Variables Affecting Organic Decay Processes
In High Tide Pools and Some Effects of This
Process in Tigriopus californicus,
(Baker 1912)
Martin Lynch
Hopkins Marine Station
Biology 175H
Spring 1977
INTRODUCTION
The copepod Tigriopus californicus is frequently abundant in high
tide pools that have a black sediment and smell of hydrogen sulfide.
The sulfide results from the anaerobic decomposition of organic matter,
primarily pieces of macroscopic algae, brought to these pools by tidal
action. It would appear that oxygen becomes limiting in these isolated
marine enviroments due to aerobic decomposition of the same algal ma¬
terial, and the process of sulfate reduction by Desulfovibrio sp.be¬
comes conspicuous. The process of aerobic and anaerobic decomposition
affect these enviroments and may in turn have an effect upon other
inhabitants such as T. californicus. This study includes a field sur¬
vey of sulphide concentrations found in tide pools of the Central Cal¬
ifornia coastal area, laboratory toxicity studies carried out using
T. californicus, and an investigation of the relationships between
water depth and sediment depth and their affects on oxygen depletion
and sulfide generation during the breakdown of the alga, Macrocystis
pyrifera.
MATERIALS AND METHODS
In the general field survey the area of study was the high tide
pools on the Montery penninsula from Mussel Pt. to Asilomar State Beach.
Oxygen was measured using a standard Winkler titration (Carritt and
Carpenter 1966). Ten milliter samples were drawn off the bottom of
the pool just above the sediment with a pipett covered with plankton
screening. Great care was exercised in making sure no bottom sediment
that might adhere to the screening was washed into the collecting flasks.
Samples were placed in 25ml Erlenmeyer flasks and "pickled" immediately
with analysis completed within two hours. Sulphide was measured using
the colorimetric method described by Strickland and Parsons (Strickland
and Parsons 1968). Sulphide samples were collected using a large vol¬
ume turkey baster that was covered with plankton screening. Once
again care was exercised in not letting any sediment get in the sample
container. Samples were stored in 30ml glass stoppered reagent bottles
that were filled to overflowing then stoppered without the inclusion
of a bubble of air. Analyses were completed within two hours. pH read¬
ings were taken from the glass stoppered reagent bottles used for sulphide
analysis. pH was measured using a Beckman Zeromatic II pH meter.
Toxicity studies were carried out using five sulphide concentra¬
tions; 2.5x10-4, 3.Ox10-“, 3.6x10-4, 4.3x10-“, and 5.2x10 M. Solutions
were made using filtered seawater and reagent grade Sodium Sulfide and
placed in 30ml glass stoppered reagent bottles. Ten animals were added
to each bottle. The bottles were filled to the top and stoppered
without the inclusion of air. Animals are unaffected by such confinement
in plain filtered sea water for periods in excess of one week. Mor-
tality was determined and defined as a total lack of movement, even
upon shaking.
Models of high tide pools were simulated in the laboratory using
large 30 x 2.8cm test tubes. Two variables, height of the water colum
and depth of sediment were varied while the amount of organic matter was
held constant at approximately one gram of Macrocystis. The three
water levels tested were 25cm, 15cm, and 5cm. Water height was measured
as the distance from the top of the sediment to the top of the water
column. Unfiltered seawater from the Hopkins Marine Station seawater
system was used. Sediment consisted of coarse beach sand. The sand
was washed several times in fresh water to remove organic matter and
dried at 60° for one and a half days. Three sediment depths were
studied; 1.5cm, 0.5cm, and Ocm sediment. Macrocystis was supplied as
circular pieces approximately 2cm in diameter, and weighing approximately
I gram. The algal pieces were buried beneath the sediment. To further
duplicate conditions in tide pools 10-20 T. californicus were added to
each tube.
Five replicates were prepared for each set of measurements, thus
permitting the daily measurements on undisturbed preparations. Oxygen
and sulphide were measured as described above. In addition dissolved
interstitial sulphide was determined after thoroughly mixing the sedi¬
ment with the water remaining after samples were taken for oxygen and
sulphide in the overlying water. During the period of the measurements
the tubes were left open to the air at room temperature in the laboratory.
Insoluble sulphide was determined after acidification with 3N HCl.
RESULT!
Table I shows the oxygen, sulphide, and pH levels encountered in
the survey of high tide pools. The highest sulphide level observed was
352 ug/liter. Results from the toxicity studies indicated a minimum
lethal dose of 3.0x10 'M sulphide. This concentration corresponds to
10,200ug/liter or thirty times the highest concentration found in the
field. Under natural conditions sulphide does not appear to reach
levels toxic to T. californicus. However, the isolated tidepools of the
high intertidal may be affected in a variety of ways by the periodic
input of organic matter in the form of drift algae. Therefore,
laboratory simulations were studied in order to elucidate the time course
of events including changes in oxygen and sulfide. Two variables
appeared most worthy of investigation, ie. depth of sediment and height
of water column.
Figure I shows the results obtained using a water column of 15cm
and three sediment depths; 1.5, 0.5, and Ocm. Looking at figure 1, one
sees significantly lower oxygen levels in tubes with sediment while
dissolved oxygen in tubes without sediment seem to reach a higher steady
state level due to a balance between diffusion and utilization. Between
the two sediment levels ther is a significant difference in dissolved
oxygen. After fourdays the dissolved oxygen appears to increase in
preparations haveng the larger depth of sediment. Another difference
between these simulations is the initial rate of oxygen depletion is
much faster in tubes with 0.5cm sediment.
Figure 2 shows the effects of varying the height of the water
column while holding the level of sediment constant at 1.5cm. There
is a significantly faster drop in oxygen levels in tubes with shallower
sediment indicating that oxygen level is determined by diffusion. This
difference in rate of the initial oxygen depletion appears to be related
to the size of the initial amount of dissolved oxygen availible. Larger
volumes buffer against rapid change. Oxygen in the 25cm column decreases
more slowly because of a greater reservoir of oxygen. This buffering
by larger volume is also shown by the higher sulphide levels reached
in shallower tubes. Another intensity feature is the increase in oxygen
occuring with increasing sulphide on day five. This is most dramatic
in the shallower tubes.
In Figure 3 the height of the water column is held constant while
sediment depth is varied. As in figure 1, oxygen drops more rapidly in
tubes with less sediment. Also seen in figure 1 but more pronounced
here is the difference in oxygen levels for days four and five. For
the 1.5cm sediment oxygen increases steadily from day four, this is
accompanied by significantly higher sulphide levels than those seen in
0.5cm sediment preparations. In the shallower sediment oxygen levels
go below lml/liter on days four and five while sulphide never gets
above 64 ug/liter in the interstitial enviroment.
Table 2 shows the relative percentages in distribution of sulphide
in a water column with the vast majority of sulphide stored as insoluble
metallic sulphidesdeposited in the sediment. There is also noticeably
more sulphide in the interstitial enviroment in tubes with deeper
sediment and less dissolved sulphide in the water column. The total
sulphide production in these two simulations is approximately the same.
DISCUSSION
Chemical changes in the simulations suggest the participation
of three microbial populations invilved in the decomposition of organic
matter. First a group of anaerobic organisms appear to be involved in
the initial breakdown of large polysaccharides in the algal material.
This group of microorganisms may also partially oxidize the carbohydrates
released by the digestive action. As these more readily utilizable mater¬
ials diffuse from the site of deposition of the algae they become availible
to the next group, the anaerobic sulfate reducers dependent upon anaerobic
conditions within the sediment. The presence of these organisms is in¬
dicated by the production of hydrogen sulphide. Those materials not
utilized by the sulphate reducers diffuse into the water column where the
final group of bacteria, the aerobic respiring microorganisms oxidize
the nutrients at the expense of dissolved oxygen. Within the time
period studied this appears to be dependent on the existence of the
initial anaerobic digestive bacteria. The evidence for the importance
of these bacteria is shown in figure 1 where anoxic sediment is required
for oxygen depletion. This model explains the effects of different
sediment depths. In deeper sediment more of the diffusable nutrients
would be trapped inside the sediment for use by the sulphate reducing
bacteria. As the population of the sulphate reducers increases they
would us an increasing proportion of the diffusably nutrients letting
correspondingly less material reach the aerobic respiring organisms.
As fewer nutrients reach the aerobes their oxygen demands decrease which
results in increasing oxygen in the water column. This effect is easily
seen in figure 3.
Neither of these chemical changes results in a deleterious affect
on the enviroment from a chemical point of view. Sulphide never reaches
high enough levels to endanger T. californicus. The only possible dele¬
terious effect to T. californicus is the decrease in oxygen near the
sediment surface. However, T. californicus can swim to less anoxic water
higher in the column. These chemical changes maybe of greater signifi¬
cance in leading to the conversion of macroscopic algae into a form
that can be more readily utilized by organisms such as T. californicus
which can graze upon the rich microbial flora associated with the organic
decay process.
ABSTRACT
The aerobic and anaerobic decomposition of organic matter in high
tide pools and the effects of these processes on Tigriopus californicus
was investigated. Changes in dissolved oxygen and sulphide were measured
in model prepartions in the laboratory and compared to field measurements.
Macrocystis pyrifera was the organic matter used in the study. Water
column height and sediment depth were varied to obtain an estimate of
the effect of these two variables on aerobic and anaerobic processes.
The effects of changing water column with showed an inverse rela¬
tionship where oxygen decreased and sulfide increase as the column height
has decreased. The effects of changeng sediment depth showed a direct
relationship where oxygen and sulphide levels both increased as sediment
depth was increased.
The amounts of sulphide in the high tide pools in the field reached
levels of 352ug/liter, approximately 1/30 the lethal dose for T. californicus.
The importance of this decomposition process to T. californicus is dis¬
cussed.
ACKNOWLEDGEMENTS
I would like to thank Dr. John Phillips for his invaluble assistance
throughout the course of these experiments.
LITERATURE CITED
1. Carritt, Dayton E., 1966, Comparison and Evaluation of Currently
Employed Modifications of the Winkler Method for Determining Dissolved
Oxygen in Seawater; A NASCO Report, J mar Res, 24(3): 286
2. Strickland, J.D.H. and Parsons, T.R., A Practical Handbook of
Seawater Analysis, Fisheries Research Board of Canada, Bulletin 167,
Ottowa, 1968, p. 41
Table 1: Field Survey of High Tide Pools
Pool
Oxygen ml/liter
Sulphide ug/liter
352
265.6
14.7
11.1
245.8
166
13.6
———
6.7


PH
7.8
8.2
8.0
8.9
7.6
1. Ocm
sediment
2. Ocm
sediment
Table 2: Percent Distribution of Sulphide in Simulations*
Dissolved S
Dissolved S
Insoluble S"
Water Column
Sulfides
Interstial
Total!
3.4
12.6
84.0
2.2x10° ug/liter
15.9
83.9
2.17x10° ug/liter
0.2

*Values are mean levels from five simulations
Figurel: Oxygen levels in simulations with a constant water column of
15cm and varying sediment depth. Bars represent +1 standard deviations.
X—x = 1.5cm sediment in ml/liter
—□ - 0.5cm sediment in ml/liter
-O = 0 cm sediment in ml/liter
O—
L



—

O


1

—
-O

20—
0


-U¬

o
Figure 2: Oxygen and sulphide in the water column, and interstitial
dissolved sulphide in simulations with a constant sediment depth of 1.5cm.
Bars are + 1 standard deviations.
X—x = 0, ml/liter in 25cm water column
C— -0, ml/liter in 5cm water column
x......x = H,S ug/liter in water column for 25cm column
g:::E = H,S ug/liter in water column for 5 cm column
x ——x = Interstitial H,S ug/liter in 25cm water column
Q——□ = Interstitial H,S ug/liter in 5cm water column
—---D--------------
—

+--


10

—
1-----------—
+------4-



22


.u
1.
.
Figure 3: Oxygen and sulphide in water column, and interstitial
dissolved sulphide in simulations with a constant water depth of 25cm.
Bars are + 1 standard deviations.
X—x = 09 ml/liter in 1.5cm sediment
Q— -0, ml/liter in 0.5cm sediment
x......* = H.S ug/liter in water column in 1.5cm sediment
D... = H,S ug/liter in water column in 0.5cm sediment
x—— x = Interstitial H,S ug/liter in 1.5cm sediment
E--E = Interstitial H,S ug/liter in 0.5cm sediment
§




x-
— — — —x——




4
r