The Endocladia Zone
Erin Leydig and Ashley Simons
ABSTRACT
The red alga, Endocladia muricata, and the barnacle, Balanus glandula,
form a widespread association in the rocky intertidal along the Pacific coast of
North America (Glynn 1965). One portion of that zone, at Hopkins Marine
Station, Pacific Grove, California, was examined to determine its vertical height
and species composition. These measurements were then compared with data
from Glynn (1965). The current upper and lower limits of E. muricata are an
average of 1.20 and 1.05 feet lower respectively than they were in 1965. At three of
Glynn’s study sites, replicate 5x5 cm quadrats were sampled in the middle of the
current Endocladia zone, taking care to duplicate as many of Glynn's original
quadrat characteristics as possible. Analysis of algal biomass showed no
significant change in the abundance of E. muricata in these areas. The species
composition of the assemblage has changed little, but there has been a significant
change in the relative abundances of species. Abundance of the bivalve,
Musculus sp., has increased significantly, while that of the barnacle, B. glandula,
has decreased. These findings indicate that much of the E. muricata animal
community has moved downward along with the algal cover, but that the
abundance of a few predominate species within this community has changed.
These data provide a base for future quantitative studies of temporal change in
the E. muricata zone and may aid in evaluating the effects of environmental
change on intertidal habitats.
The Endocladia Zone
Erin Leydig and Ashley Simons
INTRODUCTION
The red alga, Endocladia muricata, and the acorn barnacle, Balanus
glandula, are two of the most conspicuous species in the high intertidal zone.
Due to their concurrent abundance, they are referred to as the Endocladia-Balanus
association. This community extends throughout the western coast of North
America, from Alaska to Point Conception (Glynn 1965).
Glynn (1965) conducted an in-depth study of the Endocladia-Balanus
association at Hopkins Marine Station, Pacific Grove, California. He documented
both the vertical distribution of this association in the rocky intertidal, as well as
the composition of the community living within the E. muricata. Glynn (1965)
sampled sixteen 20x20 cm quadrats located in the center of the Endocladia zone,
identifying and counting the species present. In addition, he permanently
marked the locations of his sample sites with pegs, making a repeat study
possible.
The detail of Glynn (1965), the fact that it has been over thirty years since
his data were taken, and the availability of his sites for resampling, all make his
study an excellent baseline from which to assess change in the Endocladia¬
Balanus community. Resampling at his original sites minimizes the effects of
small scale heterogeneity caused by slight differences in aspect with respect to
water motion, wave action, and sun exposure; the repeatability of his sampling
protocols allowed us to make a valid temporal comparison.
The Endocladia Zone
Erin Leydig and Ashley Simons
We examined two different aspects of long term change in the Endocladig-
Balanus association at Hopkins Marine Station: changes in the vertical
distribution of the Endocladia zone and changes in species composition of the
assemblage.
MATERIALS AND METHODS
Determination of Vertical Distribution
Glynn (1965) measured the upper and lower vertical limits of the
Endocladia zone at 16 quadrat sites in the intertidal at Hopkins Marine Station
(Fig. 1). Fourteen of these original sites were relocated using Glynn's markers (or
scars from these markers) and Glynn's photograph of his study site (Fig. 1). A
surveyor’s transit and stadia rod were used to measure the current average upper
and average lower limits of the Endocladia zone at each of these relocated sites.
These average limits were estimated by eye and were within 1 to 2 m of Glynn's
sample sites. Height was measured relative to a U.S.G.S. brass peg (3.82 ft above
mean lower low water level).
Glynn also measured the height of his quadrat sites, which were in the
middle of the Endocladia zone. At three of Glynn's quadrats, we remeasured the
height of his quadrat markers. We also measured the height of our sample
quadrats, which were placed in the middle of the current Endocladia zone.
Determination of Species Composition
During lower low tides on May 4th, 5th, and 13th, 1996, samples were taken
in the middle of the current E. muricata zone at Glynn’s quadrat sites, II, III, and
The Endocladia Zone
Erin Leydig and Ashley Simons
IX respectively. At each site, two 5x5 cm quadrats were sampled and identified as
XA and XB, where x corresponds to Glynn's quadrat number.
We chose to use 5x5 cm quadrats for three reasons. First of all, preliminary
sampling at alternate sites showed that the animals living within the Endocladia
zone are small enough to be abundant within a 5x5 cm square. Secondly, using
5x5 cm quadrats allowed us to take replicate samples at each of Glynn's sites,
accounting for the small scale variation within sites.
Thirdly, because of this small scale variability in animal life in the intertidal zone,
it was important to imitate the physical characteristics and orientation of Glynn's
original quadrats as closely as possible. Using 5x5 cm - instead of 20x20 cm-
quadrats made it easier to find sample areas near Glynn’s originals that shared his
quadrat's physical characteristics.
Each of our 5x5 cm quadrats was placed haphazardly in what was
qualitatively determined to be the vertical center of the current Endocladia zone.
All sites were within Im horizontally of Glynn’s sample site. Duplicating the
physical characteristics of Glynn’s quadrats was given priority over placing
quadrats in the exact middle of the Endocladia zone.
We removed all plants, animals, and sandy sediments from the rock
within our quadrats. To keep mobile animals from leavirig the sample site, all
large tufts of algae were cut off immediately after placing the quadrat. Äfter this
initial cut, we marked the edges of our quadrats so that they could be relocated if
shifting occurred during sampling. We used scalpels, pipets, and dentist tools to
The Endocladia Zone
Erin Leydig and Ashley Simons
clear the quadrats. All material taken from each sample site was placed in a
separate, high-sided, plastic container filled with sea water.
Plastic containers holding the samples taken from the field were brought to
a lab sea table and placed in a bucket with sea water running through it. This sea
water bath maintained the samples close to ambient sea water temperature. The
containers were kept open for much of the day and new sea water was
occasionally added to the sample containers to keep them from becoming anoxic.
We examined each sample under a dissecting microscope, picking out all
the living organisms from the E. muricata with forceps and pipets. Animals were
identified to the lowest taxonomic level possible (Baxter and Watanabe pers.
com., Hartman 1968, Smith and Carlton 1975) and preserved in 70% alcohol.
Counts for each group were recorded as individual animals were found. We
included animals killed during sampling or storing in the group counts.
However, we did not count fragments of animals.
All algae in our samples was sorted and dried to constant weight at 60°C.
Each 5x5 cm quadrat took an average of four full days to sort.
Statistical Analysis of Data
Individual animal counts and algal dry weights for our quadrats were
standardized to a per 400 cm’ basis. Data from replicate 5x5 cm quadrats were
averaged for comparison to corresponding Glynn quadrats. Overall changes in
the relative abundance of species was analyzed using a chi-squared test. Species
whose expected values were less than 5 were pooled into one category for this
analysis. Changes in individual species abundance were analyzed using t-tests.
The Endocladia Zone
Erin Leydig and Ashley Simons
RESULTS
Vertical Distribution
The 1996 upper limit of the Endocladia zone is an average of 1.20 ft lower
than in 1965; the lower limit is an average of 1.05 ft lower (Fig. 2). In both 1965
and 1996, there is clear between-site heterogeneity (Fig. 3). There is no strong
correlation between 1965 and 1996 upper and lower limits of E. muricata at
individual sites. One of Glynn’s lowest sites, LI, is now one of the highest (Fig. 3).
Species Composition
Three plant species and 21 animal taxa were found in our samples. Most
animals were extremely small, measuring less than 1 mm in length. Aside from
animals that had been dislodged during sampling, animals were associated
directly with fronds of E. muricata. The greatest density of organisms was located
in the holdfasts of E. muricata. This was also the only region in which
polychaetes were found. Organisms were found in a broad range of abundances:
average counts varied from 1 to nearly 6500 per 400 cm’ area.
The 1996 dry weights of E. muricata and Mastocarpus papillatus, 23040 mg
and 4133 mg per 400 cm’ quadrat respectively, are not significantly different from
1965 (t-test, p=0.33; t-test, p=0.83).
The overall animal composition of the current Endocladia assemblage is
significantly different from the 1965 assemblage (x’= 10634.41, p ««.001). The
most abundant species in the center of the Endocladia zone in 1965, Lasaea cistula,
is no longer the most prevalent species in the Endocladia zone. Lasaea cistula is
The Endocladia Zone
Erin Leydig and Ashley Simons
still abundant in the center of the Endocladia zone today, but Musculus sp. is
now the organism in greatest abundance (Fig. 4).
Three of the four most abundant species are the same for 1965 and 1996:
Lasaea cistula, Littorina spp., and syllids (Table 1). However, the average number
of Lasaea cistula and Littorina spp. per 400 cm’ quadrat were considerably different
between 1965 and today.
Musculus sp. is the most abundant organism in our samples, but was not
one of the most abundant animals in Glynn’s quadrats. Similarly, Mytilus
californianus was the third most abundant species in Glynn's samples, but was
quite rare in ours.
The average number of individuals per 400 cm’ in 1965 and 1996 is
different for each of the 20 species found in the Endocladia zone (Table 2).
However, the increase in the abundance of Musculus sp. and the decrease in B.
glandula are the only statistically significant changes between 1965 and 1996
(p=.01; p=.04 respectively). On average, there are 6349 more Musculus sp. and 95
fewer Balanus glandula per 400 cm’ quadrat today than in 1965.
Problem Species
There were several species for which no comparisons were made. These
species fall into four categories. The first category contains those species that were
counted in our samples, but were not included in Glynn’s counts, presumably
because they are difficult to identify and sample accurately. These species include
nematodes, copepods, and ostracods.
The Endocladia Zone
Erin Leydig and Ashley Simons
The second category consists of species found in our samples that may or
may not have been present in Glynn's samples. One of these species is a
gastropod, "unidentified gastropods sp.1," which was found in abundance in our
samples (see Appendix 1). While Glynn also recorded "unidentified gastropods,
there is no way to determine whether his unidentified gastropods were the same
as ours, or if ours is a new species that was not present in 1965.
The third category of species contains those found in our samples for
which Glynn recorded only presence or absence. These species include several
algal species, mites, and bryozoans.
Finally, comparisons were not made on species found both in zero
abundance in our samples and in an abundance of fewer than 8 in Glynn's. Our
quadrat was one-sixteenth the size of Glynn's, and with two of our quadrats
sampled for each of Glynn's, a 1965 count of fewer than 8 is equivalent to fewer
than one organism in the pooled total of our two quadrats. Thus, absence from
our sample could have been due to sampling error or true absence from the
assemblage. These species include Emplectonema gracile, Perinereis monterea,
and Cyanoplax dentiens.
DISCUSSION
Vertical Distribution
It is possible that the downward shift in vertical distribution of the
Endocladia zone is due to an increase in the range of ambient temperature
extremes. Temperature readings from the United States Naval Air Facility,
Monterey (3.5 miles from Hopkins Marine Station and 1.25 miles inland) show
The Endocladia Zone
Erin Leydig and Ashley Simons
that the average maximum temperature for 1948 to 1959 and 1945 was 15.94°C
(Glynn 1965). For the same relative time period prior to our study (excluding
1980), the average maximum was 2.74°C higher; the average minimum was .39°(
lower.
When E. muricata is not covered by water, it is subject to increased
ultraviolet radiation and temperature stress, making it susceptible to bleaching
and desiccation. Extreme atmospheric conditions limit the amount of time that
E. muricata can tolerate being exposed, which in turn, limits its vertical
distribution. By moving downward in the intertidal, the upper limit of the
Endocladia zone is submerged a greater percentage of time, presumably reducing
the stress of increased atmospheric extremes.
Comparison of average water temperature for the five years prior to the
1965 and 1996 studies also show a 1.5°C increase in average maximum
temperature. However, Glynn (1965) found that E. muricata did not change its
vertical height between seasons, despite varying water temperatures (Glynn 1965).
The change in water temperature may have played a role in the Endocladia zone
shift, but is probably not as significant as the changes in ambient temperature
extrêmes. Further physiological and ecological experiments are needed to verify
this explanation.
Species Composition
Most of the organisms living in the Endocladia zone are marine. Like E.
muricata, they are vulnerable when exposed to air, especially when atmospheric
conditions, such as temperature and wind, are extreme (Glynn 1965). Organisms
The Endocladia Zone
Erin Leydig and Ashley Simons
living on bare rocks face temperatures that are 8° C higher than those in E.
muricata cover (Glynn 1965) and presumably seek shelter among fronds of E.
muricata (Glynn 1965). This protective function of E. muricata may explain why
most of the species found in the 1965 Endocladia zone are still present. Most of
the organisms living in E. muricata are better equipped to withstand prolonged
submersion than prolonged exposure to the atmosphere, making it more
advantageous for them to move down to lower tidal heights than to try to
survive atmospheric conditions without E. muricata cover (Glynn 1965).
While the majority of the species present in the 1965 Endocladia zone are
still found in the zone today, their relative abundances have changed. Lasaea
cistula, the most abundant species in 1965, is still one of the most abundant
species in the Endocladia zone today. In 1965, Glynn found that Lasaea were
confined to the Endocladia zone: they were abundant within the zone, but their
numbers tapered quickly at the upper and lower limits. This trend also seems to
be true today. Recent resampling of Glynn’s actual quadrats, now located at the
upper limit of the Endocladia zone, found approximately 500 Lasaea per 20x20cm
quadrat (Gilman and Sagarin unpublished), while our samples in the middle of
the zone found an average of over 1400 per 20x20cm quadrat.
The large decrease in average Lasaea abundance in the middle of the
Endocladia zone between 1965 and 1996 was not statistically significant. It may,
however, be biologically significant, indicating that Lasaea are not as successful at
a lower intertidal height. This decrease in success may be due to the increase in
Musculus sp.. Musculus and Lasaea are both small nestlers that brood their
The Endocladia Zone
Erin Leydig and Ashley Simons
young and are found in the holdfasts of E. muricata (Glynn 1965). Therefore,
Lasaea may be competing with Musculus for space in the Endocladia zone. This
hypothesis is consistent with the fact that Lasaea cistula was one of the species
with the highest relative abundance in Glynn's high quadrats, while Musculus
sp. was one of the species with the highest relative abundance in his lower
quadrats.
While Lasaea populations seem hindered by the shift in Endocladia's
vertical distribution, the Musculus population is thriving. Glynn described
Musculus distribution, even in his lower quadrats, as "erratic. [Tlhe species
sometimes occurred by the hundreds in some thalli and was altogether absent
from others only two to three feet away". Our sampling in the Endocladia zone
showed the opposite. Musculus was the most abundant organism in all of our
quadrats, and preliminary sampling in other areas also uncovered large quantities
of this mussel. Glynn also states that Musculus was more abundant in his lower
quadrats. Their high abundance in the middle of the current Endocladia zone is
consistent with this observation.
Like the Lasaea, Musculus has moved downward in the intertidal with E.
muricata. Resampling in Glynn’s original sites found an average of only 186
individuals per 20x20cm quadrat as compared with 6485 in the middle of the
current zone.
In Glynn (1965), it is clear that Balanus glandula was a co-dominate
organism in the Endocladia zone. However, Balanus abundance has decreased,
and it is qualitatively no longer an abundant species in the middle of the zone.
The Endocladia Zone
Erin Leydig and Ashley Simons
Resampling of Glynn’s original quadrat sites found Balanus abundances close to
Glynn’s (- 120 per 400 cm’, Gilman and Sagarin unpublished). These data suggest
that Balanus has remained at its original tidal height while the Endocladia zone
has moved down.
The average number of syllids per 20x20cm quadrat was similar in 1965 and
1996. This consistency, combined with the fact that resampling of Glynn's
quadrats found an average of zero syllids per 20x20cm quadrat, suggests that the
syllids have moved down with the Endocladia zone. Syllids rely on the
Endocladia cover to avoid desiccation (Glynn 1965), so it is expected that they
would move down in the intertidal with the algal cover. Glynn (1965) observed
that the center of the syllid population was below the 1965 lower limit of E.
muricata. The fact that our abundance counts are similar to Glynn’s suggests that
the center of the syllid population remains below the lower limit of E. muricata.
Mytilus californianus was one of the most abundant species in Glynn’s
counts, but was quite rare in ours. This change, while not statistically significant,
may have biological implications. Glynn (1965) noted that the Mytilis population
was best developed below the lower limit of the Endocladia zone. Our data
suggest that this may still be true, and that perhaps most of the current Mytilus
population is still located lower than the Endocladia zone.
Future Work
We have compared 1965 and 1996 Endocladia zone heights and species
composition at three of Glynn’s sample sites. The difference between 1965 and
1996 was not statistically significant for most individual species. However, the
The Endocladia Zone
Erin Leydig and Ashley Simons
change in overall composition of the assemblage indicates that the individual
species changes are probably biological significant. In order to determine the
extent of such biological significance, future work should include resampling of
the current Endocladia zone at additional Glynn study sites and at more replicate
quadrats within each site. The lack of significant change in individual species
abundance was probably due to large standard errors on our mean counts. These
errors are caused by small sample size and the inherent heterogeneity of the
intertidal environment. The only way to counteract this error would be to
increase sample sizes.
The data we have collected can be used as a baseline for later studies
following up on further change in the Endocladia zone. These data will also be
useful in evaluating what effect environmental changes, such as increases in
ambient temperature, are having on the species living in the intertidal zone.
Erin Leydig and Ashley Simons
The Endocladia Zone
LITERATURE CITED
Abbott, D. Haderlie, E. Morris, R. (1980). Intertidal Invertebrates of California.
Stanford, California, Stanford University Press.
Abbott, R. (1974). American Seashells, 2nd Ed. New York, Cincinnati,
Toronto, London, Melbourne, Van Nostrand Reinhold Company.
Carlton, J. and Smith, R. (1975). Light's Manual: Intertidal Invertebrates of the
Central California Coast, 3rd Ed., (ed. J. Carlton and R. Smith). Berkeley,
Los Angeles, London, University of California Press.
Glynn, P. (1965). Ecological Studies on the Endocladia muricata - Balanus
glandula association in the intertidal zone in Monterey Bay, California.
Stanford, California.
Hartman, O. (1968). Atlas of the Errantiate Polychaetous Annelids From
California. pp.443-495. Los Angeles, California: Allan Hancock
Foundation, University of Southern California.
National Organization of Air and Atmosphere-Environmental Data and
Information Service (1980-1994). Annual Summary. National Climatic
Center Asheville, North Carolina.
The Endocladia Zone
Erin Leydig and Ashley Simons
TABLE 1: FOUR MOST ABUNDANT INHABITANTS OF THE E.muricata ZONE
1996
1965
NAME, AVG. COUNT PER
NAME, AVG. COUNT PER
ABUNDANCE
20x20cm
RANKING
20x20cm
Musculus sp., 6485
Lasaea cistula, 7200
Lasaea cistula, 1465
Littorina sp.,578
Mytilus californianus, 180
Syllidae, 187
Sylidae, 165
Littorina sp., 152
The Endocladia Zone
Erin Leydig and Ashley Simons
TABLE 2: AVERAGE COUNT PER 20x20 cm, T-STAT, AND PVALUE FOR 22 SPECIES.
TVALUE BASED ON LOG TRANSFORMED DATA. ALL T-TESTS CONDUCTED
AT THE.05 ALPHA LEVEL.
1965
1996
ORGANISM NAME
AVERAGE COUNT per 20X20 CM
t-stat
Pvalue
Lasaea cistula
7200.00
1456.00
1.36
Littorina scutulata
152.00
1.39
179.67
Mytilus californianus
53.33
0.18
Syllidae (unident.)
-0.16
186.67
Dynamanella glabra
137.00
18.67
2.49
35.33
136.00
Musculus sp.
-5.74
Balanus glandula
100.33
3.50
Diaulota densissima
13.33
1.54
33.00
Nemertopsis gracilis
0.00
3.52
27.3
McClintockia scabra
0.00
27.00
Collisella digitalis
0.00
Limpets (combined)
23.00
1.85
Lottia pelta
0.00
14.67
Oligochaeta (unident.)
2.46
11.67
Chthamalus sp.
2.38
10.00
Mesostigmata (unident.
0.00
-1.65
Insect larvae (unident.)
18.67
Amphipods
6.00
10.67
0.10
Tricolia pulloides
2.67
5.33
0.11
-0.85
Tegula funebralis
2.35
26.67
Pachygrapsus crassipes
2.67
1.00
-0.17
Barleeia oldroydi
0.67
82.67
-2.55
The Endocladia Zone
Erin Leydig and Ashley Simons
FIGURE LEGENDS
Figure 1. Location of 16 quadrat sites in the study area at the Hopkins Marine
Station (January 16, 1962) (Glynn 1965).
Figure 2. The average upper and lower limits of the 1965 and 1996 Endocladia
Balanus association. Average height is measured in feet above mean lower
low water level. The error bars are + one standard error of the mean.
Figure 3. A: The vertical position of 14 site locations in the Endocladia¬
Balanus association. The Roman numerals indicate the sample site at which
the upper and lower measurements were taken. The Arabic numerals below
quadrats II, III, and IX show the heights of the 5x5cm sample plots taken at
those locations. The heights are displayed in feet above mean lower low
water level.
B: The vertical position in the intertidal zone of 16 quadrats taken in the
Endocladia-Balanus association in 1962. Quadrat numbers are indicated by
Roman numerals, while Arabic numerals show the heights of the centers of
the quadrats in feet above mean lower low water level. The arrows above
and below each quadrat point out the upper and lower limits of the
Endocladia-Balanus belt at each site. (Glynn 1965)
Figure 4. 1965 and 1996 abundances of Lasaea cistula and Musculus sp.. Bar
height shows animal count averaged over quadrats II, III, and IX. Data from
1965 are represented by the dark bar; data from 1996 are represented by the
light bar. Counts are animals per 20x20cm sampling area. The error bars are +
one standard error of the mean.
The Endocladia Zone
FIGURE 1
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Erin Leydig and Ashley Simons
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The Endocladia Zone
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Erin Leydig and Ashley Simons
1996
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Erin Leydig and Ashley Simons
The Endocladia Zone
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The Endocladia Zone
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Erin Leydig and Ashley Simons
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