Abstract
Habitat complexity influences the abundance and distribution of faunal species and is an important driver of community structure in aquatic systems. Structured habitats increase the recruitment, survival, and growth of organisms, often by increasing resource availability, providing a predation refuge, and decreasing competition. Seagrass ecosystems are structurally complex habitats that play vital ecological and economic roles, including the provision of valuable nursery habitats and supporting the health of coastal communities. Drifting algae mats, often found adjacent to seagrass habitats, can also play a vital role in the maintenance of complex systems. As seagrass coverage in many areas shrink and fragment, algae could provide structural redundancy to maintain a functioning community. While algal mats have the potential to house more organisms because of their greater structural complexity, the types of organisms able to utilize this structure is less studied. We quantified how algal presence influenced the composition of nekton communities in seagrass beds throughout the northern Gulf of Mexico using trawls and benthic sleds. Pelagic fish declined when high concentrations of algae were present, while bottom-dwelling fish, shrimp, and crabs tended to remain unchanged or increased in abundance. Smaller organisms found within the algae, however, showed an overall increase in both the number of species and total number of individuals present across all relevant sampling locations as algae increased. Algal communities, while not as picturesque as seagrass or coral reef ecosystems, may offer an important refuge for some types of juvenile organisms as other complex habitats decline.
