The role of architectural complexity in the structure of a marine phytal community

Studies examining the relationship of habitat heterogeneity and community diversity and structure are complicated by the confounding effect of surface area and the multidimensional nature of both habitat heterogeneity and community structure. Using artificial algal substrates, I examine the relative importance of surface area and multiple scales of architectural complexity (=habitat heterogeneity) on the structure of a marine phytal community and then investigate the role of habitat-mediated trophic interactions as a possible mechanism to explain habitat-related differences in community structure. Bottom-up and top-down forces are important trophic mechanisms affecting the structure of species assemblages, and both should be directly affected by the surface area and heterogeneity of a given habitat. This interaction may be responsible for differences in community structure observed among different habitats.;In this study, community structure was assessed at three levels of community organization: (1) taxa, (2) functional, and (3) trophic groupa. Variation in community structure at all three levels off organization was usually best explained by architectural factors, and not surface area. Any effects attributable to surface area were consistent with a random sampling phenomenon, and not surface area-related biological mechanisms.;Using a detritus enrichment experiment, I examined the effect of detritus quantity on the structure of the phytal community. Enriched substrates had a significantly different community compared to unenriched controls, but these differences were restricted to the biomass of taxa, and did not alter the functional or trophic composition of the community. Ordination plots showed clusters were related more to substrate architecture than detritus quantity. Data also suggested that detrital quality may be more important than detritus quantity, but this was not directly investigated here. Results from a predation study suggested that predators as a group had an affect on community structure, whereas an individual predators had little overall impact. A correlation existed between total predator biomass and community structure, suggesting that predators as a group played a role in the structure of the phytal community. Although both detritus quantity and predation did have an effect on the phytal community, neither adequately explained difference in community structure observed among substrates with different architectural complexity.