Identification of the highest quality habitats is essential for the design of effective marine protected areas. It is important to consider which habitat types and the characteristics of the species residing therein in reserve design. In the Caribbean, the macroalgae, Laurencia spp., has been shown to affect recruitment dynamics and provide important structured nursery habitat for commercially important species, such as Nassau grouper, Atlantic spiny lobster, and Queen conch. However, the effects of Laurencia spp. on faunal community structure have not been thoroughly examined. We compared macroinvertebrate and fish communities between Thalassia testudinum beds with and without Laurencia spp. in Abaco, The Bahamas. Additionally, we designed a field experiment to determine whether the effects of Laurencia spp. on seagrass macoinvertebrate and fish communities were driven by mere increases in structural complexity (e.g., refuge, shelter) or by other properties of Laurencia spp. (e.g., chemical cues, nutritional value). We added natural Laurencia spp. and structurally similar synthetic algae to a Thalassia testudinum bed in Abaco, The Bahamas, and sampled them after one month.

Results/Conclusions

Biomass of organisms in Thalassia testudinum beds with Laurencia spp. was significantly greater than similar Thalassia testudinum beds without Laurencia spp.. However, analyses suggest that biomass of organisms was greater in sites where synthetic algae was added compared to those to which natural Laurencia spp. was added. This was likely because of the loss in structural complexity in the natural Laurencia spp. sites after mortality by natural algae. These results indicate that Laurencia spp. may enhance the quality of seagrass habitats by increasing the available structure for macroinvertebrates and juvenile fishes. Therefore, seagrass beds with abundant Laurencia spp. should offer increased prey densities and higher quality nursery habitat for commercially important species. These small-scale observable patterns provide an important baseline for managers and an invaluable resource in developing and driving a conservation strategy for these marine habitats.