ABSTRACT: Benthic biodiversity of two near-shore Arctic locations, and potential impacts of sea level change, coastal erosion, and climate change.

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Abstract

Increased coastal erosion and resultant sedimentation in nearshore marine environments is a predicted effect of climate change. To evaluate possible effects of coastal erosion on Arctic benthic biodiversity, the fauna of two-nearshore Arctic locations associated with different degrees of coastal erosion have been studied. The work described was carried out on the southwest coast of Banks Island and southeast coast of King William Island, close to the communities of Sachs Harbour and Gjoa Haven, respectively. Sachs Harbour has a submergent shoreline with locally rapid coastal erosion. By contrast, Gjoa Haven has an emergent shoreline. Furthermore, the bedrock and surficial geology of Gjoa Haven make it apparently less susceptible to erosion than Sachs Harbour. A marine habitat map was constructed for the two study areas using data collected by benthic grabs, drop video, and bathymetric profiles. Habitats were distinguished based on sediment type and species composition of the benthos. Polychaetes dominated the samples in abundance and diversity followed by molluscs and echinoderms at both Sachs Harbour and Gjoa Haven study areas. The predominate nearshore marine habitat in the Sachs Harbour study area was shallow (<10 m) highly mobile rippled sand sheets with low benthic abundance and biodiversity. The most diverse environments were deep (>20 m) submerged thermokarst lake basins in the outer harbour, which hosted tube-dwelling cerianthid anemones in addition to bivalve molluscs, polychaetes, and echinoderms. Overall, the fauna within the deep submerged lake basins are likely most susceptible to the increased deposition of sediment into the nearshore area. The shallow (>10 m) nearshore marine habitats of the Gjoa Haven study area consist of a variety of substrates ranging from sandy mud through coarse gravel, cobbles, and boulders. Sediments retrieved in depths greater than 10 m were cohesive mud with gravel pebbles. Macroalgae cover was reduced in waters shallower than 5 m due to ice scour. The most diverse assemblage of fauna due to the composition of substrate: coarse gravel, cobbles, and boulders and depths reaching 30 m was found off a small island just south of Betzold Point. This area hosted tube-dwelling anemones, bivalve molluscs, polycheates, and echinoderms with extensive kelp beds. Overall, there appears to be little to noevidence of coastal erosion in the Gjoa Haven study area, except for gullying near the mouth of a small stream on the north side of Gjoa Haven harbour. Most of the coastline is protected within a bay and is not exposed to waves generated by prevailing winds. By contrast to the Sachs Harbour study area, permafrost deflation does not appear to be causing rapid nearshore marine sedimentation, suggesting that climate-change induced short-term increases in sedimentation are unlikely to impact nearshore benthic biota, however, a long-term impact from sealevel rise-induced coastal erosion, causing anincrease in the flux of sand from the land to the water, is possible. These studies provide a baseline for future research into climate change impacts on marine nearshore Arctic environments.

Bibliography of Canadian Geomorphology