Species Distribution and Abundance of Bering Sea Tunicates with Implications for Coastal Food Security

The use of sessile macroinvertebrates as leading indicators of change in marine ecosystems makes them potentially valuable as a management tool for predicting habitat suitability for more mobile, commercially important fishes. In addition to potential use as an ecosystem indicator in fisheries management, tunicates are used as a food resource by some Alaska Native communities. Variability in abundance and distribution, driven by changing physical conditions in the Bering Sea, could impact food security for these communities. I used fishery-independent NOAA survey data from the Eastern Bering Sea summer surveys from 1987 to 2019 to examine abundance and distribution of several tunicate species complexes (Halocynthia, Styela, and Boltenia) in a spatiotemporal modeling framework. Prior to fitting the models, I determined that frequency of occurrence (FoO) and catch per unit effort (CPUE) varied spatially between warm (2015-2019) and cool (2005-2010) periods for all three species. Summary statistics showed declines in biomass for all three species during a relatively warm period. Based on the literature and these preliminary analyses I hypothesized that distributions and abundances of tunicate species would shift with multiyear changes in benthic conditions, especially temperature. Given warming trends and the relatively shallow water found in the Northern Bering Sea (NBS), I expect a disproportionate negative impact on benthic communities in this region. As tunicate species are a significant proportion of the benthic community in this ecosystem, there may be a large impact on coastal Alaska Native communities' ability to harvest an important food resource. Additionally, relationships between environmental conditions, tunicate abundance, and fish distribution and abundance could lead to improved management.