The ecology of mountain lake rotifers in Canterbury, with particular reference to Lake Grasmere and the genus Filinia Bory de St. Vincent.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Aspects of the systematics, ecology and distribution of New Zealand planktonic rotifers are examined in this thesis. Thirty-five lakes and two sets of ponds in the South Island were surveyed for rotifers during 1988-1991. Of 85 taxa identified, 32 were first records for New Zealand, bringing the rotifers recorded from the country to 332 taxa. Four species (Keratella australis, K slacki, Lecane herzigi and L. tasmaniensis), previously recorded as endemic to Australia, are added to the New Zealand checklist. Species composition, seasonal abundance, and vertical distribution of planktonic rotifers were investigated in Lake Grasmere, South Island, based on a biweekly sampling program from November 1988 to January 1990. Of the 44 species identified in the lake, 17 were planktonic with Polyarthra cf. dolichoptera, Keratella cochlearis, and Pompholyx sulcata dominant. Maximum rotifer densities occurred in May (1600 ind.1-1) and October (1500 ind.1-1), and numbers were lowest in July (120 ind.1-1) and March (250 ind:-1). The majority of species were most abundant in midwater (5-9 m depth), although some showed depth preferences near the surface or the bottom. A simple, rapid technique for the preparation of rotifer trophi for scanning electron microscopy is described. The method permits careful visual monitoring of trophi during the extraction process and does not require critical point drying of specimens. Subsequently, trophi of Filinia species from 16 South Island lakes and three North Island lakes were examined and compared with specimens from Australia, Austria, Belgium, Turkey, and Yemen. Five species of Filinia (brachiata, longiseta, cf. pejleri, novaezealandiae, and terminalis) were positively identified from the New Zealand samples. Numbers of unci teeth were considered to be the most reliable features for identification within the genus. Numbers obtained from SEM are listed for the first time. Experiments on the influence of temperature (5°-25°C) on morphology, life history, and growth rate of F. terminalis and F. cf. pejleri were performed in replicated individual cultures with Oocystis sp. as food. Some morphological characteristics previously used in identification of both species were found to be affected by temperature and also by life cycle stage. However, numbers of unci teeth were not affected. Body and setal lengths, life spans, all stages of development, and growth rates of both species decreased with increasing temperature. Offspring number per female of both rotifers was highest at 20°C, but the maximum growth rate of F. telminalis was at 25°C, whereas that of F. cf. Pejleri was at 20°C. Finally, I examined the effect of salinity on survival and growth of Hexarthra fennica, a species found normally in saline waters but also found in freshwater Lake Grasmere. The freshwater euryhaline H. fennica was able to survive and reproduce at salinities up to 13%, whereas a related species H. mira (found only in freshwaters) was unable to survive at > 1%.