Biodiversity of soft sediment macrobenthic fauna of the KwaZulu-Natal Bight midshelf.
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Date
2013
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Abstract
The KwaZulu-Natal Bight is influenced by various nutrient inputs from the Thukela River and
particular oceanographic features of the shelf such as the St Lucia upwelling cell and the
Durban lee eddy that are in turn associated with Agulhas Current behaviour. Little is known
about KZN Bight community dynamics of most faunal groups and so knowledge about the
ecological functioning of this system as a whole is lacking. To address this, a large
multidisciplinary project on the Bight was conducted through the African Coelacanth
Ecosystem Programme. One aim of the programme was to establish whether nutrient inputs
have significant impacts on this oligotrophic shelf and if so, how? This study looked at the
macrobenthic compartment to examine variations in diversity across the KZN Bight in the
midshelf habitat only. Changes in diversity were explained in relation to important habitat
and/or process drivers. Replicated biological and sediment samples were collected in and
between the three focus areas of high nutrient input along the Bight spanning an area from
Durban to just south of the St Lucia Estuary mouth. Samples were collected twice at the same
stations, once during a wet period (February 2010) and once during a dry period (August 2010).
These periods were selected to represent high and low outflow and thus potentially higher and
lower nutrient inputs to the Bight, respectively. Macrobenthos collected by 0.2m2 Van Veen
grab were identified to the lowest possible taxonomic level and resulting data were analysed
using combinations of univariate and multivariate statistical procedures. Diversity was
described using well-published techniques that related to community Alpha () and Beta (β)
diversity and including several newer methods such as Taxonomic Diversity indices
(Taxonomic Distinctness (Δ*), Average Taxonomic Distinctness (Δ+), Variation in Taxonomic
Distinctness (Λ+)) to determine the taxonomic relatedness of macrobenthic communities within
the study area. Midshelf macrobenthic community and β diversity was highly variable across
the shelf with no distinct patterns related to focus area. Diversity values were however similar to
values obtained in what are considered highly diverse tropical and high latitude shelves.
Diversity was then related to hydrographic parameters measured on the Bight to understand the
possible indirect or direct roles the Agulhas Current and Thukela River have in maintaining the
macrobenthos. Findings were that diversity was only weakly related to measured environmental
variables suggesting far more complex interactions in the biophysical environment of the Bight.
This was highlighted by the finding that alpha and beta diversity measures had complimentary
relationships as an inverse trend was found between these measures along the KZN Bight. Thus,
more detailed systematic studies on the Bight are needed to fully understand the role and supply
of nutrients on specific communities and how these pertain to the ecological function of the
whole shelf ecosystem.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2013.
Keywords
Biodiversity--KwaZulu-Natal., Animals--KwaZulu-Natal., Oceanography--KwaZulu-Natal., Habitat conservation--KwaZulu-Natal., Theses--Marine biology.