Pub Date : 2022-04-03DOI: 10.2989/1814232X.2022.2066722
M. Soondur, R. Boojhawon, R. Lowe, D. Kaullysing, B. Casareto, Y. Suzuki, R. Bhagooli
This study aimed to test the effects of rainfall-driven nutrient loading on the microphytoplankton dynamics in the shallow water at Trou aux Biches lagoon on the northwest coast of Mauritius. Changes in density, diversity and estimated productivity of microphytoplankton were monitored in three zones—coast, lagoon and reef—during two rainfall periods of 4 and 3 days’ duration, respectively, in March–April 2017. The average nutrient loading from terrestrial runoff was 15.5% and the salinity decreased by 2.5%. Following the two rainfall events, a 3-fold increase in total microphytoplankton density (TMPD), with a dominance of diatoms, was noted within a week at the coast and lagoon, while it remained relatively unchanged at the reef. These changes in microphytoplankton densities were concomitant with adequate levels of silicate (>2 µM) and high nitrate:silicate ratios (2.84–6.93). During this study, the numbers of genera of diatoms, dinoflagellates and cyanobacteria observed were 28, 12 and 3, respectively. The Shannon–Wiener, equitability and evenness indices showed high diversity values for diatoms and cyanobacteria prior to the rainfall events and for dinoflagellates after the events. The chlorophyll a content, relative electron transport rate, and estimated productivity of microphytoplankton increased during and after the rainy periods. TMPD and chlorophyll a were correlated significantly and positively with nutrients, salinity and temperature. Toxic algal species such as the dinoflagellates Alexandrium, Dinophysis and Tripos were recorded, although not in bloom densities. These findings indicate that rainfall-driven nutrient loading led to an increase in microphytoplankton density and estimated productivity, and a change in its diversity.
本研究旨在测试降雨驱动的营养物质负荷对毛里求斯西北海岸Trou aux Biches泻湖浅水中微型浮游生物动力学的影响。在2017年3月至4月的两次降雨期间，分别监测了海岸、泻湖和珊瑚礁三个区域的浮游生物密度、多样性和估计生产力的变化。陆地径流的平均营养负荷为15.5%，盐度下降了2.5%。在两次降雨事件之后，海岸和泻湖的总浮游生物密度（TMPD）在一周内增加了3倍，其中硅藻占主导地位，而珊瑚礁的密度相对保持不变。这些微小浮游生物密度的变化伴随着充足的硅酸盐水平（>2µM）和高的硝酸盐与硅酸盐比例（2.84-6.93）。在这项研究中，观察到的硅藻、甲藻和蓝细菌的属数分别为28、12和3。Shannon–Wiener等稳定性和均匀度指数显示，在降雨事件之前，硅藻和蓝藻的多样性值很高，而在降雨事件之后，甲藻的多样性也很高。雨季前后，浮游植物叶绿素a含量、相对电子传输速率和估计生产力都有所增加。TMPD和叶绿素a与营养物质、盐度和温度呈正相关。有毒藻类物种，如亚历山大藻（Alexandrium）、恐龙藻（Dinophysis）和三角藻（Tripos），虽然没有开花密度，但都有记录。这些发现表明，降雨驱动的营养负荷导致浮游生物密度和估计生产力的增加，以及其多样性的变化。
{"title":"Rainfall-driven nutrient loading affects coastal phytoplankton in the southwestern Indian Ocean: a lagoon at Mauritius Island","authors":"M. Soondur, R. Boojhawon, R. Lowe, D. Kaullysing, B. Casareto, Y. Suzuki, R. Bhagooli","doi":"10.2989/1814232X.2022.2066722","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2066722","url":null,"abstract":"This study aimed to test the effects of rainfall-driven nutrient loading on the microphytoplankton dynamics in the shallow water at Trou aux Biches lagoon on the northwest coast of Mauritius. Changes in density, diversity and estimated productivity of microphytoplankton were monitored in three zones—coast, lagoon and reef—during two rainfall periods of 4 and 3 days’ duration, respectively, in March–April 2017. The average nutrient loading from terrestrial runoff was 15.5% and the salinity decreased by 2.5%. Following the two rainfall events, a 3-fold increase in total microphytoplankton density (TMPD), with a dominance of diatoms, was noted within a week at the coast and lagoon, while it remained relatively unchanged at the reef. These changes in microphytoplankton densities were concomitant with adequate levels of silicate (>2 µM) and high nitrate:silicate ratios (2.84–6.93). During this study, the numbers of genera of diatoms, dinoflagellates and cyanobacteria observed were 28, 12 and 3, respectively. The Shannon–Wiener, equitability and evenness indices showed high diversity values for diatoms and cyanobacteria prior to the rainfall events and for dinoflagellates after the events. The chlorophyll a content, relative electron transport rate, and estimated productivity of microphytoplankton increased during and after the rainy periods. TMPD and chlorophyll a were correlated significantly and positively with nutrients, salinity and temperature. Toxic algal species such as the dinoflagellates Alexandrium, Dinophysis and Tripos were recorded, although not in bloom densities. These findings indicate that rainfall-driven nutrient loading led to an increase in microphytoplankton density and estimated productivity, and a change in its diversity.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"153 - 169"},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48112367","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 : 2022-04-03DOI: 10.2989/1814232X.2022.2075937
MJ Wilcox, J. Landschoff, C. Griffiths
The recently described amphipod Sunamphitoe roberta lives only on the kelp Ecklonia maxima, where it excavates slit-like burrows along the distal margins of thicker primary fronds. Oval chambers along the bases of these slits may represent feeding areas. As burrowing proceeds, the damage progressively erodes back the frond margins, giving them characteristic attenuated and irregular profiles, and probably impacting secondary frond survival and growth, and hence kelp productivity. A kelp forest in False Bay, South Africa, was surveyed to determine what proportion of kelp was infected as well as which individuals were selected as hosts. Forty kelp heads were also dissected to ascertain numbers of amphipods per host and their size composition, and to document details of burrow structure. Of 305 adult kelps inspected, 117 (38.4%) showed visible amphipod damage. Rate of infestation was not correlated with stipe length but was positively correlated with head circumference and negatively correlated with the proportion of secondary fronds remaining. The 40 kelp heads dissected contained 786 S. roberta specimens. These comprised 154 adults (>8 mm), including 33 ovigerous females, and 632 juveniles (<8 mm). The number of amphipods per host ranged from 1 to 112 (mean 19.7 [SD 25.1]). Size distribution was bimodal, and the largest individual measured 20 mm.
{"title":"Prevalence, population structure and burrow morphology of the kelp-boring amphipod Sunamphitoe roberta","authors":"MJ Wilcox, J. Landschoff, C. Griffiths","doi":"10.2989/1814232X.2022.2075937","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2075937","url":null,"abstract":"The recently described amphipod Sunamphitoe roberta lives only on the kelp Ecklonia maxima, where it excavates slit-like burrows along the distal margins of thicker primary fronds. Oval chambers along the bases of these slits may represent feeding areas. As burrowing proceeds, the damage progressively erodes back the frond margins, giving them characteristic attenuated and irregular profiles, and probably impacting secondary frond survival and growth, and hence kelp productivity. A kelp forest in False Bay, South Africa, was surveyed to determine what proportion of kelp was infected as well as which individuals were selected as hosts. Forty kelp heads were also dissected to ascertain numbers of amphipods per host and their size composition, and to document details of burrow structure. Of 305 adult kelps inspected, 117 (38.4%) showed visible amphipod damage. Rate of infestation was not correlated with stipe length but was positively correlated with head circumference and negatively correlated with the proportion of secondary fronds remaining. The 40 kelp heads dissected contained 786 S. roberta specimens. These comprised 154 adults (>8 mm), including 33 ovigerous females, and 632 juveniles (<8 mm). The number of amphipods per host ranged from 1 to 112 (mean 19.7 [SD 25.1]). Size distribution was bimodal, and the largest individual measured 20 mm.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"181 - 187"},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44850876","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 : 2022-04-03DOI: 10.2989/1814232X.2022.2064548
B. Mann, R. Daly, G. Jordaan, W. Dalton, S. Fennessy
Movement behaviour of the endemic epinephelid Mycteroperca andersoni (formerly allocated to genus Epinephelus) along the east coast of southern Africa was investigated using both conventional dart tagging and passive acoustic telemetry. Results from both methods showed that this species is likely to be a temporary resident on shallow inshore reefs; fish showed high site fidelity and occupied relatively small home ranges for periods seldom exceeding 12 months, whereafter they appeared to undertake ranging-type movements. Adults >400 mm total length were more mobile than juveniles, and the distance moved increased with both fish size and time at liberty. Adults south of Durban, South Africa, moved farther in a northerly direction than those north of Durban, confirming that spawning likely takes place north of Durban. No direct evidence of a spawning migration was found, but anecdotal reports that they form spawning aggregations suggests that migrations for this purpose are likely to occur. The current species-specific linefish regulations and the recently expanded marine protected area network along the east coast of South Africa are believed to be adequate to ensure the future sustainable use of this species. However, improved enforcement of regulations is required, and identification of spawning aggregation sites should be a research priority.
{"title":"Movement behaviour of catface rockcod Mycteroperca (Epinephelus) andersoni (Epinephelidae) off the eastern seaboard of southern Africa","authors":"B. Mann, R. Daly, G. Jordaan, W. Dalton, S. Fennessy","doi":"10.2989/1814232X.2022.2064548","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2064548","url":null,"abstract":"Movement behaviour of the endemic epinephelid Mycteroperca andersoni (formerly allocated to genus Epinephelus) along the east coast of southern Africa was investigated using both conventional dart tagging and passive acoustic telemetry. Results from both methods showed that this species is likely to be a temporary resident on shallow inshore reefs; fish showed high site fidelity and occupied relatively small home ranges for periods seldom exceeding 12 months, whereafter they appeared to undertake ranging-type movements. Adults >400 mm total length were more mobile than juveniles, and the distance moved increased with both fish size and time at liberty. Adults south of Durban, South Africa, moved farther in a northerly direction than those north of Durban, confirming that spawning likely takes place north of Durban. No direct evidence of a spawning migration was found, but anecdotal reports that they form spawning aggregations suggests that migrations for this purpose are likely to occur. The current species-specific linefish regulations and the recently expanded marine protected area network along the east coast of South Africa are believed to be adequate to ensure the future sustainable use of this species. However, improved enforcement of regulations is required, and identification of spawning aggregation sites should be a research priority.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"125 - 137"},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46621865","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 : 2022-04-03DOI: 10.2989/1814232X.2022.2075936
D. Roos, J. Taconet, C. Gentil, B. Brisset, H. Evano, Y. Aumond, J. Huet, C. Lepetit, R. Boymond-Morales, T. Rungassamy, R. Elleboode, K. Mahé
Body length–weight (L–W) relationships of 123 fish species (122 Actinopterygii and 1 Elasmobranchii) were studied from 10 218 individuals caught around Réunion Island from 2000 to 2021. All species, except for 4 with a very small number of individuals and limited length range, showed a significant relationship between total length and total weight. For 52 species, the data showed the body becoming more elongated (i.e. b < 3.0) over their lifespan, while for 63 species the individuals became thicker (i.e. b > 3.0); only 4 species had a b-value equal to 3.0, signifying isometric growth. Of 72 species for which macroscopic observation allowed identification of sex, there was sexual dimorphism for only 9 species (12.5%), with a significant difference between the slopes of the length–weight relationships. Temporal effects were also investigated, using the annual component of time of capture for 75 species and the seasonal component for 73 species. A temporal effect was significant for 27 species (36.0%) when the sampling year was taken into account, and for 14 species (19.2%) when the sampling quarter (season) was taken into account. Finally, among 120 species tested, the relationship between total length and standard length was significant, and among 114 species the relationship between total weight and gutted (eviscerated) weight was significant.
{"title":"Variation of the relationships between lengths and weights applied to 123 fish species observed at Réunion Island (Indian Ocean)","authors":"D. Roos, J. Taconet, C. Gentil, B. Brisset, H. Evano, Y. Aumond, J. Huet, C. Lepetit, R. Boymond-Morales, T. Rungassamy, R. Elleboode, K. Mahé","doi":"10.2989/1814232X.2022.2075936","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2075936","url":null,"abstract":"Body length–weight (L–W) relationships of 123 fish species (122 Actinopterygii and 1 Elasmobranchii) were studied from 10 218 individuals caught around Réunion Island from 2000 to 2021. All species, except for 4 with a very small number of individuals and limited length range, showed a significant relationship between total length and total weight. For 52 species, the data showed the body becoming more elongated (i.e. b < 3.0) over their lifespan, while for 63 species the individuals became thicker (i.e. b > 3.0); only 4 species had a b-value equal to 3.0, signifying isometric growth. Of 72 species for which macroscopic observation allowed identification of sex, there was sexual dimorphism for only 9 species (12.5%), with a significant difference between the slopes of the length–weight relationships. Temporal effects were also investigated, using the annual component of time of capture for 75 species and the seasonal component for 73 species. A temporal effect was significant for 27 species (36.0%) when the sampling year was taken into account, and for 14 species (19.2%) when the sampling quarter (season) was taken into account. Finally, among 120 species tested, the relationship between total length and standard length was significant, and among 114 species the relationship between total weight and gutted (eviscerated) weight was significant.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"171 - 180"},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48420116","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 : 2022-04-03DOI: 10.2989/1814232X.2022.2055643
NN Gabriel, C. Chikwililwa, GM Liswaniso, S. Louw, A. Namwoonde
The anaesthetic effectiveness of separate and combined eucalyptus Eucalyptus globulus and oregano Origanum vulgare essential oils (EO) were investigated in silver kob Argyrosomus inodorus and were compared with clove oil Eugenia caryophyllata. Argyrosomus inodorus adults (595.61 [SE 11.82] g) were exposed to three concentrations of oregano EO (OEO: 25, 50 and 100 µl l−1), eucalyptus EO (EEO: 300, 500 and 600 µl l−1), and their mixtures (12.5 µl l−1 OEO to 150 µl l−1 EEO; 12.5 µl l−1 OEO to 300 µl l−1 EEO; 25 µl l−1 OEO to 150 µl l−1 EEO), with each fish treated as a replicate. Fish were also exposed to 40 µl l−1 of clove oil (CEO), which acted as a control. The two EOs and their mixtures proved to possess anaesthetic capacity in A. inodorus. Anaesthesia induction time (seconds) decreased with increased concentrations, whereas the inverse was reported for the recovery response. Only OEO qualified as an ideal anaesthetic agent for A. inodorus, especially 25 and 50 µl l−1, as the anaesthesia induction times with these concentrations were less than 180 s and recovery was within 300 s. It seems that EEO could achieve greater anaesthetic effectiveness only at a higher concentration (600 µl l−1) or when mixed with OEO (at 25 µl l−1 OEO to 150 µl l−1 EEO). This study introduces oregano as a promising anaesthetic in A. inodorus compared with clove oil and EEO. However, further evaluations are deemed necessary.
{"title":"The effects of eucalyptus Eucalyptus globulus and oregano Origanum vulgare essential oils on anaesthesia response in a Namibian marine species, silver kob Argyrosomus inodorus","authors":"NN Gabriel, C. Chikwililwa, GM Liswaniso, S. Louw, A. Namwoonde","doi":"10.2989/1814232X.2022.2055643","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2055643","url":null,"abstract":"The anaesthetic effectiveness of separate and combined eucalyptus Eucalyptus globulus and oregano Origanum vulgare essential oils (EO) were investigated in silver kob Argyrosomus inodorus and were compared with clove oil Eugenia caryophyllata. Argyrosomus inodorus adults (595.61 [SE 11.82] g) were exposed to three concentrations of oregano EO (OEO: 25, 50 and 100 µl l−1), eucalyptus EO (EEO: 300, 500 and 600 µl l−1), and their mixtures (12.5 µl l−1 OEO to 150 µl l−1 EEO; 12.5 µl l−1 OEO to 300 µl l−1 EEO; 25 µl l−1 OEO to 150 µl l−1 EEO), with each fish treated as a replicate. Fish were also exposed to 40 µl l−1 of clove oil (CEO), which acted as a control. The two EOs and their mixtures proved to possess anaesthetic capacity in A. inodorus. Anaesthesia induction time (seconds) decreased with increased concentrations, whereas the inverse was reported for the recovery response. Only OEO qualified as an ideal anaesthetic agent for A. inodorus, especially 25 and 50 µl l−1, as the anaesthesia induction times with these concentrations were less than 180 s and recovery was within 300 s. It seems that EEO could achieve greater anaesthetic effectiveness only at a higher concentration (600 µl l−1) or when mixed with OEO (at 25 µl l−1 OEO to 150 µl l−1 EEO). This study introduces oregano as a promising anaesthetic in A. inodorus compared with clove oil and EEO. However, further evaluations are deemed necessary.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"205 - 213"},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41951523","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 : 2022-04-03DOI: 10.2989/1814232X.2022.2080268
K. Ortega-Cisneros, E. Weigum, R. Chalmers, S. Grusd, A. Lombard, L. Shannon
The Ecopath with Ecosim (EwE) modelling framework was used to develop a model of Algoa Bay and test the ecosystem impacts of the implementation of the Addo Elephant National Park Marine Protected Area (MPA). The Ecopath model included 37 functional groups ranging from phytoplankton to top predators and was fitted to 12 and 14 time-series of biomass and landings, respectively, from 2010 to 2019 (calibration period), using Ecosim. Two scenarios representing different degrees of fisheries closures in the MPA were explored through a 30% and a 100% reduction in fishing effort. Temporal simulations were run until 2059. The fitting procedure identified the best-fit model as the one including the effects of fishing, the six most-sensitive predator–prey interactions, and environmental forcing (primary production anomaly on small phytoplankton). Overall, the predicted biomass and catch time-series reasonably reproduced the observed time-series for 2010–2019, with the biomass of sardine Sardinops sagax, round herring Etrumeus whiteheadi, and African penguins Spheniscus demersus showing the best fits to data. Both MPA scenarios resulted in higher total biomass compared with the baseline by the end of the simulation and decreased catches due to less fishing effort. The most profound biomass increases under the MPA scenarios were observed in apex and pelagic elasmobranchs, yellowtail Seriola lalandi and African penguins. Future research is needed to improve the more-uncertain model parameters and include other key sectors in Algoa Bay, such as shipping. However, this model provides a good foundation for future work including the application of spatially explicit modelling of the bay using Ecospace.
Ecopath with Ecosim (EwE)建模框架用于开发Algoa湾模型，并测试实施阿多大象国家公园海洋保护区(MPA)对生态系统的影响。Ecopath模型包括从浮游植物到顶级捕食者的37个功能基团，并使用Ecosim分别拟合了2010年至2019年(校准期)的12个和14个生物量和登陆时间序列。通过减少30%和100%的捕捞量，研究了两种不同程度的海洋保护区渔业关闭情景。时间模拟一直持续到2059年。拟合过程确定了最优拟合模型，即包括捕捞效应、六种最敏感的捕食者-猎物相互作用和环境强迫(小型浮游植物的初级生产异常)。总体而言，预测的生物量和捕获量时间序列较好地再现了2010-2019年的观测时间序列，其中沙丁鱼、圆鲱鱼、白头鱼和非洲企鹅的生物量与数据最吻合。在模拟结束时，两种MPA情景的总生物量都高于基线，而由于捕捞努力减少，渔获量减少。海洋保护区情景下生物量增幅最大的是顶、中上层板鳃、黄尾和非洲企鹅。未来的研究需要改进更不确定的模型参数，并包括Algoa湾的其他关键部门，如航运。然而，该模型为未来的工作提供了良好的基础，包括使用Ecospace对海湾进行空间显式建模的应用。
{"title":"Supporting marine spatial planning with an ecosystem model of Algoa Bay, South Africa","authors":"K. Ortega-Cisneros, E. Weigum, R. Chalmers, S. Grusd, A. Lombard, L. Shannon","doi":"10.2989/1814232X.2022.2080268","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2080268","url":null,"abstract":"The Ecopath with Ecosim (EwE) modelling framework was used to develop a model of Algoa Bay and test the ecosystem impacts of the implementation of the Addo Elephant National Park Marine Protected Area (MPA). The Ecopath model included 37 functional groups ranging from phytoplankton to top predators and was fitted to 12 and 14 time-series of biomass and landings, respectively, from 2010 to 2019 (calibration period), using Ecosim. Two scenarios representing different degrees of fisheries closures in the MPA were explored through a 30% and a 100% reduction in fishing effort. Temporal simulations were run until 2059. The fitting procedure identified the best-fit model as the one including the effects of fishing, the six most-sensitive predator–prey interactions, and environmental forcing (primary production anomaly on small phytoplankton). Overall, the predicted biomass and catch time-series reasonably reproduced the observed time-series for 2010–2019, with the biomass of sardine Sardinops sagax, round herring Etrumeus whiteheadi, and African penguins Spheniscus demersus showing the best fits to data. Both MPA scenarios resulted in higher total biomass compared with the baseline by the end of the simulation and decreased catches due to less fishing effort. The most profound biomass increases under the MPA scenarios were observed in apex and pelagic elasmobranchs, yellowtail Seriola lalandi and African penguins. Future research is needed to improve the more-uncertain model parameters and include other key sectors in Algoa Bay, such as shipping. However, this model provides a good foundation for future work including the application of spatially explicit modelling of the bay using Ecospace.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"189 - 204"},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46355081","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 : 2022-04-03DOI: 10.2989/1814232X.2022.2066723
A. Towner, Rga Watson, A. Kock, Y. Papastamatiou, M. Sturup, E. Gennari, K. Baker, T. Booth, M. Dicken, W. Chivell, S. Elwen, T. Kaschke, D. Edwards, M. Smale
Risk-induced fear effects exerted by top predators are pervasive in terrestrial and marine systems, with lasting impacts on ecosystem structure and function. The loss of top predators can disrupt ecosystems and trigger trophic cascades, but the introduction of novel apex predators into ecosystems is not well understood. We documented the emigration of white sharks Carcharodon carcharias in response to the presence of a pair of killer whales, Orcinus orca, at a large white shark aggregation site in South Africa. Between February and June in 2017, five white shark carcasses washed up on beaches in Gansbaai, Western Cape Province, four of which had their livers removed. Sightings per unit effort (sea days) and telemetry data demonstrated that white sharks emigrated from Gansbaai following these predation events, and in response to further sightings of this pair and other killer whale pods in the vicinity. Tagging data demonstrated the immediate departure of white sharks from Gansbaai, and some sharks were subsequently moving east. Contrary to expected and well-documented patterns of white shark occurrence at this site, their sightings dropped throughout the following 2.5 years; change-point analysis on both datasets confirmed these departures coincided with killer whale presence and shark carcasses washing out. These findings suggest that white sharks respond rapidly to risk from a novel predator, and that their absence triggered the emergence of another predator, the bronze whaler Carcharhinus brachyurus. Predator–prey interactions between white sharks, other coastal sharks, and killer whales are increasing in South Africa and are expected to have pronounced impacts on the ecosystem.
{"title":"Fear at the top: killer whale predation drives white shark absence at South Africa’s largest aggregation site","authors":"A. Towner, Rga Watson, A. Kock, Y. Papastamatiou, M. Sturup, E. Gennari, K. Baker, T. Booth, M. Dicken, W. Chivell, S. Elwen, T. Kaschke, D. Edwards, M. Smale","doi":"10.2989/1814232X.2022.2066723","DOIUrl":"https://doi.org/10.2989/1814232X.2022.2066723","url":null,"abstract":"Risk-induced fear effects exerted by top predators are pervasive in terrestrial and marine systems, with lasting impacts on ecosystem structure and function. The loss of top predators can disrupt ecosystems and trigger trophic cascades, but the introduction of novel apex predators into ecosystems is not well understood. We documented the emigration of white sharks Carcharodon carcharias in response to the presence of a pair of killer whales, Orcinus orca, at a large white shark aggregation site in South Africa. Between February and June in 2017, five white shark carcasses washed up on beaches in Gansbaai, Western Cape Province, four of which had their livers removed. Sightings per unit effort (sea days) and telemetry data demonstrated that white sharks emigrated from Gansbaai following these predation events, and in response to further sightings of this pair and other killer whale pods in the vicinity. Tagging data demonstrated the immediate departure of white sharks from Gansbaai, and some sharks were subsequently moving east. Contrary to expected and well-documented patterns of white shark occurrence at this site, their sightings dropped throughout the following 2.5 years; change-point analysis on both datasets confirmed these departures coincided with killer whale presence and shark carcasses washing out. These findings suggest that white sharks respond rapidly to risk from a novel predator, and that their absence triggered the emergence of another predator, the bronze whaler Carcharhinus brachyurus. Predator–prey interactions between white sharks, other coastal sharks, and killer whales are increasing in South Africa and are expected to have pronounced impacts on the ecosystem.","PeriodicalId":7719,"journal":{"name":"African Journal of Marine Science","volume":"44 1","pages":"139 - 152"},"PeriodicalIF":1.2,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45499213","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.2022.2028674
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":"44 1","pages":"1 - 9"},"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":"44 1","pages":"83 - 100"},"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":"44 1","pages":"35 - 48"},"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}
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