The role of sponges in altering seawater DOM on Caribbean reefs

Sponges now dominate Caribbean reefs after decades of declines of reef-building corals. Unlike most benthic reef organisms, sponges are ecosystem engineers that pump and filter huge volumes of seawater, turning-over the water-column and transforming seawater chemistry. The ability of sponges to alter dissolved organic matter (DOM) is recently the subject of increased scientific interest, along with new evidence of ample production of DOM by seaweeds, prompting novel hypotheses about the role of sponges in carbon and nutrient biogeochemical cycling and ecosystem function.

The most common species of emergent (large, non-cryptic) sponges on Caribbean reefs range from those having a high abundance of microbial symbionts in their tissues (HMA) to those with low microbial abundance (LMA). Most studies of emergent sponges have shown that HMA species are net consumers of DOM, while LMA species are net producers. While the quantity of DOM in seawater is easily measured, little is known about the composition of the DOM that is processed by sponges.

This project is using complimentary analytical approaches, including new chemical derivatization techniques, to characterize ambient and seaweed-derived DOM components in seawater and the effects of processing by HMA and LMA sponges on these components under laboratory conditions and in the coral reef environment. These studies are providing the most complete characterization of DOM and nutrient cycling by sponges on tropical reefs to date.

Broader impacts of this project include research support for two new female faculty in a Department of Chemistry and Biochemistry, STEM outreach from female role-models through UNCW’s MarineQuest program to a local charter grade school for girls that specializes in serving under-represented groups, and world-wide public outreach through educational YouTube videos.

Building on recent discoveries of the effects of sponge processing on the DOM pool in seawater, this interdisciplinary and collaborative research project is transforming our knowledge of biogeochemical cycling on coral reefs and inspiring novel explanations for differences in reef resilience across the tropics, including the continued decline of Caribbean reef corals. This project is targeting 4 HMA and 2 LMA sponge species with cylindrical shapes and uses a suite of complimentary analytical methods to characterize the naturally occurring DOM compounds in seawater before and after sponge processing using both field and laboratory experiments.

Measurements of DOM in seawater include bulk quantification, carbohydrate and amino acid quantification, and solid phase extraction before and after derivatization using targeted and untargeted approaches that employ LC-MS/MS, GC/MS and UPLC-QToF. Untargeted UPLC-QToF MS metabolomics techniques reveal which compounds are significantly altered as seawater moves through the sponge body on the reef.

Laboratory incubation experiments characterize the production of DOM by 3 common seaweed taxa and subsequent processing by each of the 6 target sponge species. Considering that DOM is one of the largest reservoirs of organic carbon on the planet, this research project is transforming our understanding of the composition and cycling of seawater DOM by sponges for a tropical reef ecosystem.

This project is funded by the Biological and Chemical Oceanography Programs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.