Macroinvertebrate Community Structure in MDOS Mesocosms: The Role of Vegetation and Response to Marsh Dry-Out

A macroinvertebrate study was conducted from May 10, 2000 through August 22, 2000 in controlled mesocosm experiments at the northern Alternative Treatment Technologies (ATT) site of Stormwater Treatment Area-1 West (STA-1W) in Palm Beach County, Florida. Weekly variations in macroinvertebrate communities were observed to evaluate abundance, richness, density, and taxonomic/functional group composition with respect to vegetation type (submergent or emergent dominated systems) and recovery response following a period of drydown.Weekly samples were collected following the reflooding of drydown systems from four mesocosms designated as submergent/flooded, submergent/drydown, emergent/flooded, and emergent/drydown using samplers specifically designed to utilize the mesocosm vegetation as substrate and to prevent loss of organisms associated with the retrieval of other sampling devices. These sampling modifications appear to have resulted in macroinvertebrate densities that exceed those found in recent Everglades’ studies.Vegetation type appeared to influence macroinvertebrate communities, with the structurally heterogeneous habitat of the emergent mesocosms having a statistically greater abundance of organisms even though dissolved oxygen concentrations were below the generally accepted critical level for macroinvertebrate tolerance (4 mg/L) in the emergent mesocosms. Crustaceans dominated emergent mesocosms (67 and 73% for emergent/flooded and emergent drydown, respectively), followed by gastropods (27 and 43% for emergent/flooded and emergent/drydown, respectively), while odonates dominated submergent mesocosms (50and 34% for submergent/flooded and submergent/drydown, respectively). Gastropods were the second-most dominant taxonomic group in the submergent/flooded mesocosm (37%). However, crustaceans were the second most dominant group in the submergent/drydown mesocosm (32%), with gastropods comprising 31% of the total community. The collector/gatherer groups (collector/gatherers, collector/gatherer-grazers, and collector/gatherer-filterers) dominated the emergent mesocosms, while predators dominated the submergent mesocosms.Both emergent and submergent/drydown mesocosms showed significantly increased abundances when compared with continuously flooded mesocosms, but relationships were not observed between hydrology and dominant taxonomic group and functional feeding group. Recovery was not observed during the study period. While functional group composition was similar to other Everglades studies, densities were highly inflated and taxonomic structure was not comparable because of differences in experimental design.