John S. Oliver

Antarctic Soft-Bottom Benthos in Oligotrophic and Eutrophic Environments

The benthos of the east and west sides of McMurdo Sound, Antarctica, is characterized by dramatically different infaunal assemblages. The eutrophic East Sound has higher infaunal densities than almost any other benthic assemblage in the world. In contrast, the oligotrophic West Sound, bathed by currents from beneath the Ross Ice Shelf, has patterns of mobile epifauna and low infauna density similar to bathyl deep-sea communities.

Destruction and Opportunity on the Sea Floor: Effects of Gray Whale Feeding

Gray whales (Eschrichtius robustus) are highly disruptive bottom feeders that remove infaunal invertebrate prey and sediments by suction. The response of the benthos to gray whale feeding was examined in the primary feeding grounds of the Bering Sea and in an ecological analog of these prey communities along the west coast of Vancouver Island. Prey communities were dominated by ampeliscid and other amphipod crustaceans that formed dense tube mats. Large feeding excavations (often 2-20 M2) were rapidly colonized by scavenging lysianassid amphipods, especially Anonyx spp., that attacked injured and dislodged infauna. Many of the attacked animals were small crustaceans ( 2 mo. Early colonists were characterized by much greater abundances inside excavations relative to the adjacent tube mat. Two numerically dominant groups of tube-dwelling amphipods were not charac- terized by a large pulse of abundance inside excavations. Ampelisca and Protomedeia gradually col- onized pits. They also swam less frequently than the early colonists, and probably had more infaunal habits. Gray whale feeding clearly has a dramatic impact on the structure of benthic communities, and also may enhance the population size of several secondary prey.

Intense and localized benthic marine pollution around McMurdo Station, Antarctica

Abstract Benthic sediments and animals are highly modified by human activities at McMurdo Station, the largest human settlement in Antarctica. The quantity of anthropogenic debris, contamination of marine sediments with hydrocarbons and metals, and gross changes in benthic communities are largely confined to Winter Quarters Bay, adjacent to the former dump site and the ice dock used by visiting ships. Levels of purgeable hydrocarbons in bay sediments are as high as 4500 ppm. Metal levels are mostly high within the bay, but are not greater than in the most polluted temperate habitats. Levels of anthropogenic chemicals are significantly higher in the back bay compared to stations established at different distances from the bay (along three potential contamination gradients), including reference sites many kilometres away. There are significant negative correlations between the total number of infauna or epifauna and the concentrations of hydrocarbons and most metals in sediments. The few animals living in the back bay are motile polychaete worms with opportunistic life histories, primarily Capitella capitata antarcticum and Ophryotrocha claparedii . Fortunately, the local physical setting apparently permits little transport of contaminated sediments from the bay, which is flanked on one side by a large submarine ridge and on the other by Hut Point. Hut Point also protects the bay from oceanic conditions. The back bay is over 30 m deep and the ridge top is only 18 m deep. The gradient of chemical and community change is extremely steep, but there are observable ecological impacts outside the bay along the front of the station. Although most historical inputs of pollution are removed or reduced and continued cleanup is planned, Winter Quarters Bay may require many decades to recover.

Distribution patterns of benthic microalgal standing stock at McMurdo Sound, Antarctica

SummaryDuring the austral summer of 1975–76 and winter of 1977 benthic and water column chlorophyll a and phaeopigments were measured at several sites along the east and west sides of McMurdo Sound, Antarctica. Estimates of in situ primary productivity were made at some McMurdo Sound locations. Additionally, water column samples were collected at 5 stations in the Ross Sea during January, 1976. Standing stock data are analyzed to identify seasonal and spatial patterns. Variability in algal standing stock was related to ambient light levels and appeared to be mediated by ice and snow cover whereby the highest algal standing stock was present under high light conditions (low ice and snow cover, shallow water, summer). Differences in published benthic invertebrate densities appear to be closely allied to differences in benthic primary production, and less so to in situ planktonic ice microalgal production.

Effects of crustacean predators on species composition and population structure of soft-bodied infauna from Mcmurdo sound, Antarctica

Abstract A tanaid crustacean (Nototanais), and especially a phoxocephalid amphipod (Heterophoxus), regulate the species composition and population-size structure of soft-bodied infauna (primarily polychaete worms) by preying on small species and small individuals of large species. Small individuals of soft-bodied infauna are rare in this dense infaunal assemblage (over 100000/m2) from Antarctica. The evidence for the regulatory role of the peracarid crustaceans comes from gut contents; from laboratory experiments where the crustaceans consume spionid larvae or juveniles and small polychaete species; from field experiments where the abundances of crustaceans and small polychaetes are negatively correlated after the colonization of defaunated sediments; from exploring the role of depth refuges in the sediment; and from community patterns along a gradient in water depth where crustacean abundance is negatively correlated with the abundance of small species and small individuals of large polychaete species. B...

Walrus feeding disturbance: Scavenging habits and recolonization of the Bering Sea benthos☆

Walruses (Odobenus rosmarus Illiger) influenced the structure of macrobenthic assemblages in a variety of ways as they excavated their major bivalve prey from soft sediments. Benthic animals were attracted to discarded bivalve shells and they colonized pits and furrows made during prey excavation. Discarded shells contained soft tissues that were eaten by several invertebrate scavengers. The most abundant and widespread scavenger was the sea star, Asterias amurensis Lutken. Sea stars out-competed brittle stars (Amphiodia craterodmeta Clark) for fresh scavenging events. They also attacked brittle stars under shells in the laboratory, and thus may have obtained two meals from discarded shells by eating remnant tissue and by consuming animals that used the shell as a habitat. In nature, brittle stars were abundant under discarded shells. In experiments, brittle stars invaded shells with soft tissue in the absence of sea stars, but not in their presence. In other experiments, brittle stars were most abundant under shells with soft tissue, but were also attracted to shells without organic matter. Large brittle stars were more abundant under shells than in the surrounding bottom, and the reverse was true of small individuals. Bottom communities recovered gradually inside experimental feeding excavations, which were not invaded by large numbers of opportunistic infaunal or epifaunal invertebrates. This is in contrast to gray whale feeding excavations, which are colonized by a large number of opportunistic peracarid crustaceans.

Patterns of survival and behavior in Antarctic benthic invertebrates exposed to contaminated sediments: field and laboratory bioassay experiments

Benthic invertebrates were exposed to chemically contaminated sediments (primarily petroleum hydrocarbons) from a well-defined pollution gradient around McMurdo Station, Antarctica in a series of field and laboratory bioassay experiments. The patterns of survival and behavior in these experiments corresponded to patterns observed in standard U.S. Environmental Protection Agency laboratory bioassays. The contaminated end of the pollution gradient is Winter Quarters Bay where total hydrocarbons are as high as 4500 μg·g sediment−1. Mortality of Heterophoxus videns K.H. Barnard, a phoxocephalid amphipod crustacean, in standard laboratory bioassays was highest in sediment from Winter Quarters Bay, high in sewage outfall sediments, and generally decreased in sediments from increasing distances from the bay. Similar survival patterns were documented for several other crustacean species. Amphipods, tanaids, and cumaceans consistently avoided sediments from Winter Quarters Bay in the survival bioassays and were more abundant in uncontaminated sediments in laboratory habitat choice experiments. Fewer H. videns and the heart urchin, Abatus shackletoni Koehler, burrowed into Winter Quarters Bay sediment compared with uncontaminated sediment in field and laboratory assays. We exposed H. videns and Eudorella splendida Zimmer, a cumacean, to Winter Quarters Bay and uncontaminated sediments for 10 and 28 days in field bioassays. Greater mortality was evident in Winter Quarters Bay sediment but the difference between treatments was not significant. In contrast, when benthic communities were transplanted along the pollution gradient and sampled a year later, there were dramatic changes in community structure in Winter Quarters Bay, less at the edge of the bay, and little at an uncontaminated site. Overall, these assays showed similar patterns of increased survival decreased avoidance of sediment along a steep and well-defined pollution gradient.

Scavenging and Other Feeding Habits of Lysianassid Amphipods (Orchomene spp.) from McMurdo Sound, Antarctica

SummaryThe distribution and scavenging habits of the two most abundant lysianassid amphipods in McMurdo Sound differ markedly. Orchomene plebs lives primarily in deep water (>100 m), where planktonic and benthic food is sparser and scavenging events are less common and predictable than in shallower water. Orchomene plebs is common in shallow areas (<100 m) only under the Ross Ice Shelf and along the western McMurdo Sound. Here Weddell seals frequent tidal cracks in which they discard carrion and defecate; otherwise food is scarce. Orchomene pinguides lives on shallow (<10 m) wave-cut benches that are rich in food along the eastern McMurdo Sound. They, along with other omnivorous invertebrates which scavenge the food-rich eastern sound benches, are rare from shallow water along the western sound. The eastern benches are bathed by dense plankton blooms and harbor a high biomass of benthic diatoms and invertebrates. Scavenging events there were observed throughout the year. Orchomene plebs is larger and more motile, and came to laboratory carrion and baited field traps more rapidly and in greater numbers than O. pinguides. The crop contents of O. plebs contained only amorphous organic matter that suggested a scavenging habit. Crops of O. pinguides contained not only amorphous organic matter but also invertebrate prey, especially planktonic copepods that impact the bottom during winter.

Recruitment, Growth and Mortality of an Antarctic Hexactinellid Sponge, Anoxycalyx joubini

Polar ecosystems are sensitive to climate forcing, and we often lack baselines to evaluate changes. Here we report a nearly 50-year study in which a sudden shift in the population dynamics of an ecologically important, structure-forming hexactinellid sponge, Anoxycalyx joubini was observed. This is the largest Antarctic sponge, with individuals growing over two meters tall. In order to investigate life history characteristics of Antarctic marine invertebrates, artificial substrata were deployed at a number of sites in the southern portion of the Ross Sea between 1967 and 1975. Over a 22-year period, no growth or settlement was recorded for A. joubini on these substrata; however, in 2004 and 2010, A. joubini was observed to have settled and grown to large sizes on some but not all artificial substrata. This single settlement and growth event correlates with a region-wide shift in phytoplankton productivity driven by the calving of a massive iceberg. We also report almost complete mortality of large sponges followed over 40 years. Given our warming global climate, similar system-wide changes are expected in the future.

Sea star and walrus predation on bivalves in Norton Sound, Bering Sea, Alaska

Abstract Pacific walruses (Odobenus rosmarus divergens) and sea stars (Asterias amurensis) are the primary predators on bivalve mollusks in Norton Sound and probably in most of the Bering and Chukchi Seas. Secondary predators in these areas include starry flounder (Platichthys stellatus) and king (Paralithodes spp.) and Tanner (Chionoecetes spp.) crabs. Walruses and sea stars consume the same species, but not the same sizes of bivalves. The primary walrus prey are large individuals of several bivalve species, which have no refuge from walrus predation. Sea stars feed on smaller species and on smaller individuals of the large bivalve species. Laboratory experiments and field observations indicate that large bivalves have refuges from sea stars. Large Serripes groenlandicus escape sea star predation by leaping, large Yoldia hyperborea by rapid burrowing into the sediment. Large Mya truncata and Macoma calcarea live too deep in the sediment (>15 cm) for capture by the shallow digging (<10 cm) Asterias amuren...