Intellectual Merit: Pleuragramma antarcticum, the Antarctic silverfish, play a key role in the trophic pyramid of the Antarctic coastal ecosystem, acting as food for larger fishes, flying and non-flying seabirds, pinnipeds, and whales. In turn, they are predators on coastal euphausiids, including both Euphausia superba and crystallorophias. Historically, Pleuragramma have been an important food source for Adélie Penguins of the Western Antarctic Peninsula (WAP), but during the last decade Pleuragramma have disappeared from the Adélie diet. We suggest that Pleuragramma?s absence from the diets of top predators is linked to the declining sea ice canopy, which serves as a nursery for eggs and larvae during the austral spring. The research will investigate four hydrographic regimes over the WAP continental shelf with the following features: (1) persistent gyral flows that act to retain locally spawned larvae, (2) spring sea ice that has declined in recent years (3) the prevalence of adult silverfish, and (4) the presence of breeding Adélie penguins whose diets vary in the proportions of silverfish consumed. The research will evaluate the importance of local reproduction versus larval advection, and the extent to which populations in the subregions of study are genetically distinct, via analysis of population structure, otolith microchemistry and molecular genetics of fish. The Pleuragramma data will be compared with penguin diet samples taken synoptically.
Broader Impacts: The proposed research brings together an international group of scientists with highly complimentary suites of skills to address the fate of Pleuragramma on the WAP shelf. Graduate students will use the data acquired as part of their Ph.D research, and will receive cross-training in ornithological field techniques, molecular genetic methods and otolith isotope chemistry. The PIs will work actively with the St. Petersburg Times to produce a blog in real time with pictures and text, which will be used to interact with local schools while we are at sea and after our return. The investigators also will collaborate with the COSEE center at USF and at local schools and museums to disseminate results to the K-12 community throughout the region.
Dr. William R. Fraser, Polar Oceans Research Group, Co-Principal Investigator in collaboration with Dr. Jose Torres, University of South Florida, Principal Investigator, and Dr. Julian Ashford, Old Dominion University, Co-Principal Investigator. Project Results. The Western Antarctic Peninsula (WAP) is one of the most rapidly warming marine ecosystems on Earth, and the loss of sea ice over the last three decades is one of many regional variables undergoing profound changes. Because sea ice plays a critical role in the life histories of many Antarctic species, its loss has had equally profound effects on regional marine food webs. A key component of these foods webs is the Antarctic Silverfish (Pleuragramma antarcticum), which spawns beneath the sea ice and whose eggs and larvae are sheltered by the ice during early growth stages. Sea ice is thus critical to Antarctic Silverfish reproduction. Antarctic Silverfish are also a key component of the diets of many Antarctic top predators, including penguins and other seabirds, seals and whales. Long-term data based on the diets of two of these predators, Adélie penguins and South Polar Skuas in the vicinity of Palmer Station, a U.S. base in the WAP, suggest that silverfish may be decreasing in the area in tandem with the loss of sea ice. One of the main objectives of this project, therefore, was to confirm the validity of this trend by fishing for this species using nets deployed from a research vessel in combination with synoptic sampling of seabird diets whose foraging movements and locations were identified using satellite telemetry. Although aspects of the data obtained during this project are still pending analysis because they are associated with a student Ph. D. dissertation, the trend in silverfish populations previously discussed was confirmed. Over a large sector of the WAP this species now occurs in low abundances when compared to abundances during previous decades. As such, this trend parallels changes in the populations of other species in the WAP whose life histories are also sea ice dependent, including Antarctic krill, Adélie and Emperor penguins and Weddell seals. From an ecosystem perspective, moreover, these findings highlight not only the dangers posed by climate change to marine food webs, but also the rapidity with which changes can occur. Other Project Impacts. Aside from the co-principal investigator, this project also supported the involvement of six other individuals including students and technicians. Three of these individuals remain associated with the home institution and continue to pursue research on related projects in the WAP as part of the Palmer Long-Term Ecological Research Program (http://pal.lternet.edu/). Of the remaining three individuals, one is using project data and findings to pursue a Ph.D. through a collaboration with Simon Fraser University, while the other two have obtained positions at Colorado State University to pursue a M.Sc. degree on terrestrial top predators and at the University of Hawaii to work on endangered seabirds, respectively. Collaborations with writer Fen Montaigne also produced two works with broad and significant outreach to both lay and professional audiences. The first, "The Ice Retreat", was published as an article in the New Yorker magazine, November 2009; the second, "Fraser’s Penguins, A Journey to the Future in Antarctica", was published as a book by Henry Holt, 2010.
