ASSESSMENT OF NEARSHORE DISTRIBUTION AND ABUNDANCE OF
ECHINODERMS IN THE VICINITY OF ANVERS ISLAND ON THE CENTRAL
WESTERN ANTARCTIC PENINSULA
by
BRITTNY A. WHITE
JAMES B. MCCLINTOCK, CHAIR
CHARLES D. AMSLER
CHRIS MAH
A THESIS
Submitted to the graduate faculty of The University of Alabama at Birmingham,
in partial fulfillment of the requirements for the degree of
Master of Science
BIRMINGHAM, ALABAMA
2011
Copyright by
Brittny A. White
2011
ASSESSMENT OF NEARSHORE DISTRIBUTION AND ABUNDANCE OF
ECHINODERMS IN THE VICINITY OF ANVERS ISLAND ON THE CENTRAL
WESTERN ANTARCTIC PENINSULA
BRITTNY A. WHITE
BIOLOGY
ABSTRACT
Antarctic nearshore benthic communities are known for their unique
richness and diversity of marine invertebrates. Bryozoans, soft corals, tunicates,
cnidarians, tunicates, sponges and echinoderms are among the dominant groups of marine
invertebrates. All five classes of Echinodermata are represented in nearshore waters of
Antarctica, however, brittle stars and sea stars are the most classes. Antarctic
echinoderms are important in contributing to carbon cycles and benthic production, as
well as playing significant roles as determinants of community structure. To date, no
systematic quantitative study has been conducted on the echinoderm fauna in nearshore
shallow waters of the Antarctic Peninsula. The present study assesses the abundance and
distribution of echinoderms at shallow depths (2 to 15 meters) at five sampling stations in
the near vicinity of Palmer Station, Anvers Island, on central western Antarctic
Peninsula. Preserved samples of echinoderms were collected by hand and using suction
of replicate quadrats along a series of benthic transects representative of discrete habitats.
All echinoderms were sorted and identified to the lowest taxonomic classification
possible. Four species of sea stars, two unidentified species of brittle stars, two identified
species of sea cucumbers, and one species of sea urchin were collected from the study
iii
area. The present study shows a significant relationship between the number of sea
cucumbers and the depths sampled, as well as a significant difference among the number
of brittle stars found at each depth sampled. The purpose of this study is to provide a
quantitative analysis of the echinoderm fauna in nearshore shallow waters of the
Antarctic Peninsula.
Keywords: echinoderms, Antarctic, peninsula
iv
ACKNOWLEDGMENTS
I would like to express my sincere gratitude to my mentor Dr. James McClintock,
as well as my committee members Dr. Charles Amsler and Dr.Christopher Mah for their
kindness, extreme patience, and help as I conducted my Master’s Thesis research. They
have helped me develop skills that reach far beyond the classroom. I would also like to
thank Dr. Robert Angus for his help with statistics. Dr. Robert Fischer and the
Department of Biology at UAB provided valuable support. My research was supported
by funds from a UAB endowment in Polar and Marine Biology held by James
McClintock. This endowment facilitated travel and living expenses so as to allow me to
spend a week working with Dr. Christopher Mah at the Smithsonian Museum of Natural
History in Washington DC. I am indebted to the Smithsonian Institute for their support
during this visit. I would like to extend my gratitude to the National Science Foundation
which supported the collections included in my study. I would like to express my
appreciation again to Dr. Charles Amsler, as well as Langdon Quetin, David Lair, Jach
Baldelli, and Robert Rowleg for the dive collections. I would also like to thank Stephanie
White, Robin Ross, and, again, Langdon Quetin for lab analysis and sorting. Lastly, I
would like to thank my family and friends for their unwavering support during my
graduate studies.
v
TABLE OF CONTENTS
Page
ABSTRACT...................................................................................................................... iii
ACKNOWLEDGMENTS ...................................................................................................v
LIST OF TABLES............................................................................................................ vii
LIST OF FIGURES ......................................................................................................... viii
ASSESSMENT OF NEARSHORE DISTRIBUTION AND ABUNDANCE OF
ECHINODERMS IN THE VINITY OF ANVERS ISLAND ON THE CENTRAL
WESTERN ANTARCTIC PENINSULA............................................................................1
LIST OF REFERENCES...................................................................................................20
vi
LIST OF TABLES
Table
1
Page
The taxa and numbers of individuals of the four classes
of echinoderms collected at each of the five sampling sites
near Anvers Island on the central western Antarctica Peninsula...........................32
vii
LIST OF FIGURES
Figure
Page
1
Estimated mean ± 1 SE densities of each of the four classes of
echinoderms collected across depths ranging from 2 to 15 m at
the five sampling sites near Anvers Island on the central
western Antarctic Peninsula. .................................................................................33
2
Graph showing total numbers of asteroids collected at five
nearshore sampling sites near Anvers Island plotted against
the four sampling sites (depth range = 2 to 15 meters). ........................................34
3
Graph showing total numbers of ophiuroids collected at five
nearshore sampling sites near Anvers Island plotted against
the four sampling depths (depth range = 2 to 15 meters). .....................................35
4
Graph showing total numbers of echinoids collected at five
nearshore sampling sites near Anvers Island plotted against
the four sampling depths (depth range = 2 to 15 meters). .....................................36
5
Graph showing total numbers of holothuroids collected at five
nearshore sampling sites near Anvers Island plotted against
the four sampling depths (depth range = 2 to 15 meters). .....................................37
6
Graph showing total numbers of the sea star Odontaster validus
collected at five nearshore sampling sites near Anvers Island
plotted against the four sampling depths (depth range = 2 to 15 meters)..............38
7
Graph showing total numbers of the sea star Granaster nutrix
collected at five nearshore sampling sites near Anvers Island
plotted against the four sampling depths (depth range = 2 to 15 meters)..............39
viii
INTRODUCTION
The Southern Ocean is comprised of all the bodies of water south of the Polar
Front, an oceanographic feature that surrounds the continent of Antarctica and
demarcates the northern extent of cold surface water (Aronson et al. 2007). Unlike its
northern counterpart, the majority of the Southern Ocean overlies extremely deep
seafloor and contains fauna that is poorly known (Brandt et al. 2007). The Southern
Ocean also includes an unusually deep continental shelf -surrounding Antarctica. The
unusual depth of the Antarctic shelf is caused in part by isostatic depression generated
from the weight of the earth’s largest continental ice sheet, but is mostly the result of
historical ice scour from ice sheets (Anderson 1999, Huybrechts 2002). Compared to that
of Antarctica, continental shelves elsewhere are much shallower; having a depth typically
down to 100-200 m and a width of only 75 km (Walsh 1988). While the shelf edges
around Antarctica are closer inshore, they average 450 m in depth, extending in some
regions down to more than 1000 m in depth (Clarke & Johnston 2003).
According to Aronson et al. (2007) marine biologists have long noticed that there
are significant similarities between the fauna of the Antarctic continental shelf and that of
the typical deep sea communities. The two most significant aspects of similarity are: 1)
the importance of echinoderms, and 2) the evolutionary connection between the fauna of
the Antarctic shelf and that of the adjacent deep sea (Aronson et al. 2007). The Antarctic
continental shelf contains a variety of taxa that are considered to be typical of shallow
continental shelves elsewhere in the world. However, Antarctica shelf taxa are living at
1
depths that are traditionally considered bathyal. Isopod crustaceans are well represented
in both the Antarctic shelf and the deep sea (Aronson et al. 2007). According to Menzies
et al. (1973), the trend of Antarctic eurybathy demonstrates what is considered to be a
complex evolutionary history. Some Antarctic taxa inhabiting shallow waters have
demonstrated evolutionary polar submergence, extending their bathymetric distribution to
deeper water. Other Antarctic taxa have demonstrated evolutionary polar emergence,
colonizing the continental shelf from deeper water (Brandt 1991,1992; Brandt et al. 2007;
Zinsmeister & Feldmann 1984). Brey et al. (1996) suggests that these bathymetric
evolutionary patterns are linked to the glacial history of Antarctica. Many taxa of the
Antarctic shelf have bathymetric ranges that are more extensive than those of similar taxa
on continental shelves elsewhere in the world. This suggests that movement in and out of
deep water, likely driven by historic glacial cycles, might represent a general
evolutionary history for the Antarctic fauna (Brey et al. 1996).
A distinctive characteristic of Antarctic marine benthic ecology is the lack of
durophagy, or skeleton-crushing predation (Aronson et al. 2007, Anrtz et al. 1994,
Dayton et al. 1974, Dell 1972, McClintock & Baker 1997). When it comes to the
structuring of food webs in the subtidal communities at temperate and tropical latitudes,
durophagous predators, including fish and decapods, are key predators that regulate the
distribution and abundance patterns of macroinvertebrates (Aronson et. al. 2007). Unlike
the aforementioned temperate and tropical latitudes, the marine benthos of Antarctica
lacks durophagous fish, lobsters, brachyuran crabs, sharks, and rays (Clarke & Johnston
1996, 2003; Dayton et al. 1994; Eastman & Clarke 1998; Long 1992, 1994). Antarctica
also lacks marine mammals that are considered to be ecologically equivalent to
2
durophagous gray whales and walruses found in the Arctic (Aronson et al. 2007).
Because Antarctica lacks modern predators, the benthic communities are considered
functionally Paleozic. In other words, the benthic communities have archaic biotas that
share an affinity with those that occur in deep sea. Marine invertebrates, such as
nemerteans and asteroids, are slow moving and are top predators, consuming a variety of
other invertebrates. There are also dense populations of epifaunal suspensions feeders
that are common in shallow-water environments including brachiopods, bryozoans,
crinoids and ophiuroids. These suspension feeding assemblages can cover hundreds of
kilometers of seafloor, and provide complex three-dimensional structures (Arntz et al.
2005, Aronson & Blake 2001, Clarke et al. 2004, Gili et al. 2006).
As is evident from the information present above, Antarctica has a marine fauna
that is unique and distinguishable from marine ecosystems elsewhere in the world.
Another unique feature of shallow nearshore marine ecosystems that surround the
Antarctic continent is the impact of ice. Ice can influence the nearshore marine
ecosystems of Antarctica both directly and indirectly. Sea-ice is of great importance to
benthic populations in the intertidal and shallow sub-littoral zones, as well as in deeper
Antarctic waters (Clarke 1996b). Ice is also of particular importance in its effect of
increasing the productivity of the water column, and hence increasing the availability of
food for benthic fauna. Other key areas in which ice is of particular importance to the
Antarctic benthos include patterns of sub-decadal variability in ice dynamics, as well as
the rafting of debris into deeper waters where isolated patches of hard-substratum habitat
are provided by “drop-stones” (Clarke 1996b). Sea-ice also has a major direct impact on
shallow water benthic communities through the process of ice scouring. Scouring events
3
can result in the complete eradication of regions of local benthic fauna; the frequency of
this eradication is related to the depth at which ice scour occurs. As ice scouring varies
with depth, it results in a unique zonation of benthic assemblages that can typify shallow
nearshore waters of Antarctica.
Ice also directly affects the shallowest of Antarctic depths through winter freezing
and/or ice scour. However, in slightly deeper water (generally 10-30m depth) anchor ice
forms via the freezing of undercooled water (Clarke 1996c). Anchor ice often freezes
around sessile benthic organisms such as sponges and soft corals. The anchor ice encases
and kills nearby organisms as it grows in situ and it can eventually lift encased organisms
off the benthos, creating new space for settling organisms (Clarke 1996a).
Deeper depths are free from the impacts of anchor, but remain subject to
occasional iceberg scour. Depth, local oceanography, and proximity to actively calving
ice-shelves are factors that influence the frequency of deep iceberg scour. Due to the
great depth of much of the Antarctic shelf, the Antarctic shelf benthos are not subject to
routine scouring (Clarke 1996a).
While sea-ice has direct effects on the marine ecosystem of Antarctica, there are
also indirect effects that are equally important. Among these indirect effects are the
impacts of surface ice in the winter and of glacial runoff. Glaciers and grounded ice
shelves emanate meltwater which can carry significant amounts of sediment of various
grain sizes. The rate of sedimentation can be very high near ice-fronts or glaciers (Clarke
1996a). Therefore, species that are not able to tolerate high inorganic loads are eradicated
by glacial runoff. As distance from the ice front increases, the impact of sedimentation
decreases. Biological material eventually dominates the sediment in deeper water.
4
Changes in position of a glacier front affect nearby benthic habitats by altering
depositional regime, hence bringing about changes in biological assemblages (Clarke
1996a). In the winter, the benthos can also be affected in numerous ways by the
formation of surface sea-ice. Sea ice stabilizes the water column by allowing suspended
particulate material to sink to the bottom to be exploited by the microbial flora as well as
macrofauna. High water clarity is also facilitated by sea ice stability, promoting early
spring blooms of microalgae that in turn impact the benthos (Clarke 1996a). Not only is
sea-ice important in stabilizing the water column, but it serves as an important habitat for
microbial communities. Sea-ice associated microbiota are released into the water column
as the ice melts, and some may sink down to the sea floor. This results in the microfauna,
meiofauna, and macrobenthos being provided with and important carbon source (Clarke
1996a).
Antarctic nearshore benthic communities display a high richness and diversity of
marine invertebrates. These communities are also known for their highly complex
physical structure. Dominant groups of marine invertebrates include bryozoans, soft
corals, tunicates, cnidarians and especially sponges and echinoderms (Dayton et al.
1974). While all five classes of the echinoderms are represented in nearshore waters of
Antarctica, brittle stars and sea stars are the most common classes of echinoderms.
Antarctic echinoderms are important not only in their contribution to benthic production,
but they are also known to play significant roles as determinants of community structure
(Dayton et al. 1974).
Therefore, just as echinoderms play an important role in the ecology of the deep
sea benthos, they are similarly important component of the fauna of the Antarctic shelf
5
(Gage & Tyler 1991). Several species of echinoderms are arguably “keystone species”
that play a role in regulating the structure of nearshore shelf benthic communities. The
most poignant example of the role of echinoderms in regulating the structure of a benthic
community can be seen in the coastal nearshore waters of McMurdo Sound, Antarctica.
The conspicuous macroinvertebrate species that comprise the benthic community of
McMurdo Sound include sponges, asteroids, and molluscs predators. A diverse
community of space-dominating sponges makes up the majority of the sessile
invertebrate community, covering up to 55% of the surface area of the benthos, and
representing nearly all of the vertical structure of this benthic community (Dayton et al.
1974). The primary predators of these sponges include the asteroids Perknaster fuscus
antarcticus, A. hodgsoni, Acodontaster conspicuous, Odontaster meridionalis, and
Odontaster validus. These conspicuous asteroids are slow-moving and digest their
sponge prey by extrusion of the cardiac stomach (Dayton et al. 1974). The
aforementioned asteroids play a key role in the community because some prey on a small
number of relatively rapidly growing sponges, effectively controlling the abundance of
the sponges and keeping them from dominating much space. One example is the sponge
Mycale acerata, a species whose growth rate is much more rapid than other Antarctic
sponge species. Mycale acerata is commonly preyed upon by Perknaster fuscus
antarcticus; therefore Mycale populations are regulated by the predation of a keystone
predator, Perknaster, and this prevents Mycale from dominating the benthos and reducing
overall species diversity (Dayton et al. 1974).
While keystone asteroids regulate fast growing sponges, they in turn must be
regulated so as to control their own population numbers. According to Dayton et al. 1974,
6
this occurs through larva filtration. For example, Acodontaster conspicuous is an
important asteroid that preys on sponges such as Mycale. Odontaster validus is a smaller
asteroid that is an opportunistic omnivore that through filter-feeding consumes the larvae
of Acodontaster. This filtration of the larva by Odontaster validus (the arms are held
upright in the water column) is extremely effective in controlling the population density
of Acodontaster (Dayton et al. 1974). Odontaster validus also preys on large adults of
Acodontaster conspicuus. During an attack, Odontaster climbs onto the aboral surface of
Acodontaster, extrudes its cardiac stomach, and digests a hole in one of arms of
Acodontaster. In response to the release of coelomic fluid by Acodontaster, other nearby
Odontaster attack the victim and digest its organs (Dayton et al. 1974). Despite the
evidence that Antarctic echinoderms such as sea stars play a significant role in regulating
the distribution and abundance of key members of Antarctic benthic communities, there
is a conspicuous lack of quantitative information on even the most basic population
biology (density and distribution) of Antarctic echinoderms both along the coast of the
continent and the Antarctic Peninsula.
Asteroids, crinoids, echinoids, ophiuroids and holothuroids are all represented
along the Antarctic Peninsula (Dearborn et al. 1974). Although all five classes of
echinoderms are found throughout the Peninsular region, trawling samples collected by
ship suggest that asteroids and ophiuroids are the most common echinoderm classes
represented (Dearborn et al. 1974). The asteroids of the peninsula are large and
conspicuous. Among the most common species are Odontaster validus, Psilaster
charcoti, Diplasterias brucei, Lysasterias perrieri, Neosmilaster georgianus, Labidiaster
annulatus (Dearborn et al. 1974). The latter is a large and multi-armed sea star that eats
7
other invertebrates, as well as other asteroids and ophiuroids (Dearborn et al. 1974).
Several of these asteroid species are considered to have circumpolar distributions (e.g.
Diplasterias brucie, Psilaster charcoti, and Odontaster validus) although recent
molecular studies have suggested that cryptic species may be more common than once
thought (e.g. Odontaster – Janoski and Halanych 2010). While asteroids are common
among the peninsula benthos, ophiuroids are the most common echinoderms to be found
in the benthic communities of the Antarctic Peninsula (Dearborn et al. 1974). About 42
species of brittle stars are known from nearshore habitats of the western Antarctic
Peninsula (Dearborn et. al. 1974). Ophiacantha pentactis, Ophioperia kochleri,
Ophiurolepis gelida and Ophionotus victoria are the four largest species of ophiuroids
and are common predators of other macroinvertebrates, including ophiuroids. Although
Dearborn’s work has contributed much to what is known qualitatively about the
representative echinoderm fauna of the Antarctic Peninsula, no systematic quantitative
studies have been conducted to date on populations of the echinoderms in nearshore
shallow waters of the Peninsula.
The purpose of this study is to not only determine what species inhabit the
nearshore shallow waters of the western Antarctic Peninsula, but how many individuals
of those species are present as well. A second objective of this study is to determine
whether or not significant relationships exist between the individuals of echinoderms and
the habitat in which these individuals were found. For example, this study will provide
insight as to whether or not there is a significant relationship between the number of
individual echinoderms and algal biomass, as well as the depths at which the individuals
were sampled. Also, this study will provide insight as to whether or not there is a
8
significant relationship between the numbers of individual echinoderms found at a given
depth.
MATERIALS AND METHODS
In a study assessing the distribution and abundance of macroalgae, Amsler et al.
(1995) defined five discrete study sites off the Antarctica Peninsula (64 S, 64 W)– along
the south-western coast of Anvers Island. These sites included: two sites on the northeastern coast of Dream Island, one site each on the north and south coasts of Hermit
Island, and one site on the south-eastern coast of DeLaca Island. All five sites were
bounded by a steep rocky shore, with the substrate generally extending to a depth of at
least 20 m. The northern coast of Hermit Island did not extend to 20 m.
At each site, linear transects were established and permanently marked. The
transects were 9 m in length and were placed along depth contours at 2, 5, 10, 15, and 20
m, however, samples were not taken from all depths at each site (Amsler et al. 1995).
Because only one sight was sampled at the 20 meter depth, data from this depth were
excluded from this study. Replicate quadrats, each measuring 0.125 m2, were then placed
at three randomly selected half-meter increments along each transect. All
macroinvertebrates and macroalgae were hand collected from these quadrats. The
macroalgal canopy which rose from holdfasts within the quadrat was cut and removed,
then placed into collecting bags made of fine mesh in order to retain any epiphytic or
mobile invertebrates (White 2002). This collection made up what was called the
“canopy” sample for each site. A benthic airlift (Amsler et al. 1995) was used in order to
collect understory samples. Vacuumed samples were preserved in a solution of buffered
9
5% Formalin sea water. The samples were then transferred to a solution consisting of
70% EtOH and 10% glycerin for storage (White 2002). After preservation, macroalgae
were removed from both the understory and canopy sample so that algal biomass could
be identified and quantified (Amsler et al. 1995).
All echinoderms were sorted from preserved understory samples either by hand,
or for smaller specimens, with the assistance of a Zeiss Stemi DV4 dissecting
microscope. Echinoderms were separated into what appeared at first observation to be
discrete species and re-preserved separately in 70% EtOH. Representative subsamples of
the preserved echinoderms were air-shipped to Chris Mah at the Smithsonian Museum of
Natural History where the author of this thesis (B. White) assisted Mah in taxonomic
identifications to the lowest taxon possible. Following taxonomic identification to the
lowest taxon possible, then numbers of individuals of each taxon of echinoderm within
each sampling quadrat at each of the five sites was enumerated. Correlation analysis was
used to evaluate potential relationships between echinoderm abundance patterns (total
echionderms, each echinoderm class, each individual species), site, depth, algal mass
(fleshy macroalgae), and crustose coralline algal percent cover.
RESULTS
Four species of sea stars were found at the sampling sites. The species include
Odontaster validus, Granaster nutrix, Lysasterias perrieri, and Adelasterias papillosa
(Table 1). Odontaster validus, G. nutrix were found at all five sampling sites. Lysasterias
perrieri was found at four of the five sampling sites, while A. papillosa and was found
only at one of the five sampling sites. Granaster nutrix occurred most abundantly in the
10
study site with 18 individuals of this species occurring in the quadrats sampled at DeLaca
Island. Odontaster validus was the second most abundant sea star in the study region.
Like G. nutrix, individuals of O. validus occurred in the highest abundance (12
individuals in the quadrats sampled) at DeLaca Island. Lysasterias perrieri occurred in
highest abundance at Dream Island and Hermit Island. Adelasterias papillosa was the
least abundant, represented by only one individual at DeLaca Island. Two unidentified
species of brittle stars belonging family Amphiuridae were found in the study region
(Table 1). Unidentified species #2 was the most abundant brittle star species collected in
the quadrats, with all 37 individuals found at Hermit Island, while brittle star species #1
was less abundant, but occurred more broadly at three of the five samples sites. Sea
cucumbers found in the study area included individuals of two species; Psolicrux coatsi
and Psolus carolineae, as well as one unidentified species in family Cucumariidae (Table
1). Psolus carolineae was the most abundant species, with 8 individuals collected from
quadrats at DeLaca Island and smaller numbers of individuals at three of the five
sampling sites. Individuals of family Cucumariidae and individuals of P. coatsi occurred
at two of the five sampling sites, DeLaca Island and Hermit Island. Sterechinus
neumayeri, a common regular sea urchin was the only species of sea urchin found in the
study region, occurring at three of the five sampling sites. The largest number (13
individuals) was collected from quadrats at DeLaca Island (Table 1).
The mean densities of each class of echinoderms in the study region was
calculated for all five sites and all depths (2 to 15 m) combined by dividing total densities
by the total number of 0.125 m-2 quadrats sampled (n = 45 quadrats) and multiplying by
eight to yield numbers per square meter. Mean ± 1 Standard Error (SE) population
11
densities were 18.7 ± 3.8 m-2 for asteroids, 8.9 ± 5.7 m-2 for ophiuroids, 3.4 ± 1.2 m-2 for
holothuroids, and 3.9 ± 1.6 m-2 for echinoids (Fig. 1).
Dr. Charles Amsler provided me with raw data from the study area, which made it
possible to use linear regression analyses in order to evaluate potential relationships
between echinoderm abundance patterns and algal mass of four categories of algae that
occurred in the quadrats at the sampling sites: brown algae (Himantothallus grandifolius
and Desmerestia spp.), branched red algae, bladed red algae, and coralline crust (percent
cover). Alga data came from three of the five transects. Linear regressions analyses
showed no significant relationships among the data, which included the quadrats that did
not contain echinoderms. However, when the quadrats containing no echinoderms were
removed from the data, analyses showed that there is a significant relationship between
abundance of Sterechinus neumayeri and Himanthothallus grandiofolius (P = 0.026).
There were no significant relationships between algal mass and abundance of sea stars,
brittle stars, or sea cucumbers.
Linear regression analyses on data, which included quadrats that contained no
echinoderms, showed that there is no significant relationship between the abundance of
echinoderms and depths. When the quadrats that contained no echinoderms were
removed from the data, linear regression analyses still showed that there is no significant
relationship between abundance of sea stars, brittle stars, and sea urchins and depths,
respectively, at the combined study sites (P = 0.334, 0.791, and 0.831 for sea stars, brittle
stars, and sea urchins, respectively, Figs. 2-4). In contrast, linear regression analysis did
reveal a significant relationship between the abundance of sea cucumbers and depth, (P =
0.017, Fig. 5). A further analysis using linear regression of the two most common sea
12
stars, Odontaster validus and Granaster nutrix indicated no significant relationship
between their abundance and the depth (P = 0.072 and 0.779 for O. validus and G. nutrix,
respectively (Fig. 6 and 7).
An Analysis of Variance (ANOVA) was also performed on data to evaluate if
there was significant difference between the numbers of individuals of each echinoderm
class and the particular depth of collection across the five sampling sites combined. This
analysis indicated there were no significant differences between numbers of individuals
at a given depth for sea stars, sea cucumbers, and sea urchins (P = 0.204 , 0.598, and
0.330 for sea stars, sea cucumbers and sea urchins, respectively). However, the ANOVA
indicated a significant effect of depth on abundance for brittle stars (P = 0.014). A pairwise test (Dunn’s test) was performed to attempt to discern at which depth brittle stars
wee most abundant. However, the pair-wise test was unable to discern at which depth
numbers of individuals were highest. This could be due to two reasons: 1) the pair-wise
test is not as powerful as the over-all ANOVA, or 2) the majority of the brittle stars
where found at a single depth (10 meters), thus confounding the pair-wise analysis.
DISCUSSION
The benthic marine invertebrate fauna of Antarctica is comprised of over the four
thousand described species (White 1984, Arntz et al. 1997, Clarke & Johnston 2003).
However, the coverage of taxa in specific regions of Antarctica remains very patchy.
According to Clarke et al. 2004, areas such as the western Antarctic Peninsula, South
Georgia, and the South Shetland Islands have been comparatively well sampled. Apart
from deeper soft sediment habitats, the benthic fauna of Antarctica is composed primarily
13
of sessile particle filter feeders which are associated with coarse grained glacial substrates
(Clarke et al. 2004). The fauna is typified by dense stratified communities of sponges,
hydroids, gorgonians, ascidians, bryozoans, crinioids, cirripedes, and soft corals that form
intricate three-dimensional frameworks at depths 30 to 50 meters below the influence of
anchor ice formation (excluding the Antarctic Peninsula where anchor ice does not form),
ice berg scour, and seasonal sea ice (Arntz et al. 1994, 1997, Gutt 2000, Cattaneo-Vietti
et al. 2000, Gambi et al. 2000). There is also rich fauna associated with these sessile
marine invertebrates including nemerteans, amphipods, isopods, pycnogonids, echinoids,
asteroids, and ophiuroids (Clarke et al. 2004). One of the most unique characteristics of
the benthic fauna of Antarctica is the paucity of skeleton-crushing predators. Sharks,
crabs, and lobsters are not found in Antarctic waters, and the diversity of durophagous
teleosts and skates is very limited (Aronson & Blake 2001). Although the echinoderm
taxa of the western Antarctic Peninsula has been qualitatively sampled (Dearborn et al.
1972, 1937), the present study is the first to conduct a systematic quantitative survey of
the abundance and distribution of nearshore echinoderms in this important biogeographic
province.
Mean population densities of the four classes of echinoderms sampled across
depths from 2 to 15 m at the five sites ranged from a high of 18.7 m-2 for asteroids to a
low of 3.9 m-2 for echinoids, with brittle stars and sea cucumbers having intermediate
densities. The relatively high densities recorded for all four classes reflect the importance
of echinoderms to the nearshore faunal community of the central western Antarctic
Peninsula. This is important not only in an ecological context as echinoderms can be
keystone predators (e.g. Paine 1966; Dayton et al., 1974; Dayton 1989), but also because
14
echinoderms play significant roles in carbon flow in marine benthic communities
including the global uptake and sequestration of atmospheric carbon in the world’s
oceans (Lebrato et al. 2010). This is because echinoderms are an exceptionally important
carbonate producing phylum contributing up to 80% of global CaCo3 at relatively
shallow to moderate ocean depths. The present study lends further support to the
importance of ehcinoderms in carbonate regimes, providing a “first glimpse” of a
signficiant role for echinoderms in carbon cycling along the Antarctic Peninsula.
Unfortunately, at present there are no data available on the densities of echinoderms from
other regions of the western Antarctic Peninsula with which to compare with the present
study.
Four of the five known classes of echinoderms found in the nearshore study
region occurred at least at one of the five sites sampled. Three classes, the asteroids,
ophiuroids, and echinoids, displayed no significant relationship between the depths at
which they were collected and their relative abundances. They were equally likely to
occur at any of the sampled depths between 2 and 15 meters. However, there was a
significant positive linear correlation between depth sampled and abundance of
holothuroids, with the greatest numbers occurring at a depth of 15 meters. The
holothuroids that were found to occur at three of the five study sites (Psolicrux coatsi and
Psolus carolineae), being most abundant at DeLaca Island, feed on small organic
particles via suspension feeding (Gutt 1991). Due to there being more large algal
holdfasts at the 15 meter depth sampled (Amsler, personal observation), it is possible that
sea cucumbers use these holdfasts to feed more efficiently.
15
The relationship between numbers of echinoderms within a given class and depth
was also analyzed by ANOVA. Here, only ophiuroids showed a significant relationship
with depth. A pair-wise Dunn’s test failed to determine at which depth ophiuroid were
most abundant. It is noteworthy that the two species that comprised the ophiuroids found
at the sites (family Amphiuridae), of which one species was found at three sites, occurred
in the largest numbers at a depth of 10 meters.
The echinoderms collected from the study region were ultimately resolved to
consist of four species of asteroids (Odontaster validus, Granaster nutrix, Lysasterius
perrieri, and Adelasterias papillosa,), two species of ophiuroids (two unidentified species
within the family Amphiuridae), at least two species of holothuroids (Psolicrux coatsi
and Psolus carolineae), and one species of echinoids (Sterechinus neumayeri). Little is
known about the biology and ecology of most of the majority of species of echinoderms
that are reported in the present study. Taxonomic issues remain to be resolved as well.
For example, recent molecular studies have revealed that there is taxonomic diversity of
Antarctic echinoderms, even at the level of genus that may be underrerepresented (e.g.
Odontaster, Janosik and Halanych, 2010). However, several of the echinoderm species
that occurred in the study sites stand out as ecologically important and as such have
received considerable attention. These include the three species discussed below.
Granaster nutrix, which is found in rocks in crevices (Dearborn and Fell, 1974),
occurred in abundance at all five nearshore sampling sites in the region of Palmer Station.
In fact, this was by far the most common sea star to occur in the study area. This species
was most abundant at the study sites located at Dream Island, Hermit Island, and
especially, DeLaca Island. Despite there being no statistically significant relationship
16
between depth and sea stars at the study sites, G. nutrix tended to occur in largest
numbers at a depth of two meters within the range of depths sampled. This small (R = 11.5 cm; M.O. Amsler, personal observation) brooding sea star is known to occur
commonly along the Antarctic Peninsula (Fell and Dawsey 1969; Dearborn and Fell
1974), and is also well known from the South Orkneys and South Georgia (Fisher 1940;
Fell and Dawsey 1969). Dearborn (1977) reported that G. nutrix has a bathymetric profile
that ranges from 0.5 to 250 meters along the Antarctic Peninsula. In this sense this
species lacks the wide eurybathic distribution noted in many other Antarctic
echinoderms. As an omnivore, G. nutrix feeds on small gastropods and macroalgae
(Dearborn 1977; Dearborn and Edwards 1984; McClintock 1994) both of which are
common in the study area (Amsler et al. 1995; White 2002). According to Dearborn
(1997), gut contents revealed that red algae were present in small amounts. Fleshy red
algae are most common at two meters depth in the study site examined in the present
study (Amsler et al. 1995), the same depth that G. nutrix appeared in largest numbers.
This suggests that drift red algal fragments are readily available to be included in the diet.
Odontaster validus was found at all five sampling sites, and was the second most
abundant sea star to occur in the study area. Odontaster validus is considered to be the
most abundant asteroid in Antarctica (Janosik and Halanych 2010), occurring in highest
abundance in shallow, near shore waters of the Antarctic shelf (Dearborn, 1977). This
asteroid is moderately sized (R approximately 4 cm, J. McClintock personal observation)
and is colored a deep purple-red to bright reddish orange. Odontaster validus is
circumpolar in its distribution (Janosik and Halanych 2010) and, while having a
bathymetric range from the intertidal to 940 meters, is found in highest densities between
17
depths of 15 and 200 meters (Dearborn 1965, 1967; Fell and Dawsey 1969: Dearborn
1977; McClintock et al. 1988). In the present study, O. validus was most abundant at the
study site located at DeLaca Island. Although there is no statistically significant
relationship between depth and sea stars at the study sites, O. validus tended to be found
mostly at a depth of ten meters. According to Dearborn (1977), O. validus can be found
on every type of substrate within its depth range. O. validus is also a voracious
omnivore, having a diet consisting of sponges, detritus, bivalves, hydroids, gastropods,
and sea stars (Dayton et al. 19974). Odontaster validus is an opportunistic feeder,
displaying feeding habits such as necrophagy, scavenging, herbivory, carnivory, and
detrital feeding (Peckham 1964; Pearse 1965, 1969: Dayton et al. 1974; Dearborn 1977,
reviewed in McClintock 1994). This species also consumes the larvae of sympatric sea
stars that predate sponges, particularly the sponge Mycale accerata, and thereby serves as
a “larval filter” via detrital feeding (McClintock et al. 2008). While it is unlikely that
O.validus plays as important a role in determining community structure in the study
region as it does in McMurdo Sound where it is even more abundant (Dayton et al.1974),
it remains to be determined if it plays a keystone role in the benthos of the western
Antarctic Peninsula.
Sterechinus neumayeri is the most abundant echinoid found in near-shore
shallow waters surrounding Antarctica (Bosch et al. 1987). This species was found to
occur at three of the five sampling sites, with highest number of individuals occurring at
DeLaca Island. While densities were moderate, they were considerably lower than
densities that occur in regions of McMurdo Sound, Antarctica (Brey et al. 1996). The
highest numbers of individuals were collected at a depth of 5 meters. Pearse and Giese
18
(1966) noted that leafy red algae (Iridaea sp.) may provide some food for S. neumayeri,
however, gut contents revealed this sea urchin feeds mostly on benthic diatoms. This is
likely the case in the study area as S. neumayeri is not seen grazing directly on
macroaglae (C. Amsler, personal communication). There is no significant relationship
between the depth distribution of this echinoid and the depths and sites reported to have
the greatest availability (wet mass) of leafy read algae in the Palmer nearshore region
(Amsler et al. 1995).
19
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Table 1. The taxa and numbers of individuals of the four classes of echinoderms collected
at the each of the five sampling sites near Anvers Island on the central western Antarctica
Peninsula. Note that both Dream Island and Hermit Island have two sampling sites each.
Class
Dream Island
Sampling Site
Number
Asteroidea
Ophiuroidea (Family
Amphiuridae)
Holothuroidea
Species
Odantaster validus
Granaster nutrix
Lysasterius perrieri
Adelasterias papillosa
1
2
5
8
4
1
12
Species
1
2
Species
Psolicrux coatsi
Psolus carolineae
1
Family
Cucumariidae
Echinoidea
Species
Sterechinus neumayeri
1
32
Delaca Island
1
Number of
Individuals
12
18
2
1
Hermit Island
1
2
8
6
1
6
17
4
6
4
37
3
3
5
1
3
5
1
13
8
Density
Mean Density/m2 ± 1 SE
25
20
15
10
5
0
Asteroidea
Ophiuroidea
Holothuroidea
Echinoidea
Figure 1. Estimated mean ± 1 SE densities of each of the four classes of
echinoderms collected across depths ranging from 2 to 15 m at the five
sampling sites near Anvers Island on the central western Antarctic Peninsula.
N = forty five 0.125 meter squared quadrats.
33
Total Number of Asteroids
Asteroidea
y = 0.1633x + 3.1094
R² = 0.0406
14
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
Depth
Figure 2. Graph showing total numbers of asteroids collected at five
Nearshore sampling sites near Anvers Island plotted against the four sampling
depths (depth range = 2 to 15 meters). There was no significant relationship
between depth and abundance (P = 0.334). 34
Total Number of Ophiuroids
Ophiuroidea
y = 0.5x + 3.3333
R² = 0.0196
35
30
25
20
15
10
5
0
0
2
4
6
8
10
12
14
16
Depth
Figure 3. Graph showing total numbers of ophiuroids collected at
Five nearshore sampling sites near Anvers Island plotted against the four sampling
depths (depth range = 2 to 15 meters). There was no significant relationship between
depth and abundance (P = 0.791).
35
Total Number of Echinoids
Echinoidea
y = 0.0363x + 1.902
R² = 0.0061
8
7
6
5
4
3
2
1
0
0
2
4
6
8
10
12
14
16
Depth
Figure 4. Graph showing total numbers of echinoids collected at five
nearshore sampling sites near Anvers Island plotted against the four sampling
depths (depth range = 2 to 15 meters). There was no significant relationship between
depth and abundance (P = 0.831). 36
Total Number of Holothuroids
Holothuroidea
6
y = 0.2063x + 0.3736
R² = 0.5297
5
4
3
2
1
0
0
2
4
6
8
10
12
14
16
Depth
Figure 5. Graph showing total numbers of holothuroids collected at
five nearshore sampling sites near Anvers Island plotted against the four sampling
depths (depth range = 2 to 15 meters). There was a significant positive relationship
between depth and abundance (P = 0.017). 37
Total Number of O. validus
Odontaster validus
y = 0.2057x + 1.3293
R² = 0.2885
8
7
6
5
4
3
2
1
0
0
2
4
6
8
10
12
14
16
Depth
Figure 6. Graph showing total numbers of the sea star Odontaster validus
collected at five nearshore sampling sites near Anvers Island plotted against
the four sampling depths (depth range = 2 to 15 meters). There was no significant
relationship between depth and abundance (P = 0.072). However, if one uses
the two-tailed test probability value of 0.01 rather than 0.05, there is a significant
positive relationship between abundance and depth. 38
Total Number of G. nutrix
Granaster nutrix
y = 0.0541x + 3.0344
R² = 0.0051
10
9
8
7
6
5
4
3
2
1
0
0
2
4
6
8
10
12
14
16
Depth
Figure 7. Graph showing total numbers of the sea star Granaster nutrix at five
sampling nearshore sites near Anvers Island plotted against the four sampling depths
(depth range = 2 to 15 meters). There was no significant relationship between
depth and abundance (P = 0.779). 39