11. An examination of the species-area-energy relationship driving decomposer diversity within “sponge” habitats in an estuarine bay

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The species-area relationship is a well-known pattern in ecology detailing a strong positive relationship between habitat area and species richness. Alternatively, the species-energy hypothesis suggests that total energy availability drives species richness, with higher richness in systems with more energy input. While these two hypotheses are difficult to separate as they are positively related, they can be mutually exclusive. Species richness may increase with both area and energy availability independently. Here we test the relative importance of habitat area vs energy availability by placing two artificial substrates, polypropylene and cellulose sponges, with four different surface areas in two estuarine habitats. Cellulose sponges are organic and therefore should increase biodiversity by providing both protective structure and nutrition, while polypropylene sponges only provide structure. Organic sponges with large surface areas should promote more diversity than synthetic sponges with the same surface area. To test this, 40 cellulose and 40 polypropylene pre-weighed sponges of each surface area were placed in salt marshes and the open ocean of Terrebonne Bay in Louisiana. After one month, organisms were removed and categorized, and dry weight of the sponges collected. Preliminary results show that abundance was negatively related to surface area, contrary to predictions. However, organic sponges lost more mass, but supported similar abundances of organisms than polypropylene sponges. These results suggest that cellulose sponges are primarily used as nutrition as their effect should be additive if used as structure as well. This project offers important insights into the complexities that habitat diversity has on decomposer systems.