Community structure of deep-water decapod crustaceans below the oxygen minimum zone in the south-east Gulf of California and analysis of environmental drivers

Despite the ecological importance of decapod crustaceans in energy transfer in marine ecosystems, little is known on their distribution below oxygen minimum zones (OMZs). To understand the spatio-temporal dynamics of benthic and benthopelagic decapod crustaceans living below the OMZ cores, four seasonal oceanographic and sledge surveys were performed in the south-east Gulf of California at depths between 730 and 2250 m. Multivariate analyses indicate the existence of three major depth-related assemblages at: 800-1000, 1000-1200 and >1200 m (mean trawl depth). Benthic detritivores dominated between 800 and 1000 m and benthopelagic (i.e. swimming) predators dominated deeper, where dissolved oxygen (DO) values were higher. Assemblages comprised the same species throughout the year, but aggregations of smaller organisms were observed in June. DO significantly controlled the distribution of decapod crustaceans, likely through physiological exclusion of swimming species from hypoxic waters. Besides, the combined effects of DO and temperature contributed to defining the depth ranges occupied by each species. Food derived from surface-water production modulated changes in community parameters with different time lags in the different depth-related assemblages. These findings demonstrate the vulnerability of bathyal communities to the global pattern of OMZ expansion.