Effects of sedimentation on coral immunity

Coral disease prevalence and diversity are increasingly affecting tropical corals worldwide, and these increases are in part due to the influence of various environmental and anthropogenic factors (e.g. temperature, seawater eutrophication). These factors have been shown to promote both coral disease prevalence and pathogen virulence. A recent study highlighted that land runoff and its associated effects (e.g. increased particulate organic matter (POC), lowered salinity) could also play a role as promoters of coral disease. Sediments associated with terrestrial runoff and seabed sediment resuspension can affect scleractinian corals trough several mechanisms including increases in POC, dissolved inorganic nutrients, sedimentation and light reduction. Sediment deposits on corals have also been suggested to act as a reservoir of coral pathogens and can lead to coral tissue necrosis. Though sediments deposited on corals can generally be removed through mucus production and ciliary beating, such actions increase metabolic costs and could impact on the coral's immune potential and health, making it more susceptible to infections. In order to explore the effects of sediment deposition on coral health and immunity, two coral species were inoculated with marine sediments under controlled conditions. The effects of this inoculation were assayed through the monitoring of several coral health and immunity proxies (e.g. phenoloxidase activity, lipid content, distribution of immune cells).