause irregular pockets of detrital distribution along
the beach (Smith, 1968). Greater amounts and variation in
fine suspended particulate matter are thus to be expected
under turbulent water conditions. This is clearly shown in
Figure 2.
On calmer days, when the littoral floor is free of stir¬
ring, "the final resting place of much of the plant detritus
of the littoral is the littoral sediments" (Smith, 1968).
There are many forces favoring the retention of this material
within the littoral: the extent of the littoral, failure of
water carrying properties with depth, and the settling ten¬
dencies of detritus, especially when further consolidated by
mucus or transformation into fecal pellets. A picture emerges
of a standing pool of littoral particulate material of rela¬
tively constant magnitude, alternating between a suspended and
settled state. This pool is in equilibrium with overall
littoral input and output rates.
In the future, quantitative and qualitative studies should
be conducted on this particulate littoral material, but its
role in the energetics of the sandy beach ecosystem is of pri¬
mary importance and must not be overlooked: Basic information
badly needed includes: 1) availability of material for feeding
organisms. 2) actual utilization of the material under field
conditions, and 3) nutritive value for the consuming species
(Darnell, 1967). The precise nutritive role of organic detri¬
tus has yet to be determined.
Though all the suspended material in the water column
is theoretically "available" to consuming species, most of
the benthic biota of sandy beaches can only utilize what is
in, on, or close to the bottom. Of the standing pool of
littoral particulate material, only a limited supply is
abailable to any specific type of feeding organism aß one
time.
Critical tide factors divide the beach into sectors
exposed to sudden sharp differences in water submersion
time (Doty, 1971). Different lengths of exposure to water
should divide the beach into sectors receiving distindly
different amounts of nutrient material. The organic carbon
content of sand from these different areas, and/or biotic
communities characteristic of them, could be a function of
critical tidal heights.
The amount of organic matter entering and leaving the
sandy beach ecosystemsis balanced against the amount retained
within the system. As Seki (1968) observes, for a continuous
input (L),
where X - amount organic material
remaining at timet
X = (L/k) (1-e-kt
decomposition rate factor
(in sandy beach ecosystems,
outflow and utilization
rates are also components)
If over long periods of time, X is a constant, steady state
(ss) amount;
Xss - L/k
If one measures the organic carbon content remaining in the
sand (Xgs) and L (the amt. suspended in the water) is the
same for two pocket beaches, then k may be a useful index for
comparing littoral sand beach communities.
SUMMARY
Some characteristics of suspended particulate matter, includ¬
ing amount, nature, and size distribution of the particles,
as well as the littoral factors affecting its availability
were investigated at two pocket sandy beaches in Monterey Bay.
The amount of suspended material varied with wave turbulence,
but differences averaged out over time.
Most (80%) of the particulate matter was detritus of algal
rigin. Zooplankton comprised 7% of the matter, followed
by phytoplankton (5%) and inorganic debris (5%).
The size distribution of particulate organic carbon was
virtually the same in both beaches. Approximately 53% of
the material was in the size range of .45 to 500 microns.
The smallest particles were the richest in protein (70%).
The hydrodynamic forces which apparently cause extensive
variation in the organic material are the same processes
which maintain a standing pool of littoral particulate
matter.
The alternation of this material between a suspended and
settled state affects its availability to different sandy
beach biota.
ERENCES
1967. The organic detritus problem.
Darnell, Rezneat M.
IN Estuaries, G. Lauff (ed.), Am. Ass. Ad. Sci. Pub.
No. 83:374-375.
1967. Organic detritus in relation
to the estuarine ecosystem. IN Estuaries, G. Lauff
(ed.), Am. Ass. Ad. Sci. Pub. No. 83:376-382
M.. 1971. Critical tide factors that are correlated
Doty
with the vertical distribution of marine algae and
IN Readings
other organisms along the Pacific coast.
in Marine Ecology, J. Nybakken (ed.). Harper & How,
New York:253-265.
1970. Particulate organic
Finenko, Z. Z., and V. E. Zaika.
matter and its role in the productivity of the sea.
IN Marine Food Chains, J. H. Steele (ed.), Univ. of
Calif. Press, Berkeley:32-14.
Fox, D. L. 1950. Comparative metabolism of organic
detritus by inshore animals. Ecology 31:100-108
Glynn, P. W. 1965. Community composition, structure, and
interrelationships in the marine intertidal Endocladia
muricata-Balanus glandula association in Monterey Bay,
California. Beaufortia 118 (12).
1969. The production of organic detritus
Heald, Eric J.
in a south Florida estuary. Doctoral Dissertation at
the University of Miami.
Organic macro-
1970.
Khailov, K. M., and Z. Z. Finenko.
molecular compounds dissolved in sea water and their
IN Marine Food Chains.
inclusion into food chains.
J. H. Steele (ed.):7-18.
1967. Detritus in the ocean and adjacent sea.
Krey
IN Estuaries, G. Lauff (ed.), Am. Ass. Ad. Sci. Pub.
No. 83:389-394.
Marshall, N. 1965. Detritus over the reef and its poten-
tial contribution to adjacent waters of Eniwetok atoll.
Ecology 16(3):343-344.
1970. Energy
MoIntyre, A. D., Munro, A., and J. H. Steele.
flow to a sand ecosystem. IN Marine Food Chains, J. H.
Steele (ed.):19-31.
Menzel, D. W., and J. H. Ryther. 1964. The composition of
particulate organic matter in the western North Atlantic.
Limnol. Oceanog. 9(2):179-186.
Menzel, D. W., and H. H. Ryther. 1965. On the production,
composition, and distribution of organic matter in the
western Arabian Sea. Deep Sea Res. 12(2):199-209.
Detritus as a major
Odum,
E., and A. de la Cruz. 1963.
component of ecosystems. A.I.B.S. Bull. 13:39-40.
1967. Particulate organic detritus in a
Georgia salt marsh-estuarine ecosystem. IN Estuaries,
G. Lauff (ed.), Am. Ass. Ad. Sci. Pub. No. 83:383-388.
Parsons, T. R., and T. D. Strickland. 1962. Oceanic detritus,
Science 136:313-314
1965. A Manual of Sea Water Analysis.
Fisheries Res. Board of Canada, Bull. 125.
Parsons, T. R., Stephens, K. and J. D. H. Strickland. 1961.
On the chemical composition of 11 species of marine
phytoplankters. J. Fish. Res. Bd. Canada, 18(6).
Seki, H. Skelding, J. and T. R. Parsons. 1968. Observations
on the decomposition of a marine sediment. Limnol,
Oceanog. 13:440-447.
Smith, L. Kent. 1968. The role of benthic marine plants on
the littoral phosphate cycle. Doctoral Dissertation
at Stanford University,
Steele, J. H., and I. E. Baird. 1961. Relations between
primary production of chlorophyll and particulate carbon,
Limnol. Oceanog. 6(1):68-78.
Strickland, T. D. 1970. Recycling of Organic Matter. IN
Marine Food Chains, J. H. Steele (ed):3-5.
Suschenya, L. M., and Z. Z. Finenko. 1966. Concentration of
suspended organic matter in tropical Atlantic water and
some quantitative relationships of its components.
Okeanologiya 6(5):835-847.
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ACKNOWLEDGEMENTS
I would like to thank the faculty, staff, and students at Hopkins
Marine Station for their help and encouragement. Special
thanks go to Dr. Gilmartin, my advisor, to Dr. Phillips, for
his (almost) unfailing good humor and aid, to Dr. Welton Lee
for his brilliant bursts of intuition and helping hand,
and to Delane Munson, without whose help this project would
have been impossible.
FIGURE 1
Beaches on which study sites were established, Mussel Point
Pacific Grove, California.
.


Marinostat
Beach
C
HOPKINS
MARINE
STATION
meters

Boatworks
90
Beach
0

7
JURE 2
Micrograms suspended organic carbon per liter versus wave
turbulence at sample time.
5000
4000
53500
22500
o

2000
1500
1000
500
Marinostat Beach
• Boatworks Beach
—
—
FIGURE
Average number micrograms suspended carbon per liter
collected at each beach at different sampling times.
and mean for each beach over entire sampling time.
0
2




2





S



e

ss
.
1


—



—
c
FIGURE 4
Amount organic carbon in each of 3 size classes at two
study sites at two sample times.
100%
90
80
10
60
50
40
30
20
L
Boatworks
Beach




Marinostat
Beach



I
5004- cm
454-500



——
0
FIGURE!
Size distribution of suspended particulate matter
at study sites.
2400
2000
1600
1200
800
400
24 X 10"
20
12
b
MAY 8 0815
MAY 8 1330










—
Hüi
m-

500u-mm
C-45A-5004






.
+


W













.
—
FIGURE 6
Composition particulate matter. Observed values are compared
with those of Glynn (1965) and values calculated from chloro¬
phyll a tests. Bars mark range of values.
C
5196
149
..
5..
1

35%


.

L
Boatworks
Beach
54%
89

:


..


38%


.
9.

Marinustat
Beach
—
L
.
454-500
5004-1 mm
1 mm-1cm
0
C
FIGURE 7
Percent protein (of suspended organic carbon) for two
size classes versus known values for other organisms.
L
—

—.






8




S
5
——



—