Spatial and temporal variability of trophic relationships among aquatic macroinvertebrates in a seasonal marsh

Abstract

We examined macroinvertebrate trophic relationships in stands of two emergent plants, pickleweed (Salicornia virginica) and alkali bulrush (Scirpus robustus), and in epiphytic and benthic habitats within pickleweed stands. Numbers of detritivores, predators, and herbivores were examined throughout the flooding season (October 1990–March 1991). Trophic structure of macroinvertebrate communities differed between epiphytic and benthic habitats; both herbivores and detritivores were abundant in epiphytic habitats, but detritivores alone were numerically dominant in benthic habitats. Macroinvertebrate communities also differed between pickleweed and alkali bulrush stands: (1) all trophic groups were abundant in pickleweed, but detritivores were numerically dominant in alkali bulrush; (2) pickleweed supported higher macroinvertebrate numbers than alkali bulrush. Species composition was similar in both vegetation types, and diversity decreased during the season. Macroinvertebrate trophic structure in the epiphytic habitats changed during the season; detritivores quickly colonized both vegetation types after flooding, and predator and herbivore numbers increased later. Herbivores were an important component of macroinvertebrate communities in these wetlands, indicating that algal herbivory may be more important than previously thought.