The link between behavioural plasticity and aerobic scope phenotypes in predicting the survival of Chrysoblephus laticeps under climate variability
- Authors: Bailey, Lauren Ashleigh
- Date: 2023-03-29
- Subjects: Chrysoblephus laticeps , Phenotypic plasticity , Fishes Climatic factors , Fishes Physiology , Fishes Behavior , Respirometry , Anthropocene , Thermal tolerance (Physiology)
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422606 , vital:71961 , DOI 10.21504/10962/422606
- Description: Thermal variability in the marine environment is likely to have a considerable effect on fishes as it impacts physiological performance and vital (i.e metabolism, foraging and swimming style) and non-vital (i.e. reproductive fitness) energetic processes. When fish are subjected to thermal stress, they may primarily respond by changing their behaviour. Species that have broad phenotypic behavioural plasticity (i.e. defined as the ability to adjust behavioural activity in presiding environmental conditions in order to remain within their optimal thermal range) may have a competitive advantage. Fish behavioural plasticity may take many forms. Some species may seek out thermal refugia by changing their phenology or distribution, while others alter the timing of their seasonal and spawning migrations in response to a changing environment. Although fishes can use behavioural changes to cope with climate change impacts, there does appear to be variability in the behavioural responses within species. However, if alterations in behaviour are insufficient to ensure that the individual remains within their optimal thermal range, physiological acclimation (i.e. defined as the process in which an organism adjusts to prevailing conditions by broadening their thermal performance curve so that their performance is maximized in the new thermal environment) may be required. Therefore, there is a critical link between the behaviour and thermal physiology of fishes, particularly in a world where they are facing increasing thermal stress. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Bailey, Lauren Ashleigh
- Date: 2023-03-29
- Subjects: Chrysoblephus laticeps , Phenotypic plasticity , Fishes Climatic factors , Fishes Physiology , Fishes Behavior , Respirometry , Anthropocene , Thermal tolerance (Physiology)
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422606 , vital:71961 , DOI 10.21504/10962/422606
- Description: Thermal variability in the marine environment is likely to have a considerable effect on fishes as it impacts physiological performance and vital (i.e metabolism, foraging and swimming style) and non-vital (i.e. reproductive fitness) energetic processes. When fish are subjected to thermal stress, they may primarily respond by changing their behaviour. Species that have broad phenotypic behavioural plasticity (i.e. defined as the ability to adjust behavioural activity in presiding environmental conditions in order to remain within their optimal thermal range) may have a competitive advantage. Fish behavioural plasticity may take many forms. Some species may seek out thermal refugia by changing their phenology or distribution, while others alter the timing of their seasonal and spawning migrations in response to a changing environment. Although fishes can use behavioural changes to cope with climate change impacts, there does appear to be variability in the behavioural responses within species. However, if alterations in behaviour are insufficient to ensure that the individual remains within their optimal thermal range, physiological acclimation (i.e. defined as the process in which an organism adjusts to prevailing conditions by broadening their thermal performance curve so that their performance is maximized in the new thermal environment) may be required. Therefore, there is a critical link between the behaviour and thermal physiology of fishes, particularly in a world where they are facing increasing thermal stress. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
The effects of temperature and exploitation on the behaviour of red roman Chrysoblephus laticeps (Sparidae) at baited video stations
- Authors: Mataboge, Bontle Boitumelo
- Date: 2022-04-06
- Subjects: Marine resources conservation South Africa Agulhas , Sparidae Effect of temperature on South Africa Agulhas , Sparidae Climatic factors South Africa Agulhas , Sparidae Effect of fishing on South Africa Agulhas , Sparidae Effect of human beings on South Africa Agulhas , Sparidae Behavior South Africa Agulhas , Overfishing South Africa Agulhas , Underwater videography in wildlife monitoring South Africa Agulhas , Red roman (Chrysoblephus laticeps)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291140 , vital:56823
- Description: Marine environments are experiencing rapidly increasing temperatures, sea levels and acidification and higher frequencies and magnitudes of extreme weather events as a result of climate change. In the Agulhas Ecoregion of South Africa, there has been an increase in the frequency and intensity of upwelling events. Upwelling events result in rapid and large decreases in water temperature which can persist for several days. Variation in water temperature is known to impact the metabolic rate of fish (which are ectotherms) and in turn their activity patterns. To promote fitness related traits, the metabolic rate of fish is maximised at a specific temperature range. Outside of this optimal temperature range, the capacity of fish to perform aerobically declines. Therefore, it is expected that an increase in upwelling may place the fish under significant physiological stress. The effects of climate change can be compounded by the effects of fisheries-induced evolution; the microevolution of a fish population due to the artificial selection of certain biological traits by fishing practices. Passive fishing gears preferentially remove large (older) and bold individuals, causing reductions in population size, genetic diversity and fecundity as well as size and age truncation and the loss of large, bold and dominant phenotypes in fish populations. These demographic changes affect the adaptive capacity of fish and exploited populations are expected to be less resilient to climate variability and long-term temperature change. The resilience of fish is largely dependent on their physiological attributes, particularly their metabolic rate. Theoretically, fish with broader aerobic scope (defined as the difference between an individual’s maximum metabolic rate and standard metabolic rate) will be more tolerant to the impacts of climate change as they have energy available for adaptation. Recent respirometry and accelerometry studies suggest that populations of the endemic southern African linefish Chrysoblephus laticeps (red roman) from inside marine protected areas (MPAs) have higher metabolic rates and broader aerobic scope compared to those found outside of MPAs, particularly at thermal extremes. As C. laticeps are highly resident it is possible that fish populations protected within well-established MPAs may be more resilient to the physiological stresses caused by upwelling if they are able to maintain their activity levels despite changing temperatures. Behaviour is a proxy that can be used to infer metabolism as behaviours have associated metabolic costs and benefits. Behaviour is also a trait that can be altered by passive fishing practices which preferentially extract more active and bold individuals. Given this context, the aim of this thesis was to determine the effects of short-term thermal variability on the population structure and behaviour of C. laticeps and whether these effects differed between protected and exploited populations. Baited remote underwater stereo-video systems (stereo-BRUVs) were used to observe C. laticeps inside two MPAs (Tsitsikamma and Goukamma) and at two exploited sites (Port Elizabeth and Cape St. Francis) over the temperature range 10-18 °C. The relative abundance, size and relevant behaviours of C. laticeps were recorded. The relative abundance (MaxN) of C. laticeps was not significantly higher inside the MPAs compared to the exploited sites. The size of C. laticeps did not vary significantly by protection level either. However, the mean size of C. laticeps was considerably smaller at Port Elizabeth compared to the three other locations. There was a notable absence of large C. laticeps size classes at Port Elizabeth. The effect of water temperature on relative abundance was only seen in the exploited areas, where temperature and abundance were positively correlated. This was not the case in the protected areas where C. laticeps abundance remained roughly consistent. Generally, the effect of temperature on all measured behaviours was consistent across protection levels. An exception was that the feeding rate at Tsitsikamma MPA was significantly higher than at Cape St. Francis at temperatures below 11.5 °C. Temperature had a significant effect on the time taken for the first individual to appear in the field of view. This time shortened with increasing temperature, regardless of protection level. This was likely a result of the metabolic constraints placed on individuals by low waters temperatures and individuals would be able to pursue the bait more readily at higher temperatures. However, there was no evidence of greater metabolic scope from the C. laticeps individuals observed in the MPAs, relative to the exploited areas. Individual size and the presence of conspecifics were also found to significantly influence behaviour. Generally, size had a positive relationship with behaviour, with larger individuals more likely to feed on the bait, chase other fish from the bait (only in the MPAs) and spend more time in the field of view. The higher displays of aggression in MPAs may be an indication of fishing practices having removed bold and dominant individuals at the exploited sites. The probability of fleeing and the feeding rates of individuals increased with increasing numbers of conspecifics, suggesting that C. laticeps behaviour is influenced by intraspecific competition. Overall, this thesis did not find strong evidence that C. laticeps from MPAs performed better than C. laticeps from exploited areas, even at low temperatures. Behavioural responses to temperature were highly variable across locations and this may be attributed to high behavioural phenotypic diversity among individuals. Environmental stressors, such as temperature changes, can illicit very different behavioural responses among individuals in a population. It is also possible that C. laticeps from the exploited areas have the same genetic predispositions to physiological stress as the individuals in the MPAs due to spillover and larval recruitment from the MPAs. Indeed, genetic studies find that all C. laticeps population in South African represent a single well-mixed genetic stock. It is likely that greater sampling effort is required to resolve the patterns in behaviour between exploited and protected populations. Nonetheless, given the influence of size on behaviour, the smaller size of C. laticeps at Port Elizabeth may be cause for concern regarding the vulnerability of future populations to ongoing climate change. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-04-06
- Authors: Mataboge, Bontle Boitumelo
- Date: 2022-04-06
- Subjects: Marine resources conservation South Africa Agulhas , Sparidae Effect of temperature on South Africa Agulhas , Sparidae Climatic factors South Africa Agulhas , Sparidae Effect of fishing on South Africa Agulhas , Sparidae Effect of human beings on South Africa Agulhas , Sparidae Behavior South Africa Agulhas , Overfishing South Africa Agulhas , Underwater videography in wildlife monitoring South Africa Agulhas , Red roman (Chrysoblephus laticeps)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291140 , vital:56823
- Description: Marine environments are experiencing rapidly increasing temperatures, sea levels and acidification and higher frequencies and magnitudes of extreme weather events as a result of climate change. In the Agulhas Ecoregion of South Africa, there has been an increase in the frequency and intensity of upwelling events. Upwelling events result in rapid and large decreases in water temperature which can persist for several days. Variation in water temperature is known to impact the metabolic rate of fish (which are ectotherms) and in turn their activity patterns. To promote fitness related traits, the metabolic rate of fish is maximised at a specific temperature range. Outside of this optimal temperature range, the capacity of fish to perform aerobically declines. Therefore, it is expected that an increase in upwelling may place the fish under significant physiological stress. The effects of climate change can be compounded by the effects of fisheries-induced evolution; the microevolution of a fish population due to the artificial selection of certain biological traits by fishing practices. Passive fishing gears preferentially remove large (older) and bold individuals, causing reductions in population size, genetic diversity and fecundity as well as size and age truncation and the loss of large, bold and dominant phenotypes in fish populations. These demographic changes affect the adaptive capacity of fish and exploited populations are expected to be less resilient to climate variability and long-term temperature change. The resilience of fish is largely dependent on their physiological attributes, particularly their metabolic rate. Theoretically, fish with broader aerobic scope (defined as the difference between an individual’s maximum metabolic rate and standard metabolic rate) will be more tolerant to the impacts of climate change as they have energy available for adaptation. Recent respirometry and accelerometry studies suggest that populations of the endemic southern African linefish Chrysoblephus laticeps (red roman) from inside marine protected areas (MPAs) have higher metabolic rates and broader aerobic scope compared to those found outside of MPAs, particularly at thermal extremes. As C. laticeps are highly resident it is possible that fish populations protected within well-established MPAs may be more resilient to the physiological stresses caused by upwelling if they are able to maintain their activity levels despite changing temperatures. Behaviour is a proxy that can be used to infer metabolism as behaviours have associated metabolic costs and benefits. Behaviour is also a trait that can be altered by passive fishing practices which preferentially extract more active and bold individuals. Given this context, the aim of this thesis was to determine the effects of short-term thermal variability on the population structure and behaviour of C. laticeps and whether these effects differed between protected and exploited populations. Baited remote underwater stereo-video systems (stereo-BRUVs) were used to observe C. laticeps inside two MPAs (Tsitsikamma and Goukamma) and at two exploited sites (Port Elizabeth and Cape St. Francis) over the temperature range 10-18 °C. The relative abundance, size and relevant behaviours of C. laticeps were recorded. The relative abundance (MaxN) of C. laticeps was not significantly higher inside the MPAs compared to the exploited sites. The size of C. laticeps did not vary significantly by protection level either. However, the mean size of C. laticeps was considerably smaller at Port Elizabeth compared to the three other locations. There was a notable absence of large C. laticeps size classes at Port Elizabeth. The effect of water temperature on relative abundance was only seen in the exploited areas, where temperature and abundance were positively correlated. This was not the case in the protected areas where C. laticeps abundance remained roughly consistent. Generally, the effect of temperature on all measured behaviours was consistent across protection levels. An exception was that the feeding rate at Tsitsikamma MPA was significantly higher than at Cape St. Francis at temperatures below 11.5 °C. Temperature had a significant effect on the time taken for the first individual to appear in the field of view. This time shortened with increasing temperature, regardless of protection level. This was likely a result of the metabolic constraints placed on individuals by low waters temperatures and individuals would be able to pursue the bait more readily at higher temperatures. However, there was no evidence of greater metabolic scope from the C. laticeps individuals observed in the MPAs, relative to the exploited areas. Individual size and the presence of conspecifics were also found to significantly influence behaviour. Generally, size had a positive relationship with behaviour, with larger individuals more likely to feed on the bait, chase other fish from the bait (only in the MPAs) and spend more time in the field of view. The higher displays of aggression in MPAs may be an indication of fishing practices having removed bold and dominant individuals at the exploited sites. The probability of fleeing and the feeding rates of individuals increased with increasing numbers of conspecifics, suggesting that C. laticeps behaviour is influenced by intraspecific competition. Overall, this thesis did not find strong evidence that C. laticeps from MPAs performed better than C. laticeps from exploited areas, even at low temperatures. Behavioural responses to temperature were highly variable across locations and this may be attributed to high behavioural phenotypic diversity among individuals. Environmental stressors, such as temperature changes, can illicit very different behavioural responses among individuals in a population. It is also possible that C. laticeps from the exploited areas have the same genetic predispositions to physiological stress as the individuals in the MPAs due to spillover and larval recruitment from the MPAs. Indeed, genetic studies find that all C. laticeps population in South African represent a single well-mixed genetic stock. It is likely that greater sampling effort is required to resolve the patterns in behaviour between exploited and protected populations. Nonetheless, given the influence of size on behaviour, the smaller size of C. laticeps at Port Elizabeth may be cause for concern regarding the vulnerability of future populations to ongoing climate change. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-04-06
Thermal tolerance and the potential effects of climate change on coastal intertidal and estuarine organisms in the Kariega Estuary and adjacent intertitdal coastline, Eastern Cape, South Africa
- Authors: Van der Walt, Kerry-Ann
- Date: 2020
- Subjects: Ectotherms -- Climatic factors , Ectotherms -- Effect of temperature on , Fishes -- Climatic factors , Fishes -- Effect of temperature on , Climatic changes -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/148459 , vital:38741
- Description: Temperature changes due to the effects of climate change are evident on all continents and oceans. As a result, there is a growing concern over how marine ectotherms will respond to extreme or fluctuating environmental temperatures. Temperature changes have strong direct and indirect effects on individual, population, and ecosystem functioning traits. A multi-scale approach determining the thermal tolerance and performance of several marine ectotherms belonging to different coastal habitats is rarely considered in thermal physiology studies but is effective for an integrated ecosystem assessment. As such, for this thesis, I aimed to quantify and compare the thermal tolerance and performance of a range of coastal marine ectotherms (fish and macro-invertebrates) with different biogeographical distributions from estuarine, subtidal and rocky intertidal habitats to available and projected in situ temperature data. This was also undertaken to gauge the local vulnerability of each species across summer and winter in a warm-temperate region of South Africa. This was done using a multi-method physiological approach, which included the dynamic method (CTmax and CTmin), static respirometry and maximum heart rate fHmax). Results of the dynamic method on several fish and macro-invertebrate species indicated that there are differences in thermal tolerance according to taxonomy, biogeography and habitat for both summer and winter. Macro-invertebrate species generally had higher CTmax endpoints, lower CTmin endpoints, higher upper and lower breadths in tolerance, higher upper and lower thermal safety margins and higher thermal scopes than the fish species. This could be a result of the macro-invertebrate species studied being less mobile compared with fish species (which are able to move to more favourable conditions) as well as having broader geographical distributions. In addition, macro-invertebrates from the intertidal rock pool habitat (Palaemon peringueyi; Pernaperna) were more tolerant of high and low temperatures compared with the macro-invertebrates from the estuarine habitat (Clibanarius virescens; Parasesarma catenatum; Upogebia africana). Overall, macro-invertebrates, with the exception of Parechinus angulosus, investigated in this study indicated that current temperatures and projected climate change scenarios across seasons would not have a significant impact on them and that they are highly adaptable to changing temperature regimes. This sign of high tolerance was further supported by the heart rates of P. perna and P. catenatum under an acute increase in temperature (1.0 °C.h-1) which showed individuals of each species physiologically depressing their metabolism until a final Arrhenius breakpoint temperature was reached (TAB). Among the fish species investigated in this study, tropical species (Chaetodon marleyi; Kuhlia mugil) had the highest CTmax and CTmin endpoints when compared with the temperate (Diplodus capensis; Sarpa salpa), warm-water endemic (Chelon dumerili; Rhabdosargus holubi) and cool-water endemic (Chelon richardsonii) fishes. This suggests that due to their lower breadths in tolerance and thermal safety margins being small, tropical species may be less tolerant of cold temperatures and thermal variability, especially in the form of summer upwelling events which are expected to increase in intensity and frequency in this region as a result of anthropogenic climate change effects. On the other hand, however, if a temperature increase of 2.0 - 4.0 °C takes place at the end of the century as predicted by the Intergovernmental Panel on Climate Change (IPCC), it is likely that tropical species such as C. marleyi will become more common. Temperate species such as D. capensis and S. salpa were able to tolerate a wide range of temperatures (wide thermal scope) compared with the other fish species. These findings may suggest that D. capensis and S. salpa are thermally resilient and may be the least vulnerable to climate change effects and temperature variability. When evaluating the different life stages of D. capensis, however, using the dynamic method (juveniles and adults), static respirometry (juveniles) and maximum heart rate (adults), results suggested that juveniles of this temperate species will be more resilient to increases in ocean temperatures compared with the adults because they have a higher thermal tolerance (CTmax/TCRIT) and a greater metabolic scope (TOPT) at higher temperatures. For both juveniles and adults, temperatures beyond 28.0 °C (upper Tpej; Tarr) will have a significant impact on their physiology. Using a multi-scale and multi-method approach thus helped to identify which species or community may be vulnerable to the effects of climate change within shallow coastal environments in this warm-temperate climate change hotspot. Adopting this type of approach will assist policy makers in developing comprehensive climate change management frameworks for coastal ecosystems globally and around South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Van der Walt, Kerry-Ann
- Date: 2020
- Subjects: Ectotherms -- Climatic factors , Ectotherms -- Effect of temperature on , Fishes -- Climatic factors , Fishes -- Effect of temperature on , Climatic changes -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/148459 , vital:38741
- Description: Temperature changes due to the effects of climate change are evident on all continents and oceans. As a result, there is a growing concern over how marine ectotherms will respond to extreme or fluctuating environmental temperatures. Temperature changes have strong direct and indirect effects on individual, population, and ecosystem functioning traits. A multi-scale approach determining the thermal tolerance and performance of several marine ectotherms belonging to different coastal habitats is rarely considered in thermal physiology studies but is effective for an integrated ecosystem assessment. As such, for this thesis, I aimed to quantify and compare the thermal tolerance and performance of a range of coastal marine ectotherms (fish and macro-invertebrates) with different biogeographical distributions from estuarine, subtidal and rocky intertidal habitats to available and projected in situ temperature data. This was also undertaken to gauge the local vulnerability of each species across summer and winter in a warm-temperate region of South Africa. This was done using a multi-method physiological approach, which included the dynamic method (CTmax and CTmin), static respirometry and maximum heart rate fHmax). Results of the dynamic method on several fish and macro-invertebrate species indicated that there are differences in thermal tolerance according to taxonomy, biogeography and habitat for both summer and winter. Macro-invertebrate species generally had higher CTmax endpoints, lower CTmin endpoints, higher upper and lower breadths in tolerance, higher upper and lower thermal safety margins and higher thermal scopes than the fish species. This could be a result of the macro-invertebrate species studied being less mobile compared with fish species (which are able to move to more favourable conditions) as well as having broader geographical distributions. In addition, macro-invertebrates from the intertidal rock pool habitat (Palaemon peringueyi; Pernaperna) were more tolerant of high and low temperatures compared with the macro-invertebrates from the estuarine habitat (Clibanarius virescens; Parasesarma catenatum; Upogebia africana). Overall, macro-invertebrates, with the exception of Parechinus angulosus, investigated in this study indicated that current temperatures and projected climate change scenarios across seasons would not have a significant impact on them and that they are highly adaptable to changing temperature regimes. This sign of high tolerance was further supported by the heart rates of P. perna and P. catenatum under an acute increase in temperature (1.0 °C.h-1) which showed individuals of each species physiologically depressing their metabolism until a final Arrhenius breakpoint temperature was reached (TAB). Among the fish species investigated in this study, tropical species (Chaetodon marleyi; Kuhlia mugil) had the highest CTmax and CTmin endpoints when compared with the temperate (Diplodus capensis; Sarpa salpa), warm-water endemic (Chelon dumerili; Rhabdosargus holubi) and cool-water endemic (Chelon richardsonii) fishes. This suggests that due to their lower breadths in tolerance and thermal safety margins being small, tropical species may be less tolerant of cold temperatures and thermal variability, especially in the form of summer upwelling events which are expected to increase in intensity and frequency in this region as a result of anthropogenic climate change effects. On the other hand, however, if a temperature increase of 2.0 - 4.0 °C takes place at the end of the century as predicted by the Intergovernmental Panel on Climate Change (IPCC), it is likely that tropical species such as C. marleyi will become more common. Temperate species such as D. capensis and S. salpa were able to tolerate a wide range of temperatures (wide thermal scope) compared with the other fish species. These findings may suggest that D. capensis and S. salpa are thermally resilient and may be the least vulnerable to climate change effects and temperature variability. When evaluating the different life stages of D. capensis, however, using the dynamic method (juveniles and adults), static respirometry (juveniles) and maximum heart rate (adults), results suggested that juveniles of this temperate species will be more resilient to increases in ocean temperatures compared with the adults because they have a higher thermal tolerance (CTmax/TCRIT) and a greater metabolic scope (TOPT) at higher temperatures. For both juveniles and adults, temperatures beyond 28.0 °C (upper Tpej; Tarr) will have a significant impact on their physiology. Using a multi-scale and multi-method approach thus helped to identify which species or community may be vulnerable to the effects of climate change within shallow coastal environments in this warm-temperate climate change hotspot. Adopting this type of approach will assist policy makers in developing comprehensive climate change management frameworks for coastal ecosystems globally and around South Africa.
- Full Text:
- Date Issued: 2020
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