Caribbean Tissue-loss Diseases Can be Linked to Fungal Invasion

Laurent Delvoye; Rolf P.M. Bak; Kristen L. Marhaver; Gerard Nieuwland; Mark J.A. Vermeij

Caribbean Tissue-loss Diseases Can be Linked to Fungal Invasion

Laurent Delvoye¹, Rolf P.M. Bak², Kristen L. Marhaver¹, Gerard Nieuwland², and Mark J.A. Vermeij^1,3,*

¹CARMABI Foundation, Piscaderabaai z/n, PO Box 2090, Willemstad, Curacao. ²Koninklijk Nederlands Instituut voor Onderzoek der Zee (NIOZ), PO Box 59, 1790 AB, Den Burg, Texel, The Netherlands. ³Department of Freshwater and Marine Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Science Park 700, 1098 XH, Amsterdam, The Netherlands. *Corresponding author.

Caribbean Naturalist, No. 82 (2021)

Abstract
Many scleractinian corals harbor endolithic fungi within their skeletal matrices. However, the possible roles of endolithic fungi in coral ecology, health, and disease remain poorly understood. We conducted a histopathological study of tissue-loss diseases in 2 Caribbean coral species (Orbicella annularis and Agaricia lamarcki) to examine whether fungi were associated with or responsible for these signs. In healthy-looking colonies, endolithic fungi were commonly observed in the skeleton directly under the coral tissue. In contrast, in samples of both coral species exhibiting whitening and tissue loss, endolithic fungi were observed infiltrating the tissues. When observed using histopathological methods, the cellular changes associated with these tissue-loss diseases were very similar in both coral species. In O. annularis, diseased tissue was characterized by apoptosis and detachment of the tissue in areas where fungal hyphae had entered the coral tissue. The same observations of tissue detachment and disintegration were made in A. lamarcki, but in this case, lytic necrosis occurred instead of apoptosis. Although tissue-loss diseases are often attributed to opportunistic infections by bacteria or bacterial pathogens, this study suggests that endolithic fungi represent additional, eukaryotic candidates capable of the biological mechanisms underlying Caribbean coral diseases.

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