Pub Date : 2023-01-02DOI: 10.2989/1814232X.2022.2163288
G. Rautenbach, J. Hermes, I. Halo, T. Morris, J. Veitch
The iSimangaliso Wetland Park, located along the coastline of northern KwaZulu-Natal, hosts South Africa’s only subtropical coral reef system. Episodic upwelling events are observed inshore and at the heads of Diepgat, Leadsman and Leven canyons within the iSimangaliso Wetland Park and may assist in larval dispersal and act as a buffer against coral bleaching. Over a 12-month period (1 June 2018-31 May 2019), two cooling events were identified from surface and subsurface temperature measurements extracted from the Sea Surface Temperature (SST) product of the Operational Sea Surface Temperature and Ice Analysis (OSTIA) satellite and data collected from underwater temperature recorders, respectively. Lagged correlations between subsurface temperatures confirmed that the anomalous cooling events were upwelling events (of 2-7 hours). The approximate upwelling rate was greatest at Diepgat Canyon, which suggests that upwelling events are enhanced by the physical structure of the canyon head and its shallow termination point which may influence the affected ecosystems. Wind measurements from the Mbazwana weather station and satellite sea-level anomalies were used to investigate the respective roles of wind stress and mesoscale ocean variability as driving forces of the upwelling events. The results indicate that the less intense and shorter cooling event was driven by a cyclonic eddy event, but that the stronger cooling event was driven by a combination of both forcing mechanisms.
{"title":"Wind- and eddy-driven upwelling over submarine canyons inshore of the northern Agulhas Current","authors":"G. Rautenbach, J. Hermes, I. Halo, T. Morris, J. Veitch","doi":"10.2989/1814232X.2022.2163288","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2163288","url":null,"abstract":"The iSimangaliso Wetland Park, located along the coastline of northern KwaZulu-Natal, hosts South Africa’s only subtropical coral reef system. Episodic upwelling events are observed inshore and at the heads of Diepgat, Leadsman and Leven canyons within the iSimangaliso Wetland Park and may assist in larval dispersal and act as a buffer against coral bleaching. Over a 12-month period (1 June 2018-31 May 2019), two cooling events were identified from surface and subsurface temperature measurements extracted from the Sea Surface Temperature (SST) product of the Operational Sea Surface Temperature and Ice Analysis (OSTIA) satellite and data collected from underwater temperature recorders, respectively. Lagged correlations between subsurface temperatures confirmed that the anomalous cooling events were upwelling events (of 2-7 hours). The approximate upwelling rate was greatest at Diepgat Canyon, which suggests that upwelling events are enhanced by the physical structure of the canyon head and its shallow termination point which may influence the affected ecosystems. Wind measurements from the Mbazwana weather station and satellite sea-level anomalies were used to investigate the respective roles of wind stress and mesoscale ocean variability as driving forces of the upwelling events. The results indicate that the less intense and shorter cooling event was driven by a cyclonic eddy event, but that the stronger cooling event was driven by a combination of both forcing mechanisms.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"45 1","pages":"1 - 14"},"PeriodicalIF":1.2,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41496259","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 : 2023-01-02DOI: 10.2989/1814232X.2022.2158131
M. Carpenter, C. Griffiths
First-time observations of courtship behaviour of the Endangered shortfin devil ray Mobula kuhlii are described from the Aliwal Shoal Marine Protected Area (MPA), KwaZulu-Natal, South Africa. Three events of M. kuhlii courtship, called ‘mating trains’, were recorded on video during the months of November 2020 and January 2021. These included a near-term pregnant female, and two lead females followed by up to four males. The common behaviours associated with courtship were documented: multiple males following a single female, rapid speed bursts, avoidance of the female, and swerving. This study confirms that M. kuhlii mating occurs in KwaZulu-Natal waters and that courtship is similar across mobulids. The findings demonstrate the importance of the habitat provided by the Aliwal Shoal MPA for this currently unprotected species.
在南非夸祖鲁-纳塔尔省阿利瓦尔浅滩海洋保护区(MPA)，首次观察到濒临灭绝的短鳍devil ray Mobula kuhlii的求爱行为。在2020年11月和2021年1月期间，用视频记录了三次被称为“交配列车”的M. kuhlii求爱事件。其中包括一只近期怀孕的雌性，以及两只领头的雌性，后面跟着多达四只雄性。与求偶有关的常见行为被记录下来:多只雄性跟随一只雌性，快速爆发，避开雌性，以及突然转向。这项研究证实，M. kuhlii交配发生在夸祖鲁-纳塔尔省水域，而且各种流动动物的求爱方式相似。这一发现证明了阿利瓦尔浅滩海洋保护区为这种目前未受保护的物种提供的栖息地的重要性。
{"title":"‘Flash Mobula’: first observations of courtship behaviour of the shortfin devil ray Mobula kuhlii","authors":"M. Carpenter, C. Griffiths","doi":"10.2989/1814232X.2022.2158131","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2158131","url":null,"abstract":"First-time observations of courtship behaviour of the Endangered shortfin devil ray Mobula kuhlii are described from the Aliwal Shoal Marine Protected Area (MPA), KwaZulu-Natal, South Africa. Three events of M. kuhlii courtship, called ‘mating trains’, were recorded on video during the months of November 2020 and January 2021. These included a near-term pregnant female, and two lead females followed by up to four males. The common behaviours associated with courtship were documented: multiple males following a single female, rapid speed bursts, avoidance of the female, and swerving. This study confirms that M. kuhlii mating occurs in KwaZulu-Natal waters and that courtship is similar across mobulids. The findings demonstrate the importance of the habitat provided by the Aliwal Shoal MPA for this currently unprotected species.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"45 1","pages":"51 - 56"},"PeriodicalIF":1.2,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43666980","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 : 2023-01-02DOI: 10.2989/1814232X.2023.2172455
A. Brandão, A. Ross-Gillespie, E. Vermeulen, D. Butterworth
Photo-identification data for southern right whale cow–calf pairs on the South African calving grounds provide one of the longest abundance time-series for any whale population worldwide. Following a very steady increase from a heavily depleted state, surveys since 2015 reflect many notably low counts. These data are analysed to investigate whether these low counts can be explained by changes in reproduction-related parameters. This necessitates a modification to an earlier reproduction model for these whales, fit to photo-identification data to allow for early abortions; hence, a whale pregnant one year can again be pregnant the next. This can account for an increase in calving intervals in a way that differs from a whale resting for another year or an increase in late-abortion probability. This modification was able to account for the low number of sightings of cow–calf pairs over the 2015 to 2020 period (excepting for 2018), though the estimated probability of sighting a cow–calf pair in 2018 is somewhat low given a nearly unchanged annual survey effort. Hence, low numbers of sightings of females with calves for five of the years from 2015 to 2020 can be explained by changes in reproduction-related parameters rather than an increased natural mortality which is inconsistent with the photo-identification data. Changing environmental (particularly feeding) conditions seems to be the likely cause, possibly associated with a changed distribution of these whales. The estimated number of all whales in the population in 2020 is 6 470 (SE 285), with the number of parous females estimated to have increased 15-fold over the last four decades.
{"title":"A photo-identification-based assessment model of southern right whales Eubalaena australis surveyed in South African waters, with a focus on recent low counts of mothers with calves","authors":"A. Brandão, A. Ross-Gillespie, E. Vermeulen, D. Butterworth","doi":"10.2989/1814232X.2023.2172455","DOIUrl":"https://doi.org/10.2989/1814232X.2023.2172455","url":null,"abstract":"Photo-identification data for southern right whale cow–calf pairs on the South African calving grounds provide one of the longest abundance time-series for any whale population worldwide. Following a very steady increase from a heavily depleted state, surveys since 2015 reflect many notably low counts. These data are analysed to investigate whether these low counts can be explained by changes in reproduction-related parameters. This necessitates a modification to an earlier reproduction model for these whales, fit to photo-identification data to allow for early abortions; hence, a whale pregnant one year can again be pregnant the next. This can account for an increase in calving intervals in a way that differs from a whale resting for another year or an increase in late-abortion probability. This modification was able to account for the low number of sightings of cow–calf pairs over the 2015 to 2020 period (excepting for 2018), though the estimated probability of sighting a cow–calf pair in 2018 is somewhat low given a nearly unchanged annual survey effort. Hence, low numbers of sightings of females with calves for five of the years from 2015 to 2020 can be explained by changes in reproduction-related parameters rather than an increased natural mortality which is inconsistent with the photo-identification data. Changing environmental (particularly feeding) conditions seems to be the likely cause, possibly associated with a changed distribution of these whales. The estimated number of all whales in the population in 2020 is 6 470 (SE 285), with the number of parous females estimated to have increased 15-fold over the last four decades.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"45 1","pages":"15 - 27"},"PeriodicalIF":1.2,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44342440","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 : 2023-01-02DOI: 10.2989/1814232X.2023.2193591
C. Wilkinson, E. Seyboth, J. Olbers, E. Vermeulen, R. Kramer, K. Findlay
Shore-based surveys of humpback whales Megaptera novaeangliae were performed from Cape Vidal, on the east coast of South Africa (iSimangaliso Marine Protected Area, Indian Ocean), from two independent platforms between 27 June and 7 August in 2018 and 2019, to estimate the relative abundance and growth rate of the C1 breeding substock of the species. Observed whale groups were tracked by analogue survey theodolites, and observed numbers were adjusted to account for daily sighting effort and the proportions of groups missed by observers. Daily sighting frequency was aggregated across the season to result in annual relative abundance estimates of 10 499 (2018) and 11 009 (2019) individuals, with peak frequencies from 28 July to 3 August in both years. When compared with previous estimates from the same study area, we estimated an average annual increase rate of 7.4% to 8.8% over 31 years from 1988. These results indicate a slowing of the rate of increase from previous estimates, which could suggest that the population is approaching pre-exploitation numbers or that yet unidentified threats are negatively impacting the growth rate. Continued monitoring of the recovering humpback whale stocks is critical to identify any possible effects of Southern Ocean ecosystem changes on the stock health of these whales.
{"title":"Estimating population changes in humpback whales Megaptera novaeangliae migrating past Cape Vidal, South Africa","authors":"C. Wilkinson, E. Seyboth, J. Olbers, E. Vermeulen, R. Kramer, K. Findlay","doi":"10.2989/1814232X.2023.2193591","DOIUrl":"https://doi.org/10.2989/1814232X.2023.2193591","url":null,"abstract":"Shore-based surveys of humpback whales Megaptera novaeangliae were performed from Cape Vidal, on the east coast of South Africa (iSimangaliso Marine Protected Area, Indian Ocean), from two independent platforms between 27 June and 7 August in 2018 and 2019, to estimate the relative abundance and growth rate of the C1 breeding substock of the species. Observed whale groups were tracked by analogue survey theodolites, and observed numbers were adjusted to account for daily sighting effort and the proportions of groups missed by observers. Daily sighting frequency was aggregated across the season to result in annual relative abundance estimates of 10 499 (2018) and 11 009 (2019) individuals, with peak frequencies from 28 July to 3 August in both years. When compared with previous estimates from the same study area, we estimated an average annual increase rate of 7.4% to 8.8% over 31 years from 1988. These results indicate a slowing of the rate of increase from previous estimates, which could suggest that the population is approaching pre-exploitation numbers or that yet unidentified threats are negatively impacting the growth rate. Continued monitoring of the recovering humpback whale stocks is critical to identify any possible effects of Southern Ocean ecosystem changes on the stock health of these whales.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"45 1","pages":"39 - 50"},"PeriodicalIF":1.2,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45209413","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 : 2023-01-02DOI: 10.2989/1814232X.2023.2185680
J. Grobler, Z. Zhao, JW Jones, A. Kotze
The Magellan mussel Aulacomya atra is a bivalve mollusc found along parts of the South African and Namibian coastline. Its numbers were low historically compared with other indigenous species but have decreased further since the 1970s owing to habitat invasion by Mediterranean mussels Mytilus galloprovincialis. We studied sequences of the mitochondrial cytochrome oxidase subunit 1 (CO1) and the nuclear internal transcribed spacer (ITS1) of A. atra to determine patterns of differentiation among three localities on the South African coastline and the phylogenetic position of these populations relative to other populations of Aulacomya species in the Southern Hemisphere. Results from both mitochondrial and nuclear genes revealed a high level of diversity within South African populations from the west and south coast, with little to no geographic differentiation among these populations. Phylogenetic trees constructed using maximum likelihood and haplotype network analysis show that individuals from all three regions sampled are intermingled in groups with low bootstrap support. Our CO1 sequences exhibited a phylogeographic structure concordant with the spatial distribution in South Africa, Argentina, Chile and New Zealand. However, results for ITS1 showed a lack of differentiation over a large spatial scale stretching from South Africa to New Zealand. Future studies should include additional samples from across the species’ distributional range and the examination expanded to include genetic markers with adaptive significance.
{"title":"Magellan mussels Aulacomya atra from the South African coast show high diversity within populations but a lack of geographic differentiation","authors":"J. Grobler, Z. Zhao, JW Jones, A. Kotze","doi":"10.2989/1814232X.2023.2185680","DOIUrl":"https://doi.org/10.2989/1814232X.2023.2185680","url":null,"abstract":"The Magellan mussel Aulacomya atra is a bivalve mollusc found along parts of the South African and Namibian coastline. Its numbers were low historically compared with other indigenous species but have decreased further since the 1970s owing to habitat invasion by Mediterranean mussels Mytilus galloprovincialis. We studied sequences of the mitochondrial cytochrome oxidase subunit 1 (CO1) and the nuclear internal transcribed spacer (ITS1) of A. atra to determine patterns of differentiation among three localities on the South African coastline and the phylogenetic position of these populations relative to other populations of Aulacomya species in the Southern Hemisphere. Results from both mitochondrial and nuclear genes revealed a high level of diversity within South African populations from the west and south coast, with little to no geographic differentiation among these populations. Phylogenetic trees constructed using maximum likelihood and haplotype network analysis show that individuals from all three regions sampled are intermingled in groups with low bootstrap support. Our CO1 sequences exhibited a phylogeographic structure concordant with the spatial distribution in South Africa, Argentina, Chile and New Zealand. However, results for ITS1 showed a lack of differentiation over a large spatial scale stretching from South Africa to New Zealand. Future studies should include additional samples from across the species’ distributional range and the examination expanded to include genetic markers with adaptive significance.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"45 1","pages":"29 - 37"},"PeriodicalIF":1.2,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48621201","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 : 2023-01-02DOI: 10.2989/1814232X.2023.2171126
H. Beckett, O. Hansen, S. von der Heyden, GF Midgley
The African penguin Spheniscus demersus, endemic to the coast of southern Africa, has suffered anthropogenic-driven population declines since 1900 and is now listed as Endangered on the IUCN Red List. Conservation efforts currently underway are informed by the species’ adaptive response with respect to colonisation capacity and breeding success, vulnerability because of anthropogenic competition for prey species, and global climate change. Here, we show how the available nesting habitat of African penguins likely declined precipitously post the Last Glacial Maximum, driven by island inundation as sea levels rose naturally, before anthropogenic global warming. The average size and numbers of islands around the southern African coast decreased almost tenfold between ∼15 kya and the mid Holocene (∼7 kya). In addition, the geographic distribution of islands shifted predominantly away from the South African west to the south and east coasts. The natural decline of island habitat likely caused a decline in the penguin population, which is likely relevant in current assessments of the vulnerability of this species to novel anthropogenic drivers of population decline. The status of the African penguin as a post-Pleistocene refugial species has amplified its extinction risk due to anthropogenic impacts, despite natural resilience to paleoclimatic change afforded by an apparent capacity for habitat colonisation and evident persistence through late-Pleistocene bottlenecks.
{"title":"A natural terminal Pleistocene decline of African penguin populations enhances their anthropogenic extinction risk","authors":"H. Beckett, O. Hansen, S. von der Heyden, GF Midgley","doi":"10.2989/1814232X.2023.2171126","DOIUrl":"https://doi.org/10.2989/1814232X.2023.2171126","url":null,"abstract":"The African penguin Spheniscus demersus, endemic to the coast of southern Africa, has suffered anthropogenic-driven population declines since 1900 and is now listed as Endangered on the IUCN Red List. Conservation efforts currently underway are informed by the species’ adaptive response with respect to colonisation capacity and breeding success, vulnerability because of anthropogenic competition for prey species, and global climate change. Here, we show how the available nesting habitat of African penguins likely declined precipitously post the Last Glacial Maximum, driven by island inundation as sea levels rose naturally, before anthropogenic global warming. The average size and numbers of islands around the southern African coast decreased almost tenfold between ∼15 kya and the mid Holocene (∼7 kya). In addition, the geographic distribution of islands shifted predominantly away from the South African west to the south and east coasts. The natural decline of island habitat likely caused a decline in the penguin population, which is likely relevant in current assessments of the vulnerability of this species to novel anthropogenic drivers of population decline. The status of the African penguin as a post-Pleistocene refugial species has amplified its extinction risk due to anthropogenic impacts, despite natural resilience to paleoclimatic change afforded by an apparent capacity for habitat colonisation and evident persistence through late-Pleistocene bottlenecks.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"45 1","pages":"57 - 62"},"PeriodicalIF":1.2,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42865454","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 : 2022-10-02DOI: 10.2989/1814232X.2022.2136243
A. Robbins, C. Griffiths, L. Nefdt
Intertidal research has focused primarily on very fine to coarse sandy beaches (grain size <1 mm) and on rocky shores, while shores with grain sizes of 1-256+ mm have rarely been studied. Within South Africa, few published accounts describe the biota of very coarse sand (1-<2 mm), granule (2-<4 mm), pebble (4-<64 mm) or cobble (64-<256 mm) shores, and only one reports on boulder (256+ mm) shores. The objective here was to determine how many distinct habitat types occur across the full spectrum of particle sizes within this region, and what taxa characterise the biota of each habitat type. Biota from 14 shores of grain sizes 1-256 mm within the Western Cape Province (southeastern Atlantic Ocean) were sampled and compared with similar published data from 32 other regional sites with either finer or coarser grain size. Three main groupings emerged from a similarity analysis: sandy shores (of particle size <1 mm); pebble (4-<64 mm) shores; and boulder (256+ mm) plus rocky shores, with cobbles serving as a transition between those two. Sandy shores were characterised by various burrowing taxa, and boulder (>256 mm) and rocky shores mostly by grazing gastropods. Shores of 4-<64 mm particle grain size were colonised by a distinctive but previously unrecognised macrofaunal community characterised by an impoverished fauna dominated by small, mobile, mostly air-breathing arthropod taxa.
{"title":"Comparisons of macrofaunal communities occupying shores across the full particle-size spectrum reveals pebble beaches to be a distinct coastal habitat type","authors":"A. Robbins, C. Griffiths, L. Nefdt","doi":"10.2989/1814232X.2022.2136243","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2136243","url":null,"abstract":"Intertidal research has focused primarily on very fine to coarse sandy beaches (grain size <1 mm) and on rocky shores, while shores with grain sizes of 1-256+ mm have rarely been studied. Within South Africa, few published accounts describe the biota of very coarse sand (1-<2 mm), granule (2-<4 mm), pebble (4-<64 mm) or cobble (64-<256 mm) shores, and only one reports on boulder (256+ mm) shores. The objective here was to determine how many distinct habitat types occur across the full spectrum of particle sizes within this region, and what taxa characterise the biota of each habitat type. Biota from 14 shores of grain sizes 1-256 mm within the Western Cape Province (southeastern Atlantic Ocean) were sampled and compared with similar published data from 32 other regional sites with either finer or coarser grain size. Three main groupings emerged from a similarity analysis: sandy shores (of particle size <1 mm); pebble (4-<64 mm) shores; and boulder (256+ mm) plus rocky shores, with cobbles serving as a transition between those two. Sandy shores were characterised by various burrowing taxa, and boulder (>256 mm) and rocky shores mostly by grazing gastropods. Shores of 4-<64 mm particle grain size were colonised by a distinctive but previously unrecognised macrofaunal community characterised by an impoverished fauna dominated by small, mobile, mostly air-breathing arthropod taxa.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"321 - 340"},"PeriodicalIF":1.2,"publicationDate":"2022-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43909697","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 : 2022-10-02DOI: 10.2989/1814232X.2022.2147999
C. Edworthy, W. Potts, S. Dupont, M. Duncan, T. Bornman, N. James
Compared with the open ocean, knowledge of pH variability in coastal waters is rudimentary, especially in Africa. This is concerning as quantifying local pH conditions is critical when assessing the response of coastal species to future ocean acidification scenarios. The objective of this study was to capture some of the variability in pH at scales and sites relevant to coastal marine organisms in a South African temperate embayment (Algoa Bay, Indian Ocean). We used a sampling approach that captured spatial (at a resolution of ∼10 km), monthly and diel (24-hour) variability in pH and associated physical and biological parameters at offshore and shallow inshore sites in Algoa Bay. We found that pH and associated parameters (temperature, calculated pCO2, chlorophyll a) varied over space and time in Algoa Bay. The range in pH was 0.30 units at offshore sites and 0.46 at inshore sites, and the average pH was 8.10 (SD 0.06) and 8.10 (SD 0.13) at these sites, respectively, which is typical for coastal environments. Our results showed that both biological factors (at the offshore sites) and salinity (at the inshore sites) may influence temporal and spatial variability in pH. We also identified a shallow inshore site with high levels of macroalgal growth that had consistently higher average daytime pH levels (8.33 [SD 0.07]), which may serve as an ocean acidification refuge for coastal marine species. This is the first comprehensive pH-monitoring study to be implemented in a nearshore coastal area in Africa and provides recommendations for monitoring in other understudied regions.
{"title":"A baseline assessment of coastal pH variability in a temperate South African embayment: implications for biological ocean acidification research","authors":"C. Edworthy, W. Potts, S. Dupont, M. Duncan, T. Bornman, N. James","doi":"10.2989/1814232X.2022.2147999","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2147999","url":null,"abstract":"Compared with the open ocean, knowledge of pH variability in coastal waters is rudimentary, especially in Africa. This is concerning as quantifying local pH conditions is critical when assessing the response of coastal species to future ocean acidification scenarios. The objective of this study was to capture some of the variability in pH at scales and sites relevant to coastal marine organisms in a South African temperate embayment (Algoa Bay, Indian Ocean). We used a sampling approach that captured spatial (at a resolution of ∼10 km), monthly and diel (24-hour) variability in pH and associated physical and biological parameters at offshore and shallow inshore sites in Algoa Bay. We found that pH and associated parameters (temperature, calculated pCO2, chlorophyll a) varied over space and time in Algoa Bay. The range in pH was 0.30 units at offshore sites and 0.46 at inshore sites, and the average pH was 8.10 (SD 0.06) and 8.10 (SD 0.13) at these sites, respectively, which is typical for coastal environments. Our results showed that both biological factors (at the offshore sites) and salinity (at the inshore sites) may influence temporal and spatial variability in pH. We also identified a shallow inshore site with high levels of macroalgal growth that had consistently higher average daytime pH levels (8.33 [SD 0.07]), which may serve as an ocean acidification refuge for coastal marine species. This is the first comprehensive pH-monitoring study to be implemented in a nearshore coastal area in Africa and provides recommendations for monitoring in other understudied regions.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"367 - 381"},"PeriodicalIF":1.2,"publicationDate":"2022-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44627774","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 : 2022-10-02DOI: 10.2989/1814232X.2022.2130427
E. Gammon, C. Moloney, Marcus Lipinski
The composition of the diet of juvenile deep-water hake Merluccius paradoxus is described and compared for three body-condition groups (below-average, average, and above-average). Diet was analysed using three metrics: occurrence, numeric and gravimetric. Juvenile hakes were caught in January and February of 2012 by means of 28 trawl deployments from the RV Dr Fridtjof Nansen between Orange Banks and Hondeklip Bay on the west coast of southern Africa at depths of 30-232 m. The 300 individuals analysed were a representative sample of all juveniles caught (3 114 fish), ranging in length from 52 to 205 mm (average length 107 mm). Their diet consisted of the euphausiid Euphausia lucens, the hyperiid amphipod Themisto gaudichaudii, the stomatopod Pterygosquilla armata capensis, and mesopelagic fishes Maurolicus muelleri and Lampanyctodes hectoris. The only significant difference in diet between the body-condition groups was for euphausiids and hyperiid amphipods in the numeric metric. A new method of assessing fish condition using otolith weight was tested. Because of the large variability in the data and small sample size, this method could not be applied effectively in this study. However, otolith weight has potential as a new fish condition metric when the variability can be lowered.
{"title":"Diet and condition of juvenile deep-water hake Merluccius paradoxus on the west coast of southern Africa","authors":"E. Gammon, C. Moloney, Marcus Lipinski","doi":"10.2989/1814232X.2022.2130427","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2130427","url":null,"abstract":"The composition of the diet of juvenile deep-water hake Merluccius paradoxus is described and compared for three body-condition groups (below-average, average, and above-average). Diet was analysed using three metrics: occurrence, numeric and gravimetric. Juvenile hakes were caught in January and February of 2012 by means of 28 trawl deployments from the RV Dr Fridtjof Nansen between Orange Banks and Hondeklip Bay on the west coast of southern Africa at depths of 30-232 m. The 300 individuals analysed were a representative sample of all juveniles caught (3 114 fish), ranging in length from 52 to 205 mm (average length 107 mm). Their diet consisted of the euphausiid Euphausia lucens, the hyperiid amphipod Themisto gaudichaudii, the stomatopod Pterygosquilla armata capensis, and mesopelagic fishes Maurolicus muelleri and Lampanyctodes hectoris. The only significant difference in diet between the body-condition groups was for euphausiids and hyperiid amphipods in the numeric metric. A new method of assessing fish condition using otolith weight was tested. Because of the large variability in the data and small sample size, this method could not be applied effectively in this study. However, otolith weight has potential as a new fish condition metric when the variability can be lowered.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"311 - 320"},"PeriodicalIF":1.2,"publicationDate":"2022-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43737572","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 : 2022-10-02DOI: 10.2989/1814232X.2022.2126525
J. Mann-Lang, B. Mann, G. Jordaan, R. Daly
Scientific output has proven the value of the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORI-CFTP) to biological and fisheries research, with more than 95 published manuscripts based on data from the ORI-CFTP. This study reviews the project from the perspective of participating anglers. A total of 267 members of the ORI-CFTP responded to an online survey designed to gather data on the profile of tagging members, their preferred methods of communication, attitudes towards fish tagging and fish conservation in general, changes in angling behaviour since becoming a member of the project, and support for the continuation of the ORI-CFTP. The results reveal that the ORI-CFTP has indeed made a considerable contribution towards improving the conservation ethics and behaviour of marine recreational anglers in South Africa. Improved communication with anglers— both taggers and non-taggers—through the ORI-CFTP has the potential to amplify much-needed conservation information to the broader angling community and thereby enhance environmental awareness. Recommendations on how to improve the ORI-CFTP and other angling-related citizen science projects are provided.
{"title":"An assessment of the impact of participation in the Oceanographic Research Institute’s Cooperative Fish Tagging Project on angler attitudes and behaviour","authors":"J. Mann-Lang, B. Mann, G. Jordaan, R. Daly","doi":"10.2989/1814232X.2022.2126525","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2126525","url":null,"abstract":"Scientific output has proven the value of the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORI-CFTP) to biological and fisheries research, with more than 95 published manuscripts based on data from the ORI-CFTP. This study reviews the project from the perspective of participating anglers. A total of 267 members of the ORI-CFTP responded to an online survey designed to gather data on the profile of tagging members, their preferred methods of communication, attitudes towards fish tagging and fish conservation in general, changes in angling behaviour since becoming a member of the project, and support for the continuation of the ORI-CFTP. The results reveal that the ORI-CFTP has indeed made a considerable contribution towards improving the conservation ethics and behaviour of marine recreational anglers in South Africa. Improved communication with anglers— both taggers and non-taggers—through the ORI-CFTP has the potential to amplify much-needed conservation information to the broader angling community and thereby enhance environmental awareness. Recommendations on how to improve the ORI-CFTP and other angling-related citizen science projects are provided.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"299 - 309"},"PeriodicalIF":1.2,"publicationDate":"2022-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49166640","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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