Histopathological investigation of the reef coral Goniastrea sp. affected by macroalgal abrasion

Abstract

Interspecific competition between corals and macroalgae is a common phenomenon on coral reefs, and its impacts on the cellular structure of corals are not well studied. Field observations in Gulf of Mannar Marine National Park (GoM), a protected reef environment, during January 2020 revealed abundant growth of the macroalga Turbinaria conoides over the coral, Goniastrea sp., causing tissue discoloration and physical injury through abrasion. Histopathological analysis revealed disruption of the gastrodermis with the loss of endosymbiotic dinoflagellates and focal ablation of the epidermis in the affected coral tissues. Cell counts confirmed a 65.1% reduction in endosymbiont density. Our results suggest that physical contact by T. conoides disrupted the coral epithelia, potentially leading to tissue loss and a reduction in live coral cover.