Megafaunal Communities in Rapidly Warming Fjords along the West Antarctic Peninsula: Hotspots of Abundance and Beta Diversity

PLOS ONE, Dec 2019

Glacio-marine fjords occur widely at high latitudes and have been extensively studied in the Arctic, where heavy meltwater inputs and sedimentation yield low benthic faunal abundance and biodiversity in inner-middle fjords. Fjord benthic ecosystems remain poorly studied in the subpolar Antarctic, including those in extensive fjords along the West Antarctic Peninsula (WAP). Here we test ecosystem predictions from Arctic fjords on three subpolar, glacio-marine fjords along the WAP. With seafloor photographic surveys we evaluate benthic megafaunal abundance, community structure, and species diversity, as well as the abundance of demersal nekton and macroalgal detritus, in soft-sediment basins of Andvord, Flandres and Barilari Bays at depths of 436–725 m. We then contrast these fjord sites with three open shelf stations of similar depths. Contrary to Arctic predictions, WAP fjord basins exhibited 3 to 38-fold greater benthic megafaunal abundance than the open shelf, and local species diversity and trophic complexity remained high from outer to inner fjord basins. Furthermore, WAP fjords contained distinct species composition, substantially contributing to beta and gamma diversity at 400–700 m depths along the WAP. The abundance of demersal nekton and macroalgal detritus was also substantially higher in WAP fjords compared to the open shelf. We conclude that WAP fjords are important hotspots of benthic abundance and biodiversity as a consequence of weak meltwater influences, low sedimentation disturbance, and high, varied food inputs. We postulate that WAP fjords differ markedly from their Arctic counterparts because they are in earlier stages of climate warming, and that rapid warming along the WAP will increase meltwater and sediment inputs, deleteriously impacting these biodiversity hotspots. Because WAP fjords also provide important habitat and foraging areas for Antarctic krill and baleen whales, there is an urgent need to develop better understanding of the structure, dynamics and climate-sensitivity of WAP subpolar fjord ecosystems.

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Megafaunal Communities in Rapidly Warming Fjords along the West Antarctic Peninsula: Hotspots of Abundance and Beta Diversity

Smith CR (2013) Megafaunal Communities in Rapidly Warming Fjords along the West Antarctic Peninsula: Hotspots of Abundance and Beta Diversity. PLoS ONE 8(11): e77917. doi:10.1371/journal.pone.0077917 Megafaunal Communities in Rapidly Warming Fjords along the West Antarctic Peninsula: Hotspots of Abundance and Beta Diversity Laura J. Grange 0 1 Craig R. Smith 0 1 Philippe Archambault, Universite du Quebec a` Rimouski, Canada 0 Current address: Ocean and Earth Science, National Oceanography Centre, University of Southampton , Southampton , United Kingdom 1 Department of Oceanography, University of Hawaii at Manoa , Honolulu, Hawaii , United States of America Glacio-marine fjords occur widely at high latitudes and have been extensively studied in the Arctic, where heavy meltwater inputs and sedimentation yield low benthic faunal abundance and biodiversity in inner-middle fjords. Fjord benthic ecosystems remain poorly studied in the subpolar Antarctic, including those in extensive fjords along the West Antarctic Peninsula (WAP). Here we test ecosystem predictions from Arctic fjords on three subpolar, glacio-marine fjords along the WAP. With seafloor photographic surveys we evaluate benthic megafaunal abundance, community structure, and species diversity, as well as the abundance of demersal nekton and macroalgal detritus, in soft-sediment basins of Andvord, Flandres and Barilari Bays at depths of 436-725 m. We then contrast these fjord sites with three open shelf stations of similar depths. Contrary to Arctic predictions, WAP fjord basins exhibited 3 to 38-fold greater benthic megafaunal abundance than the open shelf, and local species diversity and trophic complexity remained high from outer to inner fjord basins. Furthermore, WAP fjords contained distinct species composition, substantially contributing to beta and gamma diversity at 400-700 m depths along the WAP. The abundance of demersal nekton and macroalgal detritus was also substantially higher in WAP fjords compared to the open shelf. We conclude that WAP fjords are important hotspots of benthic abundance and biodiversity as a consequence of weak meltwater influences, low sedimentation disturbance, and high, varied food inputs. We postulate that WAP fjords differ markedly from their Arctic counterparts because they are in earlier stages of climate warming, and that rapid warming along the WAP will increase meltwater and sediment inputs, deleteriously impacting these biodiversity hotspots. Because WAP fjords also provide important habitat and foraging areas for Antarctic krill and baleen whales, there is an urgent need to develop better understanding of the structure, dynamics and climate-sensitivity of WAP subpolar fjord ecosystems. - Funding: This material is based upon work supported by the Office of Polar Programs (OPP), United States National Science Foundation under the LARISSA and FOODBANCS2 Projects Grant Nos. OPP-0636806 and OPP-0732711 respectively to C.R.S. Writing and publication costs were supported in part by the Biological Oceanography Program (BIO OCE), United States National Science Foundation under the BOWLs Project Grant No. BIO OCE-1155703 to C.R.S. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Fjords are deep estuaries carved by glaciers and typically contain one or more sediment-floored basins separated by sills [1], [2]. Fjords with tidewater glaciers (glacio-marine fjords) are widespread at temperate to polar latitudes and form important boundary zones between the cryosphere and the ocean [3]. At high-latitudes, such as in the polar-tundra (or subpolar) climate conditions of arctic Canada, coastal Greenland, Svalbard and the West Antarctic Peninsula (WAP), fjord ecosystems serve as major conduits for glacial ice to the sea and are thus highly sensitive to cryosphere-ocean interactions and to climate warming [4], [5], [6]. Because of their distinct geomorphology, circulation processes, and terrigenous inputs (including glacial ice, meltwater and sediments), glacio-marine fjords can exhibit substantially different ecosystem forcing than adjacent continental shelves. Fjord ecosystem studies, conducted mostly outside Antarctica, indicate that fjords may contain intense ecological disturbance gradients, unusual food-web structure, genetically isolated populations, and refugia for cold-adapted species [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. The WAP, including the Danco/Graham Coast (Figure 1), harbors the most extensive system of glacio-marine fjords on the Antarctic continent. While the glacio-marine settings of the subpolar fjords along the Danco/Graham Coast are relatively well studied from a geological perspective [3], [17], [18], [19], [20], ecosystem structure and function in these subpolar fjords remain very poorly evaluated despite the (...truncated)


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Laura J. Grange, Craig R. Smith. Megafaunal Communities in Rapidly Warming Fjords along the West Antarctic Peninsula: Hotspots of Abundance and Beta Diversity, PLOS ONE, 2013, 12, DOI: 10.1371/journal.pone.0077917