ABSTRACT
Iwo contrasting beaches characterized by heavy and light wave
action showed increasing sand organic carbon content with decreasing
tidal height.
Sand samples collected when wet and when dry from identical sites
showed significant differences in organic carbon content levels.
Evidence against the possibility that a greater number of meiofauna
was present in the wet sand samples suggest that this difference is
due to a direct contribution of organic material from the sea.
INTRODUCTION
Much work has been accomplished concerning the amount and distribu¬
tion of organic material in marine sediments off-shore and far from shore,
but relatively little work has been done on the distribution of organic
matter on sandy beaches except with respect to specific faunal distribu¬
tions or as noted as an adjunct to wave action studies. It is generally
known that "accumulation of debris in an intertidal area depends on
wave exposure, water currents, slope of the beach, coarseness of sand,
and the amount of vegetation in nearby areas." (Dahl, 1953). The material
deposited ranges in size from large pieces of wrack to dissolved organic
matter. I attempted to quantitatively measure the distribution of the
small particulate and sand-adhered organic matter including both detri¬
tus and microorganisms on a sandy beach. From the distribution of this
organic matter, I hoped to gain some insight into the amount and type
of organic matter contributed to the beach with time.
METHODS
The area of study was located on the Monterey Peninsula of Cali¬
fornia, on two contrasting pocket beaches near Hopkins Marine Station.
A diagram of the study area is presented in figure 1. The locations of
sample stations relative to tidal height is also presented. The front
beach is subjected to heavy wave action while the back beach is rela¬
tively protected. Three transects were set up on the front beach, two
on the back beach. Samples of sand were collected on three days for
each beach during the period from May 9 to May 18. Samples were col¬
lected above the higher high water line (station 4) at higher high tide
and subsequent samples were taken at four equidistant lower tidal levels
(stations 3-1) extending to just below the lower low water line as the
water receded to uncover the area. The three intertidal stations were
then again sampled starting at the lowest and moving up the beach to
obtain sand that had been uncovered as long as possible. Samples were
collected at one depth of approximately 15 cm below the surface of the
sand as little variation in organic carbon content was expected to that
depth. (Steele, 1968).
The organic carbon content was estimated by oxidation with sul¬
furic acid-dichromate with a glucose standard, using a slightly modi¬
fied procedure of the one described by Strickland and Parsons, 1968.
Fractionation of the organic matter involved use of hot and cold
trichloracetic acid for polyssacharide and nucleic acid extraction,
ether-ethanol and .IN NaOH for lipid and protein extraction, respectively.
Polyssacharides, DNA, and RNA were assayed by the Dische-Stumpf method,
(Stumpf, 1947), lipid as organic carbon by HoSO-dichromate oxidation,
and protein by the Lowry method (Lowry, 1951).
Pieces of organic material that were larger than sand grain size were
removed from the sand samples prior to extraction or analysis.
RESULTS
The front beach is characterized by coarse sand and a relatively
steep slope of about 14%, while the back beach is characterized by fine
sand and a gentle slope of approximately 6%. Off-shore kelp beds sur-
round both beaches. The sand on both beaches is well-sorted with ODø
values of .05 to .50 and SKgø values from -.1 to +.05.
Distribution of organic carbon across the beach showed no sig¬
nificant difference as determined by the "t" test.
Variation in organic carbon content with tidal height is plotted
in figures 2 and 3. In general the back beach had a 60-80% higher content
than the front beach. Mean organic carbon content increased with
decreasing tidal height for both beaches. The greatest differences
between the organic carbon content levels of consecutive stations were
observed for the front beach at low tidal heights, for the back beach
at higher tidal heights. The line separating the tidal heights of
pronounced and moderate increases between stations was approximately
2.3 feet or the mean higher low water line for both beaches.
The means of the organic content of the wet sand samples were
always greater than those of the "dry" sand samples. This difference
was significant for the front beach at the 95% confidence level. The
difference was not significant for the back beach. The level of or¬
ganic content at stations 4 were significatnly different when the two
beaches were compared, while levels at stations O were nearly identical.
The composition of the organic material was similar for all the
samples fractionated. The approximate ratio of carbohydrate to pro¬
tein to lipid was 9:2:1. Carbohydrate comprised about 75% of the total
organic matter extracted. The percentage of the estimated total organic
matter accounted for by the extraction procedure ranged from 39% to 102%,
with an average of 60%. The extraction procedure was not meant to be
exhaustive. Therefore, the results reflect only the gross composition.
DISCUSSTON
The fractionation procedure utilized indicated no real difference in
composition of the organic material at different tidal heights or between
wet and dry samples. The lack of difference tends to rule out the possi¬
bility of migration of meiofauna as the cause of the increase in organic
content in the wet samples, as meiofauna contain a considerably higher
protein content than was detected. The results suggest that the higher
organic content of wet sand is due to a direct contribution of organic
matter from the water. The fall in the organic content of wet sand with
time may be due to a number of factors including consumption by beach
inhabitants and decrease by percolation deeper into the sand. Water
drainage may be expected to be a major factor leading to the difference
between the two beaches studies. The back beach would be expected to
have more detritus clogging its smaller interstital spaces, (Eltringham,
1971) leading to retardation of water loss. This would be consistent
with the finding that an insignificant difference between wet and dry
sand organic content was found for the back beach, while the front
beach showed a difference that was significant.
ACKNOWLEDGMENTS
I greatly appreciate the advice and technical assistance given me
by the faculty, graduate students and staff of Hopkins Marine Station,
especially Dr. John H. Phillips and Dr. Welton L. Lee for their critical
reading and encouragement.
LITERATURE CITED
1971. Life in mud and sand. The English Universities
Eltringham, S.K.
Press, Ltd., London. 10 p.
1951. Protein measurements with Folin phenol rea¬
Lowry, O.H. et al.
gent. J. Biol. Chem. 193: 265-275.
Steele, J.H. and I.E. Baird. 1968. Production ecology of a sandy
beach. Limnol. Oceanogr. 13: 14-25.
Strickland, J.D.H. and T.R. Parsons. 1968. A manual of sea water
analysis. Fisheries Research Board of Canada, Ottawa.
137 p.
Stumpf. 1947. J. Biol. Chem. 169: 367-371.
0
FIGURE 1
Study area and diagram of station locations relative
to tidal height.
———
HOPKINS
MARINE
STATION
FRONT BEACH
TRANSECT
SAMPLING SSTATIONS
meters
-.-
BACK BEACH
--

40

A
N
e
FIGURE 2.
Differences between wet and dry sand sample organic
carbon content levels for the front beach.
0

1200
1000
800
600


400


200
o
3
5

2
TIDALTHEIGHTII(FT)T
QO MEAN VALUES OF CORGANIC CONTENT
-— MEAN VALUES FOR WET SAMPLES
A MEAN VALUES FOR DRY SAMPLES
FIGURE 3.
Differences between wet and dry sand sample organic
carbon content levels for the back beach.
1200
1000
800
5 600
400
200

3—
0
6 5
2
TIDAL HEIGHT (ET)
e—0—0 MEAN VALUES FOF ORGANIGECONTENT
—— MEAN VALUES FOR WETA SAMPLES
— MEAN VALUES FOR DRY SAMPLES