UWCScholar :: Browsing by Author "Gibbons, Mark J."

Browsing by Author "Gibbons, Mark J."

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Abalone nutrition – growth performance of Haliotis midae in relation to variable artificial feeds
(University of Western Cape, 2020) Mohamed, Riaaz; Gibbons, Mark J.
Abalone are among the most expensive and sought-after seafood subjects. In South Africa, Haliotis midae is the only commercially significant abalone species and it has become increasingly sold on the global market. The importance of abalone as a mariculture subject has triggered extensive research into maximizing production, with particular emphasis on optimizing growth rates. This study aimed to assess the growth performance of Haliotis midae relative to 1) standard pelleted feed, and 2) kelp-inclusive pelleted feed. I assessed feed stability of the dietary treatments and growth parameters associated with abalone weight gain. Temperature and time of feed submersion were found to significantly affect feed stability. Although there were no significant differences in water stability between feeds, the kelp-inclusive feed produced significantly lower total suspended solids (TSS) than the standard pelleted feed at upper time-temperature combinations.
Acoustic observations of jellyfish in the Namibian Benguela
(Inter-Research, 2001) Brierley, Andrew S.; Axelson, Bjorn Erik; Buecher, Emmanuelle; Sparks, Conrad A.J.; Boyer, Helen; Gibbons, Mark J.
Multi-frequency acoustic data (18, 38 and 120 kHz) were collected in conjunction with pelagic trawl sampling for gelatinous macrozooplankton during a cruise to the Namibian Benguela in September 1999. Sampling focused specifically on the scyphozoan Chrysaora hysoscella and the hydrozoan Aequorea aequorea, both of which occur in large numbers, are probably of major ecological importance, and physically hamper pelagic fishing and diamond extraction activities. C. hysoscella was detected predominantly at an inshore station and A. aequorea was found in greatest abundance further offshore in deeper water. Echo-sounder observations were linked directly to net catches, and relationships between catch density (number of individuals m–3) and nautical area scattering coefficients (sA) at each frequency were determined for both species in order to estimate target strength (TS) using the comparison method. TS for C. hysoscella (mean umbrella diameter 26.8 cm) was –51.5 dB at 18 kHz, –46.6 dB at 38 kHz and –50.1 dB at 120 kHz; for A. aequorea (mean central umbrella diameter 7.4 cm) TS was –68.1 dB at 18 kHz, –66.3 dB at 38 kHz and –68.5 dB at 120 kHz. These TS values compared favourably with previously published estimates for related species. Jellyfish were caught at high numerical densities (maxima 3 C. hysoscella per 100 m3, 168 A. aequorea per 100 m3). These high densities, combined with the not unsubstantial TS at frequencies used for fisheries surveys, imply that jellyfish could potentially bias acoustic estimates of fish abundance. We suggest a simple multifrequency approach that could be used to discriminate between echoes from jellyfish and some commercially important pelagic fish in the northern Benguela ecosystem.
Beyond the jellyfish joyride and global oscillations: advancing jellyfish research
(Oxford University Press, 2013) Gibbons, Mark J.; Richardson, Anthony J.
There has been debate in the literature recently about increases in jellyfish populations in response to anthropogenic change, and this has attracted widespread media interest. Despite an international collaborative initiative [National Center for Ecological Analysis and Synthesis (NCEAS) working group on jellyfish blooms] to investigate trends in global jellyfish numbers, interpretations from the data remain ambiguous. Although this is perhaps to be expected given the diversity of potential drivers, the debate has not been helped by a general lack of rigorous data and loose definitions. There is a need for the community to refocus its attention on understanding the implications of jellyfish blooms and managing them, because regardless of global trends, jellyfish are a problem in some coastal marine ecosystems. Here, we provide recommendations for advancing jellyfish research. These include directing research toward better managing jellyfish impacts, expanding research into socio-economic consequences to grow the money available for research, building more operational and ecosystem models for tactical and strategic management, filling in the gaps in our biological knowledge for supporting models, improving surveillance using observing systems and making jellyfish research more rigorous. Some vehicles to address these recommendations include international standardization of methods, a discipline-specific journal for jellyfish research and an international science program on the global ecology and oceanography of jellyfish.
Carybdea branchi, sp. nov., a new box jellyfish (Cnidaria: Cubozoa) from South Africa.
(Magnolia Press, 2009) Gershwin, Lisa-Ann; Gibbons, Mark J.
A common and conspicuous member of the medusan fauna of South Africa has been the subject of repeated taxonomic confusion. After having been mistakenly identified by earlier workers as either Carybdea alata or Tamoya haplonema, this large and colourful carybdeid is described herein as Carybdea branchi, sp. nov. It is distinguished from its congeners on numerous characters: body to about 8cm in life, densely scattered with nematocyst warts over the whole body and abaxial keels of the pedalia; a bulge or lateral thorn on the pedalial canal bend; with 2 dendritic velarial canals per octant, highly diverticulated; with a long manubrium; with greatly bushy epaulette-like phacellae, comprising 20 or more roots tightly clustered; with well developed mesenteries; and with conspicuous brownish pigmented areas over the proximal and distal regions of the pedalia and over the phacellae. A comparative table of the primary diagnostic characters of species in the genus Carybdea is given.
Creating opportunities through science symposia
(South African Assn. For The Advancement Of Science, 2020) Gibbons, Mark J.; Florence, Wayne K.; Musson, Maryke
For most marine scientists, unless we work in the field of fisheries development or at the interface of science and policy, it is rare to feel that we are making an impact on the lives of people in the wider community. Most research scientists at universities and government laboratories also have limited opportunity to engage with schools and the general public outside of once-a-year open days. But beyond the science and networking, conferences, especially international conferences, can provide a myriad of opportunities for us to redress both these issues in a way that enriches all. Here, we describe the programme of development-related activities that supported the 6th International Jellyfish Blooms Symposium, and their impact, and we urge it be used as a template for other scientific meetings in the future. Jellyfish are far more than merely an interesting find on the beach. On the one hand, when abundant, jellyfish can cause economic harm to the tourism, aquaculture, fisheries and energy sectors1, but on the other hand, they provide food for other animals, e.g. turtles, shelter for juvenile fish and a potential resource to exploit2. In recognition of their role in marine ecosystems, the international jellyfish community updates and renews itself at a conference every 3 years or so. The first meeting was held in the USA in January 2000 and after conferences in Australia, Argentina, Japan and Spain, Africa’s turn came in 2019, after Monty Graham (University of Southern Mississippi) convinced one of us (M.J.G.) to host the conference at the University of the Western Cape.
Diet of whale sharks Rhincodon typus inferred from stomach content and signature fatty acid analyses
(Inter Research, 2013) Rohner, Christoph A.; Couturier, Lydie I. E.; Richardson, Anthony J.; Pierce, Simon J.; Prebble, Clare E. M.; Gibbons, Mark J.; Nichols, Peter D.
Whale sharks Rhincodon typus are large filter-feeders that are frequently observed feeding in surface zooplankton patches at their tropical and subtropical coastal aggregation sites. Using signature fatty acid (FA) analyses from their subdermal connective tissue and stomach content analysis, we tested whether whale sharks in Mozambique and South Africa predominantly feed on these prey and/or what other prey they target. Arachidonic acid (20:4ω6; mean ± SD = 17.8 ± 2.0% of total FA), 18:0 and 18:1ω9c were major FA of whale sharks, while in contrast, coastal epipelagic zooplankton collected near feeding whale sharks had 22:6ω3 (docosahexaenoic acid), 16:0 and 20:5ω3 (eicosapentaenoic acid) as major FA. Stomach contents of 3 stranded sharks were dominated by mysids (61 to 92% of prey items), another one by sergestids (56%), and a fifth stomach was empty. The dominant mysids (82% index of relative importance) were demersal zooplankton that migrate into the water column at night, suggesting night-time feeding by whale sharks. High levels of bacterial FA in whale sharks (5.3 ± 1.4% TFA), indicating a detrital link, potentially via demersal zooplankton, also support night-time foraging activity. High levels of oleic acid (16.0 ± 2.5%) in whale sharks and their similarity with FA profiles of shrimp, mysids, copepods and myctophid fishes from the meso- and bathypelagic zone suggest that whale sharks also forage in deep-water. Our findings suggest that, in the patchy food environment of tropical systems, whale sharks forage in coastal waters during the day and night, and in oceanic waters on deep-water zooplankton and fishes during their long-distance movements.
Diversity and Zoogeography of South African Bryozoa
(University of the Western Cape, 2017) Boonzaaier, Melissa Kay; Gibbons, Mark J.
The taxonomic history of South African bryozoans is fragmented and outdated, with the majority of published works in the 20th Century. Sampling gaps exist in deep-sea regions and parts of the coastline, while existing collections within museums remain undetermined due to scarcity of specialist taxonomists. This project forms part of a larger project aimed at updating marine invertebrate biodiversity in South Africa. Outcomes of this project include updating bryozoan biodiversity by identifying species from existing collections housed in natural history museums (e.g., Iziko South African Museum, Cape Town and Natural History Museum, London), and analysing current regional bryozoan biogeographical and depth-related species richness patterns. The biogeography and richness of bryozoan species around South Africa was investigated using published distribution records from the literature and museum catalogues as well as examining un-worked bryozoan material from Iziko South African Museum. A total of 368 species of bryozoans were recorded, including twelve new species (Favosipora epiphyta sp. nov., Chaperiopsis (Chaperiopsis) yinca sp. nov., Aspidostoma staghornea sp. nov., Micropora erecta sp. nov., Trypostega infantaensis sp. nov., Khulisa ukhololo sp. nov., Adeonella assegai sp. nov., Celleporaria umuzi sp. nov., Hippomonavella lingulatus sp. nov., Microporella lezinyosi sp. nov., Phidolopora cyclops sp. nov. and Reteporella ilala sp. nov.) and 70 unidentified species. Distribution data for 286 valid species were separated by depth zones (shallow waters, subphotic zone, shelf edge, bathyal zone and abyss) and four biogeographic regions are recognised a priori around South Africa, namely the west, south, southeast and east coasts. This study revealed that there is a clear biogeographic structure to regional bryozoan fauna of South Africa. Species richness and endemism appear lowest on the west coast (104 species) and highest on the south coast (174 species), while local peaks are observed in the Cape Peninsula/False Bay area, East London, Durban and St. Lucia, which coincide with distinct genetic lineages for some marine taxa (e.g. octocorals, chitons, echinoderms, fishes, seaweeds). Although, the faunal break in Durban does not represent a peak in species richness in this study, but rather very low bryozoan richness, highlighting the undersampled areas north of Durban. The northward-flowing Benguela Current and strong upwelling centres may influence the low diversity on the west coast. On the south coast, the high diversity may be attributed to the Agulhas Current that can carry larvae southwards and eastward-flowing counter currents produce great variability in bryozoan communities in this region. Within any biogeographic region, bryozoan diversity was higher in shallower (< 500 m) than deeper waters, which may be attributed to sampling effort and heterogeneity (e.g. variable substrate and wave action) in shallower waters. Keywords: Bryozoa, distribution patterns, gradients, species richness, South Africa
Does phylogeny have an influence on the date of first description? A comparative study of the world's fishes
(Elsevier, 2020) Beukes, Brandon; Witbooi, Peter; Gibbons, Mark J.
The process of species description is not random, and understanding the factors that in- fluence when a species is first described (the date of first description, DoFD) allows us to target environments and/or species' traits to increase our knowledge of diversity. Such studies typically correlate species traits (e.g. maximum size, occupational depth) against DoFD, forgetting that species are not statistically independent of each other, owing to the inheritance of shared characteristics. A recent study of extant fishes by Costello et al. (2015) identified depth and geographic range size as the most important (of many) pre- dictors of the DoFD, implying that newly described species will likely occupy restricted areas and occur deep in the water column. However, these authors failed to accommodate for “identity by descent” in their analyses. We correct that oversight here, and conclude that while the adjustments strengthen the associations between the different predictors and the DoFD, the overall affects are minimal and they do not materially change Costello et al.’s (2015) conclusions. This is briefly discussed.
Does phylogeny have an influence on the date of first description? A comparative study of the world's fishes
(Elsevier, 2020) Beukes, Brandon; Witbooi, Peter Joseph; Gibbons, Mark J.
The process of species description is not random, and understanding the factors that influence when a species is first described (the date of first description, DoFD) allows us to target environments and/or species' traits to increase our knowledge of diversity. Such studies typically correlate species traits (e.g. maximum size, occupational depth) against DoFD, forgetting that species are not statistically independent of each other, owing to the inheritance of shared characteristics. A recent study of extant fishes by Costello et al. (2015) identified depth and geographic range size as the most important (of many) predictors of the DoFD, implying that newly described species will likely occupy restricted areas and occur deep in the water column. However, these authors failed to accommodate for “identity by descent” in their analyses.
Environmental responses of jellyfish polyps as drivers of medusa populations off the coast of Namibia
(National Inquiry Services Centre, 2018) Ziegler, L.; Gibbons, Mark J.
Jellyfish populations in the southeastern Atlantic off the coast of Namibia have increased subsequent to the decline of small pelagic fisheries at the end of the 1960s, although the environment there has also become warmer and the waters off Walvis Bay have become richer in zooplankton in recent years. Laboratory experiments were conducted with the scyphozoan jellyfish Chrysaora fulgida to investigate the effects of food density (0, 30, 70, 100 or 150 Artemia nauplii 200 ml–1), feeding frequency (once daily or once every third day) and water temperature (12, 16 or 20 °C) on the asexual reproduction, growth and development of polyps. The results of a generalised linear mixed-effects model reveal that all variables impacted asexual reproduction, with greater polyp production attained at higher food concentrations, increased feeding frequencies and increased temperatures. The most common mode of asexual reproduction was by lateral budding. These laboratory results suggest that polyps of C. fulgi a may have proliferated off Namibia in recent times, which would contribute to increased numbers of jellyfish there.
Feeding and vertical migration of the chaetognath Sagitta friderici (Ritter Zahony, 1911) in the southern Benguela during spring 1987, with notes on seasonal variability of feeding ecology
(NISC and Taylor & Francis, 1994) Gibbons, Mark J.; Stuart, V.
The feeding biology and the vertical migration of Sagitta friderici were examined over 24 h at two stations in the southern Benguela during spring (October) 1987. Together with studies conducted during summer (February 1991) and winter (May 1984), they serve to allow valuable generalizations of the biology and ecology of this abundant chaetognath. Populations migrate vertically and feed nocturnally, although the timing and the extent of migration vary between studies. S.friderici exhibits ontogenetic layering and the cross-shelf distribution of maturity stages differs, suggesting that it is able to take advantage of cross-shelf water movement in order to maintain populations in the nearshore waters of the West Coast. S.friderici prey almost exclusively on copepodg (cannibalism is rare), and there is a positive relationship between the lengths of predator and prey that is influenced by the size structure of the prey environment. This casts doubt on the validity of a chaetognath species-specific relationship between predator and prey size. S. friderici selects its prey on the basis of size, and not species. Daily ration is related linearly to prey density, so reflecting the low density of prey and providing support for theoretical predictions regarding ingestion rates under oceanic conditions. The impact of S. friderici predation on the copepod assemblage is generally less than 3% of the standing stock, although it could be much higher under conditions of low copepod biomass and poor secondary production.
Hydromedusae off the Orange River Mouth, Southern Africa
(NISC (Pty) Ltd and Taylor& Francis, 2003) Sparks, Conrad A.J.; Gibbons, Mark J.
A total of 242 zooplankton samples from the upper 100 m of the water column was collected discontinuously from March 1997 to January 1999 off the Orange River mouth on the west coast of southern Africa. Six species of hydromedusae were recovered at generally low abundance, of which Euphysa aurata, Leuckartia octona and Proboscidactyla menoni were dominant. E. aurata and L. octona showed evidence of seasonality in abundance. The low diversity of the fauna was remarkable and it is hypothesized that this might be attributable in part to sedimentation from the Orange River, and in part to locally weak circulation and the wide extent of the continental shelf.
An insight into the reproductive biology of the bearded goby Sufflogobius bibarbatus
(Wiley, 2013) Utne-Palm, A.C.; Locatello, L.; Mayer, I.; Gibbons, Mark J.; Rasotto, M B.
Preliminary results obtained from histological analyses of the male reproductive organs, supplemented with field and behavioural data, indicate that Sufflogobius bibarbatus, a small, slow growing gobiid exhibiting low fecundity, which plays an important role in the food web off Namibia, where large areas of the shelf are hypoxic, spawns demersally. Large males defend benthic nests, possibly at the edge of the hypoxic shelf. Male reproductive strategy appears to be flexible, and tentative evidence to suggest that polygyny and sneaking may also occur is presented.
Jellyfication of marine ecosystems as a likely consequence of overfishing small pelagic fishes: Lessons from the Benguela
(University of Miami, Rosenstiel School of Marine and Atmospheric Science, 2013) Roux, Jean-Paul; van der Lingen, Carl D.; Gibbons, Mark J.; Moroff, Nadine E.; Shannon, Lynne J.; Smith, Anthony D.M.; Cury, Philippe M.
Changes in two contrasting ecosystems of the Benguela upwelling region, one dominated at mid-trophic level by jellyfishes (Namibia, northern Benguela ecosystem, where small pelagic fish abundance has been severely depleted) and one still dominated by small pelagic fishes (South Africa, southern Benguela) were compared in an effort to determine ecosystem trajectories under different exploitation regimes. The role of small pelagic fishes (clupeoids) was highlighted in the context of their importance in maintaining interactions in marine ecosystems. In particular, we examined trophic cascades and possible irreversible changes that promote the proliferation of jellyfishes in marine systems. We found that the presence of large populations of small pelagic fishes has a fundamental role in preserving beneficial trophic interactions in these marine ecosystems. The implications of trophic cascades, such as those observed in the northern Benguela, for ecosystem-based management were apparent. In addition, this comparison provides contrasting case studies to inform the development of management scenarios that avoid ecosystem shifts that affect predators and reduce the value of fisheries production.
Mesoscale structure of neuston assemblages across the southern Indian Ocean subtropical gyre
(Elsevier, 2022-12-28) Gibbons, Mark J.; Parker, Yasmeen; Cedras, Riaan B.; Thibault, Delphine
Despite concern around plastic pollution in subtropical gyres, our understanding of the biological component of the neustonic layer (upper 20 cm of the ocean) in these areas is poor. Here we investigate the neuston (excluding copepods) assemblages across the Southern Indian Subtropical Gyre using triplicate samples collected by mantatrawls from 28 stations along a transect at latitude 20 S during June/July 2015. The vertical structure of the water column at each station was assessed using a CTD. With the exception of siphonophores, all non-copepod neuston were identified to morphospecies. Assemblages were dominated by ostracods, mysids, larval chaetognaths and siphonophores. The majority of collected specimens comprised facultative neuston, which were more common at night than during the day. Neuston assemblages from the east were quite distinct from the balance of samples, and their distribution reflected that of the warm, low salinity water associated with the Indonesian Throughflow. Two anticyclonic eddies had been documented at the time of the survey between 70 and 85◦ E, and this area was associated with a distinct neuston assemblage of generally low abundance. The key environmental factors that were linked to assemblage structure were associated with longitude – salinity, fluorescence and temperature at 200 m, emphasising the interaction between Indonesian Throughflow Water and the South Equatorial Current, eddy-related process and settlement of meroplankton. The study highlights the value of using morphospecies in studies of plankton assemblages.
A modern description of Crambionella stuhlmanni (Scyphozoa: Rhizostomeae) from St. Lucia Estuary, South Africa
(Cambridge University Press, 2011) Neethling, Simone; Channing, Alan; Gershwin, Lisa-Ann; Gibbons, Mark J.
A new record of Crambionella stuhlmanni is reported from the east coast of South Africa. The material is described using quantitative morphological data, and mitochondrial (CO1) and nuclear (ITS-1) sequence data. The species can be diagnosed by a combination of morphological features including the presence of conical projections on velar lappets, the absence of orbicular appendages among mouthlets and the short length of the terminal club on the oral arm. Mitochondrial sequence data unambiguously delineate C. stuhlmanni as a separate species from C. orsini, and phylogenetic analyses support its placement within the monophyletic genus, Crambionella
New observations on the diel vertical distribution of Hydromedusae in the southern Benguela ecosystem
(NISC (Pty) Ltd and Taylor& Francis, 2003) Buecher, Emmanuelle; Gibbons, Mark J.
Diel vertical migration (DVM) of six common species of hydromedusae was investigated during two drogue studies conducted in St Helena Bay on the west coast of South Africa in February 1995. Clytia spp., Obelia spp. and Bougainvillia macloviana, were largely confined to surface waters and did not appear to display any DVM. By contrast, Leuckartiara octona and Euphysa aurata displayed clear DVM and, like Proboscidactyla menoni, were found at greater depths than the other species. The depth distribution and amplitude of migration varied between surveys for most species, so definitive interpretations of patterns could not be made.
A new species of Magelona (Polychaeta: Magelonidae) from southern Namibia
(Iziko Museums of Cape Town, 2010) Clarke, Dylan T.; Paterson, Gordon L. J.; Florence, Wayne K.; Gibbons, Mark J.
A new species of Magelonidae, Magelona debeerei sp. nov., is described and illustrated from grab-samples collected at <100moff the southwest coast of Africa. Magelona debeerei sp. nov. has previously been identified from the region as M. papillicornis (Müller, 1858) by Day (1955, 1961, 1967) but differs from M. papillicornis sensu stricto by possessing dorsal medial lobes on chaetigers 4–8 and lateral pouches (Σ configuration) between chaetigers 10 and 11. Three species of Magelona have now been recorded from southern Africa (M. capensis Day, 1961, M. cincta Ehlers, 1908 and M. debeerei sp. nov.), and a key to Magelona from this region is provided.
Null models for null hypotheses in taxonomy: A test using Scyphozoa
(Oxford University Press, 2021) Brown, Michael K.; Gibbons, Mark J.
Although molecular tools are becoming more important in the delineation of scyphozoan species there is, perforce, a need to substantiate new species definitions using morphological data. Access to type material is often difficult and detailed, raw morphometric data are rarely provided in older type descriptions, which makes comparisons of new with old challenging. Here, we use null models based on simple measures of central tendency to generate morphometric data sets for four species of Aurelia, three species of Chrysaora and two species of Crambionella. The results of PERMANOVA and CAP analyses indicate no significant differences between random and real data within species, but significant differences between congeneric species (null or real), suggesting that this multivariate approach may be a useful tool for defining species when comparative data are scant.
Observations on euphausiid communities of the south coast of South Africa
(NISC (Pty) Ltd and Taylor& Francis, 1995) Gibbons, Mark J.
A total of 24 species of euphausiid was collected during a survey along the South African south coast during January 1992. Communities over the Agulhas Bank were of low diversity and abundance and were dominated by Nycliphanes capensis. Those at the shelf-edge were of high diversity and abundance and were dominated by Euphausia recurI'll and Thysalloessa gregaria. Such high diversity may be maintained by vertical scgregation at night. Few species displayed obvious diel vertical migration, although N. capen sis may be able to maintain itself on the shelf by means of this behaviour. E. recurl'Cl appeared to feed on phytoplankton throughout the water column at night, reflecting the distribution of food.

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