Physiological Ecology of Euryhaline Chironomid Midges in Cape Cod MA 2002-2003

In summer, 2002, hundreds of thousands of salt-tolerant midges (Chironomus decorus group, Diptera, Chironomidae) emerged from Pilgrim Lake/East Harbor, Truro, MA. The lake is a former estuary but has been separated from the sea for over 150 years by restrictions associated with railroad and highway construction. Brackish conditions caused by leaky tide gates designed to drain excess freshwater from the lake, coupled with high nutrient levels exacerbated by a massive fish kill the previous year, created conditions that supported densities of midge larvae of more than 5,000/m2 and produced a severe public nuisance in the vicinity of the lake when the adult midges emerged. The emergence coincided with National Park Service efforts to increase tidal flow into the lake, as part of a long-term commitment to restoration of restricted coastal waters within the Cape Cod National Seashore. We are studying the effects of increased tidal flow on midge populations, and in particular evaluating how high salinities need to be to reduce the potential for further nuisance outbreaks of the midges.