Boeckella major (Copepoda: Calanoida): a predator in Australian ephemeral pools

Abstract

Small ephemeral pools in the Murray-Darling basin, Australia, that dry annually lack fish and are dominated by microfauna. Community size structures and species diversity are very variable and many ponds contain one or more of the large calanoid copepods, Boeckella major, Boeckella pseudochelae and Hemiboeckella searli. Gut content analysis showed that these species were omnivores with B. major being the most carnivorous and B. pseudochelae the least. B. major guts contained 21 animal taxa (cladocerans, calanoid and cyclopoid copepodids, nauplii and rotifers), H. searli contained 15 taxa (calanoid, cyclopoid and harpacticoid copepods, nauplii and rotifers) and B. pseudochelae 8 taxa (small cladocerans, nauplii and rotifers). Mean numbers of animals per gut differed significantly between the large calanoids and in B. major, B. pseudochelae and H. searli were, respectively, 2.9, 0.6 and 0.2. In B. major Rotifers' were positively selected, Copepodites and Others neutrally selected and Cladocera and Nauplii negatively preferred. In H. searli Copepodites, Nauplii and Rotifers' were neutrally selected, and Others negatively preferred. B. pseudochelae showed negative preference for Cladocera, Nauplii and Others, and Rotifers were neutrally selected. At sites containing B. major, species diversity was significantly reduced and community size structure (measured as mean and median log-length, % of sizes >500 μm) was significantly larger than it was at sites lacking large calanoids or with only B. pseudochelae and H. searli. It is hypothesised that predation by B. major may be an important force structuring the communities of these habitats.