Notes on the ecological roles of Podostemum ceratophyllum Michx., 1803 and Cladophora glomerata (L.) Kutz., 1843 in the habitat and diet of riverine hydropsychid caddisflies (Trichoptera)

Larvae of net-spinning Hydropsychidae caddisflies (Trichoptera) are common inhabitants of lotic systems and are typically categorised as filtering-collectors, but feeding habits vary in response to the availability of food resources. This study addressed two questions. First, are Hydropsyche simulans Ross, 1938 and Cheumatopsyche Wallengren, 1891 found in higher densities in patches of the macrophyte Podostemum ceratophyllum Michx., 1803? Second, do H. simulans and Cheumatopsyche spp. assimilate the filamentous alga Cladophora glomerata (L.) Kutz., 1843 during a late summer bloom? Cladophora glomerata standing stocks increased during summer, coincident with increasing water temperatures and decreasing flow. Densities of both hydropsychid taxa were significantly greater in high (> 75% cover) P. ceratophyllum habitat. A multisource mixing model (IsoSource) using carbon and nitrogen stable isotope data showed that C. glomerata was the prominent assimilated dietary item during August and September. Overall, hydropsychid caddisfly larvae showed a clear habitat association with P. ceratophyllum and the capacity to assimilate C. glomerata when this resource is abundant during summer base-flow conditions.