Surviving in anoxic surroundings: how burrowing aquatic insects create an oxic microhabitat

Abstract

We used an infrared video system and O2 microelectrodes to record the behavior of 2 widespread burrowing insects, the predatory alderfly Sialis velata and the sediment-feeding mayfly Hexagenia limbata, to determine how they survive in anoxic sediment. Analysis of video recordings showed that both taxa have several common behaviors, including crawling, pushing sediment, turning around, and brushing their legs over their bodies for the purpose of cleaning. In contrast, these taxa differ in how they draw overlying oxic water into their burrows, i.e., H. limbata beats its abdominal gills, whereas S. velata undulates its abdomen. Feeding frequency also differs between the 2 taxa, i.e., the mayfly feeds frequently on sediment within its burrows, whereas S. velata feeds infrequently. Hexagenia limbata nymphs were rarely inactive (<1% of the time) and irrigated their burrows by gill-beating ¾ of the time, whereas S. velata nymphs were usually inactive (60% of the time). By vigorous irrigation of its burrow, H. limbata maintained its surroundings well oxygenated, whereas O2 concentrations fluctuated more widely in burrows of the less-active S. velata. This behavioral difference between the species is consistent with their reported sensitivities to the low O2 concentrations associated with eutrophication; in such situations, H. limbata is likely to be eliminated, whereas S. velata can persist. We estimate that O2 lost from water passing through an H. limbata burrow is taken up mainly by the insect rather than diffusing into the surrounding sediment.