Estuaries are dynamic and their physical and chemical characteristics can change over a scale of hours to years. Consequently, estuarine fish assemblages often exhibit large temporal variations in ...abundance and composition related to changes in a range of parameters such as river flow, estuarine mouth phase, habitat availability, temperature, salinity and turbidity, all of which are likely to be highly affected by climate change. Many organisms become more stressed towards their range boundaries and the distributions of these species can be expected to shift as environmental conditions change. Preliminary studies have highlighted the increased occurrence of tropical fish species in estuaries along the southeast coast of South Africa. Climate change is also predicted to alter precipitation patterns, which will affect the quality, rate, magnitude and timing of freshwater delivery to estuaries, and will potentially exacerbate existing human modifications of these flows. This is likely to result in changes to fish communities, as river flow has been found to have a major impact on the structure and functioning of fish communities in South African estuaries. The predicted increase in the frequency of extreme weather events, together with sea level rise, may result in a loss of estuarine habitat, which will ultimately affect estuarine fish communities and have implications for fisheries targeting estuary-associated species.
Coastal areas are experiencing high levels of development, largely driven by a number of aesthetic and recreational factors, increased mobility, availability of disposable income for middle and upper ...income groups and the promise of job opportunities and improved economic well-being for lower income groups. As existing coastal urban nodes expand development "shifts" to less developed areas and places increasing pressure on the surrounding natural environment. This article considers the coastal zone of two municipalities in the Eastern Cape, South Africa, with similar environmental characteristics but disparate socioeconomic and governance histories. It identifies and integrates the drivers of development and land use change in the coastal zone of these municipalities by means of an adapted Driver-Pressure-State-Impact-Response (DPSIR) Framework. Development and land use change are driven by a combination of social, economic, and legislative factors that need to be considered for future management and planning in this unique dynamic system.
This study compared the ichthyofaunal assemblages in 10 Eastern Cape Province, South Africa, estuaries to identify whether there were any structural variations between the assemblages and to ...determine the environmental and physical factors linked to these variations. Species belonging to both the marine migrant and estuarine resident groups, by consistent representation within each estuary grouping, were responsible for the separation of fish assemblage structures between the different types of systems. The data further revealed that fish assemblages in the three main types of estuaries investigated were distinct, linked primarily to estuary mouth status and estuary size.
The Kariega Estuary is a freshwater-deprived system due to numerous impoundments in the catchment. This system has had little or no horizontal salinity gradient over the last 15 years, with ...hypersaline conditions sometimes predominating in the upper reaches. Following high rainfall events in the catchment during the spring of 2006, including a flood event (approximate 1:10 year) in August 2006, a series of riverine pulses entered the estuary and a horizontal salinity gradient was established. This study examined the influence of this freshwater pulse on four components of the biota within the estuary, namely the zooplankton, and larval, littoral and demersal fishes. The study demonstrated that in three of these components elevated densities were recorded following the riverine input, with only the littoral fishes retaining an almost constant density. In addition, changes in the relative contributions of the estuarine utilisation classes for all three fish groups examined indicated that freshwater input into these systems positively influences the abundances. This has significant implications for water managers as it demonstrates the importance of an Ecological Reserve (defined as 'the water required to protect the aquatic ecosystems of the water resource') for this system.
This study compares the fish assemblages in a range of intertidal salt marsh creeks in the Kariega Estuary, South Africa, as well as highlighting any differences between the ichthyofaunal structure ...of the creeks and adjacent Zostera bed habitats. The superimposition of environmental variables on the creek biotic groupings (60% similarity level) indicated consistent relationships between both the creek water depth and mouth area with the major creek fish clusters. Water temperature, salinity and turbidity did not display any pattern which could explain the disparity between the ichthyofaunal groupings. The results also indicated that intertidal creeks form a unique littoral habitat within the Kariega Estuary, with ichthyofaunal compositions very different to those found in nearby eelgrass beds. Furthermore, intertidal creeks in the Kariega system appear to be similar to creeks found elsewhere in the world in that their fish assemblages are dominated by 0+ juveniles, have a conspicuous marine transient and estuarine resident component, and very few piscivorous representatives. These results also give weight to the hypothesis that southern African salt marsh creek habitats serve as temporary refuges to juvenile fishes, a role that has also been proposed in other parts of the world.
The structure and functioning of salt marsh fish communities in the overall ecology of southern African estuaries is poorly understood. This study compares the ichthyofauna associated with a salt ...marsh creek and eelgrass bed in an attempt to evaluate the relative importance of these habitats to fishes. Taylor's salt marsh creek and adjacent eelgrass bed in the Kariega Estuary were sampled twice per season between the winter of 1992 and the autumn of 1994. The average density and standing stock of fishes were found to be considerably higher in the eelgrass bed than in the intertidal creek. Both habitats had similar fish diversities but were dominated by different taxa, the most notable of which was the dominance of mugilids in the creek and their scarcity in the eelgrass. Taylor's intertidal creek and adjacent eelgrass beds were dominated by juvenile fish, with both habitats functioning as nursery areas for juvenile fish, albeit for totally different ichthyofaunal communities. The similar fish diversities but lower abundances in the intertidal creek compared to the eelgrass beds are in contrast to similar North American studies, and refute the hypothesis that intertidal salt marsh creeks have higher fish densities but lower diversities than eelgrass beds.
The Kariega Estuary channel was sampled using an otter trawl and the demersal fish catch analysed using the PRIMER statistical package. A biological-environmental (BIOENV) analysis was undertaken ...using the catch per unit effort ichthyofaunal data from the spring/summer period of 1996/97 and concurrent water temperature, salinity and turbidity data. No strong correlations between the ichthyofauna and recorded physicochemical parameters were documented, although temperature did show a weak correlation to demersal fish distributions. A second sampling programme undertaken in 2004 was specifically designed to test the influence of sedimentary characteristics on the distribution patterns of the dominant demersal species. Analyses showed that sediment size composition and organic content was strongly correlated (r = 0.70) to the distribution of the soles Solea bleekeri and Heteromycteris capensis, as well as the goby Glossogobius callidus. S. bleekeri and G. callidus showed a preference for the muddier middle and upper reaches of the Kariega Estuary channel, whereas H. capensis and Psammogobius knysnaensis were more abundant in the sandier lower reaches and mouth region of the estuary. The exact reasons for these preferences are unknown but are likely to be related to preferred prey availability, foraging success and predator avoidance in the different types of sediment. Other species caught in the otter trawl were not significantly correlated to sedimentary characteristics.
Subtidal research presents numerous challenges that restrict the ability to answer fundamental ecological questions related to reef systems. These challenges are closely associated with traditional ...monitoring methods and include depth restrictions (e.g. safe diving depths for underwater visual census), habitat destruction (e.g. trawling), mortality of target species (e.g. controlled angling and fish traps), and high operating costs (e.g. remotely operated vehicles and large research vessels). Whereas many of these challenges do not apply or are avoidable in the shallow subtidal environment, the difficulties grow as one attempts to sample deeper benthic habitats. This situation has resulted in a paucity of knowledge on the structure and ecology of deep water reef habitats around the coast of South Africa, and in most marine areas around the world. Furthermore, the inability to effectively survey deep water benthic environments has limited the capacity of researchers to investigate connectivity between shallow and deep water habitats in a standardised and comparable fashion.
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