Evaluation of the mesozooplankton functional diversity indices in Algoa Bay as proxies to assess the stability of the food chain leading to the African penguin (Spheniscus demersus)
- Authors: Rukuni, Praxedes Vimbai
- Date: 2022-12
- Subjects: Marine zooplankton --South Africa -- Algoa bay , Penguins -- South Africa -- Conservation , Fishes -- Predators of -- South Africa -- Algoa Bay
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/59956 , vital:62698
- Description: Current unprecedented environmental changes threaten food web and ecosystem stability, which is particularly concerning in areas with vulnerable species such as the endangered African penguin Spheniscus demersus. In this study I adopted a holistic approach integrating many ecosystem levels to better understand African penguin behavioural ecology and food web stability. I investigated interplay between physico-chemical parameters and zooplankton functional diversity at various temporal and spatial scales in Algoa Bay. The study further investigated the applicability of zooplankton functional diversity (FD) in inferring African penguin food web stability by comparing the FD of zooplankton found in anchovies regurgitated from African penguins and the ones found in the Bay PELTER Stations. Gut contents of anchovies regurgitated from Bird Island and St Croix penguins were also evaluated using Frequency of Occurrence and Dominance methods and compared between colonies. Zooplankton FD in Algoa Bay varied over time but not at spatial scales with chlorophyll-a, Sea Surface Temperature (SST), turbidity and salinity being potential drivers of zooplankton FD. Chlorophyll-a and salinity were positively correlated with FD, meanwhile FD was inversely correlated to turbidity and SST. The study also observed minor differences in the physico-chemical parameters associated with African penguin foraging grounds, though different dietary preferences were found between the anchovies regurgitated from penguins from the two colonies. Anchovies regurgitated by penguins from Bird Island targeted large sized groups such as Decapods, meanwhile anchovies from the St Croix penguin colony targeted small sized Ostracods and Cirripedia. This study therefore, provides insight on the influence of fluctuations in physico-chemical parameters in shaping zooplankton communities in Algoa Bay. The study also emphasises anchovy dietary plasticity, switching from selective feeding to opportunistic feeding in instances of prey shortages which contributes to a stable African penguin food web in the face of climate change. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
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- Date Issued: 2022-12
Anchovy and Sardine in Algoa Bay and their relationship with response variables in two threatened avian predators
- Authors: Potter, Cara-Paige
- Date: 2013
- Subjects: Fishes -- Predators of -- South Africa -- Algoa Bay , Anchovies -- South Africa , Sardines -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10730 , http://hdl.handle.net/10948/d1021130
- Description: Huge populations of sardine and anchovy exist in the four major upwelling systems around the world. These fish are both important ecologically and economically. Pelagic fish dominate the mid trophic level and can exert both a top-down control of zooplankton and a bottom-up control on predatory fish and marine top predators. They also make up a substantial contribution of the world catches in seas around the world where they co-exist in upwelling areas. The fluctuations of sardine and anchovy are largely influenced by recruitment from the larval stage and by the physical environmental forces that determine the planktonic compositions upon which they feed. In southern Africa, the biology and behaviour of two threatened seabird species, African penguins (Spheniscus demersus) and Cape gannets (Morus capensis), are directly influenced by the availability of sardine (Sardinops sagax) and anchovy (Engraulis encrasicolus). This study aimed to provide further insight into the fluctuations of sardine and anchovy in relation to the variability of environmental factors such as wind, sea surface temperature, rainfall and plankton abundance, focusing specifically on Algoa Bay in the Eastern Cape, South Africa. Algoa Bay is particularly important as it is home to the world’s largest African penguin colony and the world’s largest gannetry. Therefore, to further investigate the populations of these two seabird species, the fluctuations of their food source were studied.
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- Date Issued: 2013