Role of sediment in determining the vulnerability of three littoral cladoceran species to odonate larvae predation

Abstract

ABSTRACT Small cladocerans, found abundantly on surfaces of macrophytes and sediments in the littoral zone, are important prey not only for small fish but also for various invertebrates such as larvae of odonates in freshwater habitats. However, no study has documented how habitat substrates affect their behavior and vulnerability to predators and predation. We conducted laboratory experiments to examine the movement of 3 littoral cladoceran species, Chydorus sphaericus, Alona sp., and Ilyocryptus spinifer, to determine if their vulnerabilities to predation by odonate larvae changed depending on the presence or absence of bottom sediment. We observed that when sediment was present, Ilyocryptus crawled in and ceased movement. However, in the containers without sediment, they continuously swam or crawled. Similarly, Chydorus also reduced frequency of movement in a container with sediment, but Alona movement did not change regardless of the presence or absence of sediment. In the predation experiments with 2 or 3 prey species, Ilyocryptus was the most vulnerable to predation by odonate larvae in the containers without sediment but least vulnerable in those with sediment. The vulnerability of Chydorus to the odonate larvae was as low as that of Ilyocryptus in the containers with sediment. Alona was less preyed upon by odonates in containers with sediment but highly vulnerable to predation when containers had sediment with Chydorus and Ilyocryptus. These results indicate that behavior and vulnerability to predation of littoral cladocerans are species-specific and change depending on the presence of sediment and the existence of other species.