Cold water coral reefs in North Atlantic: food partitioning among three species, implications for their ecophysiologyUnderexplored Reefs

Margaux Mathieu-Resuge¹, Maxime Marinier^2,1, Loïc N Michel³, Alizé Bouriat¹, Jonas Bousquet¹, Fabienne Le Grand², Julie Tourolle¹, Lénaick Menot¹

¹Univ Brest, Ifremer, BEEP, France - ²Univ Brest, CNRS, Ifremer, IRD, LEMAR, France - ³University of Liège, Belgium

In the deep sea, cold-water corals (CWC) and their associated fauna form reefs with significant biodiversity and biomass. However, in these areas deprived of light and where organic matter produced at the surface is poorly accessible, access to food is spatially and temporally variable. The origin and partitioning of essential nutrients are still poorly understood and quantified. This study aimed to better understand the trophic functioning of CWC reefs by describing the sharing of dietary resources between CWC species and exploring links between food intake and physiological needs of species.
Therefore, we investigated feeding habits of three coexisting CWC species (Desmophyllum pertusum, Madrepora oculata and Solenosmilia variabilis) forming reefs in the Lampaul Canyon (Bay of Biscay) at depths ranging from 800 to 1600 m. To better understand how environmental heterogeneity influences the diet of cold-water corals, sampling was carried out over a 3-year period and the analyses focused on the reserve fatty acid composition. To see whether depth and changes in diet influence the membrane fluidity of CWC, we studied their membrane fatty acid composition.
Our results have shown that if all species were plankton feeders, species-specific differences in resource use by the three species were persistent over the years. D. pertusum and S. variabilis mainly fed on zooplankton, while M. oculata seemed to consume more bacterioplankton. The changes of diet over time and space did not seem to influence membrane fatty acid regulation in the same way for each species. The unsaturation index of membrane fatty acids did not change among species, while the sum of long chain polyunsaturated fatty acids and of DMA proportions varied between species but not over time, suggesting different adaptation capabilities.
These results highlight the efficient partition of trophic resources and the different ecophysiology strategies between the CWC species of the Lampaul Canyon and raises questions regarding what can be the role of the associated fauna in energy fluxes at the reef scale.