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Sponges play a key role in Antarctic marine benthic community structure and dynamics and are often a dominant component of many Southern Ocean benthic communities. Understanding the drivers of sponge distribution in Antarctica enables us to understand many of general benthic biodiversity patterns in the region. The sponges of the Antarctic and neighbouring oceanographic regions were assessed for species richness and biogeographic patterns using over 8,800 distribution records. Species-rich regions include the Antarctic Peninsula, South Shetland Islands, South Georgia, Eastern Weddell Sea, Kerguelen Plateau, Falkland Islands and north New Zealand. Sampling intensity varied greatly within the study area, with sampling hotspots found at the Antarctic Peninsula, South Georgia, north New Zealand and Tierra del Fuego, with limited sampling in the Bellingshausen and Amundsen seas in the Southern Ocean. In contrast to previous studies we found that eurybathy and circumpolar distributions are important but not dominant characteristics in Antarctic sponges. Overall Antarctic sponge species endemism is ~43%, with a higher level for the class Hexactinellida (68%). Endemism levels are lower than previous estimates, but still indicate the importance of the Polar Front in isolating the Southern Ocean fauna. Nineteen distinct sponge distribution patterns were found, ranging from regional endemics to cosmopolitan species. A single, distinct Antarctic demosponge fauna is found to encompass all areas within the Polar Front, and the sub-Antarctic regions of the Kerguelen Plateau and Macquarie Island. Biogeographical analyses indicate stronger faunal links between Antarctica and South America, with little evidence of links between Antarctica and South Africa, Southern Australia or New Zealand. We conclude that the biogeographic and species distribution patterns observed are largely driven by the Antarctic Circumpolar Current and the timing of past continent connectivity.
Responses of southern ocean seafloor habitats and communities to global and local drivers of change
(2021)
Knowledge of life on the Southern Ocean seafloor has substantially grown since the beginning of this century with increasing ship-based surveys and regular monitoring sites, new technologies and greatly enhanced data sharing. However, seafloor habitats and their communities exhibit high spatial variability and heterogeneity that challenges the way in which we assess the state of the Southern Ocean benthos on larger scales. The Antarctic shelf is rich in diversity compared with deeper water areas, important for storing carbon (“blue carbon”) and provides habitat for commercial fish species. In this paper, we focus on the seafloor habitats of the Antarctic shelf, which are vulnerable to drivers of change including increasing ocean temperatures, iceberg scour, sea ice melt, ocean acidification, fishing pressures, pollution and non-indigenous species. Some of the most vulnerable areas include the West Antarctic Peninsula, which is experiencing rapid regional warming and increased iceberg-scouring, subantarctic islands and tourist destinations where human activities and environmental conditions increase the potential for the establishment of non-indigenous species and active fishing areas around South Georgia, Heard and MacDonald Islands. Vulnerable species include those in areas of regional warming with low thermal tolerance, calcifying species susceptible to increasing ocean acidity as well as slow-growing habitat-forming species that can be damaged by fishing gears e.g., sponges, bryozoan, and coral species. Management regimes can protect seafloor habitats and key species from fishing activities; some areas will need more protection than others, accounting for specific traits that make species vulnerable, slow growing and long-lived species, restricted locations with optimum physiological conditions and available food, and restricted distributions of rare species. Ecosystem-based management practices and long-term, highly protected areas may be the most effective tools in the preservation of vulnerable seafloor habitats. Here, we focus on outlining seafloor responses to drivers of change observed to date and projections for the future. We discuss the need for action to preserve seafloor habitats under climate change, fishing pressures and other anthropogenic impacts.
