Research Articles (Bioversity and Conservation Biology)

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Video observations on the habitat association of demersal nekton in the mid-shelf benthic environment off the Orange River mouth

Gibbons, Mark J.; Sulaiman, Amina; Hissman, K.; Schauer, J.; Wickens, Patti; McMillan, Ian (NISC and Taylor & Francis, 2000)

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Abstract:

A semi-quantitative assessment is made of the animals observed in archived videotapes taken from the research submersible Jago, during diamond mining and exploratory surveys off the mouth of the Orange River on the west coast of southern Africa (28° IS'S, 29°11 'S) in November 1996. The seabed environment is described and nekton associations with substratum features are identified. The area is characterized by heterogeneity to its physical and biological struture. The variety of observed nekton is low, and communities are dominated by goby Sufflogobius bibarbatus, juvenile hake Merluccius spp. and cuttlefish Sepia spp. (on soft substrata), as well as false jacopever Sebastes capen sis and kingklip Genypterus capensis (on rocky substrata).

URI:

http://hdl.handle.net/10566/419

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GibbonsDemersalNekton2000.pdf (501.8Kb)

Hydromedusae off the Orange River mouth, Southern Africa

Sparks, Conrad, A.J.; Gibbons, Mark J. (Taylor & Francis and NISC, 2003)

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Abstract:

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.

URI:

http://hdl.handle.net/10566/380

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SparksHydromedusaeOrangeRiver2003.pdf (57.50Kb)

New observations on the diel vertical distribution of hydromedusae in the southern Benguela ecosystem

Buecher, Emmanuelle; Gibbons, Mark J. (NISC (Pty) Ltd and Taylor& Francis, 2003)

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Abstract:

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.

URI:

http://hdl.handle.net/10566/377

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BuecherDielVerticalMigration2003.pdf (121.3Kb)

Observations on euphausiid communities of the south coast of South Africa

Gibbons, Mark J. (NISC (Pty) Ltd and Taylor& Francis, 1995)

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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.

URI:

http://hdl.handle.net/10566/374

Files in this item: 1

GibbonsEuphausiid1995.pdf (584.2Kb)

Observations on the ecology of Pleurobrachia pileus (Ctenophora) in the southern Benguela ecosystem

Gibbons, Mark J.; Buecher, Emmanuelle; Thibault-Botha, Delphine (NISC (Pty) Ltd and Taylor& Francis, 2003)

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Abstract:

The vertical distribution, abundance and size composition of a population of Pleurobrachia pileus was studied during a six-day drogue study conducted off the west coast of South Africa in February 1995. The population was centred in deep water, possibly because of the presence of a potential predator, Beroe sp., at shallower depths. The population of P. pileus failed to display clear patterns of migration, although nocturnal recruitment from deeper water resulted in a deepening of the depth of occupation then. The population was dominated by individuals <4 mm polar diameter, and large animals were confined to the upper water layers. These results are discussed with reference to possible spawning activities. Using published equations relating size to clearance rates, it was estimated that the population could remove up to 27% of integrated mesozooplankton standing stocks, and in excess of 100% (293%) at some depths.

URI:

http://hdl.handle.net/10566/373

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GibbonsPleurobrachia2003.pdf (270.1Kb)

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