Pub Date : 2023-08-01DOI: 10.2989/1814232x.2023.2242890
BQ Mann, K Cox, GL Jordaan, R Daly
AbstractA tag-recapture study was undertaken on the Natal seacatfish Galeichthys troworum in the Pondoland Marine Protected Area (PMPA) on the east coast of South Africa. A total of 473 fish were tagged over a period of 8 years, and 136 individuals (28.8%) were recaptured over a period of 16 years, some of them on multiple occasions. Most recaptures (82%) were caught within 200 m of their release site, with movements ranging between 0 and 617 m, and time-at-liberty ranging between 0 and 3 407 days (9.3 years). Data analysis showed that all recaptured fish remained in relatively small home ranges (of ∼360 m linear distance) and none of them abandoned their home range and moved out of the 2-km2 sampling blocks. While the no-take area of the PMPA provided effective protection for these fish, their relative abundance was similar in an adjacent exploited area. This is likely because G. troworum is not a desired linefish species, with most individuals caught being released, coupled with high post-release survival.Keywords: exploited areafork lengthhome rangesite fidelitystation-keepingtag and release
{"title":"Movement patterns of Natal seacatfish <i>Galeichthys troworum</i> (Ariidae) tagged in the Pondoland Marine Protected Area, Eastern Cape, South Africa","authors":"BQ Mann, K Cox, GL Jordaan, R Daly","doi":"10.2989/1814232x.2023.2242890","DOIUrl":"https://doi.org/10.2989/1814232x.2023.2242890","url":null,"abstract":"AbstractA tag-recapture study was undertaken on the Natal seacatfish Galeichthys troworum in the Pondoland Marine Protected Area (PMPA) on the east coast of South Africa. A total of 473 fish were tagged over a period of 8 years, and 136 individuals (28.8%) were recaptured over a period of 16 years, some of them on multiple occasions. Most recaptures (82%) were caught within 200 m of their release site, with movements ranging between 0 and 617 m, and time-at-liberty ranging between 0 and 3 407 days (9.3 years). Data analysis showed that all recaptured fish remained in relatively small home ranges (of ∼360 m linear distance) and none of them abandoned their home range and moved out of the 2-km2 sampling blocks. While the no-take area of the PMPA provided effective protection for these fish, their relative abundance was similar in an adjacent exploited area. This is likely because G. troworum is not a desired linefish species, with most individuals caught being released, coupled with high post-release survival.Keywords: exploited areafork lengthhome rangesite fidelitystation-keepingtag and release","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135052471","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-01DOI: 10.2989/1814232x.2023.2246056
A Kunzmann, RM Imam, SJ Geist
Physiological traits of five key fish species (Cape hake Merluccius spp., pelagic goby Sufflogobius bibarbatus, Cape horse mackerel Trachurus capensis, European anchovy Engraulis encrasicolus and sardine Sardinops sagax) from the northern Benguela upwelling system (NBUS) were compared during their larval stage by measurements of enzymatic activities of key metabolic enzymes (citrate synthase [CS] and pyruvate kinase [PK]). Two distinct age classes (early larvae: 8‒14 days old; late larvae: 22‒29 days old) for each species and from two areas were compared: Terrace Bay (20° S), the main spawning ground of Cape horse mackerel and anchovy, and Kunene (17° S), near the Angola–Benguela frontal zone, where warm and hypoxic water masses intrude into the NBUS. The results revealed significantly higher CS activity in both larval age classes in Cape horse mackerel, anchovy and sardine compared with Cape hake and pelagic goby. Pelagic goby and Cape horse mackerel had significantly higher PK activity compared with Cape hake, anchovy and sardine, apparent in both larval age classes and both areas. Results for anaerobic metabolism indicate higher capacity for pelagic goby and Cape horse mackerel to recover from oxygen debt built up in prey capture and predator escape behaviour and a higher potential for hypoxia tolerance when compared with Cape hake, anchovy and sardine. These results suggest higher survival probability for pelagic goby and Cape horse mackerel compared with the other species under conditions of a shoaling oxygen minimum zone and may explain their current dominance in the NBUS.
{"title":"Low hypoxia tolerance in larvae of the sardine <i>Sardinops sagax</i> and anchovy <i>Engraulis encrasicolus</i> may limit their stock recovery in the northern Benguela upwelling system","authors":"A Kunzmann, RM Imam, SJ Geist","doi":"10.2989/1814232x.2023.2246056","DOIUrl":"https://doi.org/10.2989/1814232x.2023.2246056","url":null,"abstract":"Physiological traits of five key fish species (Cape hake Merluccius spp., pelagic goby Sufflogobius bibarbatus, Cape horse mackerel Trachurus capensis, European anchovy Engraulis encrasicolus and sardine Sardinops sagax) from the northern Benguela upwelling system (NBUS) were compared during their larval stage by measurements of enzymatic activities of key metabolic enzymes (citrate synthase [CS] and pyruvate kinase [PK]). Two distinct age classes (early larvae: 8‒14 days old; late larvae: 22‒29 days old) for each species and from two areas were compared: Terrace Bay (20° S), the main spawning ground of Cape horse mackerel and anchovy, and Kunene (17° S), near the Angola–Benguela frontal zone, where warm and hypoxic water masses intrude into the NBUS. The results revealed significantly higher CS activity in both larval age classes in Cape horse mackerel, anchovy and sardine compared with Cape hake and pelagic goby. Pelagic goby and Cape horse mackerel had significantly higher PK activity compared with Cape hake, anchovy and sardine, apparent in both larval age classes and both areas. Results for anaerobic metabolism indicate higher capacity for pelagic goby and Cape horse mackerel to recover from oxygen debt built up in prey capture and predator escape behaviour and a higher potential for hypoxia tolerance when compared with Cape hake, anchovy and sardine. These results suggest higher survival probability for pelagic goby and Cape horse mackerel compared with the other species under conditions of a shoaling oxygen minimum zone and may explain their current dominance in the NBUS.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135054810","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-01DOI: 10.2989/1814232x.2023.2245854
RGA Watson, E Frey, S Hörbst
AbstractThis study aims to describe the distribution of ocean sunfishes (family Molidae) in the greater Dyer Island ecosystem off the southwest coast of South Africa. Between 2014 and 2022, local whale watching vessels operating under Dyer Island Cruises conducted 3 227 trips which resulted in 274 trips with Molidae sightings, with a total of 300 individuals sighted. Molidae sightings showed a significant correlation to sea surface temperature and a strong seasonal pattern. Sightings in the greater Dyer Island area increased significantly after 2016, suggesting a correlation with the decline of white shark Carcharodon carcharias sightings, with further increases in 2021. This suggests that the greater Dyer Island ecosystem has become a more favoured habitat for species of Molidae.Keywords: distributionmarine megafaunaMolaseasonalitysea surface temperature
{"title":"Patterns in sightings of ocean sunfishes (Molidae) in the greater Dyer Island ecosystem, Western Cape, South Africa","authors":"RGA Watson, E Frey, S Hörbst","doi":"10.2989/1814232x.2023.2245854","DOIUrl":"https://doi.org/10.2989/1814232x.2023.2245854","url":null,"abstract":"AbstractThis study aims to describe the distribution of ocean sunfishes (family Molidae) in the greater Dyer Island ecosystem off the southwest coast of South Africa. Between 2014 and 2022, local whale watching vessels operating under Dyer Island Cruises conducted 3 227 trips which resulted in 274 trips with Molidae sightings, with a total of 300 individuals sighted. Molidae sightings showed a significant correlation to sea surface temperature and a strong seasonal pattern. Sightings in the greater Dyer Island area increased significantly after 2016, suggesting a correlation with the decline of white shark Carcharodon carcharias sightings, with further increases in 2021. This suggests that the greater Dyer Island ecosystem has become a more favoured habitat for species of Molidae.Keywords: distributionmarine megafaunaMolaseasonalitysea surface temperature","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135053255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-01DOI: 10.2989/1814232x.2023.2241885
JC Currie, LR Harris, LJ Atkinson, TP Fairweather, KJ Sink
AbstractFine-scale maps of fishing activity are valuable information layers for fisheries management, assessments of biodiversity impacts and marine spatial planning. Our aim was to develop an accurate map of demersal trawling intensity in South Africa and to demonstrate its utility at a national scale. We calculated a swept area ratio, representing demersal trawling effort for the entire study period (2005‒2018) and annually. We then plotted spatial and temporal patterns of trawling activity, identified core fishing areas, and examined spatial overlap between trawling, South Africa’s marine ecosystem types and the national network of marine protected areas. A high proportion of trawling effort (90%) was concentrated in 43% of the area exposed to trawling, with the remaining 10% spread across 57% of the fished areas. The fishery overlaps with 33 of 150 benthic and bentho-pelagic marine ecosystem types. Of those, 11 have more than 50% of their extent, and five have more than 80%, within the trawl ring-fence. Our analyses support a systematic prioritisation of ecosystem types for further management and protection. The new South African trawling-intensity map contributes an improved pressure layer for ecosystem assessments, can help identify priority fishing areas and has application in conservation, marine spatial planning and fisheries management.Keywords: benthic ecosystemseco-certificationfishing activitySouth Africaspatial prioritisationswept area ratiotrawling intensity
{"title":"Mapping fine-scale demersal trawl effort for application in ecosystem assessment and spatial planning","authors":"JC Currie, LR Harris, LJ Atkinson, TP Fairweather, KJ Sink","doi":"10.2989/1814232x.2023.2241885","DOIUrl":"https://doi.org/10.2989/1814232x.2023.2241885","url":null,"abstract":"AbstractFine-scale maps of fishing activity are valuable information layers for fisheries management, assessments of biodiversity impacts and marine spatial planning. Our aim was to develop an accurate map of demersal trawling intensity in South Africa and to demonstrate its utility at a national scale. We calculated a swept area ratio, representing demersal trawling effort for the entire study period (2005‒2018) and annually. We then plotted spatial and temporal patterns of trawling activity, identified core fishing areas, and examined spatial overlap between trawling, South Africa’s marine ecosystem types and the national network of marine protected areas. A high proportion of trawling effort (90%) was concentrated in 43% of the area exposed to trawling, with the remaining 10% spread across 57% of the fished areas. The fishery overlaps with 33 of 150 benthic and bentho-pelagic marine ecosystem types. Of those, 11 have more than 50% of their extent, and five have more than 80%, within the trawl ring-fence. Our analyses support a systematic prioritisation of ecosystem types for further management and protection. The new South African trawling-intensity map contributes an improved pressure layer for ecosystem assessments, can help identify priority fishing areas and has application in conservation, marine spatial planning and fisheries management.Keywords: benthic ecosystemseco-certificationfishing activitySouth Africaspatial prioritisationswept area ratiotrawling intensity","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135051702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-01DOI: 10.2989/1814232x.2023.2239871
CD McQuaid
AbstractUnderstanding the future of Southern Ocean ecosystems requires approaches at micro to macro scales. The Southern Ocean has experienced both top-down and bottom-up perturbations driven by man. The removal of whales and finfish was a top-down disruption, removing enormous levels of biomass of consumers and driving competitive release for other predators. In contrast, climate change is altering physical conditions in complex, interrelated ways likely to change primary-producer community structure, with bottom-up consequences for the efficiency of energy transfer to top predators, and for the biological pump. The physiological effects of increasing ocean temperatures on animal species are likely to be less important than three key physical changes: loss of sea ice, changes to water-column stability, and patterns of water transport; these will affect krill abundances, primary producer community structure, and prey availability to land-breeding predators, respectively. The Southern Ocean is vast and critically influenced by global teleconnections, with different regions already exhibiting different patterns of physical and biological change. Given the strong physical forcing of these ecosystems, many of the initial consequences of climate change will operate through direct physiological effects on the primary producers and indirect effects on the larger organisms. This will disrupt species interactions and drive new ecological relationships.Keywords: advective flowecosystem structurephytoplankton community structuresea icesub-Antarctic islandswater-column stability
{"title":"Understanding the effects of climate change on Southern Ocean ecosystems","authors":"CD McQuaid","doi":"10.2989/1814232x.2023.2239871","DOIUrl":"https://doi.org/10.2989/1814232x.2023.2239871","url":null,"abstract":"AbstractUnderstanding the future of Southern Ocean ecosystems requires approaches at micro to macro scales. The Southern Ocean has experienced both top-down and bottom-up perturbations driven by man. The removal of whales and finfish was a top-down disruption, removing enormous levels of biomass of consumers and driving competitive release for other predators. In contrast, climate change is altering physical conditions in complex, interrelated ways likely to change primary-producer community structure, with bottom-up consequences for the efficiency of energy transfer to top predators, and for the biological pump. The physiological effects of increasing ocean temperatures on animal species are likely to be less important than three key physical changes: loss of sea ice, changes to water-column stability, and patterns of water transport; these will affect krill abundances, primary producer community structure, and prey availability to land-breeding predators, respectively. The Southern Ocean is vast and critically influenced by global teleconnections, with different regions already exhibiting different patterns of physical and biological change. Given the strong physical forcing of these ecosystems, many of the initial consequences of climate change will operate through direct physiological effects on the primary producers and indirect effects on the larger organisms. This will disrupt species interactions and drive new ecological relationships.Keywords: advective flowecosystem structurephytoplankton community structuresea icesub-Antarctic islandswater-column stability","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135004354","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-01DOI: 10.2989/1814232x.2023.2252020
BA Ziko, TS Murray, TF Næsje, JD Filmalter, PD Cowley
AbstractThe spotted grunter Pomadasys commersonnii is an important estuarine-dependent fishery species known to spawn along the east coast (KwaZulu-Natal Province) of South Africa. However, recent evidence suggests that this species also spawns along the southwest coast in the Western Cape Province (WC), which has necessitated the investigation of estuary–sea movements of adult P. commersonnii in the WC, and their link with spawning season and changing environmental conditions. Seasonal gonad maturation of adult P. commersonnii (n = 112) was investigated using histology and the gonadosomatic index. Seven adult P. commersonnii were acoustically tagged and monitored in the Breede Estuary (WC) between November 2016 and March 2020. Tagged individuals spent more time in the estuary (83.5%) than in the adjacent marine environment. Sea trips (n = 90) lasted on average 3.23 (SD 4.55) days (range 1–37 days), with most sea trips (82.6%) having a duration of less than 5 days. The majority of sea trips (>50%) occurred in austral summer, which coincided with the peak spawning season. Increases in estuary water temperatures in summer and river inflow in winter also influenced the presence of tagged fish in the sea. The high degree of residency of P. commersonnii in the Breede Estuary and short sea trips, along with increased frequency of reproductively ripe fish during summer months, supports the conclusion that regional spawning is occurring along the southwest coast. We suggest that management strategies should be put in place to protect the P. commersonnii population along the South African southwest coast, especially during summer, for the recovery of this population.Keywords: environmental variablesmovementsea tripsspawningspotted gruntertaggingWestern Cape
{"title":"Acoustic telemetry reveals the drivers behind estuary–sea connectivity of an important estuarine-dependent fishery species, <i>Pomadasys commersonnii</i> , in the Breede Estuary, South Africa","authors":"BA Ziko, TS Murray, TF Næsje, JD Filmalter, PD Cowley","doi":"10.2989/1814232x.2023.2252020","DOIUrl":"https://doi.org/10.2989/1814232x.2023.2252020","url":null,"abstract":"AbstractThe spotted grunter Pomadasys commersonnii is an important estuarine-dependent fishery species known to spawn along the east coast (KwaZulu-Natal Province) of South Africa. However, recent evidence suggests that this species also spawns along the southwest coast in the Western Cape Province (WC), which has necessitated the investigation of estuary–sea movements of adult P. commersonnii in the WC, and their link with spawning season and changing environmental conditions. Seasonal gonad maturation of adult P. commersonnii (n = 112) was investigated using histology and the gonadosomatic index. Seven adult P. commersonnii were acoustically tagged and monitored in the Breede Estuary (WC) between November 2016 and March 2020. Tagged individuals spent more time in the estuary (83.5%) than in the adjacent marine environment. Sea trips (n = 90) lasted on average 3.23 (SD 4.55) days (range 1–37 days), with most sea trips (82.6%) having a duration of less than 5 days. The majority of sea trips (>50%) occurred in austral summer, which coincided with the peak spawning season. Increases in estuary water temperatures in summer and river inflow in winter also influenced the presence of tagged fish in the sea. The high degree of residency of P. commersonnii in the Breede Estuary and short sea trips, along with increased frequency of reproductively ripe fish during summer months, supports the conclusion that regional spawning is occurring along the southwest coast. We suggest that management strategies should be put in place to protect the P. commersonnii population along the South African southwest coast, especially during summer, for the recovery of this population.Keywords: environmental variablesmovementsea tripsspawningspotted gruntertaggingWestern Cape","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135005602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-24DOI: 10.2989/1814232X.2023.2211118
L. Maritz, C. Attwood, D. Pillay, GM Branch
Diamond mining in southern Namibia creates seawalls that hold the ocean at bay, yet seawater overwashes or seeps through to fill landward excavated areas, forming numerous coastal ponds that reach 380 000 m2. These ponds span ages of 1–40 years, with the oldest ponds lying in the north, and the younger ponds in the central and southern areas. We investigated occupation of these mining ponds by marine fishes. The ponds offer sheltered, warm, nutrient-enriched environments, but become hypersaline after 10–12 years. The ponds contained predominantly west coast steenbras Lithognathus aureti and southern mullet Chelon richardsonii, with smaller numbers of seven other fish species, and all nine species being marine. The ichthyofauna was thus depauperate, but similar to that of periodically closed estuaries in the region. The size composition and gonadal development of both predominant species suggest they may breed in at least the younger ponds. However, in older, hypersaline, northern ponds, L. aureti transitions into an entirely female population via protandry, precluding breeding there. Body condition was low for both species in the northern ponds, and gut fullness greatest in the southern ponds. Growth of both species was faster in the ponds than in the sea, but after initially fast growth, L. aureti reached a plateau, suggesting stunting thereafter. Chelon richardsonii attained larger sizes in the ponds than in the ocean. For 10–12 years before hypersalinity sets in, the ponds constitute suitable habitat for fish. They are not estuaries as they have minimal freshwater input, but they do create conditions corresponding to closed estuaries that are otherwise scarce along this arid coastline. However, for a nursery function to be realised, the marine fish must return to the sea or else the ponds become an ‘ecological trap’.
{"title":"The ecology of coastal wetland ponds created by diamond mining in southern Namibia. 3. Fish","authors":"L. Maritz, C. Attwood, D. Pillay, GM Branch","doi":"10.2989/1814232X.2023.2211118","DOIUrl":"https://doi.org/10.2989/1814232X.2023.2211118","url":null,"abstract":"Diamond mining in southern Namibia creates seawalls that hold the ocean at bay, yet seawater overwashes or seeps through to fill landward excavated areas, forming numerous coastal ponds that reach 380 000 m2. These ponds span ages of 1–40 years, with the oldest ponds lying in the north, and the younger ponds in the central and southern areas. We investigated occupation of these mining ponds by marine fishes. The ponds offer sheltered, warm, nutrient-enriched environments, but become hypersaline after 10–12 years. The ponds contained predominantly west coast steenbras Lithognathus aureti and southern mullet Chelon richardsonii, with smaller numbers of seven other fish species, and all nine species being marine. The ichthyofauna was thus depauperate, but similar to that of periodically closed estuaries in the region. The size composition and gonadal development of both predominant species suggest they may breed in at least the younger ponds. However, in older, hypersaline, northern ponds, L. aureti transitions into an entirely female population via protandry, precluding breeding there. Body condition was low for both species in the northern ponds, and gut fullness greatest in the southern ponds. Growth of both species was faster in the ponds than in the sea, but after initially fast growth, L. aureti reached a plateau, suggesting stunting thereafter. Chelon richardsonii attained larger sizes in the ponds than in the ocean. For 10–12 years before hypersalinity sets in, the ponds constitute suitable habitat for fish. They are not estuaries as they have minimal freshwater input, but they do create conditions corresponding to closed estuaries that are otherwise scarce along this arid coastline. However, for a nursery function to be realised, the marine fish must return to the sea or else the ponds become an ‘ecological trap’.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45385033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-24DOI: 10.2989/1814232X.2023.2214170
MC Manyilizu
East African coastal waters in the tropical western Indian Ocean experience strong seasonality which varies yearly, leading to the establishment of a prominent interannual Indian Ocean Dipole (IOD). This has a significant influence on regional and global socio-economic, climatic and human development. Sea surface temperature (SST) variability in these waters and its association with ocean–atmosphere feedbacks and internal subsurface ocean dynamics in relation to the IOD is the subject of this study. The research used reference simulation accompanied with sensitivity simulations with forcings from higher frequency variabilities against climatological signals of ocean–atmosphere or internal subsurface ocean dynamics from 1980 to 2007. Wind forcing with higher-frequency variabilities was applied in all simulations. Cooling and warming during pure and positive IOD events leading El Niño events in the region is caused by a combination of both surface heat fluxes associated with ocean–atmosphere feedbacks, and internal subsurface ocean dynamics, from July and peaking in August and October, respectively. Such processes also dominate the warming (cooling) in the region during pure El Niño (La Niña) events from July to December (July to October) where the SST patterns extend southwards. The warmest (coolest) SST anomalies during positive (negative) IOD events co-occurring with El Niño (La Niña) events stay longer than other events, being characterised by bimodal peaking in August and December. Such SST patterns are significantly forced with ocean–atmosphere feedbacks that might be associated with Walker circulation driving links between the Indian and Pacific oceans; however, the peaking in August might be enhanced by small ocean dynamics off the Somali coast, probably owing to the existing upwelling systems during these conditions.
{"title":"Sensitivity simulation of sea surface temperature variability in coastal waters off East Africa in relation to the Indian Ocean Dipole","authors":"MC Manyilizu","doi":"10.2989/1814232X.2023.2214170","DOIUrl":"https://doi.org/10.2989/1814232X.2023.2214170","url":null,"abstract":"East African coastal waters in the tropical western Indian Ocean experience strong seasonality which varies yearly, leading to the establishment of a prominent interannual Indian Ocean Dipole (IOD). This has a significant influence on regional and global socio-economic, climatic and human development. Sea surface temperature (SST) variability in these waters and its association with ocean–atmosphere feedbacks and internal subsurface ocean dynamics in relation to the IOD is the subject of this study. The research used reference simulation accompanied with sensitivity simulations with forcings from higher frequency variabilities against climatological signals of ocean–atmosphere or internal subsurface ocean dynamics from 1980 to 2007. Wind forcing with higher-frequency variabilities was applied in all simulations. Cooling and warming during pure and positive IOD events leading El Niño events in the region is caused by a combination of both surface heat fluxes associated with ocean–atmosphere feedbacks, and internal subsurface ocean dynamics, from July and peaking in August and October, respectively. Such processes also dominate the warming (cooling) in the region during pure El Niño (La Niña) events from July to December (July to October) where the SST patterns extend southwards. The warmest (coolest) SST anomalies during positive (negative) IOD events co-occurring with El Niño (La Niña) events stay longer than other events, being characterised by bimodal peaking in August and December. Such SST patterns are significantly forced with ocean–atmosphere feedbacks that might be associated with Walker circulation driving links between the Indian and Pacific oceans; however, the peaking in August might be enhanced by small ocean dynamics off the Somali coast, probably owing to the existing upwelling systems during these conditions.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48096446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-07-21DOI: 10.2989/1814232X.2023.2213728
T. Probyn, M. Pretorius, F. Daya, A. du Randt, A. Busby
This study provides a follow-up to prior measurements of the impact of mussel Mytilus galloprovincialis farming on benthic macrofauna and biogeochemistry and includes the first measurements of the effect of oyster Crassostrea gigas farming in Saldanha Bay, South Africa. The Shannon–Wiener index was significantly lower for farm than for control sites, indicating reduced diversity at farm sites. The lowest values of the Warwick statistic were recorded at the established farm site (R-old). Nested PERMANOVA showed no significant difference in community composition between farm and control sites. Suspension feeders (the mudprawn Upogebia capensis, clam Venerupis corrugata, and holothurian Thyone aurea) dominated at control sites and were important contributors to dissimilarity. Deposit feeders and predatory/scavenging gastropods tended to be more abundant at the farm sites. nMDS ordination showed a clear separation of the more exposed Big Bay stations. The proportions of mud and very coarse sand were moderately associated with community structure. Biogeochemical fluxes showed insignificant differences in sediment oxygen demand between the farm and control sites. Ammonium (NH4) regeneration dominated nitrogen (N) fluxes and was greater at the farm (313 µmol N m−2 h−1) than at the control (187 µmol N m−2 h−1) sites, and maximum rates were restricted to the established mussel raft (R-old) during winter. In contrast, fluxes of oxidised N were less at farm sites relative to the controls. There was no significant difference in phosphate (PO4) regeneration at farm and control stations, leading to higher inorganic N to PO4 regeneration ratios at farm sites.
本研究提供了先前测量贻贝贻贝养殖对底栖大型动物和生物地球化学影响的后续研究，并包括对南非萨尔达尼亚湾牡蛎长牡蛎养殖影响的首次测量。农田的Shannon-Wiener指数显著低于对照，表明农田的多样性降低。沃里克统计的最低值记录在已建立的农场现场(R-old)。巢式PERMANOVA群落组成在农场和对照点之间无显著差异。悬浮食饵(Upogebia capensis、Venerupis walgata和holothurian Thyone aurea)在对照点占主导地位，是造成差异的重要因素。沉积食饵动物和掠食性/食腐性腹足类动物在养殖场更丰富。nMDS排序显示大湾暴露程度较高的监测站明显分开。泥浆和粗砂的比例与群落结构有中等相关性。生物地球化学通量显示，农田与对照地沉积物需氧量差异不显著。铵态氮(NH4)再生主导了氮(N)通量，在养殖场(313µmol N m−2 h−1)大于对照(187µmol N m−2 h−1)，并且在冬季最大速率仅限于已建立的贻贝筏(R-old)。相比之下，与对照相比，农场地点的氧化氮通量较少。磷肥(PO4)再生在场址与对照场址无显著差异，导致场址无机氮与PO4再生比较高。
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Pub Date : 2023-07-06DOI: 10.2989/1814232X.2023.2213724
RA Ojwala
Gender equality is key to achieving the objectives of the United Nation’s Decade of Ocean Science for Sustainable Development. In patriarchal societies, men’s dominance has long overshadowed women’s participation in science-related fields, including ocean science. The lack of gender-disaggregated data in ocean science has made it difficult to establish the extent of gender bias across institutions and at all levels. Providing baseline data can help to address the difficulty of women accessing employment opportunities in managing coastal and marine resources. This study aims to fill the gap in gender data in ocean science in Kenya by presenting a case study on gender ratios of ocean science professionals in Kenyan research institutions. Data on the gender composition of staff were collected from a range of local to international ocean research, conservation and management organisations situated in Kenya. The results show fewer women were represented in government agencies than in nongovernmental organisations (NGOs) and intergovernmental organisations (IGOs). There was also an underrepresentation of women in senior positions, with only two out of nine directors in government agencies being women. The majority of women occupied junior positions. Further research through in-depth interviews will be needed to establish the reasons for the disparities in representation and career advancement.
{"title":"Status of gender equality in ocean research, conservation and management institutions and organisations in Kenya","authors":"RA Ojwala","doi":"10.2989/1814232X.2023.2213724","DOIUrl":"https://doi.org/10.2989/1814232X.2023.2213724","url":null,"abstract":"Gender equality is key to achieving the objectives of the United Nation’s Decade of Ocean Science for Sustainable Development. In patriarchal societies, men’s dominance has long overshadowed women’s participation in science-related fields, including ocean science. The lack of gender-disaggregated data in ocean science has made it difficult to establish the extent of gender bias across institutions and at all levels. Providing baseline data can help to address the difficulty of women accessing employment opportunities in managing coastal and marine resources. This study aims to fill the gap in gender data in ocean science in Kenya by presenting a case study on gender ratios of ocean science professionals in Kenyan research institutions. Data on the gender composition of staff were collected from a range of local to international ocean research, conservation and management organisations situated in Kenya. The results show fewer women were represented in government agencies than in nongovernmental organisations (NGOs) and intergovernmental organisations (IGOs). There was also an underrepresentation of women in senior positions, with only two out of nine directors in government agencies being women. The majority of women occupied junior positions. Further research through in-depth interviews will be needed to establish the reasons for the disparities in representation and career advancement.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43959845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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