Functional Biogeography: Evaluating community assemblage patterns and ecosystem functioning in intertidal systems using trait-based approaches
For my PhD in Marine Biology, in the Coastal Research Group under the supervision of Professor Christopher McQuaid at Rhodes University I mapped the functional biogeography of the South African coastline based on a suite of species' reproduction and development traits. Functional trait data were compiled for macroinvertebrate species collected from fifty-two rocky shore sites from three main bioregions (east, south, and west) and two transition zones (south-west and south-east). Biological trait analysis and functional diversity indices were used to evaluate how traits related to species development and reproduction respond to temperature and chlorophyll-a (used as a proxy for food availability) gradients along the coastline.
GLMM and hierarchical cluster analyses showed distinct patterns/shifts in SST and chlorophyll-a gradients across bioregions, with two main breaks in SST separating the east and south-east overlap (SEO) bioregions from the south, south-west overlap (SWO) and west bioregions. In contrast, chlorophyll-a exhibited three major breaks with the east, SEO–south–SWO, and west clustering independently of each other.
In summary, considering the deterministic processes governing ecosystem functioning and community assemblage, the mass ratio and limiting similarity hypotheses showed complementary effects. Different bioregions provided variable support for these two hypotheses, but overall, the mass ratio hypothesis (weighted by species biomass) received stronger support and may be more meaningful to the interpretation of ecosystem functioning and persistence within rocky shore systems. Lastly, although, the SWO showed some of the characteristics of a subtraction zone based on the relatively low abundance, diversity, and biomass measures. Nonetheless, there was evidence of high functional redundancy across all other four bioregions. This suggests that in the context of development and reproduction traits, the rocky shore ecosystem along the SA coastline may be functionally stable at this stage.
GLMM and hierarchical cluster analyses showed distinct patterns/shifts in SST and chlorophyll-a gradients across bioregions, with two main breaks in SST separating the east and south-east overlap (SEO) bioregions from the south, south-west overlap (SWO) and west bioregions. In contrast, chlorophyll-a exhibited three major breaks with the east, SEO–south–SWO, and west clustering independently of each other.
In summary, considering the deterministic processes governing ecosystem functioning and community assemblage, the mass ratio and limiting similarity hypotheses showed complementary effects. Different bioregions provided variable support for these two hypotheses, but overall, the mass ratio hypothesis (weighted by species biomass) received stronger support and may be more meaningful to the interpretation of ecosystem functioning and persistence within rocky shore systems. Lastly, although, the SWO showed some of the characteristics of a subtraction zone based on the relatively low abundance, diversity, and biomass measures. Nonetheless, there was evidence of high functional redundancy across all other four bioregions. This suggests that in the context of development and reproduction traits, the rocky shore ecosystem along the SA coastline may be functionally stable at this stage.
A community–wide trophic structure analysis in intertidal ecosystems on the south coast of South Africa
I graduated with a Masters’ degree in Marine Biology in April, 2018 at Rhodes University under the supervision of Distinguished Professor Christopher McQuaid and Dr Tatenda Dalu. My research involved integrating different techniques to such as stable isotope techniques and community-wide trophic metrics to investigate the effects of short-term seasonal variability and small scale habitat properties on rock pool food web size and structure.
Another component of my thesis involved laboratory based microcosm experiments to investigate grazing and nutrient trade-offs in plankton communities PDF.
The influence of sardines (Limnothrissa miodon) population densities and lake level fluctuations on the tiger fish (Hydrocynus vittatus) sizes in Lake Kariba: 1974-2013
In November, 2014, I graduated with a BSc Honours, in Forest Resources and Wildlife Management from the National University of Science and Technology. For my research project, I conducted a study to evaluate and establish the sustainability of the commercial/recreational fishing industry of Hydrocynus vittatus and its impacts on the biometrics of other species in Lake Kariba. My study covered a 40-year period i.e., between 1974-2013 we aimed at assessing how the introduction of the clupeid sardine species (Limnothrissa miodon) possibly brought about transformations within the closed freshwater ecosystem of Lake Kariba; some of which included the feed and habitat preference of the native tiger fish.
It is established that, the introduction of the Lake Tanganyika sardine led to the dietary and habitat shift of species such as the predatory tiger fish. Lake Kariba fisheries have exhibited a general downward trend in fish stocks over the past four decades. Therefore, the main objectives of this study were (i) to determine how the tiger fish sizes (length and weight) have been influenced by sardine densities, lake levels fluctuations and time (ii) secondly to determine how introduction of exotic species and commercial harvesting have impacted the size of tiger fish in Lake Kariba. We hypothesized that sardine population densities, lake level fluctuations, gonad state and time influence the average size of tiger fish in Lake Kariba. Lake Kariba ’s productivity is driven by both environmental and anthropogenic factors. Our results confirmed that CPUE as a proxy for Kapenta densities significantly influences the average sizes (length and weight) of tiger fish. Evolutionary trends (time) exhibited a significant impact on this predator species. Lake level fluctuations insignificantly affected the tiger fish sizes. Due to paucity of data, the impacts of factors such as, temperature changes and cray fish influences could not be scientifically accounted for.
It is established that, the introduction of the Lake Tanganyika sardine led to the dietary and habitat shift of species such as the predatory tiger fish. Lake Kariba fisheries have exhibited a general downward trend in fish stocks over the past four decades. Therefore, the main objectives of this study were (i) to determine how the tiger fish sizes (length and weight) have been influenced by sardine densities, lake levels fluctuations and time (ii) secondly to determine how introduction of exotic species and commercial harvesting have impacted the size of tiger fish in Lake Kariba. We hypothesized that sardine population densities, lake level fluctuations, gonad state and time influence the average size of tiger fish in Lake Kariba. Lake Kariba ’s productivity is driven by both environmental and anthropogenic factors. Our results confirmed that CPUE as a proxy for Kapenta densities significantly influences the average sizes (length and weight) of tiger fish. Evolutionary trends (time) exhibited a significant impact on this predator species. Lake level fluctuations insignificantly affected the tiger fish sizes. Due to paucity of data, the impacts of factors such as, temperature changes and cray fish influences could not be scientifically accounted for.