An Ecological Profile of Hydropsyche alternans (Trichoptera: Hydropsychidae) in Lake Superior, the Last Stronghold of a Once-Dominant Great Lakes Surf Zone Caddisfly

Abstract

We studied the life history, diet, and trophic ecology of Hydropsyche alternans in four rocky sites located along the south-central coast of Lake Superior. The H. alternans life history and broad trophic niche space were similar to those of its riverine relatives. Quantitative sampling over the course of one ice-free season revealed that most individuals lived univoltine life histories that featured early to mid-summer mating, and oviposition and rapid growth and development through summer into fall. Most individuals overwintered as ultimate or penultimate larval instars. Pupation followed ice-out in the spring. Gut content sampling and δ13C and δ15N stable isotope analyses indicated that the typical larval diet is a mix of benthic, pelagic, and terrestrial food resources, including diatoms, small arthropods, sloughed periphyton, and in one site, fugal hyphae apparently of foredune origin. As a suspension-feeding omnivore that relies on waves and currents to deliver food to its nets, H. alternans larvae form energetic links between coastal, nearshore, and offshore food webs. These connections have been lost throughout the lower Laurentian Great Lakes as a consequence of the invasion and spread of Dreissena mussels.

Low redundancy among caddisflies sharing a mid‐mountain stream

“…The genus is usually classified among predators and being a commonly abundant taxon, this implies that streams are described as characterised by overwhelming predator abundance (Masese et al., 2014a). It has been shown, however, that net‐spinning caddisflies are able to consume filamentous algae and to perform seasonal dietary shifts according to resource availability (Miess et al., 2022; Tinsley et al., 2016). In the Gilgil, Cheumatopsyche was consistently associated with intermediate δ 15 N values, which indicate a rather omnivorous diet, different from Hydropsyche and E. belladotae that were placed at significantly higher δ 15 N (Figure 3) indicating that they represented true predators.…”

The Grand Caddis hatch of JASM 2022: Trichoptera natural history observations at the Joint Aquatic Sciences Meeting in Grand Rapids, Michigan (USA)

“…Based on these observations, we speculate that the "head-to-tail" position could be a precopulatory behavior in which H. morosa males are ensuring their interspecific mate selection by engaging with the female's pheromonal glands, which are located on the 5 th abdominal sternite (Löfstedt et al 1994;Miess et al 2022). The "head-to-tail" holding behavior may serve as a physical prerequisite for successful mating.…”

“…Male and female pairs of Hydropsyche remained in the "head-to-tail" position for as long as 40 min, before successfully pairing off in a coital position. Directly east of Grand Rapids, Miess et al (2022) observed premating behavior of the conspecific taxa H. alternans Walker along the edge of Lake Superior, which they described as a "dizzying blend of low swarming flights, frenetic scrambling over, under, and around lakeshore rocks, and excited nuzzling by males alongside of females." Our observations of "head-to-tail" behavior in H. morosa directly parallel the "nuzzling" behavior described among H. alternans.…”