Effects of Butterfly Fish on Disease Transmission in Corals. undefined

Marine diseases have caused large scale decreases in coral cover across the Caribbean because they can be transmitted via waterborne, direct contact, and vector-borne pathways. Unfortunately, marine diseases are projected to increase as sea surface temperatures rise so understanding the factors that lead to quicker transmission rates need to be identified. This study investigates the transmission rates of Stony coral tissue loss disease across coral fragments as well as identifies the effect of mechanical injury and direct contact feeding transmission by foureye butterflyfish feeding on transmission across Montastraea cavernosa (MCAV) coral fragments. First, half M. cavernosa fragments were placed in direct contact with diseased Orbicella and Montastraea colonies with purposes of creating disease MCAV fragments. Three treatments were used to investigate waterborne transmission (control), mechanically injury to a healthy coral (limited), and direct contact feeding across a diseased and healthy coral (unlimited). Direct contact transmission took on average 3.9 days in 2019 and 11.9 days in 2020 with significantly quicker rates of transmission between donor diseased Orbicella and Montastraea than Montastraea to Montastraea. Foureye butterflyfish fed significantly more around the tank than on the coral tissue types and there were significantly more bites being taken in the limited treatment than in the unlimited treatment. The limited treatment had the quickest time to transmission with day 2 already having 30% of the healthy MCAV corals showing signs of infection and by the end of day 4 infections increased by another 54%. The control and unlimited treatment surprisingly had similar transmission rates: the control treatment had no active disease signs until day 4 where infection increased by 33 percent and by day 5, 50% of the corals were infected. The unlimited treatment in the green had 14% of the coral infected by day 2 but held steady until day 5 when 57% of fragments were infected. Test of Symbiodinium clade showed no significant differences amongst coral fragments used in transmission study suggesting susceptibility due to the Symbiodinium does not explain differences amongst treatments. This study provides evidence that foureye butterflyfish play a role in increasing the rates of disease transmission from causing mechanical injury to healthy coral fragments.