Habitats and Benthos of an Evolving Fjord, Glacier Bay, Alaska

Glacier Bay National Park and Preserve is located in southeastern Alaska. It is a fjord system that bifurcates into two main northern tributaries: the West Arm and Muir Inlet, also known as the East Arm. This chapter focuses on the main southern bay and Muir Inlet, the 41-km long, 1-4-km wide fjord. Historic deglaciation of the region is well documented, resulting in a dynamic estuarine environment with vigorous tidal currents and rapid sedimentation. These factors lead to seafloor instability and constantly change benthic environments. The diverse settings in the estuary generate productive food webs; recreational, commercial, and subsistence fisheries; large populations of marine mammals and seabirds; and vessel-based tourism. Benthic habitat mapping has been completed for Glacier Bay (in 2005) and Muir Inlet (in 2010) following multibeam sonar surveys in these areas. Though different classification schemes were used, the classes are based on geomorphologic features, substrate classes, and depth zones, which make the results comparable. There is greater diversity of habitat (and epifauna) in Glacier Bay as compared to Muir Inlet. Substrate classes ranging from sand to coarser sediments make up the majority of habitat in Glacier Bay, whereas mud is the dominant substrate in Muir Inlet. These results suggest that Muir Inlet and other inlets to the north of Glacier Bay are very efficient traps of fine glacial sediment and should be considered distinct biotopes for ecological management purposes.