Environmental associations and assemblage structure of shrimp species in the Gulf of St. Lawrence (Canada) following dramatic increases in abundance

ABSTRACT: Decapod shrimps typically occupy lower trophic levels, often as omnivores, and many have high population turnover rates, which makes shrimp populations susceptible to changes in predator abundance and environmental change. The increased biomass of northern shrimp Pandalus borealis in many parts of the NW Atlantic has been associated with the collapse of predatory fish populations and changes in water temperature. In this study, we show that biomass of many shrimp species in the Gulf of St. Lawrence (Canada) increased between 4- and 100-fold between the late 1980s and mid-2000s. Multivariate analyses based on trawl survey data during a period of relative stability (2004-2015) that followed the increase revealed species assemblages that were strongly spatially structured and which were associated with depth and bottom water temperatures. Univariate analyses of the associations between individual species’ densities and depth and temperature revealed that approximately half of the species had narrow temperature associations, suggesting that these species may be susceptible to projected warming of the ecosystem. Furthermore, all species in the northern Gulf of St. Lawrence will be affected by recent and ongoing increases in predator biomass. In contrast, predator biomasses continue to decrease in the southern Gulf of St. Lawrence.