Project Summary for 2005–10B: Predation pressure and antipredator defenses in temperate reef sponges
A variety of morphological, physiological, and behavioral adaptations have evolved to deter predators in marine habitats (Vermeij 1978, Menge and Lubchencho 1981, Paul 1992, Pennings and Paul 1992). An anti–predator mechanism that continues to be intensively studied and increasingly better understood is the effectiveness of secondary metabolites (Paul 1992, Pawlik et al. 1995, Bolser and Hay 1996). While the soft, fleshy, sessile nature of sponges would appear to render them susceptible to intense predation, their widespread abundance and distribution suggests otherwise. Several studies have shown secondary metabolites produced by sponges serve as anti-predator agents against generalist fishes and invertebrates (Pennings et al. 1994, Pawlik et al. 1995, Waddell and Pawlik 2000). This may be particulary important on tropical reefs where predation intensity is believed to be greatest. Therefore it has been hypothesized that chemically undefended sponges on tropical reefs are restricted to cryptic habitats or to predator free environments (Pawlik 1997). Similarly, it has also been suggested that spongivorous fishes feed on the few chemically undefended reef sponges to avoid ingestion of noxious chemical compounds (Pawlik 1997). At latitudes where coral reefs are absent, sponges are often the most dominant sessile organism in benthic communities with hard substrata. Despite their abundance and importance on temperate reef like GRNMS, how spongivory affects sponge demography on temperate reefs has not been well studied.
Preliminary data collected from GRNMS during summer 2003 demonstrated the following three points:
Therefore, the goals in year one of this two–year project were to document fully the effectiveness of chemical defenses of these temperate reef sponges, determine which species are chemically defended, and investigate if any structural defenses are used in those sponge species that are chemically undefended. During 2004, these goals were achieved by carrying out a variety of feeding bioassays involving carageenan-based foods. These foods were impregnated with either secondary metabolites extracted from sponge tissues or structural sponge elements that had been cleared of their secondary compounds. In both cases these carageenan-based foods were offered to natural assemblages of reef fish for palatability tests. Results of these feeding assays were combined with surveys of sponge distributional patterns observed on temperate reefs.
This project directly addresses two initiatives of the 2004 NOAA/NURP research objectives and in so doing has both theoretical and practical implications. Within the category of living resources, this study is of theoretical importance because it will investigate the role of chemical ecology in affecting the predation and distribution of marine species. In addition, it will be one of the few studies to investigate proximate, as well as ultimate, controls on sponge secondary metabolites. Within the category of sanctuary science, this project has practical implications for management of the GRNMS and addresses a high priority research area for understanding biological processes within the sanctuary. GRNMS Strategy Development Workshops conducted in 2001 and 2002 were based on key issues identified by the public and Gray’s Reef Advisory Council members as areas in need of change or further research and development in regards to the management and preservation of the sanctuary. Many of these issues relate directly to sessile benthic invertebrates that, through their existence on the reef, create additional topographic complexity and food resources that are used by higher order consumers. Discussions conducted during these Strategy Development Workshops made it clear that there is a lack of biological and physical baseline information from which to conclude which natural processes are most important in controlling population and community dynamics in the benthos. To begin closing this knowledge gap, it was recommended that the Sanctuary establish collaborations with regional University research scientists that have the resources to investigate these questions. The project being carried out here represents such a collaboration and is providing an opportunity to extend other on -going our studies of benthic inbertebrates and benthic processes in the GRNMS. In addition, funding for the project described here is beinge leveraged by funds and logistical support received from the National Marine Sanctuary Program.
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