Coping with Saltwater: The Condition of Aquatic Insects in Estuaries as Determined by Gut Content Analysis

The immature stages of freshwater insects can sometimes be found in densities of up to 25,000 m -2 in saltwaterinundated regions of estuaries, however little is known of their condition there. The gut fullness and contents of larvae of two species of hydropsychid caddisfly (Hydropsyche siltalai and H. instabilis) from freshwater and saltwater-inundated sites on the Aber Estuary, Wales were compared in an attempt to assess if the insects were functioning normally, or were in a degraded state after having been displaced downstream by the current. The findings suggest that the downstream larvae were in some ways functioning normally (i.e., attaching to rocks, spinning catch-nets, ingesting locally available food), although the lesser amounts of food contained in their guts (half-full or less) likely indicate that these downstream populations were existing in suboptimal conditions. Further data, for example, on growth rates and success at pupation and adult emergence, will be required to determine if such saltwater inundated populations are truly viable.