Invertebrate Colonization of Submerged Wood in a Cypress-Tupelo Swamp and Blackwater Stream

Abstract

We examined the effects of location within a swamp-stream ecosystem on colonization rate and community structure of the macroinvertebrate assemblages of submerged wood. Uniform-sized sections of freshly cut wood from water tupelo trees (Nyssa aquatica L.) were suspended below floating platforms at swamp and stream sites for periods of 1-8 weeks. The location of wood substratum affected community structure to a large degree and patterns of colonization to a slight extent. Logs in the swamp-tributary site held almost three times as many individuals and twice as many taxa as did logs in the swamp and outflow stream sites. Stream sites, however, were similar in proportions of various functional and taxonomic groups. Except for the abundance of true midges (Chironomidae), the densities of most major taxonomic groups were significantly affected by location within the swamp-stream ecosystem. Recruitment of individuals and species were extremely rapid and reached a rough steady state at most sites within 1 week. Filter-feeding taxa were numerically dominant early but soon were subordinate to gatherer and scraper functional feeding groups. This trend resulted primarily from the progressive increase in abundances of riffle beetles and mayflies. Current velocity, seston particle size, dispersal capacity and competition for space may be important factors affecting community structure and colonization patterns in this aquatic ecosystem.