Habitat Requirements of Burrowing Mayflies (Ephemeridae:Hexagenia) in Lakes, with Special Reference to the Effects of Eutrophication

Abstract

Hexagenia nymphs are large sediment burrowers that are sensitive to hypoxia. Major declines in some lake populations have been attributed to reduced concentrations of dissolved oxygen near the substrate resulting from eutrophication. This study was carried out on lacustrine populations of Hexagenia in the Quebec Eastern Townships (81 sampling sites in 12 lakes). It quantifies the suitability of littoral and sublittoral lake habitats for Hexagenia by means of discriminant functions that classify sites, with and without these larvae, in terms of a number of variables that are thought to be related to both sediment oxygen demand, and oxygen supply to sediments. These environmental variables include sediment oxidation-reduction potential, sediment water content (a surrogate of particle size), water column chlorophyll a concentration (a measure of lake trophic status), aquatic macrophyte biomass, and two morphometric parameters that reflect the physical energy regime (site exposure, and bottom slope). The biomass of Hexagenia was also related, by multiple regression analysis, to the environmental variables. The predictions from the habitat suitability models (discriminant functions and multiple regression models) were compared with independent data from the literature on the distribution and abundance of Hexagenia, and found to predict both presence/absence and biomass reasonably well. Furthermore, the models support the contentions made by previous authors that dramatic declines in lacustrine Hexagenia populations are the result of eutrophication. In addition, the suitability of a site for Hexagenia was positively related to bottom slope and exposure to waves at the site, and negatively related to the abundance of submerged macrophytes, especially when high macrophyte biomass was developed near the substrate.