Hydrology and Aquatic Invertebrate Communities of Riverine Rock Pools: Effects of Seasonality and the Penobscot River

Small pools on rock outcrops are a common feature on the banks of Maine rivers, however the unique aquatic insects inhabiting these rock pools have been little studied. This is problematic, as climate change is altering seasonal river flooding and rainfall patterns that may control pool filling and drying. These changes may impact potentially unique species in these pools, or make them more susceptible to invasion by disease vectors such as mosquitos. This project surveyed the insect communities of 40 natural pools in a rocky outcrop on the Penobscot River near Milford. The pools were spread between four zones: two zones that were close to the river (A and B) and two zones that were out of the range of summer flooding (C and D). Both the physiochemical and biological aspects of pools were influenced by their distance to the river. The amount of both fine and coarse detritus was significantly greater in pools farther from the river than those pools near the river. Conductivity, pH, and the amount of time pools held water varied significantly across zones. Pools closer to the river had higher pH and were inundated longer than pools farther from the river. Conductivity showed different patterns, with pools of intermediate distance from the river having lower conductivity than those at either end of the gradient. Invertebrate communities reflected differences in environmental conditions among zones. Pools that were close to the river were dominated by river-dwelling taxa during the summer and pools that were farther from the river were dominated by mosquito and midge larvae. Pools became more similar in the fall as pools near the river lost some or all of their lotic specialist taxa found within them, with the second zone near the river losing all lotic-specialized taxa. Changes in river flow regimes and rainfall patterns are likely to affect the hydrology of riverine rock pools and therefore will likely alter the structure of these unique insect communities