Understanding resource partitioning in three species of Gobiidae living in the warm-temperate Sundays Estuary
- Authors: Ndaleni, Phumza Malibongwe
- Date: 2022-10-14
- Subjects: Gobiidae South Africa Sundays Estuary (Eastern Cape) , Gobiidae Reproduction , Gobiidae Food , Gobiidae Geographical distribution , Gobiidae Morphology , Resource partitioning (Ecology)
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365655 , vital:65773 , DOI https://doi.org/10.21504/10962/365655
- Description: Estuaries represent a transition zone where saline water combines with freshwater, and this results in temporal and spatial variability in both biotic and abiotic parameters. Because the environmental gradient changes so rapidly in areas and the estuarine environment is harsh, fish need to either be able to specialise to one particular suite of abiotic contexts or have the physiological mechanisms to allow them to move throughout the gradient of the estuary. Apart from this, other factors such as climate change, habitat degradation, over exploitation of resources and the introduction of alien species also negatively influence fish species living in estuaries. These anthropogenic stressors can cause species exclusion in areas which were previously suitable for species with particular suites of traits. Measuring resource partitioning within functional groups not only helps in determining the functional structure of communities but also explains how organisms use resources in a community. Resource partitioning studies provide a useful conceptual framework to understand species interactions in a community and identify major resource dimensions along which species segregate. This study aimed to describe resource partitioning among the Gobiidae species, as the family is well represented in South African estuaries (24 species), is highly abundant and has several species which co-exist in individual estuaries. To accomplish this, different forms of resource partitioning that promote the coexistence of the three most abundant species found in warm-temperate South African estuaries; the Knysna sand goby Psammogobius knysnaensis (Smith, 1935), Prison goby Caffrogobius gilchristi (Boulenger, 1898) and River goby Glossogobius callidus (Smith, 1937) were investigated in the Sundays Estuary. This was accomplished by determining the reproductive biology, interspecific differences in feeding morphology, feeding ecology and habitat partitioning among the three species. The distribution and abundance of potential prey in the estuary (mesozooplankton and macrozoobenthic communities) were investigated, with both mesozooplankton and macrozoobenthic communities grouping into three distinct communities along the environmental gradient. Feeding morphological traits responsible for prey location, chasing, capture, mastication, ingestion and digestion were investigated. Little morphological overlap was observed between P. knysnaensis and C. gilchristi, indicating little dietary overlap between these two species. In contrast, the feeding morphology of Glossogobius callidus overlapped with both P. knysnaensis and C. gilchristi, indicating the potential to compete with both species for food. The trophic ecology of the three species was investigated using stomach content analysis, whereby prey abundance, frequency of occurrence and percentage of volume were determined. For P. knysnaensis, the incorporation of cyclopoids and ostracods decreased with fish size and that of bivalves and amphipods increased. Caffrogobius gilchristi was found to be a specialist feeder on cyclopoids but as the species increased in size the incorporation of amphipods, mysids, brachyurans and gastropods increased. Glossogobius callidus was found to be a generalist feeder, feeding on cyclopoids, amphipods and chironomids. The incorporation of cyclopoids decreased with fish size and the consumption of large sized amphipods and chironomids increased with fish size. To assess their reproductive biology, gonadosomatic index (GSI) was used to study the breeding season. In all three species, reproduction peaked in spring and summer, and this is associated with peak phytoplankton and zooplankton biomass in estuaries. Length at 50% maturity and fecundity were also determined. The three species predominated in different locations in the estuary, which explains why they were able to use similar resources and reproduce at the same time. Psammogobius knysnaensis was abundant in the sandy mouth region, with sediment type and prey (bivalves and mysids) availability affecting its distribution. Caffrogobius gilchristi was abundant in the muddy lower reaches of the estuary, with its distribution influenced by sediment composition and temperature. Glossogobius callidus was abundant in the turbid upper reaches, with its distribution influenced by prey (amphipods) availability and turbidity. Different habitat preferences and diet among the specific size ranges enabled coexistence among the species. This explains the high abundances and coexistence of gobies in South African estuaries. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Ndaleni, Phumza Malibongwe
- Date: 2022-10-14
- Subjects: Gobiidae South Africa Sundays Estuary (Eastern Cape) , Gobiidae Reproduction , Gobiidae Food , Gobiidae Geographical distribution , Gobiidae Morphology , Resource partitioning (Ecology)
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365655 , vital:65773 , DOI https://doi.org/10.21504/10962/365655
- Description: Estuaries represent a transition zone where saline water combines with freshwater, and this results in temporal and spatial variability in both biotic and abiotic parameters. Because the environmental gradient changes so rapidly in areas and the estuarine environment is harsh, fish need to either be able to specialise to one particular suite of abiotic contexts or have the physiological mechanisms to allow them to move throughout the gradient of the estuary. Apart from this, other factors such as climate change, habitat degradation, over exploitation of resources and the introduction of alien species also negatively influence fish species living in estuaries. These anthropogenic stressors can cause species exclusion in areas which were previously suitable for species with particular suites of traits. Measuring resource partitioning within functional groups not only helps in determining the functional structure of communities but also explains how organisms use resources in a community. Resource partitioning studies provide a useful conceptual framework to understand species interactions in a community and identify major resource dimensions along which species segregate. This study aimed to describe resource partitioning among the Gobiidae species, as the family is well represented in South African estuaries (24 species), is highly abundant and has several species which co-exist in individual estuaries. To accomplish this, different forms of resource partitioning that promote the coexistence of the three most abundant species found in warm-temperate South African estuaries; the Knysna sand goby Psammogobius knysnaensis (Smith, 1935), Prison goby Caffrogobius gilchristi (Boulenger, 1898) and River goby Glossogobius callidus (Smith, 1937) were investigated in the Sundays Estuary. This was accomplished by determining the reproductive biology, interspecific differences in feeding morphology, feeding ecology and habitat partitioning among the three species. The distribution and abundance of potential prey in the estuary (mesozooplankton and macrozoobenthic communities) were investigated, with both mesozooplankton and macrozoobenthic communities grouping into three distinct communities along the environmental gradient. Feeding morphological traits responsible for prey location, chasing, capture, mastication, ingestion and digestion were investigated. Little morphological overlap was observed between P. knysnaensis and C. gilchristi, indicating little dietary overlap between these two species. In contrast, the feeding morphology of Glossogobius callidus overlapped with both P. knysnaensis and C. gilchristi, indicating the potential to compete with both species for food. The trophic ecology of the three species was investigated using stomach content analysis, whereby prey abundance, frequency of occurrence and percentage of volume were determined. For P. knysnaensis, the incorporation of cyclopoids and ostracods decreased with fish size and that of bivalves and amphipods increased. Caffrogobius gilchristi was found to be a specialist feeder on cyclopoids but as the species increased in size the incorporation of amphipods, mysids, brachyurans and gastropods increased. Glossogobius callidus was found to be a generalist feeder, feeding on cyclopoids, amphipods and chironomids. The incorporation of cyclopoids decreased with fish size and the consumption of large sized amphipods and chironomids increased with fish size. To assess their reproductive biology, gonadosomatic index (GSI) was used to study the breeding season. In all three species, reproduction peaked in spring and summer, and this is associated with peak phytoplankton and zooplankton biomass in estuaries. Length at 50% maturity and fecundity were also determined. The three species predominated in different locations in the estuary, which explains why they were able to use similar resources and reproduce at the same time. Psammogobius knysnaensis was abundant in the sandy mouth region, with sediment type and prey (bivalves and mysids) availability affecting its distribution. Caffrogobius gilchristi was abundant in the muddy lower reaches of the estuary, with its distribution influenced by sediment composition and temperature. Glossogobius callidus was abundant in the turbid upper reaches, with its distribution influenced by prey (amphipods) availability and turbidity. Different habitat preferences and diet among the specific size ranges enabled coexistence among the species. This explains the high abundances and coexistence of gobies in South African estuaries. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-10-14
Invasion status and potential impacts of bluegill Lepomis macrochirus Rafinesque, 1819 in the Kariega River, Eastern Cape, South Africa
- Authors: Ndaleni, Phumza Malibongwe
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7586 , vital:21276
- Description: The impact of alien invasive species is one of the greatest threats to biodiversity globally. All of the major drainages of South Africa are invaded by non-native fishes, yet little information is available on their impact. This thesis focusses on providing a better understanding of the potential impacts of bluegill Lepomis macrochirus Rafinesque, 1819, a species introduced into South Africa from the USA in 1938. The study assesses the distribution, establishment success and feeding ecology of L. macrochirus in an invaded South African River system in order to better understand and document its potential impacts. Specifically; this thesis (1) assesses the distribution and relative abundance of L. macrochirus in the Kariega System of the Eastern Cape, (2) determines the diet of the species in one of the major impoundments of the system, and (3) uses an experimental comparative functional response approach to assess whether this species has heightened predatory capabilities when compared with fishes with which it cooccurs. Ninety-six sites in the Kariega River system were sampled from the headwaters down to the estuary. Small native fish species (Enteromius anoplus and Enteromius pallidus) occurred mostly in the upper reaches, while in the middle and lower reaches, the centrarchid alien largemouth bass Micropterus salmoides and bluegill L. mocrochirus dominated. There was overlap between the centrarchids and introduced banded tilapia Tilapia sparrmanii and southern mouthbrooder Pseudocrenilabrus philander, but never with small-bodied native species. The stomach contents of L. macrochirus were examined during winter and summer and prey were identified to family level. Crustaceans and insects were an important component in their diet, but in summer fish eggs were common. Comparisons of bluegill diet with published literature indicated that there was potential for competition with largemouth bass, banded tilapia and southern mouthbrooder. Feeding experiments were conducted to compare the functional responses of these four species using a common prey item. Banded tilapia had significantly lower attack rates than the other species with no significant difference observed in other species. Bluegill has a similar impact to that of banded tilapia and southern mouthbrooder, but lower than that of largemouth bass. Results of the present study highlight that L. macrochirus introduced into dams will likely result in both upstream and downstream invasion of river systems. It is likely that this species does not, however, have as much of a predatory impact as M. salmoides in that its predatory capacity is relatively reduced and more comparable to South African native cichlids. These results are discussed within the context of invasion success/failure in other regions of southern Africa.
- Full Text:
- Date Issued: 2017
- Authors: Ndaleni, Phumza Malibongwe
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7586 , vital:21276
- Description: The impact of alien invasive species is one of the greatest threats to biodiversity globally. All of the major drainages of South Africa are invaded by non-native fishes, yet little information is available on their impact. This thesis focusses on providing a better understanding of the potential impacts of bluegill Lepomis macrochirus Rafinesque, 1819, a species introduced into South Africa from the USA in 1938. The study assesses the distribution, establishment success and feeding ecology of L. macrochirus in an invaded South African River system in order to better understand and document its potential impacts. Specifically; this thesis (1) assesses the distribution and relative abundance of L. macrochirus in the Kariega System of the Eastern Cape, (2) determines the diet of the species in one of the major impoundments of the system, and (3) uses an experimental comparative functional response approach to assess whether this species has heightened predatory capabilities when compared with fishes with which it cooccurs. Ninety-six sites in the Kariega River system were sampled from the headwaters down to the estuary. Small native fish species (Enteromius anoplus and Enteromius pallidus) occurred mostly in the upper reaches, while in the middle and lower reaches, the centrarchid alien largemouth bass Micropterus salmoides and bluegill L. mocrochirus dominated. There was overlap between the centrarchids and introduced banded tilapia Tilapia sparrmanii and southern mouthbrooder Pseudocrenilabrus philander, but never with small-bodied native species. The stomach contents of L. macrochirus were examined during winter and summer and prey were identified to family level. Crustaceans and insects were an important component in their diet, but in summer fish eggs were common. Comparisons of bluegill diet with published literature indicated that there was potential for competition with largemouth bass, banded tilapia and southern mouthbrooder. Feeding experiments were conducted to compare the functional responses of these four species using a common prey item. Banded tilapia had significantly lower attack rates than the other species with no significant difference observed in other species. Bluegill has a similar impact to that of banded tilapia and southern mouthbrooder, but lower than that of largemouth bass. Results of the present study highlight that L. macrochirus introduced into dams will likely result in both upstream and downstream invasion of river systems. It is likely that this species does not, however, have as much of a predatory impact as M. salmoides in that its predatory capacity is relatively reduced and more comparable to South African native cichlids. These results are discussed within the context of invasion success/failure in other regions of southern Africa.
- Full Text:
- Date Issued: 2017
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