Sponges are the most diverse, and in many places the most abundant, sessile animals of Caribbean coral reefs, mangroves, and seagrass meadows. They play key functional roles, many of which are not covered by other organisms. Recent changes in distribution and abundance of common sponge species have highlighted how little is understood of ecological processes influencing tropical marine sponges, and how these are affected by rapid changes occurring in tropical marine environments. This experimental study aims to increase knowledge of basic sponge ecology, while generating the sort of comprehensive data sets needed to identify patterns that can lead to predictive generalizations about context-dependency of interaction outcomes, as well as for testing theory relating to trade-offs among competing functions, and maintenance of diversity patterns.
For 36 of the most common sponge species of Caribbean coral reefs, mangroves, and seagrass meadows, reciprocal transplant experiments, augmented by predator-free and competitor-free spaces, will be implemented to compare growth and survival among sponges of the same genotype and initial size grown: a) with vs. without predators, competitors, and mutualistic partners, and b) in their usual habitat vs. in other habitats. The experiments will be repeated at four sites in Belize, Panama, and Florida. Repeated censuses at each site, combined with the experimental results, will characterize each species by rates of mortality, abiotic constraints on distribution, recruitment, and context-dependency of interactions (competition, predation, mutualism). These data will allow tests of the following general hypotheses: 1) Interactions of individual sponge species with other taxa are context-dependent; and, as a corollary, habitat distributions can change in response to changes in abiotic factors and in abundance or habitat distribution of predators and competitors. 2) Trade-offs among resistance to predators, resistance to competitors, and resistance to abiotic challenges constrain habitat distribution of sponge species, maintaining habitat-distinct sponge faunas. 3) Ecological interactions play key roles in regulating within-habitat diversity of sponges; and therefore in maintaining exceptionally high regional diversity.
Broader impacts will be particularly far-reaching in the context of education about tropical marine ecosystems. Photographic documentation, in time series, of sessile animals as they respond to changes in their environment, is one of the most valuable resources for public and academic education about coral reefs and other tropical marine systems. Thus the collection of photos that will document all stages of the proposed transplant experiments will be a rich resource for classroom teaching, museums and traveling exhibits, and all other tropical marine educational programs.
