VARIABILITY OF PLANKTONIC AND BENTHIC COMMUNITIES ON TWO SUBTROPICAL ESTUARIES ON THE EAST COAST OF SOUTH AFRICA
Kelly Ortega-Cisneros and Ursula Scharler
University of KwaZulu-Natal, School of Life Sciences

 

Abstract
Estuaries are among the most productive ecosystems in the world. Unfortunately, they are also one of the most impacted aquatic systems. The South African coastline has 252 estuaries, of which 70% have been classified as temporarily open/closed estuaries (TOCE) and about 18% as permanently open estuaries (POE). The number of POEs in South Africa has declined due to increased freshwater abstraction in their catchment areas. Rainfall patterns differ between biogeographical regions in South Africa, with summer precipitation (October-April) being characteristic of the subtropical (east coast) region. The aim of this study was to determine the spatio-temporal variability of planktonic and benthic communities of two estuaries in KwaZulu-Natal over a dry/wet climate cycle. Phytoplankton biomass, zooplankton density and biomass, as well as macrobenthos density and biomass are described for a period of 13 months between May 2010 – May 2011 for a POE and a TOCE.Our study underlines the contrasting responses of planktonic communities to increased river inflow in POEs and TOCEs. Macrobenthic communities, independently of the estuary type, responded negatively (lower density and biomass) to the increased river inflow, but planktonic biota showed opposite responses. The increased rainfall and freshwater input to the estuaries results in flushing of sediments and biomass to the sea, creating instability for benthic communities, which explains the low densities and biomass during the wet season. Both dry and wet period, as well as state of mouth phase (open/closed) determined marked changes on the estuarine communities of both type of estuaries. Alterations in river inflow will have negative, but different, consequences on the functioning and productivity of both types of estuaries, thereby impacting on their ecosystem services.

 

Presentation Topic
VARIABILITY OF PLANKTONIC AND BENTHIC COMMUNITIES ON TWO SUBTROPICAL ESTUARIES ON THE EAST COAST OF SOUTH AFRICA
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