Impacts of Aplysina Red Band Syndrome on Secondary Metabolite Profiles and Antibacterial Activity of the Caribbean Sponge Genus Aplysina

Coral reef ecosystems continue to decline due to abiotic and biotic factors, including disease. Although much of the existing scientific literature has focused on coral diseases, reports of sponge diseases have been increasing. This is a cause for concern, as sponges are increasingly dominant components of coral reef communities, where they are responsible for a wide range of ecological functions. A sponge disease of particular interest is Aplysina Red Band Syndrome (ARBS), which impacts the Caribbean\u27s most abundant genus of sponges, Aplysina. Three morphotypes of branching sponges within this genus are affected, including Aplysina fulva, and the thin and thick morphotypes of Aplysina cauliformis, although the morphotypes have different levels of susceptibility to ARBS. Sponges produce an extensive arsenal of secondary metabolites as chemical defenses to protect against threats, including pathogenesis, predation, and competition, and it was hypothesized that variability in chemical defenses could explain, at least in part, why sponges vary in their susceptibility to ARBS. The causative agent(s) of ARBS have yet to be identified, so three known coral pathogens and a human enteric bacterium were used to evaluate generalized antibacterial activity of sponge extracts. This study compared chemical profiles and antibacterial activity between healthy and ARBS-infected sponges from the Bahamas and Belize to assess variability of these parameters based on health status, morphotype, and geographic location. Each group of sponges produced a distinct chemical profile. Antibacterial activity also varied between health status, morphotypes, and collection sites, suggesting that chemical variation translates into variability in antibacterial activity. Thus, a sponge\u27s chemical profile may determine, at least in part, its susceptibility to disease. ARBS-infected sponges exhibited stronger antibacterial effects than their healthy counterparts, indicating that a sponge\u27s chemical defenses could be inducible. Variability in secondary metabolite production and antibacterial activity between the three morphotypes demonstrates that chemotaxonomy, in addition to gross morphology, could be used to distinguish among the three morphotypes even though microscopic and genetic methods fail to do so. Geographic variability in chemical profiles and antibacterial activity suggests that level of human impact, sponge-associated microbial communities, or pathogen virulence may differ regionally, possibly explaining differential prevalence of ARBS across the Caribbean