Browsing Biodiversity & Conservation Biology by Subject "Diversity"
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Maneveldt, Gavin; Eager, Rosemary; Bassier, Aghmat (NISC (Pty) Ltd and Taylor & Francis, 2009)[more][less]
Abstract: Zonation patterns on rocky shores are typically as a result of both physical factors and biological interactions. Physical factors generally set the upper limits of species distributions, while biological interactions generally set their lower limits. Recent research has shown, however, that biological factors often can also influence the upward recruitment and colonisation by species. While such evidence exists in the international literature, very little experimental evidence exists for South Africa. This study provided experimental evidence for the biological effects of long-term exclusion (2003-2008) of the South African herbivorous limpet Cymbula oculus (Born), on the community structure of the Kalk Bay rocky intertidal. To demonstrate this, an herbivore exclusion experiment was set up in the mid-Eulittoral zone in May 2003. Initially, all herbivores were removed from the exclusion plots; after one year, 2 only C. oculus individuals recruiting into the plots were continually removed. Algal recruitment (percent cover abundance) was determined monthly for the first 12 months and then annually thereafter, while invertebrate recruitment (density) was monitored only annually. The results firstly show that the natural density of C. oculus had increased dramatically during the first year (from 4.87 ± 1.09 individuals m-2 to 12.35 ± 1.70 individuals m-2, p = 0.001). Secondly, grazing by C. oculus is the primary biological factor preventing the recruitment and colonization of macroalgae and some invertebrates onto the Kalk Bay intertidal. Not only does herbivory by C. oculus prevent recruitment and colonization, but it also decreases algal diversity and prevents algal succession. Within the mid-Eulittoral zone of the Kalk Bay rocky intertidal, herbivory by C. oculus is thus more important in shaping this marine community than physical factors associated with desiccation stress. URI: http://hdl.handle.net/10566/635 Files in this item: 1
ManeveldtIntertidalOrganisms2009.pdf (215.3Kb) -
Sparks, Conrad, A.J.; Gibbons, Mark J. (Taylor & Francis and NISC, 2003)[more][less]
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 Files in this item: 1
SparksHydromedusaeOrangeRiver2003.pdf (57.50Kb) -
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)
Now showing items 1-3 of 3