Trends in Northwest Atlantic Habitat Occupation: Joint Effects of Climate Variation and Harvest Removals

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The impacts of climate variability on coastal ecosystems are dependent on several factors, including assemblage structure and geographic locality. Moreover, in areas of intense harvest, removals often contribute to instability of populations and may increase the ability of climate to cause community-level reorganization. We used trawl survey data from the U.S. National Marine Fisheries Service to assess the impact of these factors on the spatial structure of four contiguous Northwest Atlantic communities. We used ordinary least squares regression (OLS) to evaluate the interspecific abundance-occupancy (A-O) relationship for each community. Yearly A-O slopes and coefficients of determination served as indices of organismal density and spatial heterogeneity, respectively. The indices were regressed on time series of average surface temperature, Gulf Stream location and regional landings data. We found the strength of trends to increase with latitude, coinciding with regional shifts in assemblage structure. There was also regionally variable evidence for the effect of each external factor on community spatial utilization. Our results highlight the complexity and variety of biological responses to disturbance, even for adjacent communities. Lastly, our research will be important for future evaluations focused on ecological impacts of extrinsic factors on communities, beyond simple depletion or translocation of populations.