Project: RAPID - Abnormal bleaching in Cliona varians in the Florida Keys: Consequences for coral reef health

NSF Award Abstract:
Sponges feed on bacteria and extract other material from the water column as they pump water through their tissues. This bio-filtration plays important ecological roles on coral reefs, and may serve as the base of food webs in these habitats by turning dissolved and particulate organic material into detritus (shed sponge cells) that can be eaten by a variety of organisms. This ecological function is known as the sponge loop, and the proposed research tests an unexplored aspect of the sponge loop. Sponges typically support dense and diverse symbiont communities that contribute to their overall ecological performance. It is unknown how the symbiont communities contribute to the ecological performance of the host sponge. During the recent mass coral bleaching event (i.e., loss of algal symbionts) in the Florida Keys, sponges with algal symbionts, that normally do not bleach, were also found to have bleached. This unusual observation offers the opportunity to test ideas about the role of symbionts in the sponge loop. That is, the hypothesis under consideration is that disruption of symbiotic associations compromises a sponge's bio-filtration capacity. The broader impacts of this project includes training undergraduate students, producing new scientific information, presenting public talks, and tying this work into existing integrated science courses at the University of Richmond.

The health of coral reef ecosystems may be tied directly to the normal functioning of coral reef sponges through the sponge loop. Detrital food webs may rely on the continued input of shed sponge cells through which dissolved and particulate organic matter are processed into biologically usable material. Previous work indicates that the symbiont state of the host sponge might influence feeding and pumping behavior, but no direct test of the impact symbiont state has on the sponge loop has been conducted. A recent bleaching event involving clionaid sponges in the lower Florida Keys provides an opportunity to test the hypothesis that reef health is a function of health of sponge symbiont populations through host filtration efficiency and feeding behavior. This research project focuses on interactions between symbiotic systems, host behavior, and ecosystem function using Cliona varians. Water samples will be collected using IN-EX sampling followed by flow cytometry and microscopic analysis of the material expelled by sponges. Stable isotopic signatures of the hosts will be compared before, during, and after bleaching events.