Temporal changes in temperature may suggest microhabitat shifts in larval spongillafly Climacia areolaris Hagen (Neuroptera: Sisyridae) abundance and density in a temperate freshwater lake

Abiotic factors such as temperature and depth are known to affect aquatic insect populations and are thought to be major variables that directly impact how communities are assembled and populations distributed. The purpose of this study was to examine the role of temperature and depth in structuring C. areolaris populations within a temperate freshwater quarry. Larval densities among individual sponges at different depths were determined over six months in a Pennsylvania quarry. Sponges from four depths (7.0 - 8.0 m; 8.1 - 9.0 m; 9.1 - 10.0 m and 10.1 - 12.0) were collected once per month (n = 3) using SCUBA. Temperature data were collected at four depths (n = 3 samples/depth). Larval densities significantly varied over the study period, but were not significantly different between depths on any date. Mean total larval density was significantly higher in March, April and May compared to dates later in the season. This result followed an inverse pattern where there was a significant effect of date on temperature, but no difference between depths. There was a detectable change in relative abundance of the sisyrid populations among the depths; the two shallowest depth ranges collectively represented >50% of the population during March and April, but were < 50% throughout the rest of the summer. There was also a significant negative relationship of larval density with temperature. Few studies have documented the role of abiotic factors such as depth and temperature on the spatial and temporal structuring of spongillafly microdistribution within a quarry environment.