The comparative ecology of Natal's smaller estuaries.
Loading...
Date
1983
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Fifty one of Natal's 73 estuaries have been almost completely
overlooked in terms of any scientific study, despite which a marine
nursery function has commonly been attributed to each of them. In the
knowledge that many of these systems were normally closed and others
were in a seriously degraded state, this study was undertaken with the
aims of examining their present day community structure in order to
provide a basis upon which their future condition can be monitored and
to provide a classification of these coastal resources.
The study area incorporated 62 different systems extending over
240 km of the Natal coastline south of the Tugela River. During the
three year study period (Sep 1979 - Nov 1982) 82 515 specimens,
comprising an assemblage of 125 different species, were caught by
means of a small beam trawl. These comprised 86 species of fish, 21
species of crabs and 18 species of prawns. The data obtained were
correlated to abiotic variables such as mouth condition, salinity,
temperature, dissolved oxygen, water transparency, depth, nature of
the substratum and peripheral vegetation.
Based on the ability of biota to synthesize environmental
variables into one common response, multi-variate analysis is used to
demonstrate the similarity in community structure between open and
closed systems (for example) or between fresh and saline systems, and
thereby resolve an age-old argument about estuary classification. The
data also suggest that in their present day condition only six of the
systems studied make a significant contribution to the recruitment of
estuarine-dependent marine stocks (sensu stricto) principally because
of their open mouth condition. Closed systems, deliberately
classified as lagoons, have a different resource value, being utilized
primarily by resident species that can complete their life cycle
within the system. An appreciation of this salient difference helps
to reinforce the critical need for an effective management strategy to
be implemented to prevent Natal's dwindling estuarine resources from
deteriorating any further.
The term 'estuarine-dependence' is critically examined in this
context to show that a species more dependent on estuaries than any
other, is man. It is argued that man's continued abuse of these
resources is shortsighted, and that the most serious threat of all is
sedimentation, accelerated in this instance beyond the geological norm
by catchment mismanagement.
The practical application and value of classification to planning
and management is demonstrated and a methodology proposed, based on
community responses, for the monitoring of the future environmental
condition of each estuary and lagoon in Natal.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1983.
Keywords
Estuarine ecology--KwaZulu-Natal., Estuaries--KwaZulu-Natal., Theses--Ecology.