Pub Date : 2022-01-02DOI: 10.2989/1814232X.2022.2028674
N. Martin, S. Clusella‐Trullas, T. Robinson
Predator–prey relationships can drive community dynamics in marine systems, but it remains unclear how future changes in seawater temperatures and pH will influence these relationships. This study assessed the effect of predicted future temperatures and pH on the prey choice of the girdled dogwhelk Trochia cingulata (family Muricidae) when offered native (Aulacomya atra, Choromytilus meridionalis) and alien (Semimytilus algosus) mussels. Whelks were exposed to three pH levels: 8.0 (current), 7.7 (intermediate) and 7.5 (extreme), at each of three temperatures: 9 °C (cooling), 13 °C (current) and 17 °C (warming) for 6 weeks. Thereafter, the prey preference and predation rate were compared among treatments. Within two weeks, 98% of whelks exposed to warming died, precluding assessment of how warming affects their prey preference. Despite high mortality, the highest predation rates were recorded at 17 °C regardless of the pH level, likely reflecting increased energy costs and ingestion rates associated with warming. In the remaining treatments whelks preferred S. algosus irrespective of the levels of seawater cooling or acidification. These results align with previous work that demonstrated a preference by T. cingulata for S. algosus and suggest that the predator–prey relationship between this whelk and its mussel prey is unlikely to be disrupted under future marine conditions.
{"title":"Predicted future changes in ocean temperature and pH do not affect prey selection by the girdled dogwhelk Trochia cingulata","authors":"N. Martin, S. Clusella‐Trullas, T. Robinson","doi":"10.2989/1814232X.2022.2028674","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2028674","url":null,"abstract":"Predator–prey relationships can drive community dynamics in marine systems, but it remains unclear how future changes in seawater temperatures and pH will influence these relationships. This study assessed the effect of predicted future temperatures and pH on the prey choice of the girdled dogwhelk Trochia cingulata (family Muricidae) when offered native (Aulacomya atra, Choromytilus meridionalis) and alien (Semimytilus algosus) mussels. Whelks were exposed to three pH levels: 8.0 (current), 7.7 (intermediate) and 7.5 (extreme), at each of three temperatures: 9 °C (cooling), 13 °C (current) and 17 °C (warming) for 6 weeks. Thereafter, the prey preference and predation rate were compared among treatments. Within two weeks, 98% of whelks exposed to warming died, precluding assessment of how warming affects their prey preference. Despite high mortality, the highest predation rates were recorded at 17 °C regardless of the pH level, likely reflecting increased energy costs and ingestion rates associated with warming. In the remaining treatments whelks preferred S. algosus irrespective of the levels of seawater cooling or acidification. These results align with previous work that demonstrated a preference by T. cingulata for S. algosus and suggest that the predator–prey relationship between this whelk and its mussel prey is unlikely to be disrupted under future marine conditions.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42884016","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 : 2022-01-02DOI: 10.2989/1814232X.2022.2041094
C. Simon, J. Kara, DT Clarke, S. Sedick
Originally published in 1967, John H Day’s work ‘A monograph on the Polychaeta of southern Africa’ is still used widely to identify polychaetes. However, ongoing taxonomic revisions have revealed that several putative cosmopolitan or locally widespread taxa contained in the monograph are complexes of species with discrete distributions, globally and locally. This study therefore aimed to develop lists of taxa, including unresolved cosmopolitan and widespread indigenous species, that should be prioritised for revision to unlock their hidden diversity. A total of 609 species (56 families and 316 genera) were scored according to their time since description, global and local distribution, availability of genetic data and vouchers, alien status and economic importance, and then ranked. At least half the taxa reported locally are unresolved cosmopolitan complexes, and a quarter have wide local distributions, probably hiding cryptic diversity. Accordingly, we estimate that approximately 500 polychaete species are still undescribed in southern Africa. The four highest-scoring families (Syllidae, Nereididae, Spionidae and Eunicidae) comprise 25% of the species and 53–85% of the unresolved cosmopolitans, while multiple species are considered pests, used as bait or possible aliens. Prioritised genera (e.g. Eunice, Syllis, Nereis, Prionospio, Dipolydora) and species (e.g. Pseudonereis variegata) are usually members of prioritised families, but some species are not (e.g. Sabella cf. pavonina, Fimbriosthenelais zetlandica, Paleanotus chrysolepis, Gunnarea gaimardi, Capitella capitata). All taxon levels should therefore be considered to ensure that all species most in need of revision are identified. Ways to facilitate revisions are discussed.
约翰·H·戴(John H Day)的著作《非洲南部多毛体专著》(A monograph on polycheta of southern Africa)最初出版于1967年，至今仍被广泛用于识别多毛体。然而，正在进行的分类学修订表明，专著中包含的一些假定的世界性或局部分布的分类群是全球和局部离散分布的物种复合体。因此，本研究旨在制定分类群清单，包括尚未确定的世界性和广布的本土物种，这些分类群应该优先进行修订，以解锁其隐藏的多样性。根据描述时间、全球和本地分布、遗传数据和证据的可获得性、外来物种地位和经济重要性对609种(56科316属)进行评分，并进行排名。当地报告的分类群中至少有一半是未解决的世界性复合体，四分之一在当地分布广泛，可能隐藏着神秘的多样性。据此，我们估计在非洲南部仍有大约500种多毛类未被描述。得分最高的4个科(飞虱科、蠓科、刺蚊科和蠓科)占物种总数的25%，占未解决的世界蚊的53-85%，而多个物种被认为是害虫，被用作诱饵或可能的外来生物。优先属(如尤尼斯、西尼斯、奈尼斯、Prionospio、Dipolydora)和种(如Pseudonereis variegata)通常是优先科的成员，但有些种不是(如Sabella cff . pavonina、fibriosthenelais zetlandica、palanotus chrysolepis、Gunnarea gaimardi、Capitella capitata)。因此，应考虑所有分类单元水平，以确保所有最需要修订的物种都得到确认。讨论了促进修订的方法。
{"title":"Revisiting ‘A monograph on the Polychaeta of southern Africa’: establishing taxonomic research priorities in southern Africa","authors":"C. Simon, J. Kara, DT Clarke, S. Sedick","doi":"10.2989/1814232X.2022.2041094","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2041094","url":null,"abstract":"Originally published in 1967, John H Day’s work ‘A monograph on the Polychaeta of southern Africa’ is still used widely to identify polychaetes. However, ongoing taxonomic revisions have revealed that several putative cosmopolitan or locally widespread taxa contained in the monograph are complexes of species with discrete distributions, globally and locally. This study therefore aimed to develop lists of taxa, including unresolved cosmopolitan and widespread indigenous species, that should be prioritised for revision to unlock their hidden diversity. A total of 609 species (56 families and 316 genera) were scored according to their time since description, global and local distribution, availability of genetic data and vouchers, alien status and economic importance, and then ranked. At least half the taxa reported locally are unresolved cosmopolitan complexes, and a quarter have wide local distributions, probably hiding cryptic diversity. Accordingly, we estimate that approximately 500 polychaete species are still undescribed in southern Africa. The four highest-scoring families (Syllidae, Nereididae, Spionidae and Eunicidae) comprise 25% of the species and 53–85% of the unresolved cosmopolitans, while multiple species are considered pests, used as bait or possible aliens. Prioritised genera (e.g. Eunice, Syllis, Nereis, Prionospio, Dipolydora) and species (e.g. Pseudonereis variegata) are usually members of prioritised families, but some species are not (e.g. Sabella cf. pavonina, Fimbriosthenelais zetlandica, Paleanotus chrysolepis, Gunnarea gaimardi, Capitella capitata). All taxon levels should therefore be considered to ensure that all species most in need of revision are identified. Ways to facilitate revisions are discussed.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48903737","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 : 2022-01-02DOI: 10.2989/1814232X.2022.2032826
R. Daly, G. Jordaan, D. Parker, G. Cliff, N. Nkabi, R. Kyle, S. Fennessy, B. Mann
The diamond ray Gymnura natalensis is endemic to southern Africa where its preference for shallow coastal habitats makes it vulnerable to recreational shore-based angling. Although it makes up approximately 1% of the shore-based tag numbers, little is known about its movements, reproduction or population status in South Africa. This study used three independent long-term (34–41 years) datasets, including tagging by recreational anglers, competitive shore angling catches and shark net catches, to investigate the species’ movements, catch composition and population status in South Africa. Of the 3 739 individuals tagged (1984–2018), only 30 (1%) were recaptured after an average of 487 days at liberty. The majority (60%) of the recaptures occurred within 10 km of the release site, while 7% had moved more than 1 000 km along the coast. The longest recorded movements (1 577 and 1 756 km) were undertaken by adult rays tagged in the Western Cape Province moving to KwaZulu-Natal Province (KZN). The competitive shore angling catch (1977–2018; n = 9 150) from KZN was dominated by adult rays caught north of Durban, while the shark net catch in KZN (1981–2018; n = 584) was dominated by juvenile rays primarily from the central beaches of Durban. All the datasets exhibited strong seasonal trends with most catches taking place in summer. A risk assessment confirmed a stable to increasing population trend over four generations, suggesting that the population sampled along the east coast of South Africa should be classified as Least Concern.
{"title":"Movement patterns and catch trends of the diamond ray Gymnura natalensis (Dasyatidae) in South African waters","authors":"R. Daly, G. Jordaan, D. Parker, G. Cliff, N. Nkabi, R. Kyle, S. Fennessy, B. Mann","doi":"10.2989/1814232X.2022.2032826","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2032826","url":null,"abstract":"The diamond ray Gymnura natalensis is endemic to southern Africa where its preference for shallow coastal habitats makes it vulnerable to recreational shore-based angling. Although it makes up approximately 1% of the shore-based tag numbers, little is known about its movements, reproduction or population status in South Africa. This study used three independent long-term (34–41 years) datasets, including tagging by recreational anglers, competitive shore angling catches and shark net catches, to investigate the species’ movements, catch composition and population status in South Africa. Of the 3 739 individuals tagged (1984–2018), only 30 (1%) were recaptured after an average of 487 days at liberty. The majority (60%) of the recaptures occurred within 10 km of the release site, while 7% had moved more than 1 000 km along the coast. The longest recorded movements (1 577 and 1 756 km) were undertaken by adult rays tagged in the Western Cape Province moving to KwaZulu-Natal Province (KZN). The competitive shore angling catch (1977–2018; n = 9 150) from KZN was dominated by adult rays caught north of Durban, while the shark net catch in KZN (1981–2018; n = 584) was dominated by juvenile rays primarily from the central beaches of Durban. All the datasets exhibited strong seasonal trends with most catches taking place in summer. A risk assessment confirmed a stable to increasing population trend over four generations, suggesting that the population sampled along the east coast of South Africa should be classified as Least Concern.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41908054","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 : 2022-01-02DOI: 10.2989/1814232X.2022.2036234
HJ Truter, L. Atkinson, Ceo von der Meden, D. Bailey, W. Goschen, A. Lombard
Unconsolidated marine sediment habitats spatially make up the majority of global ocean seabed, yet benthic faunal patterns and their abiotic drivers remain poorly understood. Benthic research in Algoa Bay, on the south coast of South Africa, has largely focused on rocky reefs, while the dominant unconsolidated sediment habitats have been poorly studied. This study describes epibenthic assemblages associated with unconsolidated sediment in Algoa Bay, at between 30 and 100 m depth, and investigates the relationship between biotic patterns and physical drivers. Epibenthic abundance data were quantified from benthic imagery and tested against the long-term means and coefficients of variation of 12 abiotic factors, including depth, mean grain size and bottom temperature. Multivariate analyses revealed two statistically distinct epibenthic communities. This pattern was largely explained by depth, mean grain size, mean bottom temperature and mean current speed (cumulative variation of 52.49%). To a lesser extent, the long-term variability of bottom temperature, current speed and dissolved oxygen also influenced the community (cumulative variation of 34.44%). Visual classification of the substrates indicated that a mixed substrate type (i.e. sand and a low percentage of rock) significantly influences the benthic community. The findings suggest that a combination of depth and substrate type are largely responsible for the epibenthic assemblages observed.
{"title":"Characterising epibenthic diversity and physical drivers in unconsolidated marine habitats of Algoa Bay, South Africa","authors":"HJ Truter, L. Atkinson, Ceo von der Meden, D. Bailey, W. Goschen, A. Lombard","doi":"10.2989/1814232X.2022.2036234","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2036234","url":null,"abstract":"Unconsolidated marine sediment habitats spatially make up the majority of global ocean seabed, yet benthic faunal patterns and their abiotic drivers remain poorly understood. Benthic research in Algoa Bay, on the south coast of South Africa, has largely focused on rocky reefs, while the dominant unconsolidated sediment habitats have been poorly studied. This study describes epibenthic assemblages associated with unconsolidated sediment in Algoa Bay, at between 30 and 100 m depth, and investigates the relationship between biotic patterns and physical drivers. Epibenthic abundance data were quantified from benthic imagery and tested against the long-term means and coefficients of variation of 12 abiotic factors, including depth, mean grain size and bottom temperature. Multivariate analyses revealed two statistically distinct epibenthic communities. This pattern was largely explained by depth, mean grain size, mean bottom temperature and mean current speed (cumulative variation of 52.49%). To a lesser extent, the long-term variability of bottom temperature, current speed and dissolved oxygen also influenced the community (cumulative variation of 34.44%). Visual classification of the substrates indicated that a mixed substrate type (i.e. sand and a low percentage of rock) significantly influences the benthic community. The findings suggest that a combination of depth and substrate type are largely responsible for the epibenthic assemblages observed.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42827940","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 : 2022-01-02DOI: 10.2989/1814232X.2022.2030797
E. Steyn, J. Groeneveld, J. Santos, XI Mselegu
The brown mussel Perna perna is the dominant indigenous mussel along the east coast of South Africa, where it is harvested by recreational and subsistence fishers. High fishing pressure near urban areas led to declining abundance and consequently to the closure of some reefs to fishing in 1998. We estimated trends in mussel population dynamics at exploited and unexploited sites, along fixed transects, over a 27-year period (1993–2019). Trends in recreational fishing effort were inferred from yearly permit sales and existing catch statistics. At high levels of fishing effort, short-term trends in mussel cover and densities were inversely related to fishing effort at three of the four sites considered, while the fourth site was influenced by intermittent breaching of a nearby estuary. Mussel size was inversely related to population densities. The effects of longer-term harvesting bans were partially obscured by sharp declines in fishing effort across the entire recreational fishery. Seasonal and interannual patterns in cover and density were partially synchronised among sites, indicating environmental forcing at similar time-scales. The long-term dataset was invaluable in disentangling the relative effects of fishing and environmental factors on mussel population dynamics and should be continued as a baseline for assessing future climate-induced effects on rocky-shore biota.
{"title":"Trends in mussel cover, density and size at exploited and unexploited intertidal reefs in eastern South Africa","authors":"E. Steyn, J. Groeneveld, J. Santos, XI Mselegu","doi":"10.2989/1814232X.2022.2030797","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2030797","url":null,"abstract":"The brown mussel Perna perna is the dominant indigenous mussel along the east coast of South Africa, where it is harvested by recreational and subsistence fishers. High fishing pressure near urban areas led to declining abundance and consequently to the closure of some reefs to fishing in 1998. We estimated trends in mussel population dynamics at exploited and unexploited sites, along fixed transects, over a 27-year period (1993–2019). Trends in recreational fishing effort were inferred from yearly permit sales and existing catch statistics. At high levels of fishing effort, short-term trends in mussel cover and densities were inversely related to fishing effort at three of the four sites considered, while the fourth site was influenced by intermittent breaching of a nearby estuary. Mussel size was inversely related to population densities. The effects of longer-term harvesting bans were partially obscured by sharp declines in fishing effort across the entire recreational fishery. Seasonal and interannual patterns in cover and density were partially synchronised among sites, indicating environmental forcing at similar time-scales. The long-term dataset was invaluable in disentangling the relative effects of fishing and environmental factors on mussel population dynamics and should be continued as a baseline for assessing future climate-induced effects on rocky-shore biota.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43014262","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 : 2022-01-02DOI: 10.2989/1814232X.2022.2033321
L. Maritz, D. Pillay, GM Branch
Coastal diamond mining in southern Namibia involves constructing seawalls to hold the sea at bay, and seaward accretion of the shoreline by up to 800 m opens what was previously the surf zone for excavation and extraction of bedrock alluvial diamonds. This has created large coastal wetland ponds of up to 380 000 m2 as the sea overtops the seawalls or seeps into the excavated areas. The ages of these ponds span 1–38 years. We investigated physical conditions in the ponds to determine whether they can function as saline wetlands equivalent to blind estuaries. Water temperatures were 6–10 °C higher than in the sea, as expected of shallow enclosed waterbodies. Dissolved oxygen was 82–137%, peaking at midday owing to photosynthesis, and the ponds were never hypoxic. Correlated with oxygen levels, pH values spanned 7.7–8.3, and always exceeded the pH of seawater. Chlorophyll a concentrations matched or exceeded the levels in seawater, reaching 76 µg l−1. The southern and central ponds had salinities close to those of seawater, but the salinity of northern ponds exceeded 80 after ∼15 years, thus limiting their capacity to support wetland communities. Apart from this, these ponds are viable habitat that can support flora and fauna typical of saline wetlands, a habitat that is scarce along this arid coastline.
纳米比亚南部的沿海钻石开采需要建造海堤来阻挡海水，海岸线向海增加了800米，使以前的冲浪区成为挖掘和提取基岩冲积钻石的场所。这创造了多达38万平方米的大型沿海湿地池塘，因为海水超过海堤或渗入挖掘区域。这些池塘的年龄跨度为1-38年。我们调查了池塘的物理条件，以确定它们是否可以作为相当于盲河口的盐水湿地。水温比海中温度高6-10°C，与预期的浅封闭水体一致。溶解氧为82-137%，由于光合作用，溶解氧在中午达到峰值，池塘从不缺氧。与氧含量相关，pH值在7.7-8.3之间，并且总是超过海水的pH值。叶绿素a浓度达到76 μ g l−1，与海水中的水平相当或超过了海水中的水平。南部和中部池塘的盐度接近海水，但北部池塘的盐度在约15年后超过80，从而限制了其支持湿地群落的能力。除此之外，这些池塘是可行的栖息地，可以支持典型的含盐湿地的动植物，这是干旱海岸线上稀缺的栖息地。
{"title":"The ecology of coastal wetland ponds created by diamond mining in southern Namibia. 1. Physical conditions","authors":"L. Maritz, D. Pillay, GM Branch","doi":"10.2989/1814232X.2022.2033321","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2033321","url":null,"abstract":"Coastal diamond mining in southern Namibia involves constructing seawalls to hold the sea at bay, and seaward accretion of the shoreline by up to 800 m opens what was previously the surf zone for excavation and extraction of bedrock alluvial diamonds. This has created large coastal wetland ponds of up to 380 000 m2 as the sea overtops the seawalls or seeps into the excavated areas. The ages of these ponds span 1–38 years. We investigated physical conditions in the ponds to determine whether they can function as saline wetlands equivalent to blind estuaries. Water temperatures were 6–10 °C higher than in the sea, as expected of shallow enclosed waterbodies. Dissolved oxygen was 82–137%, peaking at midday owing to photosynthesis, and the ponds were never hypoxic. Correlated with oxygen levels, pH values spanned 7.7–8.3, and always exceeded the pH of seawater. Chlorophyll a concentrations matched or exceeded the levels in seawater, reaching 76 µg l−1. The southern and central ponds had salinities close to those of seawater, but the salinity of northern ponds exceeded 80 after ∼15 years, thus limiting their capacity to support wetland communities. Apart from this, these ponds are viable habitat that can support flora and fauna typical of saline wetlands, a habitat that is scarce along this arid coastline.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48335481","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 : 2022-01-02DOI: 10.2989/1814232X.2022.2035818
L. Maritz, D. Pillay, GM Branch
Diamond mining on the southern Namibian coastline has created multiple large coastal ponds of up to 380 000 m2 adjacent to the coastline, as the sea overtops erected seawalls or seeps into excavated areas. These ponds span ages of 1–38 years. We investigated whether the ponds offer an environment for the establishment, growth and dispersal of saltmarsh vegetation along the coast, which is otherwise devoid of natural wetlands apart from at the Orange River estuary and Lüderitz Bay. Most ponds supported saltmarshes, but they comprised only a single species, Salicornia natalensis. The abundance of this succulent, mat-forming, salt-tolerant plant was greatest around old ponds, but its health decreased with increasing age and hence salinity of the ponds. The orientation of saltmarshes around the ponds was correlated with prevailing wind direction, suggesting that wind determines dispersal of this plant along the coast. However, any saltmarsh communities that have developed will be disturbed by possible future mining activities. In addition, once mining ends, the saltmarshes will become stressed owing to rising salinities as ponds age. Nevertheless, the ponds are capable of supporting saltmarshes for up to 15 years, and new ponds will be created as mining progresses; this offers an ongoing opportunity for the ponds to serve as ‘stepping stones’ in the dispersal and establishment of S. natalensis along the coast.
{"title":"The ecology of coastal wetland ponds created by diamond mining in southern Namibia. 2. Saltmarsh vegetation","authors":"L. Maritz, D. Pillay, GM Branch","doi":"10.2989/1814232X.2022.2035818","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2035818","url":null,"abstract":"Diamond mining on the southern Namibian coastline has created multiple large coastal ponds of up to 380 000 m2 adjacent to the coastline, as the sea overtops erected seawalls or seeps into excavated areas. These ponds span ages of 1–38 years. We investigated whether the ponds offer an environment for the establishment, growth and dispersal of saltmarsh vegetation along the coast, which is otherwise devoid of natural wetlands apart from at the Orange River estuary and Lüderitz Bay. Most ponds supported saltmarshes, but they comprised only a single species, Salicornia natalensis. The abundance of this succulent, mat-forming, salt-tolerant plant was greatest around old ponds, but its health decreased with increasing age and hence salinity of the ponds. The orientation of saltmarshes around the ponds was correlated with prevailing wind direction, suggesting that wind determines dispersal of this plant along the coast. However, any saltmarsh communities that have developed will be disturbed by possible future mining activities. In addition, once mining ends, the saltmarshes will become stressed owing to rising salinities as ponds age. Nevertheless, the ponds are capable of supporting saltmarshes for up to 15 years, and new ponds will be created as mining progresses; this offers an ongoing opportunity for the ponds to serve as ‘stepping stones’ in the dispersal and establishment of S. natalensis along the coast.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45787585","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 : 2022-01-02DOI: 10.2989/1814232X.2022.2030796
O. B. A. Hadj Hamida, N. B. Hadj Hamida, H. Chaouch, B. Nafkha, N. Ben Ali, D. Abidi, H. Missaoui
The blue swimming crab Portunus segnis (Forskål, 1775) (family Portunidae) is one of the earliest Lessepsian invaders of the Mediterranean Sea and has been recorded for several decades in various Mediterranean areas. However, its presence on the southeastern Tunisian coast is very recent. This study describes the reproductive biology of the species in the Gulf of Gabes, including sex ratio, ovarian maturation, size at sexual maturity, spawning season and fecundity. Samples for biological investigation were collected from the commercial catches of trawlers and artisanal fishing units, from January to December in 2018. A total of 2 762 specimens, ranging from 19 to 158 mm carapace width (CW) and 0.638 to 356.109 g body weight (BW), were analysed. Females outnumbered males by 1.3 to 1 (1 581 vs 1 181 individuals). Sexual maturity was classified into five stages for females and three stages for males, based on visual observation of the colour and shape of the gonads. Spawning occurred three times during the year, with the first peak in May, the second in July, and the third—the most intensive peak—in October–November. Size at sexual maturity was 93.1 mm CW for males, and 93.6 mm CW for females. Females carried 142 242–2 640 080 eggs on their abdomen, with a positive linear relationship between fecundity and CW. The data presented in this study should be useful not only to detect variations in the reproductive cycle of P. segnis between regions but also to ensure sustainable management of the new fishery for the species in Tunisian waters.
{"title":"Reproductive biology of the blue swimming crab Portunus segnis (Forskål, 1775) (Brachyura: Portunidae) in the Gulf of Gabes (southeastern Tunisia, central Mediterranean Sea)","authors":"O. B. A. Hadj Hamida, N. B. Hadj Hamida, H. Chaouch, B. Nafkha, N. Ben Ali, D. Abidi, H. Missaoui","doi":"10.2989/1814232X.2022.2030796","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2030796","url":null,"abstract":"The blue swimming crab Portunus segnis (Forskål, 1775) (family Portunidae) is one of the earliest Lessepsian invaders of the Mediterranean Sea and has been recorded for several decades in various Mediterranean areas. However, its presence on the southeastern Tunisian coast is very recent. This study describes the reproductive biology of the species in the Gulf of Gabes, including sex ratio, ovarian maturation, size at sexual maturity, spawning season and fecundity. Samples for biological investigation were collected from the commercial catches of trawlers and artisanal fishing units, from January to December in 2018. A total of 2 762 specimens, ranging from 19 to 158 mm carapace width (CW) and 0.638 to 356.109 g body weight (BW), were analysed. Females outnumbered males by 1.3 to 1 (1 581 vs 1 181 individuals). Sexual maturity was classified into five stages for females and three stages for males, based on visual observation of the colour and shape of the gonads. Spawning occurred three times during the year, with the first peak in May, the second in July, and the third—the most intensive peak—in October–November. Size at sexual maturity was 93.1 mm CW for males, and 93.6 mm CW for females. Females carried 142 242–2 640 080 eggs on their abdomen, with a positive linear relationship between fecundity and CW. The data presented in this study should be useful not only to detect variations in the reproductive cycle of P. segnis between regions but also to ensure sustainable management of the new fishery for the species in Tunisian waters.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47420953","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 : 2021-10-02DOI: 10.2989/1814232X.2021.1974557
DC van den Berg, K. Sethebe, G. Maneveldt
Following a long-term herbivore-exclusion study (2003-2008) in the mid-eulittoral zone at Kalk Bay, Cape Town, South Africa, the post-herbivore-exclusion effect (12 years later) of the limpet Cymbula oculus, the dominant herbivore in the community, was examined after it had recolonised the area. Despite the limpet having recruited into all plots (previous exclusion plots and control plots), the species richness, percentage cover of sessile organisms, invertebrate densities and invertebrate biomass were all significantly higher in previous exclusion plots compared with in control plots. Cymbula oculus density was higher in previous exclusion plots (11.11 [SD 12.54] ind. m−2) than in control plots (9.26 [SD 7.97] ind. m−2) (p = 0.038); however, its biomass was similar between the previous exclusion plots and control plots (366.39 [SD 421.63] vs 367.96 [SD 285.44] g m−2, p = 0.179), indicating that limpets outside exclusion plots were generally larger. This was likely because of younger C. oculus individuals, heightened interspecific competition, or insufficient space in previous exclusion plots. The observed differences might be attributed to a combination of factors, including the persistence of species that have achieved a size refuge from grazing and bulldozing by C. oculus, as well as the establishment of invasive mussels Mytilus galloprovincialis which offer secondary substrates and microhabitats for the establishment of macroalgae and other invertebrates. The recruitment of M. galloprovincialis into the previous exclusion plots is likely to be the cause of the alternative community state observed. Unless some extreme disturbance event occurs, the community from which C. oculus was previously excluded is unlikely to revert to its pre-C. oculus exclusion state.
{"title":"Determining the post-herbivore-exclusion effect on an intertidal community by the recovery response of a known dominant herbivore","authors":"DC van den Berg, K. Sethebe, G. Maneveldt","doi":"10.2989/1814232X.2021.1974557","DOIUrl":"https://doi.org/10.2989/1814232X.2021.1974557","url":null,"abstract":"Following a long-term herbivore-exclusion study (2003-2008) in the mid-eulittoral zone at Kalk Bay, Cape Town, South Africa, the post-herbivore-exclusion effect (12 years later) of the limpet Cymbula oculus, the dominant herbivore in the community, was examined after it had recolonised the area. Despite the limpet having recruited into all plots (previous exclusion plots and control plots), the species richness, percentage cover of sessile organisms, invertebrate densities and invertebrate biomass were all significantly higher in previous exclusion plots compared with in control plots. Cymbula oculus density was higher in previous exclusion plots (11.11 [SD 12.54] ind. m−2) than in control plots (9.26 [SD 7.97] ind. m−2) (p = 0.038); however, its biomass was similar between the previous exclusion plots and control plots (366.39 [SD 421.63] vs 367.96 [SD 285.44] g m−2, p = 0.179), indicating that limpets outside exclusion plots were generally larger. This was likely because of younger C. oculus individuals, heightened interspecific competition, or insufficient space in previous exclusion plots. The observed differences might be attributed to a combination of factors, including the persistence of species that have achieved a size refuge from grazing and bulldozing by C. oculus, as well as the establishment of invasive mussels Mytilus galloprovincialis which offer secondary substrates and microhabitats for the establishment of macroalgae and other invertebrates. The recruitment of M. galloprovincialis into the previous exclusion plots is likely to be the cause of the alternative community state observed. Unless some extreme disturbance event occurs, the community from which C. oculus was previously excluded is unlikely to revert to its pre-C. oculus exclusion state.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46702351","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 : 2021-10-02DOI: 10.2989/1814232X.2021.1979096
Candice Jansen van Rensburg, A. Robbins, C. Griffiths
The only previous study on the macrobiota of South African boulder shores showed this assemblage to be more diverse than on nearby rocky platforms, but the drivers of that difference remain unresolved. We recorded water and air temperatures under intertidal boulders and on adjacent exposed rocky platforms, at both the upper- and lower-shore level, at Kommetjie, South Africa, over 2-week tidal cycles, repeating this during summer and winter. The macrobiota in each location was also sampled during diurnal low tides. The most-extreme temperatures, and greatest ranges, occurred during summer on upper-shore open rock (13.9–37.7 °C, range difference of 23.8 °C), while under upper-shore boulders the maximum temperature was lower at 28.9 °C and the range spanned only 15.5 °C. In winter, maximum temperatures and ranges were lower at all locations. Maximum temperatures did not coincide with spring tides, but occurred several days later, when low tides happened during the heat of the day. Closer analysis of daily fluctuations revealed influence of weather on temperatures attained and showed that durations of elevated temperatures were much shorter in the lower shore. The upper shore exhibited low biodiversity, supporting only 9 species, with 8 found only under boulders during diurnal low tide; the lower shore was more diverse, with 11 species on open rock and 29 under boulders. Biomass and abundance were also higher under boulders at both levels, especially on the upper shore. More-benign under-boulder conditions thus facilitate more abundant and diverse biota sheltering there than occurs on adjacent exposed rocks, particularly on the upper shore.
{"title":"Temperature cycles beneath, and adjacent to, intertidal boulders and associated differences in biotic composition","authors":"Candice Jansen van Rensburg, A. Robbins, C. Griffiths","doi":"10.2989/1814232X.2021.1979096","DOIUrl":"https://doi.org/10.2989/1814232X.2021.1979096","url":null,"abstract":"The only previous study on the macrobiota of South African boulder shores showed this assemblage to be more diverse than on nearby rocky platforms, but the drivers of that difference remain unresolved. We recorded water and air temperatures under intertidal boulders and on adjacent exposed rocky platforms, at both the upper- and lower-shore level, at Kommetjie, South Africa, over 2-week tidal cycles, repeating this during summer and winter. The macrobiota in each location was also sampled during diurnal low tides. The most-extreme temperatures, and greatest ranges, occurred during summer on upper-shore open rock (13.9–37.7 °C, range difference of 23.8 °C), while under upper-shore boulders the maximum temperature was lower at 28.9 °C and the range spanned only 15.5 °C. In winter, maximum temperatures and ranges were lower at all locations. Maximum temperatures did not coincide with spring tides, but occurred several days later, when low tides happened during the heat of the day. Closer analysis of daily fluctuations revealed influence of weather on temperatures attained and showed that durations of elevated temperatures were much shorter in the lower shore. The upper shore exhibited low biodiversity, supporting only 9 species, with 8 found only under boulders during diurnal low tide; the lower shore was more diverse, with 11 species on open rock and 29 under boulders. Biomass and abundance were also higher under boulders at both levels, especially on the upper shore. More-benign under-boulder conditions thus facilitate more abundant and diverse biota sheltering there than occurs on adjacent exposed rocks, particularly on the upper shore.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2021-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45388396","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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