Carla Edworthy

PhD Candidate
Carla Edworthy


The impact of multiple drivers of climate change on the nursery function of estuaries.

South African estuaries serve as important nursery habitats for numerous marine spawned fish species. The surrounding marine inshore areas along the coast of South Africa are typically harsh conditions with turbulent wave action whereas estuaries are calm, sheltered and shallow providing suitable protection and sufficient food for growing juvenile fish. As a result of these nursery characteristics, estuaries are dominated by juvenile marine fish species with varying estuarine associations. Some species are wholly dependent on estuarine nursery areas whereas others use these favourable habitats opportunistically. There are also some species that complete their life cycles in estuarine habitats. The concern is that coastal areas and estuaries are suggested to be particularly vulnerable to climate change but despite this there is little information on the variability of various climate change drivers in these systems and their impact on marine life, with most research on this using global averages rather than local conditions. As a result, the impacts of climate change on many marine organisms could be either over, or underestimated.

The aim of this study is twofold, first it will monitor the impact of anthropogenic climate change drivers of salinity, temperature and acidification in a permanently open estuary on the south-eastern coastline of South Africa. The combined impact of these drivers on species with varying estuarine associations will then be evaluated using physiological and behavioural assessments including metabolism, swimming ability and recruitment behaviour. The tolerance of species to fluctuations in environmental conditions are likely explained by species-specific differences in physiology and physiological adaptation.  Understanding energy trade-offs under the stress of multiple drivers of change is therefore essential to determine which life history strategies may be favoured in the future. Furthermore, the changing availability of energy under environmental stress may impact other processes such as swimming ability and behaviour which is essential in understanding how organisms will recruit into these environments when faced with these and other stressors.

Registered at: Rhodes University, (Department of Ichthyology and Fisheries Science)

Supervisors: Dr Nikki James (SAIAB), Dr Warren Potts (Department of Ichthyology and Fisheries Science, Rhodes University)