The influences of hydrology and vegetation on emergent insect and benthic macroinvertebrate communities across space and time in seasonally inundated, geographically isolated wetlands

Abstract

Geographically isolated wetlands are vulnerable to both land use and climate change because they are typically small, and are embedded in uplands. However, they support a diverse community of aquatic macroinvertebrates, including insects that serve as energy in upland food webs when they emerge as adults. How aquatic macroinvertebrate communities, particularly emergent aquatic insects, respond to vegetation and differences in long-term patterns of water permanency in isolated wetlands is unknown. To understand the influences of vegetation type and historical hydrology in isolated wetlands, we investigated benthic and emergent macroinvertebrate community characteristics from February - early August 2023 in five swamps and six marshes. We hypothesized that macroinvertebrate communities would reflect adaptation to both hydrology and vegetation communities through their richness and biomass, with long hydroperiod sites and marshes having the greatest richness and biomass of both benthic macroinvertebrates and emergent aquatic insects. We found that both hydroperiod length and vegetation type were important predictors of some but not all of our community characteristics. Benthic macroinvertebrate richness and biomass were greater in marshes than in swamps and influenced by both hydrology and vegetation, while emergent insect richness and biomass flux were most influenced by hydrology and greatest in long hydroperiod wetlands. Community composition was not predictable based on either hydrology or vegetation alone, but combined they explained around a third of the variation in community composition. Our results indicate that insects and non-insect macroinvertebrates with faster life cycles were more common in short hydroperiod sites and swamps, and longer-lived aerial insects were more common and diverse in long hydroperiod marshes. Predicted shorter hydroperiods will likely reduce biodiversity and insect biomass exported to the surrounding landscape, an important subsidy that supports terrestrial food webs. The export of material from aquatic to terrestrial systems is not often considered in conservation planning, but may occur during critical periods for terrestrial species, making the conservation of GIWs increasingly important.