The biology of benthic cladocerans in flowing freshwaters

Abstract

A community of benthic cladocerans (Crustacea) from the River Thames at Twickenham, comprising seven chydorid and two macrothricid species, was studied. The species present were Alona affinis, A. quadrangularis, A. rectangula, Disparalona rostrata, Leydigia leydigi, Pleuroxus uncinatus, P. trigonellus, Iliocryptus sordidus and Macrothrix laticornis.

A general trend, among the chydorid species, of a midsummer peak in abundance followed by a rapid decline was noted. Alona affinis, A. rectangula and Pleuroxus uncinatus also exhibited an autumn peak in abundance. The Iliocryptus sordidus (Macrothricidae) population did not follow this pattern. Birth and death rates were calculated for the populations of Alona affinis, Disparalona rostrata and Leydigia leydigi.

Results obtained from qualitative sampling of rivers in Southeast England, and from a survey of the literature, indicated the presence of a taxocene of benthic cladocerans characteristic of the unvegetated substrate of lakes and rivers.

The life histories of Disparalona rostrata and Leydigia leydigi were examined in detail. The number and duration of adult and juvenile instars, duration of egg development and mean length of life were determined at four temperatures. A study of the relationship between egg volume and parent length for Alona affinis, Disparalona rostrata and Leydigia leydigi revealed a highly significant positive regression of egg volume on parent length.

The life cycle strategy of the Chydoridae as a whole was examined and found to differ from that of both the large and small planktonic Cladocera. Like the small planktonic cladocerans, the Chydoridae produce large young relative to their size at maturity. However, unlike these, the Chydoridae exhibit curtailment of growth after maturity and in this resemble the large planktonic Cladocera.

The annual production of the benthic chydorid community in the River Thames, Twickenham was calculated and was found to be 0.876g C m-2 in 1982.