Browsing by Subject "Langebaan Lagoon"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Open Access
    Assessing the effects of trampling and bait-collecting on population, morphological and reproductive metrics of a key ecosystem engineer in Langebaan Lagoon
    (2025) Madell, Kezia; Pillay, Deena
    Coastal sedimentary habitats, like Langebaan Lagoon, provide vital ecological and economic services that many human livelihoods rely upon. However, they are vulnerable to multiple human-related disturbances such as intense bait collection and trampling, that compromise ecosystem resilience and functionality. Research on how human disturbance impacts keystone species, such as the endobenthic sandprawn Kraussilichirus kraussi, an important ecosystem engineer, has proven to be valuable and effective in monitoring ecosystem health and improving ecosystem management. Knowledge of how human disturbance impacts these sandprawns is however, limited as it is primarily focused on population-level metrics such as abundance and morphology. Therefore, this study aimed to advance our understanding of how human disturbance impacts sandprawn populations, their reproduction, and the potential implications for the essential services they provide, across a spatial putative human disturbance gradient in Zone A, Langebaan Lagoon. Moreover, I aim to determine whether the reproductive responses of sandprawns can serve as novel, ecological indicators of benthic stress in intertidal sedimentary systems. The results demonstrate that sandprawn reproductive responses effectively indicate ecological stress. Increased human numbers correlate with increased sediment compaction and reduced dissolved oxygen concentrations. As an indirect result of these changes, there were significantly high percentages of sandprawn embryos which displayed abnormalities and arrested development in these sites with increased human numbers. However, at a sandprawn population-level, increased human numbers had no significant difference in sandprawn catch per unit effort and sandprawns had better body conditions at these sites. These findings suggest resource trade-offs as a response to low sediment oxygen, in which sandprawns in highly disturbed sites shift resources from reproduction to prioritise self-maintenance and survival. Recent literature has shown a growing interest in using keystone sandprawns as ecological stress indicators and this study further expands on this idea by linking human recreational disturbance to their reproductive biology of sandprawns. Adverse effects on sandprawn reproductive outputs are a cause of great concern, as chronic legacy effects of recreational disturbance may lead to population-level consequences, and thus compromise the vital ecological functions that these crustaceans provide. These effects are likely further exacerbated in intertidal systems with high frequencies of human disturbance and lack of management/regulation of human numbers. Overall, further research which links human disturbance to sandprawn reproduction in other coastal ecosystems is crucial to improving our understanding of this phenomenon and our future management of these systems.
  • Thumbnail Image
    Item
    Open Access
    Ecology and ecophysiology of Zostera capensis: responses and acclimation to temperature
    (2020) Lawrence, Cloverley Mercia; Pillay, Deena; Jarre, Astrid; Bolton, John
    This study aimed to understand the ecology of the threatened, habitat-forming seagrass, Zostera capensis in Langebaan Lagoon, a marine protected area that forms part of the West Coast national park, South Africa; and the physiological strategies that allow this habitat to persist in sub- and supra-optimal temperatures. First, the environmental drivers responsible for spatial and temporal variability in Zostera and its associated macro-epifauna were determined. Secondly, the effects of temperature and the role of algal grazing in maintaining seagrass performance under temperature stress were investigated. Seasonal field collections of seagrasses and their associated macro-epifauna were undertaken, along with regular measurements of key environmental variables. Thereafter, mesocosm experiments were performed to measure the responses of Zostera to thermal stress and grazing using morphometry, fluorometry, chromatography and biochemistry. Significant seasonal variability in seagrass distributions with severe diebacks in summer were found, which influenced associated macro-epifauna communities. Populations responded to environmental stress by changing their growth form producing small-leaves in high densities in the high intertidal, while those in low intertidal and subtidal areas produced sparse, large-leaved populations. These distinct populations supported unique faunal diversities, which were dominated by grazing invertebrates. Temperature was a consistent driver of seagrass density and leaf size, while turbidity and exposure were key environmental factors that influenced macro-epifaunal patterns. Macro-epifaunal abundances were highly positively correlated with seagrass leaf width and biomass. Different growth forms displayed different responses to thermal stress, including a higher photosynthetic rate, and accumulations of carbon and nitrogen as phenolic compounds, in small- compared to large-leaved plants. This implies that large-leaved populations are more vulnerable to stress from fouling, which was evident in their larger epiphyte loads, compared to small-leaved populations. In addition, grazers were ineffectual at regulating epiphyte growth which increased under warming conditions. These findings suggest differences in resilience between sub-populations of Zostera, and attest to their capacity to recover from environmental stress. They further emphasise the significance of identifying characteristics and acclimation strategies that allow habitats to persist under climate change, and thus sustain biodiversity and productivity, as well as continue to provide important ecosystem services.