| Summary: | Water temperature is a critical factor affecting the abundance and richness of freshwater
stream aquatic macroinvertebrate communities. Variable seasonal river temperature
patterns are a critical factor in maintaining temporal segregation in aquatic invertebrate
communities, allowing for resource partitioning and preventing competitive exclusions,
while spatial differences in water temperatures permit zonation of species. This research
investigated whether the degree of predictability in a stream’s water temperature profile
may provide some indication of the degree of structure and functional predictability of
macroinvertebrate communities. Quarterly aquatic macroinvertebrate sampling over a
single year along the longitudinal axes of two river systems, Keurbooms River in the
southern Cape, and the Kowie River in the Eastern Cape, were undertaken as the core
component of this research. The two river systems shared similar ecoregions and profile
zones, however were expected to differ in their thermal variability, based on the
hydrological index and flow regimes for their respective quaternary catchments. Hourly
water temperature data were collected at each sampling site from data loggers installed
at five paired sites on each stream system. The aquatic biotopes sampled were in close
proximity to the loggers. Multivariate analysis techniques were performed on the
macroinvertebrate and water temperature data. Macroinvertebrate taxon richness was
greater on the perennial Keurbooms than the non-perennial Kowie River where, on a
seasonal basis, taxon richness increased from winter to autumn on both systems.
Macroinvertebrate species turnover throughout the seasons was higher for sites having
lower water temperature predictability values than sites with higher predictability
values. This trend was more apparent on the Keurbooms with a less variable flow
regime. Temporal species turnover differed between sites and streams, where reduced
seasonal flows transformed the more dominant aquatic biotopes from stones-in-current
into standing pools. Findings included aquatic macroinvertebrates responding typically
in a predictable manner to changing conditions in their environment, where water
temperature and flow varied. The findings of this research demonstrate that
macroinvertebrate taxa do respond in a predictable manner to changes in their
environment. This was particularly evident in relation to variability in water temperature
and flow. === Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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