Fine‐scale mapping of deep‐sea habitat‐forming species densities reveals taxonomic specific environmental drivers.

Aim: Environmental variables are strongly tied to species occurrence and population growth, but approaches to predicting the location of deep‐sea species or their ability to withstand a changing environment stem primarily from presence data. We coupled environmental data with observed densities of deep‐sea habitat‐forming corals and sponges to determine the environmental variables and geomorphology that contributed best to their occurrence. Location: Northwest Atlantic. Time period: 2013 and 2014. Major taxa studied: Deep‐sea coral and sponge communities. Methods: Multivariate and univariate analyses were used to determine significant environmental contributors to densities of genera and families of corals and sponges. We then assessed the relationship of densities of genera and families of corals and sponges with environmental variables found to be significant contributors to their occurrence and to geomorphology. Results: Sponge and coral genera and families were influenced by different environment variables. Temperature, salinity and dissolved oxygen contributed to the occurrence of sponges, whereas seafloor properties of slope and substrate contributed to the occurrence of corals. Although individuals of corals and sponges were observed across a range of a contributing environmental variable, high densities were observed only in very narrow ranges. Main conclusions: Geomorphic setting is an effective approach for discerning the associations of coral with seabed features. High densities of coral and sponge genera and families restricted to narrow environmental ranges might be at greater risk of local extinction. Differences in the occurrence of coral and sponge genera and families with environmental conditions suggest that they will differentially respond to predicted environmental changes. As conditions in the deep sea change with ongoing changes in climate, population expansion might be limited owing to suboptimal conditions, and established populations might persist but might have fewer individuals or species, which might lead to a loss in biodiversity. [ABSTRACT FROM AUTHOR]