Water and Estuary

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  • Topic: Water, Estuary, Freshwater
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  • Published : April 28, 2013
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An integrated study of the Mpenjati estuary-beach system. (Biological component) Abstract
A study was carried out to find the abundances of animal organisms between both sides of the Mpenjati estuary. Zooplankton, Macro fauna, Meiofauna and Fish was sampled .Each of the species that reside in the estuary contribute to the diversity of the area and are essentially driving forces, ensuring optimal functioning of the ecosystem. The purpose of sampling such ecosystems is to find out how the interactions amongst these organisms show a relation towards environmental conditions and how they could be affecting the estuary in the abundances that they are found. Samples was collected at different sampling stations were it was collected and labelled for further analyse in a laboratory at the University of KwaZulu Natal. Different sampling methods were used, which was designed effectively to collect different types of organisms. A seine net was used to collect fish in the estuary side and a fry net on the beach side. An Ekman grab was used to collect the sediment that possessed macro fauna and the meiofauna samples was extracted from sediment corers respectively. Zooplankton was sieved and collected using a 200 micron mesh at the high energy swash zone. The results showed a great variation of species present in the estuary system. Results showed that calanoid copepods were in great abundance on the beach side accounting for 85 percent of the zooplankton measured. Nematodes were the only species found in the meiofaunal samples. There was 34.18 ind.m2 of macrofauna. No fish species was netted in on the beach side and this could be due to the low tide that was currently in bay while sampling was conducted at that sampling station.

Introduction
A general understanding of an estuary is a region through which a river discharges into a sea. In a Southern African context the following is a widely accepted and concise definition of an estuary “It is a partially enclosed coastal body of water in which is either permanently or periodically open to the sea and within which there is a reasonable variation of salinity due to the mixture of sea water and fresh water derived from land drainage”.(Day,1980).The necessity of estuarine sampling and one of the topics being investigated, is that the organisms present in the estuary are direct mediators on mans impact to their habitat as well as to impact on the ocean. One is thereafter able to identify the state of the estuary by examining the conditions of the organisms in the abundances they represent. Primary photosynthetic producers that exist in the estuary are phytoplankton and microphytobenthos. Their consumers being zooplankton and meiofauna which in turn are eaten by fish species, which are primarily dominated by Mullets and Sparids. Zooplankton is essentially the primary consumers of the water column. In some cases of prolonged closure of the estuary mouth, much of these biomasses generally lead to a few dominant species arising. The presence of these producers depend largely on turbidity, these pelagic organisms are passively transported through the water column. Meiofauna however are generally not affected by the turbidity or current and would most likely be found whether the estuary is either opened or closed. . (Perissinotto et al, 2010).

Light is essentially the limiting factor in all aquatic habitats, light regulates photosynthetic processes allowing primary producers to produce food. Temperatures of the water affect not only chemical and biological processes but also the migration patterns of fish. Salinity is a key factor in determining organism distribution in estuaries. The hydrodynamics of the estuary also has a great influence on the state of life; the depths, flow velocities, waves, tides and current that mixes the coastal waters and bottom sediments all aid in playing an essential role on the biological structure and functioning of the estuary system. Macrobenthic and...
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