Drivers of concentrated predation in an Antarctic marginal-ice-zone food web.

Predators impact preyscapes (3-D distribution of forage species) by consuming prey according to their abilities or by altering prey behavior as they avoid being consumed. We elucidate prey (Antarctic silverfish[Pleuragramma antarctica] and crystal krill[Euphausia chrystallorophias]) responses to predation associated with the marginal ice zone (MIZ) of the McMurdo Sound, Antarctica, polynya. Prey abundance and habitat was sampled across a 30 × 15 km area by remotely-operated vehicle, and included locations that were accessible (ice edge) or inaccessible (solid fast ice) to air-breathing predators. Prey and habitat sampling coincided with bio-logging of Adélie penguins and observations of other air-breathing predators (penguins, seals, and whales), all of which were competing for the same prey. Adélie penguins dived deeper, and more frequently, near the ice edge. Lowered abundance of krill at the ice edge indicated they were depleted or were responding to increased predation and/or higher light levels along the ice edge. Penguin diet shifted increasingly to silverfish from krill during sampling, and was correlated with the arrival of krill-eating whales. Behaviorally-mediated, high trophic transfer characterizes the McMurdo Sound MIZ, and likely other MIZs, warranting more specific consideration in food web models and conservation efforts.

Anthropogenic disturbance and biodiversity of marine benthic communities in Antarctica: a regional comparison.

The impacts of two Antarctic stations in different regions, on marine sediment macrofaunal communities were compared: McMurdo, a very large station in the Ross Sea; and Casey, a more typical small station in East Antarctica. Community structure and diversity were compared along a gradient of anthropogenic disturbance from heavily contaminated to uncontaminated locations. We examined some of the inherent problems in comparing data from unrelated studies, such as different sampling methods, spatial and temporal scales of sampling and taxonomic uncertainty. These issues generated specific biases which were taken into account when interpreting patterns. Control sites in the two regions had very different communities but both were dominated by crustaceans. Community responses to anthropogenic disturbance (sediment contamination by metals, oils and sewage) were also different. At McMurdo the proportion of crustaceans decreased in disturbed areas and polychaetes became dominant, whereas at Casey, crustaceans increased in response to disturbance, largely through an increase in amphipods. Despite differing overall community responses there were some common elements. Ostracods, cumaceans and echinoderms were sensitive to disturbance in both regions. Capitellid, dorvelleid and orbiniid polychaetes were indicative of disturbed sites. Amphipods, isopods and tanaids had different responses at each station. Biodiversity and taxonomic distinctness were significantly lower at disturbed locations in both regions. The size of the impact, however, was not related to the level of contamination, with a larger reduction in biodiversity at Casey, the smaller, less polluted station. The impacts of small stations, with low to moderate levels of contamination, can thus be as great as those of large or heavily contaminated stations. Regional broad scale environmental influences may be important in determining the composition of communities and thus their response to disturbance, but there are some generalizations regarding responses which will aid future management of stations.

Antarctic research bases: local sources of polybrominated diphenyl ether (PBDE) flame retardants.

Contemporary studies of chemical contamination in Antarctica commonly focus on remnants of historical local releases or long-range transport of legacy pollutants. To protect the continent's pristine status, the Antarctic Treaty's Protocol on Environmental Protection prohibits importation of persistent organic pollutants. However, some polybrominated diphenyl ether (PBDE) congeners exhibit similar properties. Many modern polymer-containing products, e.g., home/office furnishings and electronics, contain percent levels of flame retardant PBDEs. PBDE concentrations in indoor dust and wastewater sludge from the U.S. McMurdo and New Zealand-operated Scott Antarctic research bases were high. Levels tracked those in sludge and dust from their respective host countries. BDE-209, the major constituent in the commercial deca-PBDE product, was the dominant congener in sludge and dust, as well as aquatic sediments collected near the McMurdo wastewater outfall. The pattern and level of BDE-209 sediment concentrations, in conjunction with its limited environmental mobility, suggest inputs from local sources. PBDE concentrations in fish and invertebrates near the McMurdo outfall rivaled those in urbanized areas of North America and generally decreased with distance. The data indicate that reliance on wastewater maceration alone, as stipulated by the Protocol, may permit entry of substantial amounts of PBDEs and other chemicals to the Antarctic environment.

Benthic changes during 10 years of organic enrichment by McMurdo Station, Antarctica.

A benthic habitat along the coast of McMurdo Station in the Ross Sea, Antarctica is enriched by sewage from the station and altered by hydrocarbons and heavy metals in an adjacent historic dumpsite. We report on 10 years of change in the benthic communities from 1988 to 1998 and compare enrichment effects at Australia's Casey Station, East Antarctica. Despite being 14 km apart, reference communities upcurrent and downcurrent of McMurdo Station remained closely similar over time, dominated in all years by a tube building polychaete, Spiophanes tcherniae. The community bordering McMurdo Station was generally a third as abundant as communities at the reference sites over the decade of sampling, although diversity was as high or higher, except in the most contaminated areas. In 1992, organic enrichment of the outfall community intensified and within the year, the opportunistic polychaetes Aphelochaeta sp., Ophryotrocha notialis, Capitella perarmata, and Leitoscoloplos kerguelensis became dominant. Since 1996, two of the three enriched communities have increased in resemblance to the reference communities. Given the observed responsiveness of the benthos to the outfall so far, further changes are anticipated within the year following implementation of sewage treatment in 2003. Organic enrichment by McMurdo Station has had a greater impact on benthic community structure than at Australia's Casey Station.