Relationships between taxa assemblages and substratum types on cold-water coral reefs

Cold-water corals form complex three-dimensional reef structures. These reefs are most commonly formed by Lophelia pertusa , now synonymous with Desmophyllum pertusum , and are present in all of the world’s oceans. The reefs provide habitats for a range of species and are known biodiversity hotspots. Scale matters within the reef; there are differences in assemblages of taxa on and off the reefs as well as between different reef zones. Sites from nine reefs off the coast of Norway were investigated to determine whether taxa assemblages are related to the depth, substratum types, and/or geographical position of the reef. Data were obtained from video transects taken using the video platform CAMPOD as part of the MAREANO program. The environmental conditions and substrata present at the reefs were described and covariant factors identified. The multivariate statistical method, distance-based redundancy analysis (db-RDA), was used to identify relationships between the environmental variables and the taxa assemblages. The abundance of the live coral substratum type was found to be the most significant factor for determining the taxa assemblage present. Additionally, in order of decreasing influence, taxa assemblage was found to be influenced by depth, latitude, longitude, abundance of the coral rubble substratum, and abundance of the pebbles substratum. The sponge Mycale (mycale) lingua was associated with the living coral substratum. The anemone Protanthea simplex was found to be associated with sites where dead coral was the most common substratum type, yet it is also associated with high percentages of coral rubble. This association suggests that micro-habitats (e.g. coral rubble within the dead coral zone or vice versa) are important. Location was found to account for some of the variance in taxa assemblages, but this variable likely represents a proxy for other local environmental factors.