African Journal of Marine Science 2021-02-04T19:44:18+00:00 Publishing Manager Open Journal Systems <p>The <em>African</em> (formerly <em>South African</em>) <em>Journal of Marine Science</em> provides an international forum for the publication of original scientific contributions or critical reviews, involving oceanic, shelf or estuarine waters, inclusive of oceanography, studies of organisms and their habitats, and aquaculture. Papers on the conservation and management of living resources, relevant social science and governance, or new techniques, are all welcomed, as are those that integrate different disciplines. Priority will be given to rigorous, question-driven research, rather than descriptive research. Contributions from African waters, including the Southern Ocean, are particularly encouraged, although not to the exclusion of those from elsewhere that have relevance to the African context. Submissions may take the form of a paper or a short communication. The journal aims to achieve a balanced representation of subject areas but also publishes proceedings of symposia in dedicated issues, as well as guest-edited suites on thematic topics in regular issues.</p><p class="MsoNormal">The <em>African Journal of Marine Science</em> is available full text online and more information can be accessed <a href="" target="_blank">here</a>. </p> Intercolony health evaluation of wild African penguins Spheniscus demersus, in relation to parasites, along the southwest coast of South Africa 2021-02-04T19:44:17+00:00 M.P.A. Espinaze C. Hui L. Waller S. Matthee <p>Clinical parameters of African penguins Spheniscus demersus have been recorded mostly from birds admitted<br>to rehabilitation centres and are typically presented as mean values across a region. It is uncertain whether these values are representative of wild penguins and whether they are influenced by parasite infestations. We assessed general clinical parameters from 793 African penguins (210 adults and 583 chicks) at five South African&nbsp; colonies, in 2016 and 2017, and then established the relationship between those values and parasite infestations. Penguins at Dassen Island had indications of a different health status: lower body condition and total plasma protein, and higher haematocrit and ectoparasite richness. Overall, haematocrit values were lower for the mainland colonies than for the island colonies. All clinical parameters were significantly lower in spring than in autumn/winter. Both ectoparasite and haemoparasite taxon richness were negatively related to&nbsp; haematocrit values, while helminth taxon richness was positively related to body mass and haematocrit. At the Stony Point colony, tick abundance and ectoparasite and haemoparasite taxon richness were associated with lower haematocrit in adults and chicks. This study highlights intercolony variations in the health status of African penguins and potential factors (such as parasite infestations and/or food-resource accessibility) that might affect specific colonies, thereby helping to focus conservation efforts.</p> <p><strong>Keywords</strong>: body condition, clinical parameters, ectoparasite abundance, haematocrit, health status, intercolony variation, parasite infestation, seasonal variation </p> 2021-02-03T00:00:00+00:00 Copyright (c) 2021 Composition, structure and diversity of fish assemblages across seascape types at Príncipe, an understudied tropical island in the Gulf of Guinea (eastern Atlantic Ocean) 2021-02-04T08:27:37+00:00 F. Otero-Ferrer F. Tuya NE Bosch Guerra A. Herrero-Barrencua A.D. Abreu R. Haroun <p>Coastal seascapes are often composed of a mosaic of interconnected habitats. Transitions between adjacent habitats are of special relevance to the ecology of many reef-associated organisms. In this study, we tested (i) whether the degree of similarity in the composition and structure of coastal fish assemblages differed between three interconnected seascape types, and (ii) whether differences in taxonomic and phylogenetic diversity of the<br>fish assemblages were consistent between the seascape types. We sampled fish species from diverse habitats in the shallow coastal waters surrounding the island of Príncipe (Gulf of Guinea, eastern Atlantic Ocean), an understudied and remote tropical island. Specifically, video transects were carried out by SCUBA divers at three seascape types: rocky reefs, rocky reef–rhodolith bed transitions, and rocky reef–sandy bottom transitions, to extract presence/absence and ordinal abundance data, across a range of depths (9–31 m), covering the entire perimeter of the island. A total of 71 fish taxa were recorded. Both the composition and structure of the fish assemblages differed between the studied seascapes. The mean number of fish species (taxonomic diversity) was higher on ‘reefs’ than in both the ‘reef–rhodolith bed’ and ‘reef–sandy bottom’ transitions. In contrast, the taxonomic distinctness index (phylogenetic diversity) was higher for fish assemblages in both transitional seascape types than on rocky reefs. Hence, at the island-scale, the protection of local fish assemblages needs to consider a representative network of interconnected&nbsp; habitats, including at these seascapes boundaries where important ecological functions seem to occur.</p> <p><strong>Keywords</strong>: biodiversity, conservation, ecotones, equatorial West Africa, ichthyofauna, tropical reefs, underwater video, Wallacean shortfall </p> 2021-02-04T00:00:00+00:00 Copyright (c) Presence of microplastics in benthic macroinvertebrates along the Kenyan coast 2021-02-04T11:28:09+00:00 W. Awuor A.W.N. Muthumbi D.V. Robertson-Andersson <p>Microplastics (MPs) are plastics less than 5 mm in diameter. Their small size renders them invisible to deposit- and filter-feeding fauna, leading to unintentional ingestion. This study investigated the presence of MPs in an oyster (<em>Saccostrea cuccullata</em>) and three species of brachyuran crabs (<em>Tubuca dussumieri, Cranuca inversa </em>and<em> Gelasimus vocans</em>) along the Kenyan coast. Sampling was carried out at eight stations distributed between three sites: Tudor, Port Reitz and Mida creeks, in January and February 2018, during low spring tide. The sample comprised 206 crabs and 70 oysters. Samples were digested using 10% KOH at 60 °C for 24 hours and then passed through 38-µm sieves. Sieved products (&lt;38 µm) were filtered through Whatman filter membranes (0.8 µm) and viewed under a dissecting microscope for MPs. The study identified mainly MP fibres, which were of different colours: red, yellow, black, pink, orange, purple, green, blue and colourless. Colourless fibres were the most prevalent, comprising at least 60% of the total MPs. Mean lengths of MPs fibres of different colours were between 0.1 and 4.2 mm. The mean concentration of MPs (MPs g−1 wet tissue) was 0.65 (SE 0.13) in crabs and 3.36 (SE 0.53) in oysters, and the difference between the two taxa was significant (independent two-sample t-test: t = 5.61, df = 14, p = 0.01). The higher mean concentration in oysters was attributed mainly to their filter-feeding habit. This study exposes MP pollution along the Kenyan coast and its uptake by marine fauna, and thus strengthens the case for better control of<br>plastic wastes in the ocean.</p> <p><strong>Keywords</strong>: deposit feeders, East Africa, filter feeders, genus Uca, ingested microplastics, marine fauna, plastic pollution, <em>Saccostrea cuccullata</em></p> 2021-02-04T00:00:00+00:00 Copyright (c) Spatial and temporal diversity of non-native biofouling species associated with marinas in two Angolan bays 2021-02-04T11:49:54+00:00 L.B. Pestana G.M. Dias A.C. Marques <p>Artificial structures in coastal areas provide substrates which facilitate the spread of non-native species. Published records of introduced benthic species in the coastal waters of Angola are scarce, and so far these have numbered 29 non-native species and seven cryptogenic species. This study aimed to describe the spatial and temporal diversity of non-native biofouling species (<em>Cnidaria, Annelida, Cirripedia, Bryozoa </em>and<em> Ascidiacea</em>) in marinas in Luanda and Lobito bays. Settlement plates were employed for three months to enable development of the sessile community. We then<br>identified all organisms retreived and compared the composition of introduced species between the sites and seasons (dry and wet). Species composition varied between seasons and sites, and 13 taxa (11 introduced) were recorded for the first time for Angolan waters, including nuisance species, such as the <em>bryozoans Watersipora subtorquata and Amathia verticillata</em>. Of the 35 taxa recorded, 21 were introduced species, 10 were not identified to species level, and only two species were native to the Angolan coast—corroborating the role of marinas and ports as main pathways for<br>introductions, and the need for studies in Angola and on the tropical west coast of Africa in general. Our study expands, from 36 to 49, the number of introduced sessile animals recorded for the Angolan coast. Species known to cause harmful effects on coastal facilities elsewhere were among those most frequently recorded in the studied marinas. The findings indicate that monitoring initiatives and comparisons of biological communities between artificial and natural habitats are essential for the management of bioinvasions, to prevent both ecological and economic losses.</p> <p><strong>Keywords</strong>: alien species, artificial substrate, bioinvasion, fouling species, marine introduced species, <em>Watersipora subtorquata</em>, eastern Atlantic</p> 2021-02-04T00:00:00+00:00 Copyright (c) Spatial and ontogenetic variability in the diet and trophic ecology of two co-occurring catsharks (Scyliorhinidae) off South Africa 2021-02-04T12:08:42+00:00 G.M. van der Heever C.D. van der Lingen R.W. Leslie M.J. Gibbons <p>The Izak catshark Holohalaelurus regani and the yellow-spotted catshark <em>Scyliorhinus capensis</em> both occur over the continental shelf around South Africa and are often caught together as bycatch in demersal trawls. Yet our understanding of their diet is fragmented, which makes determination of their place in ecosystem models difficult. Using material collected along the coastline and at a variety of depths, we analysed the diet and assessed the trophic ecology of different size classes of each species, using analyses of stomach contents and stable isotopes. The most important prey items consumed by both species were crustaceans, cephalopods and teleosts. Highertrophic-level prey were more important for <em>H. regani</em> than for S. capensis, and these prey were also more common in the diet of each species on the west coast than on the south coast. Differences in the prey species consumed, compared by coast, size class and depth, were also detected, with the catshark species feeding on the (presumed) most-abundant prey on each coast. Individual catsharks consumed larger, higher-trophic-level prey items with increasing size and depth. Dietary differences were also reflected in the stable isotopes: generally higher δ15N values were noted from samples on the west coast than on the south coast; a significant interspecific difference in δ15N values was detected; and δ15N values increased with increasing size in both species. The present study provides a multidisciplinary framework for a better understanding of the diet and trophic ecology of these catshark species and emphasises the important structuring role (through food-web effects) that these fish play in benthic communities off South Africa’s coast.</p> <p><strong>Keywords</strong>: benthic community, demersal fish, Holohalaelurus regani, mesopredator, nitrogen-15, prey types, <em>Scyliorhinus capensis</em>, stable isotopes</p> 2021-02-04T00:00:00+00:00 Copyright (c) Common dolphin <I>Delphinus delphis</I> occurrence off the Wild Coast of South Africa 2021-02-04T12:32:00+00:00 M. Caputo P.W. Froneman S. Plön <p>Despite their typical large group sizes, limited research exists on the occurrence of common dolphins <em>Delphinus delphis</em> because of the pelagic, offshore nature of this species and the lack of barriers to their movement in this environment. The main purpose of our study was to investigate the occurrence of common dolphins off the Wild Coast of South Africa (western Indian Ocean) and whether spatiotemporal and environmental conditions affected their encounter rate, relative abundance and mean group size. The annual sardine run in this region, during austral winter (May to July), is considered a main driver of dolphin occurrence; however, our boat-based surveys over the period 2014–2016 indicated that common dolphins occur and feed in this area outside of this time-frame. In terms of environmental factors, the largest group (~1 250 animals) was found in the deepest waters. Additionally, at Hluleka, dolphins were observed primarily feeding, which could suggest that this coastal area is highly&nbsp; productive. As common dolphin distribution is thought to be correlated with prey distribution, our findings suggest that sufficient prey exists along the Wild Coast both during and outside the annual sardine run to sustain large groups of the dolphins and that their presence in the area is not solely a function of the sardine run.</p> <p><strong>Keywords</strong>: boat-based survey, encounter rate, feeding behaviour, group size, relative abundance, sardine run </p> 2021-02-04T00:00:00+00:00 Copyright (c) Effects of nest management methods on hatching success and predation rates of hawksbill turtles on Cousine Island, Seychelles 2021-02-04T17:52:03+00:00 J. Gane C.T. Downs I. Olivier M. Brown <p>Sea turtle populations have declined globally and are of conservation concern. We investigated the effects of nest management methods on hatching success and egg/hatchling predation rates of hawksbill turtles Eretmochelys imbricata on Cousine Island, Seychelles. We determined the effectiveness of two different crab-barrier methods (netted and fenced) on hatching success and predation rates. We examined the relative influence of nest-site cover (full sun, partial sun or full shade) and location (zones of high risk or low risk of predation) on hatching success and predation rates. We also examined temperature disparity between netted and control nests to estimate potential effects on sex ratios and measured typical beach-substrate temperatures in the different nesting habitats. We compared data from 40 netted, 40 fenced and 40 control nests during the 2014/2015 breeding season. Overall, hawksbill turtle hatching success was not significantly affected by treatment or cover; however, netted nests and nests incubating in full sun had the highest mean hatching success. Predation rate was generally low but variable, and the rates differed significantly between the three treatments. Nest temperatures differed significantly between the netted and control nests, with netting used to protect nests having a substantial cooling effect. Hatchling sex ratios for natural nests were skewed towards females and those for netted nests skewed towards males. With climate change and increasing ambient temperatures imminent, a better understanding of how the spatial distribution of nests and variations in environmental factors influence hawksbill turtle hatching success and the levels of predation on eggs and hatchlings will assist future conservation measures.</p> <p><strong>Keywords</strong>: <em>Eretmochelys imbricata</em>, ghost crab, nest temperature, pivotal temperature, predation barrier, sea turtle conservation, sex ratio, western Indian Ocean</p> 2021-02-04T00:00:00+00:00 Copyright (c) Age estimates of chokka squid <I>Loligo reynaudii</I> off South Africa and their use to test the effectiveness of a closed season for conserving this resource 2021-02-04T18:15:13+00:00 M.R. Lipiński C.H. Mwanangombe D. Durholtz D. Yemane J. Githaiga-Mwicigi W.H.H. Sauer <p>This study presents age distributions in an exploited population of spawning chokka squid<em> Loligo reynaudii</em> together with their back-calculated spawning times, and considers the results in relation to the exploitation of this species. Samples were collected during two closed fishing seasons, in 2003 and 2004. Age after hatching ranged, in males, from 168 to 484 days, with a mean of 323 days (71–425 mm mantle length [ML]), and in females from 125 to 478 days, with a mean of 316 days (83–263 mm ML). Detailed analysis of catches during nine days of fishing after the end of the closed season indicated strongly that the closed season (October–November) has been beneficial for both the chokka resource and the fishery. The temporal distribution of egg-laying events for parental populations, and a high abundance of squid in the days immediately after the end of the closed season, indicate a link between the parental spawning stock and the resulting spawning stock. This hypothesis was formulated using the&nbsp; distribution of egg-laying events in time, the strength of egg-laying events, and data for the daily catch immediately (i.e. nine days) after the closed season. However, the hypothesis requires rigorous testing using statoliths collected over a longer period.</p> <p><strong>Keywords</strong>: age distribution, catch pattern, commercial jig catches, egg-laying date, statoliths, stock–recruitment relationship </p> 2021-02-04T00:00:00+00:00 Copyright (c) Application of a general methodology to understand vulnerability and adaptability of the fisheries for small pelagic species in the Benguela countries: Angola, Namibia and South Africa 2021-02-04T19:16:47+00:00 K.L. Cochrane K. Ortega-Cisneros J.A. Iitembu C.I. dos Santos W.H.H. Sauer <p>The fisheries for small pelagic species in Angola, Namibia and South Africa fulfil important social and economic roles but have undergone substantial changes in recent years, some of which are likely to be related to climate change. This assessment of vulnerability and possible adaptation options for the main stakeholder groups in these fisheries was based on a framework encompassing ecological, social and economic vulnerability and the broader economic and governance context of the countries. Information was gathered through stakeholder consultations and workshops as well as from published information. Adaptation options were identified primarily through consultation with stakeholders. Namibia was considered to have the most vulnerable fishery because of the poor state of the sardine population and limited alternatives. Angola and South Africa were estimated to be moderately vulnerable for different reasons. Alternative sources of livelihoods are scarce, and the wellbeing of&nbsp; stakeholders is highly dependent on the resilience and adaptive capacity of individual fishing companies. For land-based and sea-going workers (fulltime and permanent), skills improvement to increase their flexibility and employability within and beyond fisheries is a primary adaptation&nbsp; option. Key roles for governments include ensuring effective governance and facilitating sustainable economic development, especially in&nbsp; underdeveloped coastal areas.</p> <p><strong>Keywords</strong>: adaptation options, climate change, consultation, fishery vulnerability, national fisheries, recommendations, southern Benguela, stakeholders </p> 2021-02-04T00:00:00+00:00 Copyright (c) Towed passive acoustic monitoring complements visual survey methods for Heaviside’s dolphins <I>Cephalorhynchus heavisidii</I> in the Namibian Islands Marine Protected Area 2021-02-04T19:24:22+00:00 T. Gridley M.J. Martin J. Slater J-P Roux R.J. Swift SH Elwen <p>The genus Cephalorhynchus contains four dolphin species, of which three are classified as Near Threatened or Endangered and one subspecies is close to extinction. Understanding the species’ abundance, distributions and habitat preferences is necessary for effective management to prevent further population declines. Heaviside’s dolphin C. heavisidii is endemic to the Benguela ecosystem off southwest Africa, and like other&nbsp; Cephalorhynchus species these dolphins produce narrowband high-frequency (NBHF) echolocation clicks with a centroid frequency around 125 kHz. We conducted dedicated visual and acoustic line-transect surveys within and adjacent to the Namibian Islands Marine Protected Area in 2012–2014. Acoustic data were processed in the passive acoustic monitoring software PAMGuard, using the default porpoise click detector and classifier to identify NBHF echolocation clicks. Click detection and classification in PAMGuard included a large excess of false positives, which were easily identified by manual verification of events, and ultimately provided 52 definite detections. The acoustic methods provided data in offshore areas and during overnight periods, but were imperfect and not suitable for ecologically important shallow coastal areas. While demonstrating the utility of passive acoustic monitoring in line-transect surveys targeting Cephalorhynchus species, the study shows that both visual and acoustic methods were needed to collect data throughout the range of Heaviside’s dolphin.</p> <p><strong>Keywords</strong>: click detection and classification, echolocation, encounter rate, line-transect survey, narrowband high-frequency clicks, PAMGuard,<br>southwestern Atlantic</p> 2021-02-04T00:00:00+00:00 Copyright (c) Status of a decennial marine invasion by the bisexual mussel <I>Semimytilus algosus</I> (Gould, 1850) in South Africa 2021-02-04T19:44:18+00:00 K.C.K. Ma C.D. McQuaid A. Pulfrich T.B Robinson <p>The invasion history and current distribution of the alien marine mussel, the bisexual mussel <em>Semimytilus algosus</em>, on rocky shores of South Africa is described in this study. The eastern edge of its distribution has been monitored since 2014, and the most-recent observations were made between January and March of 2020, at 16 sites between Hondeklipbaai on the west coast and Nature’s Valley on the south coast. From these 2020 records, the species ranged across approximately 840 km along the coast, from Hondeklipbaai to Hermanus. The species’ invasion history and distribution suggests that this mussel has persisted on the west coast over the past decade, and spread along the coast in both northward and south–southeastward directions. Since 2010, the species has spread predominantly in a southerly and then easterly direction, extending its range by ~270 km into the Agulhas ecoregion. In contrast, its spread has been slower to the north, with a range extension of only ~75 km. Long-term, routine monitoring of the coast to track the spread of <em>S. algosus</em> and other invasive marine species, and to identify new incursions, is recommended to support evidence-based management of biological invasions.</p> <p><strong>Keywords</strong>: biological invasion, bivalve, invasive species, monitoring, Mytilidae,&nbsp; Namibia, rocky shore, southern Africa</p> 2021-02-04T00:00:00+00:00 Copyright (c) 2021