Ecology of deep-water coral reef sponges: Dr. Joe Pawlik, University of North Carolina at Wilmington

Sponges are an important component of Caribbean coral reef communities, yet they are often overlooked in ecological studies. One species, the giant barrel sponge, Xestospongia muta, is particularly prominent on deep-water reefs. Interestingly, like reef-building corals, the tissues of X. muta contain photosynthetic symbionts. Also, they have recently been observed to "bleach" like corals during summer months, resulting in sponge death. This Aquarius mission is designed to answer important questions about the biology and ecology of X. muta.

How old are these sponges? How often do new sponges appear in the population? How fast do they grow? How common is bleaching? Is bleaching always fatal, or do some sponges recover? How does bleaching affect chemical defenses used by the sponge against predatory fishes and microbial pathogens? Is bleaching a response to summer temperature extremes, or is it a result of post-reproductive trauma. The specific objectives of this mission, designed to answer these questions, are as follows:

1. Establish permanent radial transects at 18 and 34 meter depths, tagging all X. muta within the transects (to complement transects already established at 14 meter depth). Importantly, these depths experience significantly different temperature regimes, as recorded by long-term monitoring programs maintained at the site. 2. Photograph X. muta within the transects will be photographed and measured to monitor sponge growth and bleaching. 3. Tissue samples will be collected to evaluate sponge chemistry relative to feeding deterrence by predatory fishes, and antimicrobial activity.

Two additional projects will be conducted to study various aspects of sponge ecology. First, a controversial hypothesis will be tested that states that when the sponge Aplysina spp. is wounded by predators (due to feeding), the sponge responds by changing its chemistry to produce biologically active defensive molecules. Second, some sponges are associated with brittle stars that live on or inside the sponge surface. It is not known, however, if the brittle stars ever leave their host sponges? And if they do, do they return to the same sponges (exhibiting homing behavior), or to different sponges of the same species, or different species? Specimens of the brittle star Ophiothrix suensonii, found in the tube sponges Callyspongia and Niphates will be mapped, tagged, and monitored to assess how far they travel and their host specificity.