Decadal shifts in macrobenthic community structure in a permanently open freshwater-deprived Eastern Cape Estuary

Limbada, Zahrah

Decadal shifts in macrobenthic community structure in a permanently open freshwater-deprived Eastern Cape Estuary

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

The decadal shifts in the macrobenthic community structure in the permanently open, freshwater-deprived Kariega Estuary along the southeastern coastline of South Africa were investigated between 2010 and 2022. The macrobenthic community structure was investigated at six stations in four distinct ecological zones: Zone I was made up of Zostera capensis, Zone II was made up of mud, Zone III was made up of Spartina maritima, and Zone IV was made up of Sarcocornia perrenis along the length of the estuary. The average abundance and biomass of macrobenthic organisms during the 2010 survey ranged from 16 to 504 ind/m2 and from 0.03 to 245 g wwt/m2, respectively. In 2022, the average abundance of macrobenthic organisms ranged from 6 to 216 ind/m2. The average macrobenthos biomass was 2.60 to 93.40 g wwt/m2. There were no significant differences in the estimates of the total macrobenthic abundance and biomass between the two surveys or the different ecological zones (P > 0.05 in all cases). Site-specific differences were, however, evident. During both surveys, the highest abundance and biomass values were recorded in the middle reach, corresponding to the region with the highest biomass of submerged macrophytes. Multidimensional scaling revealed a high degree of overlap in the macrobenthic community compositi on between the two surveys. The absence of any significant spatial or temporal patterns in the microbenthic community structure along the length of the estuary can likely be related to the reduced freshwater inflow into the estuary, creating a homogenous marine-dominated system. Closer inspection of the macrobenthic community structure, however, revealed that there have been species-specific declines in the abundance of several species routinely collected for bait by subsistence fishers, including the mud prawn (Upogebia africana), pencil bait (Solen cylindraceus) and redworm (Marphysa sanguina). The decline of these species suggests increased exploitation of estuarine resources over the past decade, most likely in response to high levels of unemployment and poverty.

Keywords

Eastern Cape Estuary

water

Reference:

Collections

Masters

Full item page