Prevalence of tissue necrosis and brown spot lesions in a common marine sponge

Sponges form a highly diverse and ecologically significant component of benthic communities. Despite their importance, disease dynamics in sponges remain relatively unexplored. There are reports of severe disease epidemics in sponges from the Caribbean and the Mediterranean; however, extensive sponge mortalities have not yet been reported from the Great Barrier Reef (GBR) and Torres Strait, north-eastern Australia. Marine sponge surveys were conducted in the Palm Islands on the central GBR and Masig Island, Torres Strait, to determine the health of the Demosponge Ianthella basta. Using tissue necrosis and the presence of brown lesions as a proxy of health, sponges were assigned to predetermined disease categories. Sponges with lesions were present at all sites with 43 and 66% of I. basta exhibiting lesions and symptoms of necrosis in the Palm Islands and Torres Strait, respectively. Sponges from the Torres Strait also showed a greater incidence of significant and extensive necrosis in comparison to sponges from Palm Island (11.5 v. 6%). These results indicate the widespread distribution of a disease-like syndrome affecting the health of I. basta, and highlight the critical need for regular monitoring programs and future research to assess patterns in disease dynamics and ascertain the etiological agents of infection.