Abstract
Wrack macrofauna on North Moss Beach, Monterey County,
California, were studied in an attempt to determine if a faunal
succession occurs in aging wrack. Samples of naturally occur¬
ring wrack and of wrack artificially placed on the beach were
An attempt was made to establish the
collected and studied.
relative age of wrack by determining its moisture content,
assuming that wrack loses moisture gradually and steadily as it
ages. However, wrack at different stages of decay can have the
same moisture content. Therefore, no definite conclusions could
be made in regard to succession in naturally occurring wrack.
Yet, it was found that among wrack banks seemingly in the same
general state of decay, great variation in species composition
and species abundance may take place. This was also demonstrated
in samples of artificial wrack over both short and long periods
of time. The evidence suggests that typical terrestrial succession
Sporadic and sudden changes in species
does not occur in wrack.
composition and species population sizes seem to be the rule.
In an attempt to explain more clearly how such changes in the
community of wrack macrofauna may take place with time, an
hypothesis has been formulated which takes into account the
spatial and temporal variability in the state of beach wrack and
the mechanism by which typical wrack fauna may respond relative
to possible pre-adaptations to similar kinds of environmental
situations.
Introduction
The sandy beach, though virtually devoid of visible vegetation,
supports a fairly diverse animal community (Backlund, 1945). As Back-
lund (1945) has shown, wrack, i.e. detached marine algae deposited on
the beach, provides food, moisture, and shelter for many members of
this community. Yet, because of tidal variations, the residence time
of wrack on sandy beaches varies considerably (Backlund, 1945 and Evans,
1972). For instance, very high tides such as the extreme spring tides
that occur each year, may deposit wrack so high on a gradually sloping
beach that it remains there for months or even years. In contrast,
daily tides may result in a dynamic process whereby, lower on the beach,
the deposition and removal of wrack occurs on successive high tides.
The animal community inhabiting wrack is subjected to a wide variety
of changes, two of the most important being the continuous moisture
loss from, and bacterial decomposition of, the wrack itself (Backlund,
1945). These changes should have a profound effect on the wrack fauna
for, as Backlund has found, "Every schizophagous species can only utilize
dead organic matter which has a special degree of moistness, and usually
also quite a special degree of decaying."
Therefore, it seems probable
that gradual changes might occur in faunal species composition and
population densities as wrack ages on the beach. It is quite possible
that a distinct series of different associations occur in wrack as it
progresses through successive stages of drying and decay. The system
envisioned would then somewhat resemble typical terrestrial succession
as is known to occur in other biomes.
Though Backlund and Remmert (1964) acknowledge that there is a
difference between the fauna of fresh and old wrack, neither has con¬
ducted studies to determine what the differences are or how the
animal community may change as wrack ages. Therefore, the following
study was initiated in hopes of shedding some light on this subject.
The study was conducted at North Moss Beach (also known as
Asilomar Beach), Monterey County, California. The beach is about
one-half mile in length and is exposed to open ocean except at each
end where rocky outcrops screen much of the incoming surf. This
gradually sloping sandy beach is bordered on the east by small dunes,
on the north by a public road and one of the rocky areas just mentioned,
and on the south by cliffs and rocks. A small freshwater stream is
located within the northern quarter of the beach.
-3
Materials and Methods
Only wrack macrofauna were considered in this study. For con¬
venience, these were defined as all organisms larger than 0.5 mm. (in
any dimension).
Three types of sampling were attempted: random sampling of
four-week
naturally occurring wrack; a long-term study involving weekly collec¬
tions of wrack samples experimentally placed on the beach; and a
three-day short-term study involving daily collections of wrack samples
experimentally placed on the beach.
Random sampling
On each of three successive days, April 25-27, five banks of wrack
were chosen at random and samples of both wrack and the sand immediately
beneath the wrack were taken. These were taken progressively from north
to south along the beach and at different intertidal levels. Samples
were characterized as being either in a high intertidal area (+5.5 to
+7.0 ft.) or a mid intertidal area (+4.5 to + 5.5 ft.). No samples of
wrack were taken in the surf zone and the lower intertidal areas (below
+4.5 ft.) since preliminary observations indicated that few, if any,
organisms inhabited wrack located there.
Prior to taking samples, the following data were determined and
recorded: date and time of day; air temperature (approximately 3 ft.
above the sand); wrack surface temperature; temperature 5 cm. down in
wrack and 5 cm. down in sand under wrack; dimensions of the wrack
bank; location of wrack in the intertidal zone; the algal species
composing the wrack and their per cent composition by volume. The last
figure was determined merely by visual estimation.
Samples of wrack were removed from the wrack banks by means of
pruning shears. The volume of samples varied but all included a seg¬
surface
ment extending from the wrackdown to the sand, with samples varying
in both length and width from 10 cm. to 25 cm. After the wrack sample
was bagged, the sand sample was taken by moving the wrack bank aside
and immediately placing a box with one-fourth square meter openings on
the sand such that all animals on the sand surface were trapped within
The sand to a depth of 5 cm. was then dug
the four sides of the box.
out of the box and returned to the laboratory.
Since it was thought that the moisture content of wrack decreases
with residence time on the beach, the moisture content was determined
for each wrack and sand sample. These values could then be used as
relative measures of the age of the wrack banks sampled.
In the
laboratory, after the wet weight had been determined for each sample,
wet and dry weights of small portions of each sand sample and the major
algal species of each wrack sample were determined. Small pieces of
the wettest and the dryest algae, and of each plant part present for
each algal species,were dried collectively for each wrack sample. The
moisture content of the collection was determined and assumed to be
an estimation of the average moisture content of the algae in the wrack.
The macrofauna was then extracted from each sample. Sand samples
were washed through a series of screens with screen openings of succes¬
sively smaller size, the smallest openings being 0.5 mm. Animals in
the wrack samples were extracted using a Tullgren apparatus as described
by Backlund (1945). The samples were left in the apparatus for 24 hours,
after which time, most, if not all, macrofauha had been extracted.
Long-term study
The second aspect of the study involved placing approximately ten¬
pound samples of fresh Macrocystis integrifolia.(acquired from the surf
zone) on the beach. Three rows of five samples per row were layed out,
each row being parallel with the water's edge. The rows were
placed approximately 30 feet apart at three successive levels, the
highest level being at the foot of the sand dunes (approximately +6.5
ft.). Initially, an 18 inch stake was driven well into the sand in
the center of each pile. The following day, it was found that six of
the samples had been washed away, so in an attempt to prevent this
from happening with the remaining samples, the others were wrapped
with wire and attached to the stake,
The purpose of this part of the study was to determine macrofaunal
changes that occur within wrack at different levels on the beach over a
relatively long time period. It was intended that one sample per week
from each row would be collected. However, all samples except four at
the highest level were washed away within one week. As a result, it
was possible only to study changes that occur over four weeks at a very
high intertidal level (approximately +6.5 ft.). These samples were
collected and processed in the same manner as described earlier, with
the exception that the entire bank of wrack was collected and processed,
It should be noted that all these samples had been washed by surf and
were almost completely covered by sand at the time they were ultimately
collected. Therefore, a considerable amount of sand was collected with
the wrack. The sand that was mixed with the wrack was sifted and the
animals obtained were recorded as being in the wrack itself.
-6-
Oshort-term study
Three ten-pound samples of fresh Macrocystis integrifolia (cut
from the kelp beds off Hopkins Marine Station) were staked out parallel
with the water's edge at a high intertidal location (approximately+6.5
ft.). The banks were approximately 30 feet apart. On each of the
next three succeeding days, one bank was collected, as was a sample of
the sand under it. Determination of moisture content and animal extrac¬
tion procedures were the same as described earlier.
-7-
Results
It should be noted that in this study, data for all Dipterans and
Diptera larvae are not as quantitatively accurate as the other data.
This is especially true for adult flies, since the sampling procedures
were not sufficient to allow for the quantitative capture of flies.
Hence, only flies that were residing deep within the wrack were caught.
Higher numbers of the Dipteran species Leptocera johnsoni were caught
than other species, probably because this species tends to inhabit
the deeper layers of the wrack (Hyatt, 1972).
Many of the animals found in the sand samples actually had fallen
out of the wrack when it was picked up. It can be assumed then, that
many of the animals found in the sand samples actually were in the
wrack at the time of sampling. This was a problem especially in the
short-term study because the samples had not greatly diminished in
volume as a result of moisture loss as previous samples had, and they
were therefore, more difficult to collect. Many more animals were
able to escape from the wrack because of the longer time required to
bag the samples.
Many small larvae were probably overlooked because they could not
easily be detected in the detritus and small amounts of sand that were
mixed in with animals during extraction procedures. Also because of
this fact, the unidentified egg cases found in some samples may have
been overlooked in other samples. These egg cases were small and were
coated with sand grains, making them very difficult to detect when
mixed with sand.
Random sampling
The moisture content of sample wrack and the relative abundance
of each species found associated with it is given in table 1. The same
type of data for sand samples is given in table 2.
In figure 1, the wrack samples are arranged in order of increasing
moisture content and the total abundance of animals for each sample is
indicated. This figure shows that there is no direct relationship
between wrack moisture content and abundance of macrofauna in wrack.
For each dominant species, the abundance is plotted against wrack
This figure again
moisture content for wrack samples in figure 2.
shows that a relationship between wrack moisture content and individual
species abundance does not seem to exist. In all cases, there is
considerable variation in abundance as wrack moisture content increases.
In order to determine if the algal species composition of wrack is
important in determining the distribution of wrack fauna, the
species composition of each wrack pile sampled is indicated and the
samples are arranged in order of increasing total abundance of animals
in figure 3. It is evident from this figure that the distribution of
wrack fauna is not directly related to the species composition of the
wrack.
Temperature data are plotted in order of sample number in figure
4. Directly beneath this graph, the total animal species abundance
is indicated for each sample. It does not appear as if a close
relationship exists between temperature and the presence or absence
of wrack macrofauna.
In figure 5, each bank of wrack sampled is diagrammatically
shown. These are arranged in order of increasing moisture content
and the outlined area representing each wrack bank is a relative
indication of the volume occupied by the wrack as seen on the beach.
By comparing the high intertidal samples with the others, it becomes
evident that wrack moisture content does not seem to depend on the
location of the wrack on the beach. Therefore, since old wrack
located high on the beach may have a moisture content comparable to
newer wrack located low on the beach, it is not possible to use
moisture content as an indicator of age.
Long-term study
In figure 6, the concentrations of the dominant species in each
weekly wrack sample are indicated. For the first sample, the species
are arranged in order of decreasing concentration, and the same order
of species is followed in the remaining three samples. Weekly fluctu¬
ations took place in almost every species, some of which were very
great. The greatest abundance of animals occurred in the sample of
the second week, but decreases followed in the remaining two weeks.
Loss in moisture content from the fresh Macrocystis integrifolia
during the four weeks of the experiment was considerable. Water con¬
tent decreased from 89.6% at the beginning of the experiment, to a
value of 47.4% in the fourth sample.
Short-term study
Figure 7 shows the concentrations of the dominant species in
each daily wrack sample. The arrangement is the same as in figure
6. A surprisingly large number of species were found in the wrack
samples, even after only one day on the beach. As in the case of the
long-term study, great fluctuations in population densities took place
In many species, there was a significant increase in population density
from the first day to the second, with a great decrease the following
day. Moisture content of the Macrocystis integrifolia decreased from
89.3% at the beginning of the experiment to 66.5% in the third sample.
It should be noted that most data for sand samples has not been
except in the appendix.
presented One reason for this is that, in most cases, the abundance
of animals in the sand samples was so small as to be insignificant.
Changes in abundance many times involved decreases or increases of
only one or a few individuals. Also, no significant differences were
found between the species composition of the fauna of wrack and sand.
has already been mentioned, most of the animals found in the
As
sand samples actually had escaped from the wrack sample when it was
being collected.
Discussion
The results of the random sampling program suggest very strongly
that there is no clear relationship between wrack moisture content
and the species composition and abundance of wrack macrofauna. It
has been impossible to show any relationship between wrack moisture
content and wrack age, therefore no conclusions can be made regarding
macrofaunal succession in aging wrack from the results of this aspect
of the study
One factor that seems to be important in determining the abun-
dance of wrack macrofauna is the location of the wrack on the beach.
Figure 8 shows the correlation of total species abundance in wrack
samples with the approximate location of the sample longitudinally
along the beach. It can be seen that species abundance is very low
at the north end of the beach but increases greatly as one moves
south, and most especially in samples taken just south of the fresh-
water stream. There are many possible reasons for this phenomenon.
For instance, the rocky outcrop at the north end of the beach appears
to prevent wrack from being deposited on the north quarter of the
beach in as great amounts as it is deposited in the sampling area
south of the stream. Since it is possible that most wrack animals
aggregate where the food is in most abundant supply we might expect
the distribution seen in figure 8. In addition however, the presence
of the road and the fact that the north quarter of the beach is more
frequented by people could both be factors that might affect the
presence of wrack animals there.
It has been shown that in both the long-term and the short-
term sampling experiments great fluctuations take place in the pop-
ulation densities of some wrack animals as wrack ages. Assuming
that, to some extent, wrack placed artificially on the beach simu-
lates natural wrack, it appears that gradual species replacements
and gradual changes in species population densities do not take
place in wrack in periods of from three days to four weeks. Rather
sporadic and sudden increases and decreases in populations of species
seem to be the common occurrence. The species involved in these
changes often show correspondance in their appearance or disappear¬
ance. For instance, in the long-term study, the sample of the
second week contained significantly higher populations of Cercyon
fimbriatus and Tarphiota geniculata than did the sample of the
first week. This may suggest the existence of an association
between these two species. Possibly the simultaneous increases
in population sizes of the two species merely results from a common
need of wrack of the same moisture content and/or same state of
decay for both species. However, this does not seem to be the case
in all samples for these two species. In the short-term study,
while C. fimbriatus was found in high numbers in the sample of
the second day, the abundance of T. geniculata was not great.
The differences between naturally-occurring wrack and wrack
placed artificially on the beach, as discussed by Backlund (1945)
must be noted. A basic difference is that wrack deposited on the
beach as a result of wave action is compacted by the water while
wrack artificially placed on the beach is loosely packed. The
effect of this is increased aeration and consequent faster drying
of the artificial wrack over that of the natural wrack. Also,
wave action tends to partially bury wrack as it is being deposited
further decreasing its aeration.
Naturally-occurring wrack is possibly subjected to partial
decomposition in the sea before being deposited on the shore, whereas
in the short-term study, Macrocystis was cut from living plants,
and had not begun to decompose prior to its placement on the beach.
This difference may result in a slower inhabitation rate in the
artificial wrack for those animals that utilize wrack only after
a certain stage of decay has been reached.
In both the short-term and the long-term studies, fresh
Macrocystis was placed very high intertidally on dry sand. It is
obvious that this situation never occurs naturally. Such a good
source of food and moisture at that location on the beach is, indeed,
a very attractive commodity to animals living there. This might
explain why, especially in the short-term experiments, unusually
high numbers of animals were found in the wrack.
A very important difference between natural and artificial
wrack in this study is that the artificial wrack was staked down
and was not moved around by surf or wave action. Natural wrack
may be moved from place to place on the beach and as well, from
zone
subtidal to intertidal zone and back, many times during its life
history.
It seems probable then that the animal community in artificial
wrack will not develop and change in precisely the same manner as
will that of the natural wrack. However, the results obtained in
the studies involving artificial wrack may indicate trends which
help to explain the uneven distribution and abundance of species
among natural wrack banks.
Insects have been found in this study to be the most well-
represented class of animals inhabiting wrack and, as Backlund (1945)
notes, "...most insects are usually spread to wrack...by active
flight." Backlund also tells of seeing swarms of beetles flying
around the beach at night. Possibly entire swarms may converge on
a wrack bank. If this does occur, it might explain the great
fluctuations in numbers of animals, especially beetles, that have
been found to take place in wrack fauna over time. A particular
swarm may be attracted to a specific bank for any number, and
possibly a combination, of reasons. A few factors that may be
important are (1) wrack moisture content and its state of decay,
(2) wrack odor, (3) other organisms already present in the wrack,
temperature of the wrack,
(4
and (5) the location of the wrack on the beach. Possibly the
presence on a bank of a female emitting a pheromone would attract
entire swarms of males. Furthermore, a species may be attracted
to a bank for only a very short period of time.
This might
account for the great fluctuations in numbers of some insects that
were found to occur in the artificial wrack banks even over short
time periods.
Still another factor must be considered when trying to explain
the seemingly random distribution of wrack animals, that factor
being the life history of the wrack itself. After wrack becomes
deposited on the beach, basically one of three things will happen
to it: (1) It may be washed out to sea again; (2) It may be moved
from one part of the beach to another by the surf; (3) It may be
covered by sand. In all wrack, these changes probably take place
numerous times and in varying ways such that each individual bank of
-15-
wrack on the beach will have a unique life history. As well.
wrack of different ages and species become mixed, further compli¬
cating the picture (Evans, 1972).
So it becomes evident that
animals living in wrack are subjected to constant change of
their habitat which makes the assessment of any kind of pattern
of succession impossible utilizing the more traditional approaches
such as attempted in this study.
In short, the results of this study suggest strongly that
a complex combination of biotic and abiotic factors operate to
determine the characteristics of a wrack bank. This might
explain why no simple correlation could be found between either
wrack moisture content and the vertical position of the wrack on
the beach or wrack
moisture content and the structure of the
wrack macrofauna community. Furthermore, no clearcut stages of
macrofaunal succession could be elucidated as a result of the
inability to age wrack with respect to its state of decay. How-
ever, the study has shown that there are indeed distinct and
peculiar groupings of species which occur over time, even short
periods of time, suggesting that in some fashion there is a
succession of wrack fauna associated with different stages of
decay and perhaps other secondary environmental factors. Yet,
instead of a situation where the habitat remains permanent in
a spatial sense and changes in character with time, allowing for
a series of different associations to develop over time, we have a
situation where there is both spatial variability and temporal
variability.
Figure 9 illustrates the essentials of the hypothesis
developed from the results of this study. Although a limited
number of factors are dealt with in the figure, it nevertheless
illustrates how spatial as well as temporal variability may affect
the distribution of wrack macrofauna. The figure shows a section
of a hypothetical beach on which there are nine evenly-spaced
banks of wrack, represented by circles, which are numbered for
reference. The beach is shown progressively at four different
points in time, as indicated by the Roman numerals down the left
side of the figure. The relative moisture content and state of
decay of each wrack bank is indicated by the letters within the
circles, with state of decay represented by lower case letters
and moisture content represented by upper case letters (see key).
At time I, banks 1,2, and 3 are shown to be below the tidal level.
the level of the water being indicated by the jagged horizontal
line. These banks are located low intertidally, whereas banks
4,5, and 6 are located mid intertidally and banks 7,8, and 9 are
at a high intertidal level.
Two types of macrofaunal associations, represented by
horizontal and vertical hatching within the circles, are shown
to be present within the wrack banks. Association #1 (vertical
hatching) is found in wrack banks of dryness C and state of
decay c. Association +2 is found in banks of dryness B and state
of decay a. At time I, association #l is in wrack bank 8 and
association #2 is in wrack bank 6.
Upon studying figure 9 it becomes evident that both spatial
and temporal change occurs on the beach, and therefore, the
location of a wrack bank on the beach will have a great affect on
-17
the way that it develops. The rate of decay and moisture loss in
wrack is influenced by a number of factors. For instance, the
state of decay of wrack when it is deposited will probably affect
both its rate of decay and its rate of moisture loss on the beach.
The size of the wrack bank, of course, will greatly affect both
decay rate and rate of moisture loss. The vertical location of
the wrack on the beach will determine how often the wrack will be
washed by the tides and the length of tiime it will remain on the
beach. To illustrate the importance of some of these factors, we
can discuss one of the hypothetical wrack banks in figure 9. At
time I in the figure, wrack bank 1 has, of course, a high moisture
content, since it is below the tide level. Its state of decay is
b. It becomes deposited on the beach at time II, but no change
is immediately seen in moisture content. Perhaps the bank is quite
large or possibly it has become partially covered with sand. Both
of these factors would probably greatly influence rate of moisture
loss. No change is seen in the state of decay of wrack bank 1
immediately after deposition. In this case, the size of the bank,
its algal species composition, and/or its state of decay at the
time of deposition may be the influencing factors. The bank
starts to dry out and its moisture content becomes B at time III,
but still no change is seen in its state of decay. This would be
understandable if the wrack were composed of fresh algae which
would probably have a slow initial decay rate due to its short
amount of time of exposure to bacterial decomposition. At time
IV, the state of decay of wrack bank 1 has proceeded to c, but
now the bank is again below the tide level and so its moisture
-18-
content is back to A.
Other wrack banks in figure 9 could be discussed and
explanations for change, or lack of change, could be proposed.
For instance, a number of factors might cause a wrack bank like 5
to remain static over time or a bank like 9 to decay rapidly. The
point to be made is that there are a complex number of ways that
wrack banks can change over time because of the great number of
factors influencing them.
Now, how do wrack organisms cope with such irregular and
extreme changes in wrack? Many typical marine or maritime organ¬
isms live in the sand and move with the tide. Such organisms
utilize wrack primarily as a food source and only occaisonally
as a source of shelter and moisture. However, it would seem that
typical wrack animals, since they depend upon wrack not only as
a source of food but as their only source of shelter and moisture,
would be highly adapted to finding wrack containing the appropriate
constellation of factors necessary for the species involved. As
well, because of the limited amount of wrack that is available on
most beaches, the competition for niche space among wrack animals
would be high, and any specialization would be advantageous to
these animals. Such specialization might result in different
wrack animals utilizing wrack at different stages of decay and
moisture content. Because wrack banks are continually changing
in this regard, and because they are subjected to other changes
such as inundation as result of tidal action, it would seem that
wrack organisms would benefit greatly if they were able to detect
the state of decay and moisture content of wrack and to move
quickly from one wrack bank to another. In particular, insects
appear to be especially pre-adapted to this type of life. They
are often able to detect the presence of very small quantities
of compounds over some distance and use this ability to find an
appropriate place in which to live. Bark beetles, for example,
are well known for such abilitiese
Another
excellent example of this is the ability of many male insects
to detect the presence of minute quantities of pheromones emitted
virtually miles away by females of their species. It seems
possible then, that wrack animals might be able to determine the
state of decay of wrack by detecting small amounts of compounds
given off into the air as a result of decomposition. Flying
wrack insects especially would be at an advantage since they would
be able to move quickly to the most desirable wrack. These ideas
are illustrated in figure 9. Association 1 is found only in old,
dry wrack. When wrack bank 8 becomes buried at time II, association
fl is forced to seek out another old, dry wrack bank. The entire
association then moves to wrack bank 4. As other wrack ages, more
old, dry wrack becomes available, and the association utilizes
this as well (wrack bank 9, in this case). So in this example, the
association benefits by being able to quickly find old, dry wrack
when forced to, and by being able to utilize all sources of old,
dry wrack available on a stretch of beach.
Association +2 in figure 9 is found in moist, new wrack. At
times I and II then, it is in wrack bank 6. However, as this bank
ages and another bank of moist, new wrack becomes available as a
result of wave and tidal action, the association moves to the
-20-
more preferable bank. Yet, this bank becomes submerged by the
tides again, and the association is forced to seek out wrack on
another portion of the beach.
As has already been mentioned, flying insects, such as the
many species of Staphylinids that have been found in this study,
would be able to move more quickly to desirable wrack than would
non-flying insects such as the Tenebrionid beetles. This might
explain why such great fluctuations have been found to occur in
over time.
wrack populations of Staphylinids It may also explain why such
insects are found in great numbers on the beach, comparatively,
since they are able to more efficiently utilize wrack as a food
source.
Evidence from this study is in full accord with the
hypothesis proposed. However, sufficient data are not available
to prove the hypothesis as yet. Further study is required if we
are to achieve an understanding of the complex community of wrack
macrofauna, and of wrack itself as a unique biome.
0
Footnotes
1. Backlund, Helge Alfred Oskar, 1945. Wrack fauna of Sweden
and Finland; ecology and chorology. Opuscula entomologica.
Supplementum, 1945. pp. 127-128.
2. Ibid, p. 143
22
Literature Cited
Backlund, Helge Alfred Oskar. 1945. Wrack fauna of Sweden and
Finland; ecology and chorology. Opuscula entomologica.
Supplementum, 1945. 296 pp.
Evans, Elaine, 1972.
Unpublished, on file at -Hopkins Marine Station library.
Hyatt, Joel 1972. Behavior of wrack Dipterans Fucellia rufitibia
(Anthomyiidae), Coelopa vanduzeei (Coelopidae), and Leptocera
johnsoni (Sphaeroceridae) on a California beach. Unpublished,
on file at Hopkins Marine Station library.
Remmert, Hermann 1964. Distribution and ecological factors con¬
trolling distribution of the European wrack fauna. In Proc.
Fifth Mar. Biol. Symp.: T. Levring, ed. pp. 179-184.
2
Acknowledgements
I especially wish to thank Dr. Welton Lee of Hopkins
Marine Station for his invaluable suggestions and undying
patience. A more devoted teacher probably cannot be found.
My thanks go also to Dr. I.M. Newell and Ian Moore of
the University of California who identified the Coleopterans
found in this study. Also helping with identification were
Sam Johnson, Joel Hyatt, and Helen Kompfner, as well as Dr.
Lee, all of Hopkins Marine Station. Their help was greatly
appreciated.
Special thanks go to Delane Munson, also of Hopkins
Marine Station.
2
Table Captions
Table 1. Moisture content of wrack and relative abundance of
each species found in random wrack samples. Relative abundance
indicated by length of bar, according to key. Wrack moisture
content shown as percentage of total wet weight.
Table 2. Moisture content of sand and relative abundance of
each species found in random sand samples. Relative abundance
Sand
indicated by length of bar, according to key. moisture content
shown as percentage of total wet weight.
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5.5
Figure Captions
Figure 1. Relative abundance of macrofauna in each random wrack
sample in relation to wrack moisture content. Moisture content
of sample wrack increases in samples from left to right along
horizontal axis. Corresponding relative abundance indicated on
vertical axis. Scale: 1= macrofauna least abundant; 6= macro-
fauna most abundant.
Figure 2. Relative abundance of predominant animal species in
random wrack samples in relation to wrack moisture content.
Species from left to right, top to bottom are: Orchestoidea
benedicti, Orchestoidea californiana, Cafius canescens, Cercyon
fimbriatus, Pontamalota californica, Leptocera johnsoni. Moisture
content indicated on horizontal axis.
Relative abundance
indicated on vertical axis. Scale: 1= scarce; 2= common; 3-
abundant; 4= very abundant.
Figure 3. Algal species composition of wrack sampled in relation
to abundance of wrack macrofauna. Abundance of macrofauna in
sample wrack increases in samples from left to right along hori-
zontal axis. Per cent composition of each algal species for each
sample indicated on vertical axis according to key.
Figure 4. Comparison of temperature data for each sample with
relative abundance of macrofauna in random wrack samples. Upper
graph shows temperature data for wrack and sand samples according
to key. Odd sample numbers are wrack samples; even sample numbers
are sand samples. Lower graph shows corresponding relative
abundance of macrofauna for each random wrack sample, with
2
abundance for each wrack sample indicated directly beneath
temperature data for each sample on upper graph. See fig. 1 for
scale of abundance.
Figure 5. Height and volume of wrack banks sampled in relation
to moisture content. Moisture content of sampled wrack indicated
(in %) by number under each illustration. Illustrations arranged
from left to right, top to bottom in order of increasing moisture
content. Height of each wrack bank indicated by vertical scale.
Area occupied by each illustration is relative indication of
volume occupied by wrack bank. Illustrations with diagonal
hatching indicate wrack banks sampled at high intertidal level.
Figure 6. Concentrations of dominant species for each weekly
wrack sample in long-term study. Species indicated by number
on horizontal axis according to key. Concentration (in number
of individuals per kilogram wrack, wet weight) indicated on
vertical axis. Note that two scales are used on vertical axis.
Values above 10 on right scale are shown by broken bar, with
value at top of bar.
Figure 7. Concentrations of dominant species for each daily
wrack sample in short-term study. Species indicated by number
on horizontal axis according to key. Concentration (in number
of individuals per kilogram wrack, wet weight) indicated on
vertical axis
Figure 8. Map of North Moss Beach and location of sampling areas,
with abundance of macrofauna for each random wrack sample indicated
directly beneath approximate location of wrack bank sampled.
Different sampling areas indicated on map according to key
2
at lower left of figure. Relative abundance of macrofauna for
each sample indicated directly beneath approximate location of
wrack bank sampled. See figure 2 for scale of abundance.
Figure 9. Temporal and spatial change on a hypothetical beach
and its possible affect on wrack banks and their macrofauna.
Each
box represents same section of beach at four points in time.
Circles represent nine hypothetical wrack banks (numbered for
reference). Top three circles in each box represent wrack
located low intertidally; middle three represent wrack located
mid intertidally; bottom three represent wrack located high
intertidally. Tidal level indicated by jagged horizontal line.
Moisture content of each bank over time indicated by upper case
letters according to key. State of decay of each bank indicated
by lower case letters according to key. Two macrofaunal associa-
tions represented by horizontal and vertical hatching according to
key. Movement of associations among wrack banks through time
indicated by arrows.
.







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Fucellio
spp. larvoe

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Bledius monstratus
+
Aleochoro sulcicollis

Cercyon fimbriotus
Torphioto geniculota
6 Cafius conescens
Soprinus sp.
8 Leptocero johnsoni
Alloniscus perconvexus
10 Cafius luteidennis
I
90
Epontius lobscurus
6 78
larvae

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larvoe

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5 Tarphiota geniculata

6 Cafius luteidennis


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old
0
APPENDIX
Table Captions
Table 1. Concentration of each species found in random wrack
samples. Concentration expressed as number of individuals per
kilogram wrack, wet weight.
Table II. Concentration of each species found in random sand
samples. Concentration expressed as number of individuals per
10 kilograms sand, wet weight.
Table III. Concentration of each species found in short-term
and long-term study samples. Wrack sample concentrations
expressed as number of individuals per kilogram wrack, wet
weight. Sand sample concentrations expressed as number of
individuals per 10 kilograms sand, wet weight.
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