Browsing Biodiversity & Conservation Biology by Title
Previous Page
Now showing items 24-35 of 35
-
Gibbons, Mark J. (NISC (Pty) Ltd and Taylor& Francis, 1995)[more][less]
Abstract: 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) -
Gibbons, Mark J.; Buecher, Emmanuelle; Thibault-Botha, Delphine (NISC (Pty) Ltd and Taylor& Francis, 2003)[more][less]
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 Files in this item: 1
GibbonsPleurobrachia2003.pdf (270.1Kb) -
Barange, M; Macpherson, E; Gibbons, Mark J. (NISC and Taylor & Francis, 1994)[more][less]
Abstract: Information on vertical and horizontal distribution patterns, abundance and morphology of the decapod Pasiphaea semispinosa in the Benguela upwelling system is presented. P. semispinosa is the dominant pelagic decapod in the system, occurring between 19 and 32°S along the mid and inner shelf in concentrations of 10-100•m-2• Although it is more abundant during abated than during active upwelling in the northern Benguela, it would appear to be equally abundant during both upwelling scenarios in the southern Benguela. In the southern Benguela, reproductive females are present during winter and juveniles dominate during active upwelling, but juveniles appear to be more common during abated upwelling in the northern Benguela. The estimates of abundance of P. semispinosa presented in this study are subject to sampling biases attributable to their vertical migratory behaviour and net avoidance capabilities. URI: http://hdl.handle.net/10566/307 Files in this item: 1
GibbonsPasiphaea1994.pdf (692.3Kb) -
Robertson-Andersson, Deborah; Wilson, D.T.; Bolton, John J.; Anderson, R. J.; Maneveldt, Gavin (NISC, 2009)[more][less]
Abstract: Tissue nitrogen content and thallus colour were quantified using a rapid assessment method based on the Pantone® matt uncoated formula guide for raft-cultivated Gracilaria gracilis Steentoft Irvine et Farnham at Saldanha Bay and tank-cultivated Ulva lactuca Linnaeus at Jacobsbaai in 2001 – 2002. A relationship between thallus colour and tissue nitrogen, as well as a transition between green-yellows and yellow-browns that occurs between 0.8 – 1.3 mg N per g tissue (Pantone® colours 460U – 455U) for Gracilaria were found, with the green-yellow colour indicating nitrogen-starved material and the yellow-browns indicating nitrogen-replete material. For Ulva a transition between green and yellow-green occurred at a tissue nitrogen content of between 1.5 – 1.7 mg N per g tissue (Pantone® colours 585U and 583U). This relationship can be used by seaweed farmers for cultivation management as a quick guide to determine nutritional status of the seaweeds, and as an indication of protein content when the seaweeds are used as feeds. URI: http://hdl.handle.net/10566/778 Files in this item: 1
-
Samaai, Toufiek; Gibbons, Mark J.; Kelly, Michelle (Cambridge University Press, 2009)[more][less]
Abstract: The sponge genus Strongylodesma is reviewed and redefined, and now accommodates eight closely related species. The type species of Strongylodesma Le´vi is redescribed and an additional two new species are described from the Indo-Pacific: S. novaecaledoniae sp. nov. and S. tongaensis sp. nov. Several specimens previously identified as species of Batzella (Poecilosclerida: Chondropsidae) have been re-assigned to Strongylodesma, as the new species S. purpureus sp. nov. and S. nigra sp. nov. With the description here of new species from the Pacific Ocean and Caribbean Atlantic, the biogeographical distribution of Strongylodesma now appears to be generally tropical with a subtropical South African component, whereas previously it was only known from South Africa. Although species of Strongylodesma have not previously been recorded from the intermediate locations (Western Indian Ocean, South-east Asia, central west Pacific, and New Zealand), re-evaluation here will facilitate more readily the recognition of taxa in these intermediate regions, if they exist, in the future. The species are not widespread, except perhaps along the south-east coast of South Africa, and where they occur they are not abundant. Species occur over a wide depth range, from the intertidal in Tsitsikamma, South Africa, to 140 m in the Caribbean. URI: http://hdl.handle.net/10566/248 Files in this item: 1
SamaaiRevision2009.pdf (893.7Kb) -
Maneveldt, Gavin; Wilby, Deborah; Potgieter, Michelle; Hendricks, Martin G.J. (Springer Verlag, 2006)[more][less]
Abstract: Kalk Bay, South Africa, has a typical south coast zonation pattern with a band of seaweed dominating the mid-eulittoral and sandwiched between two molluscan-herbivore dominated upper and lower eulittoral zones. Encrusting coralline algae were very obvious features of these zones. The most abundant herbivores in the upper eulittoral were the limpet, Cymbula oculus (10.4 + 1.6 m-2; 201.65 + 32.68 g.m-2) and the false limpet, Siphonaria capensis (97.07 + 19.92 m-2; 77.93 + 16.02 g.m-2). The territorial gardening limpet, Scutellastra cochlear, dominated the lower eulittoral zone, achieving very high densities (545.27 + 84.35 m-2) and biomass (4630.17 + 556.13 g.m-2), and excluded all other herbivores and most seaweeds, except for its garden alga and the encrusting coralline alga, Spongities yendoi (35.93 + 2.26 % cover). For the upper eulittoral zone, only the chiton Acanthochiton garnoti 30.5 + 1.33 % and the limpet C. oculus 2.9 + 0.34 %, contained encrusting coralline algae in their guts. The lower eulittoral zone limpet, Scutellastra cochlear also had a large percentage of encrusting coralline algae in its gut with limpets lacking gardens having higher (45.1 + 1.68 %) proportions of coralline algae in their guts than those with gardens (25.6 + 0.8 %). Encrusting coralline algae had high organic contents, similar to those of other encrusting and turfy algae, but higher organic contents than foliose algae. Radula structure, grazing frequencies as a percentage of the area grazed (upper eulittoral 73.25 + 3.60 % d-1; lower eulittoral 46.0 + 3.29 % d-1), and algae organic content provided evidence to support the dietary habits of the above herbivores. The data show that many intertidal molluscs are actively consuming encrusting coralline algae and that these seaweeds should be seen as an important food source. URI: http://hdl.handle.net/10566/902 Files in this item: 1
-
Maneveldt, Gavin; Keats, Derek; Chamberlain, Yvonne (Elsevier, 2008)[more][less]
Abstract: Polychaete worm tubes within the mid to lower intertidal zone along the South African west coast were frequently observed to be overgrown by a minutely papillate species of encrusting coralline algae. Analysis of the vegetative and reproductive morphology and anatomy of this alga shows that it is new to science and belongs to the subfamily Melobesioideae and, in particular, to the genus Synarthrophyton, which is for the most part restricted to the Southern Hemisphere. Synarthrophyton papillatum is the tenth species from this genus and the sixth recorded from southern Africa. The new species is described in detail and compared with recently documented species found to conform to the generic description of Synarthrophyton. Synarthrophyton papillatum differs from S. patena and S. eckloniae in being epilithic, not epiphytic; from S. munimentum and S. robbenense in lacking raised rims on the tetrasporangial conceptacles; and from S. magellanicum in bearing minutely warty to fruticose protuberances and generally lacking the leafy to layered, weakly attached thalli present in the latter species. A key to the southern African species of Synarthrophyton is provided. URI: http://hdl.handle.net/10566/768 Files in this item: 0
-
Villas-Boas, A.B.; Riosmena-Rodriguez, G.M.; Amado-Filho, Gilberto M.; Maneveldt, Gavin; de O. Figueiredo, Marcia A. (International Phycological Society, 2009)[more][less]
Abstract: The taxonomy of the rhodolith-forming species of Lithophyllum (Corallinales, Rhodophyta) found from Espirito Santo State, Brazil, were evaluated based on extensive subtidal sampling. A comparative analysis of the Brazilian material with recently described species lead us to conclude that three known species (Lithophyllum corallinae, L. johansenii, L. stictaeforme) and one species new to science (Lithophyllum espiritosantense Villas-Boas, Figueiredo et Riosmena-Rodriguez) are present in the area. All four species can be distinguished primarily by their tetrasporangial conceptacle roof anatomy. This study has shown that Brazilian rhodolith beds are comparatively more diverse in number of Lithophyllum species than other areas of the world. URI: http://hdl.handle.net/10566/903 Files in this item: 1
-
Brierley, Andrew S.; Boyer, David C.; Axelson, Bjorn Erik; Lynam, Christopher P.; Sparks, Conrad A.J.; Boyer, Helen; Gibbons, Mark J. (Inter-Research, 2005)[more][less]
Abstract: Acoustic target strengths (TSs) of the 2 most common large medusae, Chrysaora hysoscella and Aequorea aequorea, in the northern Benguela (off Namibia) have previously been estimated (at 18, 38 and 120 kHz) from acoustic data collected in conjunction with trawl samples, using the ‘comparison method’. These TS values may have been biased because the method took no account of acoustic backscatter from mesozooplankton. Here we report our efforts to improve upon these estimates, and to determine TS additionally at 200 kHz, by conducting additional sampling for mesozooplankton and fish larvae, and accounting for their likely contribution to the total backscatter. Published sound scattering models were used to predict the acoustic backscatter due to the observed numerical densities of mesozooplankton and fish larvae (solving the forward problem). Mean volume backscattering due to jellyfish alone was then inferred by subtracting the model-predicted values from the observed water-column total associated with jellyfish net samples. Zooplankton-corrected echo intensity/jellyfish density data pairs were in close agreement with linear relationships determined previously from uncorrected data. Small sample sizes precluded recalculation of TS, but nonparametric pair-wise tests failed to detect any significant differences between echo intensities for jellyfish densities observed in the present study and echo intensities predicted for those densities by density–intensity relationships arising from the previous study. Previous linear density–intensity relationships had y-axis intercepts greater than zero. On the assumption that the positive intercepts were due to backscatter from unsampled mesozooplankton, new TS relationships were calculated from downward-adjusted density–intensity relationships. New values agreed closely with TS estimates determined elsewhere using single-target echo detection techniques. Given that estimates of jellyfish TS appear robust, it should now be feasible to identify jellyfish acoustically at sea and to assess their abundance, even in the presence of mixed mesozooplankton assemblages. URI: http://hdl.handle.net/10566/247 Files in this item: 1
BrierleyAcoustic2005.pdf (103.7Kb) -
Gibbons, Mark J.; Stuart, V; Verheye, H M (NISC and Taylor & Francis, 1992)[more][less]
Abstract: Carnivorous zooplankton in the Benguela system have tended to be ignored by all but early taxonomists and a handful of recent researchers. An attempt is made here to address the importance of carnivores in this system but, because the database is poor, it was necessary to apply material from outside the region. The taxa covered include ctenophores, cnidarians (Scyphozoa and Hydrozoa, including Siphonophora), chaetognaths and hyperiid amphipods as well as such minor groups as pelagic gastropods and decapods. Most groups of carnivores within the Benguela are represented by only one or two "common" species. These tend to be epiplanktonic and generally concentrated inshore of the shelf-break, where their distributions are influenced by changes in local hydrography. Their densities frequently exceed those of herbivores. The dominant carnivores share a number of attributes: wide-ranging diets, high assimilation and growth efficiencies and mostly a Type I functional response to food concentration. They fall into two categories. The first is the gelatinous species, which have short lifespans and exhibit rapid growth and often massive reproductive response to high concentrations of food. They are patchily distributed and some appear to have behavioural traits that enable them to stay within localized patches of prey on which they may be dependent because of high metabolic costs. In the second category are crustacean predators and chaetognaths which have slower response times to the food environment but may have longer lifespans, lower daily maintenance needs and an ability to store lipids. They are less dependent on high densities of food organisms and can survive throughout winter, when gelatinous predators are rare. The effect of predation on abundance of copepods is estimated on the basis of both published and unpublished data. Should swarms of predators coincide with a critical gateway of zooplankton or larvae, then there may be total depletion. This applies especially to the nearshore zone of the West Coast and to semi-enclosed bays. The role of carnivorous zooplankton in the diets of commercially important fish species is stressed, but their importance in the regeneration of nutrients may be insignificant. URI: http://hdl.handle.net/10566/305 Files in this item: 1
GibbonsTrophicEcology1992.pdf (1.199Mb) -
Gibbons, Mark J.; Hendricks, Martin G. J. (Magnolia Press, 2010)[more][less]
Abstract: Perepsilonema benguelae sp. nov. and Leptepsilonema saldanhae sp. nov. are described and illustrated from coarse sand sediments in Saldanha Bay, along the west coast of South Africa. Perepsilonema benguelae sp. nov. is characterised by a large swollen body in the genital region, the annuli are not clearly orientated into anteriorly and posteriorly directed margins and copulatory thorns are restricted to three pairs in the precloacal region. In Leptepsilonema saldanhae sp. nov. the somatic setae in the pharyngeal region are very long and the first ambulatory setae of the external subventral row are short. Other distinguishing features include the shape of the amphidial fovea and the copulatory apparatus, and the presence of six ventro-lateral copulatory thorns around the cloaca. These descriptions are the first for the family Epsilonematidae from the west coast of South Africa. URI: http://hdl.handle.net/10566/244 Files in this item: 1
HendricksGibbons2010.pdf (245.4Kb) -
Gibbons, Mark J.; Sulaiman, Amina; Hissman, K.; Schauer, J.; Wickens, Patti; McMillan, Ian (NISC and Taylor & Francis, 2000)[more][less]
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 Files in this item: 1
GibbonsDemersalNekton2000.pdf (501.8Kb)
Previous Page
Now showing items 24-35 of 35