Variability in Antibacterial Chemical Defenses in Caribbean Sponges of the Genus Aplysina

Coral reefs represent one of the most diverse ecosystems on earth, providing habitat for at least 25% of all marine species. Coral ecosystems are faced with many stressors, both physical and biological, that are causing their continuing decline. Understanding the impacts of these stressors, and the resilience of coral reefs, is important to the long-term survival of these critical ecosystems. As a major constituent of marine communities, sponges are an important phylum contributing to the ecology of coral reefs. Like other components of coral reef habitats, sponges also face a wide variety of biological stressors including pathogens, predators, and competitors. Chemical defenses serve as a key source of protection against these ecological threats. Aplysina is one of the most abundant genera of sponges found in the Caribbean, and these sponges are particularly susceptible to a disease that differs in prevalence among geographic locations, suggesting variability in resistance. Unfortunately, to date, the pathogen(s) responsible for causing this sponge disease remain elusive, but to determine whether chemical variation associated with different morphotypes and geographic locations translates into variability in bioactivity, this study evaluated the general antibacterial activity of sponge extracts against known coral pathogens and human enteric bacteria. This study assessed the chemical variability among healthy individuals of three distinct sponge morphotypes, thin and thick Aplysina cauliformis and A. fulva, found over various geographic regions in the Caribbean, including a pristine site in the Bahamas and sites in St. Thomas, US Virgin Islands, that vary in their amount of human impact. These sponges produce different chemical profiles between morphotypes and locations. This suggests possible genetic differences between morphotypes and supports using chemotaxonomic methods for classifying them as species. This study also assessed the antibacterial activity of organic extracts from each morphotype against four strains of bacteria. The bacteria selected included known coral pathogens and potential marine pathogens found in human waste. Antibacterial activity for all three morphotypes was highly selective against the four bacterial strains, and varied among morphotypes and their locations of origin. This variability in bioactivity may explain some of their differential susceptibility to disease