Eco-physiological responses of cold-water soft corals to anthropogenic sedimentation and particle shape

Anthropogenic disturbances in the marine environment, such as excessive sedimentation produced by mine tailing deposition, can affect the physiology and behavior of benthic fauna. Mine tailing particles are sharper than natural occurring sediments and could therefore cause more harmful effects. Cold-water coral ecosystems are among the habitats in danger of being affected by dumping of mine tailings. Cold-water corals have very slow growth rates but the habitats they provide support high levels of species richness and functional diversity. Two soft corals, cauliflower coral (Duva florida) and red tree coral (Primnoa resedaeformis), were chosen as model organisms to study the effects of excessive mine tailing sedimentation and the effect of particle shape in a three-month long experiment. The corals were exposed to a concentration of 8 mg l−1 of two types of sediment, rough edged mine tailings (MT) and smooth edged spherical glass beads (GB). Glass beads were mimicking natural, smooth sediment, and both sediment types had a particle size distribution of 0-63 μm. Sedimentation effects were investigated using 13C/12C isotope ratio to assess food intake, time-lapse images to determine the effects on tissue and behavior, and histological samples to identify and quantify particles inside the polyps. When exposed to MT, food intake decreased significantly in D. florida and increased significantly in P. resedaeformis. Duva florida exhibited a behavioral response under MT treatment, being contracted for prolonged periods. Primnoa resedaeformis lost a significant proportion of polyps under both treatments. Histology showed mine tailing particles of sizes <10 μm embedded in the tissue of both species. The results suggest that sharp particles are more harmful than smooth edged particles to both species, in the size range studied. This should be considered when assessing the impacts of anthropogenic activities that increase sedimentation in benthic habitats.