Macrofaunal associations with seagrass epiphytes - Relative importance of trophic and structural characteristics

Attached epiphytes often make important contributions to total primary prod uction in seagrass meadows. Additionally, they may increase the spatial com plexity of seagrass habitats. Experiments conducted using artificial seagra ss units (ASU) manipulated both epiphytic structure and epiphytic food reso urces. Previous work suggested that the increase in faunal density associat ed with epiphytes was related to increases in structure, but our results in dicate that the primary impact of epiphytes lies in their trophic role. Dat a showed that epifaunal density was significantly greater in conditioned AS Us fouled with a live community of epiphytes (12 285 individuals m(-2)) com pared to ASUs with artificially created epiphytic structure (5099 inds. m(- 2)) and to control ASUs (5955 inds. m(-2)). This response to epiphytic trop hic resources was significant for most herbivore/omnivore taxa, but not nec essarily for filter feeding or predatory epifauna. However, densities of tw o predatory taxa (fish and mud crabs) were significantly greater where epip hytic biomass was higher, which may reflect their response to increased pre y abundance. Additionally, ASUs conditioned with live epiphytes had greater taxa richness than other ASUs. Epiphytic structure appeared to play only a limited role in determining the density of most mobile epifauna, but epiph ytic structure appeared to be important in augmenting the settlement of biv alves. By using ASUs we were able to control aspects of blade Length and sh oot density, but the pre-experiment conditioning of treatments fouled with live epiphytes may have played a role in determining absolute differences i n macrofaunal density among ASU treatments. Overall, our work suggests that the trophic role of epiphytes can have a dramatic impact on associated epi faunal communities, although future investigations are needed to assess thi s relationship more fully. (C) 1999 Elsevier Science B.V. All rights reserv ed.