Geographical Variability in Antibacterial Chemical Defenses of the Caribbean Sponge Xestospongia muta

Coral reefs are important and diverse marine ecosystems, and sponges represent the majority of species in Caribbean reefs. Xestospongia muta is a giant barrel sponge that is one of the most abundant and visible sponges on Caribbean reefs, and has been the subject of many studies. Xestospongia muta produces a diversity of secondary metabolites that have various ecological functions including allelopathy, anti-fouling, predation deterrence, and antibacterial activity. The chemical defenses produced by a sponge can change in response to various biotic and abiotic stressors, including water temperature, sedimentation, nutrient runoff, and predation. This study compared the antibacterial activity of X. muta samples from sites at four countries in the Caribbean: Belize, Curaçao, Grand Cayman, and St. Croix, US Virgin Islands, to characterize geographic variation in the bioactivity of secondary metabolites from X. muta. There are currently no known sponge pathogens of X. muta, so antibacterial activity was tested against three known coral pathogens, and one human enteric bacteria that can be discharged onto reefs. Antibacterial assays compared the growth of the bacterial strains exposed to sponge extracts with bacterial growth in control broth. The sponges from each country had different antibacterial activity profiles, with sponges from Belize having the most inhibitory interactions and sponges from St. Croix having the least. The differences in activity between countries suggest that large-scale geographic patterns in metabolite production do occur. Within countries, the antibacterial activity was largely the same, but there were some examples of significant differences. Many of the factors that can affect secondary metabolite production were similar except for the amount of human activity in the area, suggesting that anthropogenic factors can cause large changes in reef ecosystems. The sponges also varied in the amount of activity against each bacteria, suggesting that there is specificity in the action of the chemical defenses of X. muta. As sponges continue to increase in abundance and biomass on Caribbean reefs, they will be exposed to greater impacts from natural and anthropogenic changes. Data from this study indicate that such changes could have important ecological implications on the ability of X. muta to produce chemical defenses to protect itself from potential pathogens and other stressors