Mortality event of the Mediterranean Invasive Sea Urchin Diadema setosum from Gökova Bay (Southern Aegean Sea)

Abstract

The mass mortality of the long-spined sea urchin Diadema setosum, which has become invasive in the eastern Mediterranean and is originally common in tropical seas, was observed along the Mediterranean coast of Türkiye in the summer of 2022. The mass mortality event led to a significant decline in the sea urchin population in Gökova Bay, with over 90 % mortality. The culture method monitored pathogenic bacteria, while the diversity of bacteria, fungi, and protozoa was monitored metagenomically. Vibrio alginolyticus and Vibrio diabolicus were isolated as dominant bacteria in diseased individuals. The metabarcoding analysis confirmed a high presence of the genus Vibrio in diseased sea urchins. Although pathogenic species among the fungal species were detected, it was determined that the distribution of these species did not constitute a significant difference between healthy and diseased individuals. However, Philaster apodigitiformis ciliate genome was detected only in diseased individuals. Detecting different pathogenic agents in sea urchins may suggest that more than one agent could plays a role in mass mortality. Furthermore, environmental changes, including temperature variations and degraded water quality, likely heightened the susceptibility of sea urchins to infections. This study underscores the critical importance of understanding the pathogenic factors contributing to mass mortality events in marine species, with a particular focus on the impact of climate change on aquatic ecosystems. Further research, including histological examinations and experimental tests, is needed to comprehensively assess the role of specific pathogens in these events.