Showing papers by "Alan K. Whitfield published in 2019"

Hypersalinity: Global Distribution, Causes, and Present and Future Effects on the Biota of Estuaries and Lagoons

Abstract: Estuaries, lagoons, and marine embayments that become hypersaline (salinity > 40) are found around the world, but are most common in tropical, arid, and warm temperate climates with low and/or highly seasonal rainfall. The area of these systems range markedly from 10,000 km2, but are generally shallow ( 100, which can result in mass mortalities of flora and fauna and a simplification of the biotic community and food web. Climate change over the coming decades will potentially influence the extent of hypersalinity in estuaries and lagoons, by altering the frequency and magnitude of rainfall and the sea-level height. Changes in rainfall and sea level will also influence the extent of connectivity with the ocean.

The importance of different juvenile habitats as nursery areas for a ubiquitous estuarine-dependent marine fish species

Abstract: Estuarine-dependent marine fish species rely on shallow, sheltered and food rich habitats for protection from predators, growth and ultimately recruitment to adult populations. Hence, habitats within estuaries function as critical nursery areas for a variety of fish species. Results from stomach content analysis and dietary diatom composition of a ubiquitous estuarine-dependent species Rhabdosargus holubi (Steindachner, 1881) in the main vegetated and un-vegetated habitats in the Bushmans Estuary, South Africa, were interpreted along with published information on habitat complexity, relative abundance and behaviour of this species. Although the complexity of seagrass, together with the higher abundance and behaviour of R. holubi in seagrass suggests that this is the main nursery habitat (in terms of both feeding and protection from predation), the dominance of red filamentous algae and the presence of some invertebrates mainly in the diet of fish from un-vegetated habitats indicates that this species is using a mosaic of habitats, including un-vegetated areas, for foraging. Based on the above findings, and results from other studies, it is concluded that juvenile R. holubi in permanently open estuaries makes use of a range of habitats according to macrophyte shelter from predators, the availability of preferred food resources and physical drivers such as water depth and tidal phase. This study demonstrated that a multi-method approach, as opposed to a single method approach (diet alone) is useful to assess the nursery value of juvenile fish habitats.

Characterisation of selected micro-estuaries and micro-outlets in South Africa using microalgal, zooplanktonic and macrozoobenthic assemblages

Abstract: South Africa has approximately 200 micro-estuaries and micro-outlets along its more than 3 000 km of coastline. Many of these microsystems (i.e. micro-outlets and micro-estuaries) share some charac...