Evidence of Coralline White Patch Disease in a rhodolith bed of the Egadi Islands

Coralline algae are among the most important marine calcifiers on a global scale, and are sensitive to rising temperatures and ocean acidification from the ongoing global climate change. Although diseases of coralline algae are known since the nineties in the Pacific Ocean, still few observations and studies are available on this topic. In the Mediterranean, similar events have been reported starting from 2015, in the north-western Mediterranean Sea, within 30 m of water depth. One of the commonest disease is the Coralline White Patch Disease (CWPD), that shows the bleaching of thallus patches due to cell necrosis. The CWPD is temperature-dependent, and it is suggested a relationship with the effects of global climate change. This contribution is aimed at describing CWPD in a rhodolith bed of the Egadi Islands (western Mediterranean). Two sites at a distance of 3 km have been sampled, at 86 and 103 m, by Van Veen grab, 60 l, three replicates each. Living rhodoliths have been selected and analysed for the occurrence of CWPD. A one-way ANOVA has been elaborated to test the difference in percent occurrence of diseased rhodoliths at the two sites. Rhodoliths affected by CWPD ranging in size between 1 and 4 cm are 5% and 5,7% of the total live rhodoliths, with no statistically significant difference between the two sites. At the depth of sampling, the influence of the rising temperature should be negligible, and other factors should be explored to explain the cause of the CWPD.