Status and distribution of Odonates at Cape Cod National Seashore

Nikula, Blair; Cook, Robert

doi:10.36967/2303254

Odonates are significant components of most wetland habitats and important indicators of their health. At Cape Cod National Seashore (CACO), we compiled odonate records dating back to the 1980s and, based partly on that data, identified 41 wetland sites for sampling, representing six freshwater habitats (kettle pond, inter-dune pond, dune slack, riparian marsh, vernal pool, and bog). We surveyed these sites for adult odonates during the 2016–2018 field seasons. Ten sites were surveyed all three years (total 19-20 surveys/site); all ten had at least some historical data. The remaining 31 sites were surveyed for one field season, a total of 6-8 times each. We conducted 391 surveys, recording 53,435 individuals and 74 species (45 dragonflies and 29 damselflies); not all individuals were identified to species. Abundance and species richness varied significantly between habitats. For all individuals recorded, abundance was greatest at vernal pools and kettle ponds. Riparian sites had the lowest abundance. Species richness was highest at kettle ponds, including several species of conservation concern, two listed as Threatened by the state of Massachusetts. Riparian marshes and dune slacks had relatively low richness. Among the 10 sites surveyed three years, we found significant annual variation in abundance and species richness. There was significant and generally greater between-site variation in abundance within a year than between years at sites. Community analysis found pond depth, habitat type, and presence of predaceous fish were significant factors explaining between-site variation in community composition. Habitats also differed significantly in community composition. Multidimensional scaling showed sites tend to cluster together by habitat type. Vernal ponds have the highest average community similarity to all other habitats (53.5%), with dune slack (52.9%), bog (52.0%) and inter-dune (51.5%) close behind. In contrast, riparian sites (46.3%) and kettle ponds (39.5%) are least similar to other habitats. Overall, 86 species of odonates have been recorded at CACO, a rich and diverse assemblage reflecting the variety and quality of freshwater habitats present. Although these habitats are relatively well-protected, stressors include climate change, nutrient inflow from adjacent development, road runoff, and trampling of emergent vegetation. A plan for monitoring is beyond the scope of this project. Ideally, it would be best to use the insight into odonate variation obtained from these surveys to develop a monitoring program designed to meet standards of statistical confidence and power currently employed in NPS monitoring programs.

Status and distribution of Odonates at Cape Cod National Seashore

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