Physiological Ecology of Euryhaline Chironomid Midges (Cape Cod MA)

• Investigators: Elizabeth Colburn, John Portnoy
• Contact: Elizabeth Colburn
• Start date: 2002-01-01
• End date: 2003-12-31
• Location: Pilgrim Lake / East Harbor (Truro MA)
• Latitude:
• Longitude:
• Elevation: 0 to 1 meters
• Taxa: Chironomus decorus
• Keywords: chironomids, coastal wetlands, nuisance midges, salinity tolerance, salt marsh restoration, wetland restoration
• Abstract:

  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.

• Methods:

  In response to initial nuisance levels of midges, National Park Service personnel began monitoring larval densities and lake salinities in the field in 2002. Initial spot sampling has been expanded to include both sampling across an east-west transect in the lake and random sampling across the basin for estimation of overall population levels. Larvae are sampled with a corer (diameter), sieved (500 um mesh), and counted. Salinities are measured using a hand-held refractometer with periodic calibration using a conductivity bridge. For experimental assessment of effects of salinity and temperature on midge populations, we sieved larvae from lake sediment in late 2002 and early 2003, and maintained them in the laboratory in shallow (10 cm deep) trays filled with natural substrate and lake water or artificial seawater. In controlled experiments, larvae were held at salinities of 0-35 % at low temperatures (0-4 C) comparable to winter ambient conditions, and their survival was monitored over time. Subsequent experiments investigated effects of salinity and temperature on pupation and adult emergence.

• Related datasets: