Spatial trends and environmental drivers of epibenthic shelf community structure across the Aleutian Islands

Abstract

The continental shelf around the Aleutian Islands supports important commercial and subsistence fisheries as well as multiple seabird and marine mammal populations. To sustainably manage these populations, more information is needed on the distribution of the benthic communities that support some of the top level consumers. Given the vast size and highly variable physical environment of the Aleutian Islands, it is likely that epibenthic community structure on the continental shelf will vary among geographic areas according to their physical and oceanographic conditions. This project examined spatial patterns in Aleutian epibenthic shelf communities among oceanographic regions (defined here as island groups separated by major oceanographic passes) and islands within these regions, and identified environmental drivers responsible for variation in these communities. Benthic trawls were conducted at 12 Aleutian islands that spanned four oceanographic regions to characterize epibenthic shelf community structure. Specifically, variability in shelf community structure among regions and islands within each region was examined for correlations with multiple environmental variables, including bottom water temperature, water depth, distance from shore, hydrodynamic exposure, bottom rugosity, sediment grain size, sediment chlorophyll content, and drift algal (i.e., food subsidies) biomass. Overall, these communities varied both among regions and among islands within regions. In particular, communities in the Far Western region (Near Strait to Buldir Strait) differed from communities in other regions, largely due to a high density of sand dollars in the Far West. However, none of the measured environmental characteristics explained this difference. Additionally, there was no evidence for a break in epibenthic shelf community structure across Samalga Pass between the East and the Central regions, even though this pass represents a biogeographic break for other Aleutian community types. Within the Central region, a soft-sediment community characterized by the flatfish Atheresthes spp. and the crabs Labidochirus splendescens and Chionoecetes bairdi distinguished Adak Island from other Central islands. Compared with groundfish trawl surveys conducted by the Alaska Fisheries Science Center (AFSC), this study captured fewer fish but more invertebrate biomass, which is likely related to differences in the sampling gear used by the two studies. This study provides information on the distribution of Aleutian shelf communities that complement existing information from AFSC surveys. In particular, an important division in epibenthic shelf communities was observed across Buldir Strait. Furthermore, this study suggests that future assessments of Aleutian epibenthic communities should utilize multiple sampling gear types to better represent various epibenthic taxa.