Ecological studies on Antarctic tardigrades and rotifers.
thesisposted on 19.11.2015, 08:49 by Peter G. Jennings
The general development of Antarctic research and the reasons for the research presented in this thesis were outlined. The Antarctic region was divided into continental, maritime and sub-Antarctic areas on climatic and floral characteristics. Physical and biotic features of the maritime Antarctic were then described, particularly those on Signy Island. Features of taxonomic significance in the phylum Tardigrada were discussed, with particular reference to those of the Antarctic tardigrades. The tardigrade species recovered from the Antarctic in this study were described and illustrated. The recoveries in this investigation are compared with those of previous workers in the Antarctic region. The total Antarctic tardigrade fauna was found to number 23 species, only 11 of which had been found by two or more investigators. It was suggested that the lack of species confirmation may relate to the difficulties in identification of the Diphascon group. Only four species had not been recorded in other regions of the world, and two of these were only recently known to science. The taxonomic difficulties encountered with the Rotifera meant that only four categories were recognised: Adineta Bdelloidea, Monogononta and inactive rotifers. A total of 43 sampling sites on Signy Island were described, eight in detail since they were considered to be representative of the most common vegetation types of the Antarctic, and these were used to determine tardigrade and rotifer population densities. Tardigrades were assumed to be cylindrical with the exception of Echiniscus which was assumed to be half a prolate spheroid. Samples of mosses and lichens were collected from 70 sites in the Antarctic Peninsula and Scotia Ridge region. The microclimate at locations along the Antarctic Peninsula and Scotia Ridge region was deduced for macro-climatic data, it was then used to account for tardigrade densities and species diversity in the region. Two sites on Signy Island were chosen as being representative of two moss communities which are common throughout the maritime Antarctic. These sites were the Signy Island terrestrial reference Sites (SIRS 1 and 2). Four species of Tardigrada were found to occur regularly on the SIRS. The population density estimates of each of the four species/species-groups showed little consistent pattern over the period of study on either site. Only Echiniscus showed any suggestion of mortality over the winter months. There was no apparent correlation between tardigrade densities in individual cores and any other measured factor. Up to 80% of the tardigrades were found in the upper 6 cm of the moss cores. The reasons for this were discussed. Oxygen uptake of M. furciger was investigated using a Cartesian Diver micro-respirometer. Direct body length measurements of M. furciger were unreliable. The length of the buccal tube and placoid line, therefore, were used to derive body lengths for each experimental animal. The body weight of each animal was estimated from the body length. A total of 55 oxygen uptake rates were obtained. From these rates two regression lines were derived. The rate of oxygen uptake of a 600 um individual of M. furciger at 10°C was compared with that of an individual of M. dispar at 20°C from a temperate climate. The higher rate advanced as evidence of physiological adaptation to low temperatures. Size-frequency analysis of M. furciger populations did not show the discontinuities usually associated with the moult. It was impossible, therefore, to divide the population into instar size classes. In order to apply respiratory data to field populations, five equal size classes were chosen at 100 um intervals between 151 to 651 um. The proportion of individuals in each class was then determined for selected months on SIRS 2. Using respiration data, population densities, size class structure and field temperatures on SIRS 2, total population metabolism of M. furciger was calculated. Assuming the respiration was negligible at field temperatures below 0°C, the annual population metabolism of this species was 127 m1 02 m-2. The calculation was repeated for SIRS*1 assuming that the population size structure was similar to that on SIRS 2. Annual metabolism of M. furciger on SIRS 1 was 23 m1 02 m-2. The respiration data for M. furciger were extrapolated for all species of Tardigrada present on the SIRS. The presence and survival of the Antarctic terrestrial mesofauna, with particular emphasis on the tardigrades, was discussed. Soma observations ware made on the food requirements of the SIRS Tardigrada. The research presented in this thesis was compared with that on other groups at the SIRS and with other works of a similar nature elsewhere. It was suggested that the Tardigrada were not as insignificant as was previously believed. (Abstract shortened by UMI.).