Microhabitat of Anthopotamus verticis (Ephemeroptera: Potamanthidae)

Abstract

A field and laboratory study was designed to elucidate the microhabitat of the North American riverine mayfly Anthopotamus verticis (Say). Previous reports have suggested that these mayflies are surface sprawlers or clingers; but despite a flattened body shape that is often associated with sprawling or clinging benthos, our investigation showed that larvae of A. verticis burrow and inhabit the hyporheic biotope. Substrate particle size was found to be a primary limiting factor in the microdistribution of the larvae. When homogeneous substrates (either fine, medium, or coarse gravel, or small or large pebbles) were provided, small, mid-sized, and large larvae significantly preferred coarse gravel or small pebbles. Small larvae were better represented in coarse gravel, and large larvae were better represented in small pebbles. Vertical distribution was deeper in coarse gravel than in medium gravel, and smaller larvae were generally found deeper than large larvae. In the field, larvae occur in gravel or pebbles (excluding coarse sand or smaller particles) or mixed substrates, often at the interface of large rocks and finer substrates. Videomacroscopic examination also indicated larvae to be interstitial dwellers. Although relatively crude burrowers, larvae do use their tusks to excavate substrate, and their gills to generate interstitial current. We distinguish the fossorial behavior of Anthopotamus from most other ephemeroid mayflies because tube burrows are not formed. Minimum-sized interstices may be required for filter feeding and/or adequate ventilation, and may explain a deeper penetration of smaller larvae in finer substrates.