Pub Date : 2021-01-02DOI: 10.2989/1814232X.2020.1857836
K. Osuka, J. Kawaka, M. Samoilys
Gillnets are a widely used fishing gear in Kenya’s artisanal fisheries, yet their mesh sizes are inadequately monitored or regulated. This study evaluated the impacts of gillnets of seven stretched-mesh sizes, through comparative analysis of species-related metrics and catch per unit effort (CPUE), to inform Kenya’s small-scale fisheries regulations. Data were collected from June 2014 to May 2015. Three mesh-size groups were identified from catch composition data using non-metric multidimensional scaling and comprised small (1.3, 5.1 and 7.6 cm), medium (10.2 and 15.2 cm) and large (20.3 and 25.4 cm) mesh. The dominant species (and their mean lengths) that were caught in the small, medium and large mesh sizes, respectively, were whitespotted rabbitfish Siganus sutor (21.7 cm [SD 5.3]), mackerel tuna Euthynnus affinis (40.8 cm [SD 9.1]) and honeycomb stingray Himantura uarnak (87.3 cm [SD 37.4]). Values of length at first capture (L 50) for S. sutor and E. affinis caught with the small and medium mesh sizes were below length at maturity (L m). Catches of juveniles were proportionately high in the small meshes (61.3–74.2%) and lower in the medium (38.3–50.9%) and large (9.1–36.2%) mesh sizes. Catches with small mesh tended to be species categorised as Least Concern on the IUCN Red List, in contrast to catches with large mesh which tended to be Near Threatened or Vulnerable species. Biomass CPUE differed between mesh-size groups, with the small sizes recording low CPUE. The medium sizes caught mid- to high-trophic-level species with high-income returns, displayed moderate CPUE, and had the lowest juvenile retention and capture of threatened species. Medium mesh sizes are therefore recommended for artisanal fisheries, given low trade-offs between ecological impact and fishery returns.
{"title":"Evaluating Kenya’s coastal gillnet fishery: trade-offs in recommended mesh-size regulations","authors":"K. Osuka, J. Kawaka, M. Samoilys","doi":"10.2989/1814232X.2020.1857836","DOIUrl":"https://doi.org/10.2989/1814232X.2020.1857836","url":null,"abstract":"Gillnets are a widely used fishing gear in Kenya’s artisanal fisheries, yet their mesh sizes are inadequately monitored or regulated. This study evaluated the impacts of gillnets of seven stretched-mesh sizes, through comparative analysis of species-related metrics and catch per unit effort (CPUE), to inform Kenya’s small-scale fisheries regulations. Data were collected from June 2014 to May 2015. Three mesh-size groups were identified from catch composition data using non-metric multidimensional scaling and comprised small (1.3, 5.1 and 7.6 cm), medium (10.2 and 15.2 cm) and large (20.3 and 25.4 cm) mesh. The dominant species (and their mean lengths) that were caught in the small, medium and large mesh sizes, respectively, were whitespotted rabbitfish Siganus sutor (21.7 cm [SD 5.3]), mackerel tuna Euthynnus affinis (40.8 cm [SD 9.1]) and honeycomb stingray Himantura uarnak (87.3 cm [SD 37.4]). Values of length at first capture (L 50) for S. sutor and E. affinis caught with the small and medium mesh sizes were below length at maturity (L m). Catches of juveniles were proportionately high in the small meshes (61.3–74.2%) and lower in the medium (38.3–50.9%) and large (9.1–36.2%) mesh sizes. Catches with small mesh tended to be species categorised as Least Concern on the IUCN Red List, in contrast to catches with large mesh which tended to be Near Threatened or Vulnerable species. Biomass CPUE differed between mesh-size groups, with the small sizes recording low CPUE. The medium sizes caught mid- to high-trophic-level species with high-income returns, displayed moderate CPUE, and had the lowest juvenile retention and capture of threatened species. Medium mesh sizes are therefore recommended for artisanal fisheries, given low trade-offs between ecological impact and fishery returns.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"15 - 29"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42096515","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 : 2021-01-02DOI: 10.2989/1814232X.2021.1886988
C. Fagg, NL Phair, L. Claassens, R. Barnes, S. von der Heyden
Seagrass ecosystems face many anthropogenic pressures, yet globally there is a lack of knowledge of their associated biodiversity. Molecular barcoding can aid in biomonitoring efforts, but few South African invertebrates are accounted for. We provide 48 new sequences for 15 invertebrate species across a range of taxonomic groups sampled from Zostera capensis meadows, eight of which were not previously barcoded. Our work presents an important effort to strengthen the mitochondrial DNA cytochrome c oxidase subunit I (mtDNA-COI) reference database for estuarine macrofauna in South Africa, supporting regional and global conservation efforts.
{"title":"Strengthening the DNA barcode reference library for South African estuarine macrofauna","authors":"C. Fagg, NL Phair, L. Claassens, R. Barnes, S. von der Heyden","doi":"10.2989/1814232X.2021.1886988","DOIUrl":"https://doi.org/10.2989/1814232X.2021.1886988","url":null,"abstract":"Seagrass ecosystems face many anthropogenic pressures, yet globally there is a lack of knowledge of their associated biodiversity. Molecular barcoding can aid in biomonitoring efforts, but few South African invertebrates are accounted for. We provide 48 new sequences for 15 invertebrate species across a range of taxonomic groups sampled from Zostera capensis meadows, eight of which were not previously barcoded. Our work presents an important effort to strengthen the mitochondrial DNA cytochrome c oxidase subunit I (mtDNA-COI) reference database for estuarine macrofauna in South Africa, supporting regional and global conservation efforts.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"141 - 145"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45482124","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 : 2021-01-02DOI: 10.2989/1814232X.2021.1879268
H. Skrypzeck, C. van der Lingen, M. Gibbons
Large and small specimens of two species of metagenic Scyphozoa (true jellyfishes) can be found in nearshore waters off central Namibia throughout the year. Whereas populations of Chrysaora africana are largely restricted to inshore waters, C. fulgida occurs across the shelf, with small individuals found inshore and large individuals primarily found offshore. We examined stable isotopes δ15N and δ13C of both species in Walvis Bay and found that large-sized C. fulgida have lower δ15N values than small individuals and C. africana throughout the year. These differences are interpreted to reflect cross-shelf changes in δ15N baseline levels, with greater nitrogen recycling (and hence lower δ15N values) occurring offshore. The occasional/seasonal nearshore appearance of large C. fulgida with low δ15N values therefore implies routine, onshore advection. The values of δ13C did not show cross-shelf differences, which suggests that jellyfish populations across the shelf are supported by phytoplankton-based food chains. This study emphasises the value of using stable isotopes to examine the mesoscale structuring of jellyfish populations.
{"title":"Cross-shelf movement of Chrysaora fulgida (Scyphozoa; Discomedusae) off Namibia inferred from stable isotopes (δ15N and δ13C)","authors":"H. Skrypzeck, C. van der Lingen, M. Gibbons","doi":"10.2989/1814232X.2021.1879268","DOIUrl":"https://doi.org/10.2989/1814232X.2021.1879268","url":null,"abstract":"Large and small specimens of two species of metagenic Scyphozoa (true jellyfishes) can be found in nearshore waters off central Namibia throughout the year. Whereas populations of Chrysaora africana are largely restricted to inshore waters, C. fulgida occurs across the shelf, with small individuals found inshore and large individuals primarily found offshore. We examined stable isotopes δ15N and δ13C of both species in Walvis Bay and found that large-sized C. fulgida have lower δ15N values than small individuals and C. africana throughout the year. These differences are interpreted to reflect cross-shelf changes in δ15N baseline levels, with greater nitrogen recycling (and hence lower δ15N values) occurring offshore. The occasional/seasonal nearshore appearance of large C. fulgida with low δ15N values therefore implies routine, onshore advection. The values of δ13C did not show cross-shelf differences, which suggests that jellyfish populations across the shelf are supported by phytoplankton-based food chains. This study emphasises the value of using stable isotopes to examine the mesoscale structuring of jellyfish populations.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"74 9","pages":"87 - 93"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41281952","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 : 2021-01-02DOI: 10.2989/1814232X.2021.1882574
F. Coleman, G. Diedericks, A. Theron, J. Lencart e Silva
False Bay is the largest coastal embayment along South Africa’s coastline. Despite notable contributions of various historical observational studies on the circulation within False Bay and the associated physical processes driving these flows, there remains significant uncertainty largely because the studies to date have been undertaken over short durations and on limited spatial scales. This article aims to expand upon the findings of these historical observational studies by providing a thorough evaluation of intra-annual hydrodynamics within False Bay, with particular emphasis on providing greater definition on current circulation. To evaluate the effects of different processes on coastal hydrodynamics, a 3D hydrodynamic model was developed which included the influence of spatially varying wind forcing and daily averaged temperature-depth profiles on the model boundaries and atmospheric heat exchange. The model results relating to current circulation are consistent with historical studies that described a cyclonic (clockwise) circulation within the bay under southeasterly wind conditions. The development of this cyclonic pattern is primarily caused by the spatially varying wind field. During warmer months, upwelling events were noted at Cape Hangklip. Interestingly, under northwesterly wind conditions, the model results deviated from historical findings by showing a spatially uniform current field across the bay. Under these conditions, strong bottom return currents are generated, which contribute significantly to cold-water intrusion events within the bay.
{"title":"Three-dimensional modelling of the circulation in False Bay, South Africa","authors":"F. Coleman, G. Diedericks, A. Theron, J. Lencart e Silva","doi":"10.2989/1814232X.2021.1882574","DOIUrl":"https://doi.org/10.2989/1814232X.2021.1882574","url":null,"abstract":"False Bay is the largest coastal embayment along South Africa’s coastline. Despite notable contributions of various historical observational studies on the circulation within False Bay and the associated physical processes driving these flows, there remains significant uncertainty largely because the studies to date have been undertaken over short durations and on limited spatial scales. This article aims to expand upon the findings of these historical observational studies by providing a thorough evaluation of intra-annual hydrodynamics within False Bay, with particular emphasis on providing greater definition on current circulation. To evaluate the effects of different processes on coastal hydrodynamics, a 3D hydrodynamic model was developed which included the influence of spatially varying wind forcing and daily averaged temperature-depth profiles on the model boundaries and atmospheric heat exchange. The model results relating to current circulation are consistent with historical studies that described a cyclonic (clockwise) circulation within the bay under southeasterly wind conditions. The development of this cyclonic pattern is primarily caused by the spatially varying wind field. During warmer months, upwelling events were noted at Cape Hangklip. Interestingly, under northwesterly wind conditions, the model results deviated from historical findings by showing a spatially uniform current field across the bay. Under these conditions, strong bottom return currents are generated, which contribute significantly to cold-water intrusion events within the bay.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"95 - 118"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43120616","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 : 2021-01-02DOI: 10.2989/1814232X.2020.1855246
Eng Shoopala, M. Wilhelm, SC Paulus
The fishing industry is an important economic sector in Namibia and South Africa, with the shallow-water hake Merluccius capensis being an important target species. Recent genetic studies of M. capensis found two stocks in the Benguela Current Large Marine Ecosystem, one in the north (17–29° S) and one in the south (29–36° S), and a proposed mixed stock in the Orange River area (around 29° S). The present study investigated the use of otolith shape analysis for purposes of stock-structure analysis of M. capensis. Merluccius capensis otolith samples were collected during demersal-trawl surveys along the Benguela, for the years 1992, 2004 and 2005. Different years were selected to investigate temporal stability in otolith shape in the northern Benguela. A total of 1 628 otolith images were analysed using the shapeR library in R. Otolith shape was analysed using wavelet transformation, and ANOVA-like permutation tests indicated no significant differences between the northern (17°31′–25°29′ S) and central (25°30′–29°05′ S) Benguela for all years but showed significant differences between the northern and southern (29°05′–35°50′ S) Benguela. This study therefore demonstrated that otolith shape could be used for stock discrimination of M. capensis. It confirmed one stock of M. capensis in the northern and central Benguela and another in the southern Benguela, which supports the current, separate management approach for this species. It also showed some differences in otolith shape from the 1990s to the 2000s, which could be explained by increased movement of the southern Benguela stock to the northern Benguela and increased hybridisation in the later years.
{"title":"Stock separation of the shallow-water hake Merluccius capensis in the Benguela ecosystem using otolith shape analysis","authors":"Eng Shoopala, M. Wilhelm, SC Paulus","doi":"10.2989/1814232X.2020.1855246","DOIUrl":"https://doi.org/10.2989/1814232X.2020.1855246","url":null,"abstract":"The fishing industry is an important economic sector in Namibia and South Africa, with the shallow-water hake Merluccius capensis being an important target species. Recent genetic studies of M. capensis found two stocks in the Benguela Current Large Marine Ecosystem, one in the north (17–29° S) and one in the south (29–36° S), and a proposed mixed stock in the Orange River area (around 29° S). The present study investigated the use of otolith shape analysis for purposes of stock-structure analysis of M. capensis. Merluccius capensis otolith samples were collected during demersal-trawl surveys along the Benguela, for the years 1992, 2004 and 2005. Different years were selected to investigate temporal stability in otolith shape in the northern Benguela. A total of 1 628 otolith images were analysed using the shapeR library in R. Otolith shape was analysed using wavelet transformation, and ANOVA-like permutation tests indicated no significant differences between the northern (17°31′–25°29′ S) and central (25°30′–29°05′ S) Benguela for all years but showed significant differences between the northern and southern (29°05′–35°50′ S) Benguela. This study therefore demonstrated that otolith shape could be used for stock discrimination of M. capensis. It confirmed one stock of M. capensis in the northern and central Benguela and another in the southern Benguela, which supports the current, separate management approach for this species. It also showed some differences in otolith shape from the 1990s to the 2000s, which could be explained by increased movement of the southern Benguela stock to the northern Benguela and increased hybridisation in the later years.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"1 - 14"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41542421","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 : 2021-01-02DOI: 10.2989/1814232X.2020.1864472
C. Jones, A. Nel, A. Adesola, T. Shipton, H. Kaiser
A balanced combination of protein sources to partially replace fishmeal in the diets of cultured carnivorous fish can promote optimal fish health and production performance. In the present study, the growth, body condition and gut microbiota of juvenile dusky kob Argyrosomus japonicus fed fishmeal-substituted diets comprising different blends of animal and plant protein sources, with crystalline amino acid supplementation, were compared. The fish (15.7 [SE 0.12] g fish−1) were fed one of three isonitrogenous (41% protein) and isoenergetic (13 kJ g−1) diets for 60 days. Fish fed a diet with no fishmeal (D0; blood meal and soybean protein sources only) displayed the lowest specific growth rate (p < 0.001). Longer body lengths were achieved in fish fed a 50% fishmeal diet (D50; supplemented with poultry meal, bloodmeal, canola meal and soybean) (13.2 [SE 0.4] cm) compared with those fed either a 100% fishmeal diet (D100) (12.8 [SE 0.4] cm) or a diet with no fishmeal (D0) (12.1 [SE 0.08] cm) (p < 0.001). There were no differences in condition factor, hepatosomatic index (HSI) and feed conversion ratio (FCR) between fish fed diets D50 and D100; whereas fish fed diet D0 had a lower HSI and a higher FCR when compared with the other treatments (p < 0.01). The dietary protein source did not alter the gut microbiota of these fish. In conclusion, 50% replacement of dietary fishmeal with a favourable balance of meals processed from poultry, blood, canola and soybean improved length gain in juvenile dusky kob compared with those fed a diet with no fishmeal replacement.
{"title":"The effect of fishmeal replacement with terrestrial protein sources on growth, body condition and intestinal microbiota of juvenile dusky kob Argyrosomus japonicus","authors":"C. Jones, A. Nel, A. Adesola, T. Shipton, H. Kaiser","doi":"10.2989/1814232X.2020.1864472","DOIUrl":"https://doi.org/10.2989/1814232X.2020.1864472","url":null,"abstract":"A balanced combination of protein sources to partially replace fishmeal in the diets of cultured carnivorous fish can promote optimal fish health and production performance. In the present study, the growth, body condition and gut microbiota of juvenile dusky kob Argyrosomus japonicus fed fishmeal-substituted diets comprising different blends of animal and plant protein sources, with crystalline amino acid supplementation, were compared. The fish (15.7 [SE 0.12] g fish−1) were fed one of three isonitrogenous (41% protein) and isoenergetic (13 kJ g−1) diets for 60 days. Fish fed a diet with no fishmeal (D0; blood meal and soybean protein sources only) displayed the lowest specific growth rate (p < 0.001). Longer body lengths were achieved in fish fed a 50% fishmeal diet (D50; supplemented with poultry meal, bloodmeal, canola meal and soybean) (13.2 [SE 0.4] cm) compared with those fed either a 100% fishmeal diet (D100) (12.8 [SE 0.4] cm) or a diet with no fishmeal (D0) (12.1 [SE 0.08] cm) (p < 0.001). There were no differences in condition factor, hepatosomatic index (HSI) and feed conversion ratio (FCR) between fish fed diets D50 and D100; whereas fish fed diet D0 had a lower HSI and a higher FCR when compared with the other treatments (p < 0.01). The dietary protein source did not alter the gut microbiota of these fish. In conclusion, 50% replacement of dietary fishmeal with a favourable balance of meals processed from poultry, blood, canola and soybean improved length gain in juvenile dusky kob compared with those fed a diet with no fishmeal replacement.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"45 - 52"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43756900","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 : 2021-01-02DOI: 10.2989/1814232X.2020.1862913
W. Dalton, S. Porter, T-C Livingstone, B. Mann
The KwaZulu-Natal shelf, on the east coast of South Africa, is inhabited by diverse communities of demersal fishes; however, previous studies deeper than 30 m have largely investigated these with extractive techniques. Using baited remote underwater videos (BRUVs), this study quantified how depth and substrate type correlated with the composition of demersal fish communities between 35 and 100 m, and assessed whether the communities displayed congruence with three benthic biozones, which were modelled using abiotic surrogates for purposes of conservation planning: Biozone 1 (warm; coarse sediment dominant; low seafloor oxygen, phosphate and organic carbon concentrations), Biozone 2 (flat; coarse sediment dominant; high seafloor oxygen and low phosphate and organic carbon concentrations) and Biozone 3 (shallow; warm; fine sediment dominant; low seafloor oxygen and higher organic carbon concentrations). A total of 118 fish taxa were recorded from 200 BRUV deployments conducted on different substrate types. All diversity indices differed significantly among substrate types, whereas depth correlated significantly with only the number of fish species per site and Margalef’s diversity index. Multivariate analyses determined that substrate type and depth explained significant amounts of the variation in fish communities. A significant difference was also detected between the fish communities of Biozones 1 and 3, with Biozone 3 being the most distinct of the three biozones investigated. Overall congruence between fish communities and their associated biozones ranged between 41% and 45%. This suggests that, at a broad spatial scale, the demersal fish communities could be adequately represented by Biozone 3 and a second biozone comprising Biozones 1 and 2 combined.
{"title":"Demersal fish communities in KwaZulu-Natal, South Africa, indicate partial congruence with proposed conservation biozones","authors":"W. Dalton, S. Porter, T-C Livingstone, B. Mann","doi":"10.2989/1814232X.2020.1862913","DOIUrl":"https://doi.org/10.2989/1814232X.2020.1862913","url":null,"abstract":"The KwaZulu-Natal shelf, on the east coast of South Africa, is inhabited by diverse communities of demersal fishes; however, previous studies deeper than 30 m have largely investigated these with extractive techniques. Using baited remote underwater videos (BRUVs), this study quantified how depth and substrate type correlated with the composition of demersal fish communities between 35 and 100 m, and assessed whether the communities displayed congruence with three benthic biozones, which were modelled using abiotic surrogates for purposes of conservation planning: Biozone 1 (warm; coarse sediment dominant; low seafloor oxygen, phosphate and organic carbon concentrations), Biozone 2 (flat; coarse sediment dominant; high seafloor oxygen and low phosphate and organic carbon concentrations) and Biozone 3 (shallow; warm; fine sediment dominant; low seafloor oxygen and higher organic carbon concentrations). A total of 118 fish taxa were recorded from 200 BRUV deployments conducted on different substrate types. All diversity indices differed significantly among substrate types, whereas depth correlated significantly with only the number of fish species per site and Margalef’s diversity index. Multivariate analyses determined that substrate type and depth explained significant amounts of the variation in fish communities. A significant difference was also detected between the fish communities of Biozones 1 and 3, with Biozone 3 being the most distinct of the three biozones investigated. Overall congruence between fish communities and their associated biozones ranged between 41% and 45%. This suggests that, at a broad spatial scale, the demersal fish communities could be adequately represented by Biozone 3 and a second biozone comprising Biozones 1 and 2 combined.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"31 - 44"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44699653","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 : 2021-01-02DOI: 10.2989/1814232X.2021.1873858
T. Toolsee, T. Lamont, M. Rouault, I. Ansorge
Located between the sub-Antarctic Front and the Antarctic Polar Front, the Prince Edward Islands (PEIs) provide an essential breeding ground for top predators and are an ideal location to investigate disturbances linked to climate change. This study provides the first seasonal characterisation of surface hydrography at the PEIs, using satellite and reanalysis products from 1993 to 2016. Sea surface temperature (SST) showed consistently higher values to the north, while wind, currents and eddy kinetic energy all showed higher values to the south of the islands. The highest SST (8 °C) occurred in summer and the lowest (2 °C) in winter, with a one-to two-month delay between the maximum incoming solar radiation (in December–January) and the highest SST (in February). The highest wind speed occurred in July (10.8 m s−1) and the minimum in February (7 m s−1). Geostrophic currents were four-times larger than Ekman currents, showing lower speeds between April and June (0.25–0.30 m s−1) and a peak in August (0.45 m s−1). There were no significant differences for SST and Ekman currents between the regions upstream and downstream of the PEIs. In contrast, surface total and geostrophic current velocities were weaker downstream because the islands act as a barrier to the flow. A zone of lower wind speed, coinciding with enhanced positive wind stress curl (WSC), favouring downwelling, occurred directly upstream throughout the year. Although WSC over the PEIs was negative (upwelling-favourable), no corresponding cooling was evident in SST. This seasonal characterisation provides a baseline against which interannual/decadal variability and future changes in these parameters can be assessed.
爱德华王子群岛(pei)位于亚南极锋和南极极锋之间，为顶级食肉动物提供了重要的繁殖地，也是调查与气候变化有关的干扰的理想地点。本研究利用卫星和再分析产品，首次提供了1993年至2016年PEIs地表水文的季节特征。海温(SST)在岛屿的北部持续较高，而风、海流和涡旋动能均在岛屿的南部较高。海温最高(8°C)出现在夏季，最低(2°C)出现在冬季，最大太阳入射辐射(12 - 1月)与最高海温(2月)之间有1 - 2个月的延迟。7月风速最大(10.8 m s−1)，2月最小(7 m s−1)。地转流比埃克曼流大4倍，速度在4 - 6月较低(0.25-0.30 m s - 1)， 8月达到峰值(0.45 m s - 1)。海温和Ekman流在上游和下游地区之间没有显著差异。相比之下，由于岛屿对水流起到了屏障的作用，下游的地表总流速和地转流速较弱。一个风速较低的区域，与增强的正风应力旋度(WSC)一致，有利于下沉，全年发生在直接上游。尽管PEIs上的WSC为负(有利于上升流)，但海温没有明显的相应冷却。这种季节性特征提供了一个基线，可据此评估这些参数的年际/年代际变率和未来变化。
{"title":"Characterising the seasonal cycle of wind forcing, surface circulation and temperature around the sub-Antarctic Prince Edward Islands","authors":"T. Toolsee, T. Lamont, M. Rouault, I. Ansorge","doi":"10.2989/1814232X.2021.1873858","DOIUrl":"https://doi.org/10.2989/1814232X.2021.1873858","url":null,"abstract":"Located between the sub-Antarctic Front and the Antarctic Polar Front, the Prince Edward Islands (PEIs) provide an essential breeding ground for top predators and are an ideal location to investigate disturbances linked to climate change. This study provides the first seasonal characterisation of surface hydrography at the PEIs, using satellite and reanalysis products from 1993 to 2016. Sea surface temperature (SST) showed consistently higher values to the north, while wind, currents and eddy kinetic energy all showed higher values to the south of the islands. The highest SST (8 °C) occurred in summer and the lowest (2 °C) in winter, with a one-to two-month delay between the maximum incoming solar radiation (in December–January) and the highest SST (in February). The highest wind speed occurred in July (10.8 m s−1) and the minimum in February (7 m s−1). Geostrophic currents were four-times larger than Ekman currents, showing lower speeds between April and June (0.25–0.30 m s−1) and a peak in August (0.45 m s−1). There were no significant differences for SST and Ekman currents between the regions upstream and downstream of the PEIs. In contrast, surface total and geostrophic current velocities were weaker downstream because the islands act as a barrier to the flow. A zone of lower wind speed, coinciding with enhanced positive wind stress curl (WSC), favouring downwelling, occurred directly upstream throughout the year. Although WSC over the PEIs was negative (upwelling-favourable), no corresponding cooling was evident in SST. This seasonal characterisation provides a baseline against which interannual/decadal variability and future changes in these parameters can be assessed.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"61 - 76"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49021750","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 : 2021-01-02DOI: 10.2989/1814232X.2021.1879267
E. Acheampong, P. Mantey, A. Weremfo
Reports suggest that the Gulf of Guinea (northeastern tropical Atlantic) frequently experiences marine heatwaves (MHW)—prolonged periods of anomalously warm seawater—of ≥1.5 °C above baseline. We assessed the likely impact of this anomaly on two microalgae, Thalassiosira weissflogii (diatom) and Gymnodinium sp. (dinoflagellate), adapted to the surface temperature (28 ± 1.5 °C) of the gulf during stable hydrographic periods. The algae were adapted over ∼400 generations. They were assessed for specific growth rate (μ), dry weight, and protein content after exposure to 5 or 6 days of warming (+2 °C or +4 °C above the temperature of the stock cultures), in line with the minimum duration of MHW. Under each of the investigated warming scenarios, the effect of warming on the diatom was immediate, occurring during the first day of exposure, and μ had decreased by ∼75% by the end of the warming period. In contrast, the warming effect on the dinoflagellate became significant during the second day, with μ reduced by ∼78–86%. Also, the protein content of the dinoflagellate had been reduced by ∼32% by the end of the warming period. The dry weight of T. weissflogii increased three-fold under +2 °C of warming. In contrast, the dry weight of Gymnodinium sp. decreased by ∼78% and did not recover when warming was removed. These results highlight vulnerability of these algae to MHW and their unique responses to the anomaly.
{"title":"Potential impact of marine heatwaves on selected phytoplankton adapted to the Gulf of Guinea during stable hydrographic periods","authors":"E. Acheampong, P. Mantey, A. Weremfo","doi":"10.2989/1814232X.2021.1879267","DOIUrl":"https://doi.org/10.2989/1814232X.2021.1879267","url":null,"abstract":"Reports suggest that the Gulf of Guinea (northeastern tropical Atlantic) frequently experiences marine heatwaves (MHW)—prolonged periods of anomalously warm seawater—of ≥1.5 °C above baseline. We assessed the likely impact of this anomaly on two microalgae, Thalassiosira weissflogii (diatom) and Gymnodinium sp. (dinoflagellate), adapted to the surface temperature (28 ± 1.5 °C) of the gulf during stable hydrographic periods. The algae were adapted over ∼400 generations. They were assessed for specific growth rate (μ), dry weight, and protein content after exposure to 5 or 6 days of warming (+2 °C or +4 °C above the temperature of the stock cultures), in line with the minimum duration of MHW. Under each of the investigated warming scenarios, the effect of warming on the diatom was immediate, occurring during the first day of exposure, and μ had decreased by ∼75% by the end of the warming period. In contrast, the warming effect on the dinoflagellate became significant during the second day, with μ reduced by ∼78–86%. Also, the protein content of the dinoflagellate had been reduced by ∼32% by the end of the warming period. The dry weight of T. weissflogii increased three-fold under +2 °C of warming. In contrast, the dry weight of Gymnodinium sp. decreased by ∼78% and did not recover when warming was removed. These results highlight vulnerability of these algae to MHW and their unique responses to the anomaly.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"77 - 86"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45047157","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 : 2021-01-02DOI: 10.2989/1814232X.2020.1864471
S. Paarman, E. Vermeulen, E. Seyboth, M. Thornton, K. Findlay
The Antarctic blue whale Balaenoptera musculus intermedia was hunted to near extinction in the twentieth century. Current data on the abundance and distribution of the species are lacking owing to the difficulty and expense of surveys under adverse weather conditions in open-ocean habitats, and to the small population size. The most recently accepted global abundance estimate, based on the middle survey (1997/1998) of three circumpolar Antarctic surveys conducted between 1991/1992 and 2003/2004, was less than 1% of the original pre-whaling population size. The present study used a visual line-transect survey off the Queen Maud Land coast of Antarctica, in an area between 0° and 18° E and south of 67° S, in January 2014, to estimate the abundance of Antarctic blue whales in this area. Effort-accounted densities of sightings averaged 13.3 individuals per 1 000 nautical miles of survey effort (CV = 0.26) and reinforce recent findings that the area has significantly higher densities than averaged in circumpolar surveys (0.17–1.48 per 1 000 nautical miles). Distance sampling resulted in a population density estimate of 0.019 whales nautical-mile−2 (CV = 0.24) and an estimated abundance of 1 026 Antarctic blue whales (CV = 0.20, 95% CI 632–1 450) in the surveyed area. Obtaining such current estimates of abundance is crucial for assessment of the conservation status of the Antarctic blue whale population and for monitoring its recovery.
{"title":"Abundance and distribution of Antarctic blue whales Balaenoptera musculus intermedia off the Queen Maud Land coast of Antarctica","authors":"S. Paarman, E. Vermeulen, E. Seyboth, M. Thornton, K. Findlay","doi":"10.2989/1814232X.2020.1864471","DOIUrl":"https://doi.org/10.2989/1814232X.2020.1864471","url":null,"abstract":"The Antarctic blue whale Balaenoptera musculus intermedia was hunted to near extinction in the twentieth century. Current data on the abundance and distribution of the species are lacking owing to the difficulty and expense of surveys under adverse weather conditions in open-ocean habitats, and to the small population size. The most recently accepted global abundance estimate, based on the middle survey (1997/1998) of three circumpolar Antarctic surveys conducted between 1991/1992 and 2003/2004, was less than 1% of the original pre-whaling population size. The present study used a visual line-transect survey off the Queen Maud Land coast of Antarctica, in an area between 0° and 18° E and south of 67° S, in January 2014, to estimate the abundance of Antarctic blue whales in this area. Effort-accounted densities of sightings averaged 13.3 individuals per 1 000 nautical miles of survey effort (CV = 0.26) and reinforce recent findings that the area has significantly higher densities than averaged in circumpolar surveys (0.17–1.48 per 1 000 nautical miles). Distance sampling resulted in a population density estimate of 0.019 whales nautical-mile−2 (CV = 0.24) and an estimated abundance of 1 026 Antarctic blue whales (CV = 0.20, 95% CI 632–1 450) in the surveyed area. Obtaining such current estimates of abundance is crucial for assessment of the conservation status of the Antarctic blue whale population and for monitoring its recovery.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"43 1","pages":"53 - 59"},"PeriodicalIF":1.2,"publicationDate":"2021-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48117903","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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