Showing papers by "Alan K. Whitfield published in 2014"
TL;DR: This review shows that motor boats impact on the biology and ecology of fishes but the effects vary according to the species and even particular size classes, as well as the use of recreational boats as vectors of aquatic invasive organisms.
84 citations
TL;DR: In this article, the responses of water column nutrients, plankton density and biomass to inlet phase changes of these systems, for which information was collated on dissolved inorganic nitrogen and phosphorus concentrations, phytoplankton biomass, zooplankon density, and biomass from 16 TOCEs in South Africa.
Abstract: Temporarily open/closed estuaries (TOCEs) are systems temporarily closed off from the sea due to the development of a sandbar across the mouth during low rainfall periods. Due to their generally small size and overall higher retention times during the closed phase, these environments are highly susceptible to anthropogenic changes such as catchment degradation, climate change, pollution and changing river flow patterns. Several authors have reported marked fluctuations in biomass and density of biotic communities between the open and closed phases of specific estuaries. This study determines the responses of water column nutrients, plankton density and biomass to inlet phase changes of these systems, for which information was collated on dissolved inorganic nitrogen and phosphorus concentrations, phytoplankton biomass, zooplankton density and biomass from 16 TOCEs in South Africa. Our analyses detected higher phytoplankton chlorophyll- a concentrations, zooplankton density and biomass during the closed phase of these estuaries. The analysis of temporal dynamics of five systems showed that plankton biomass can attain pre-breaching levels 10 days after mouth closure. Estimates showed that plankton standing stocks during the closed phase can be 26 to 10 000 times higher than during the open phase. Our findings have significant implications for the management and conservation of TOCEs, especially the regulation of freshwater inflow and artificial breaching of their mouths, and highlight the vulnerability of these systems to current and expected impacts of anthropogenic and climatic changes on their productivity and functioning.
20 citations
TL;DR: It is concluded that the highly mobile A. japonicus consumes both pelagic and benthic fauna from the littoral and channel zones of the estuary, thereby playing a key functional role in linking food webs.
Abstract: In this study, food web connectivity within the Kowie Estuary on the south-east coast of South Africa was evidenced by the trophic behaviour of the predominantly piscivorous Argyrosomus japonicus. We examined stable isotopes of carbon (δ13C) and nitrogen (δ15N) in the dominant consumers (zooplankton, invertebrates and fishes) and food sources (particulate organic matter, epibionts and benthic microalgae) in the system. An SIAR (Stable Isotope Analysis in R) mixing model was used to interpret the possible food sources for this dominant top predatory fish. Small fishes and large epibenthic invertebrates dominated the diet of A. japonicus. Based on the contrasting diet of these prey fish and invertebrates, we propose that organic matter enters the predatory fish community via two major pathways: (1) a littoral pathway dominated by benthic microalgae production and epibionts, and (2) a channel pathway dominated by suspended particulate organic matter (including phytoplankton). We conclude that the highly mobi...
10 citations
TL;DR: The relationship between catchment land cover and the health of the East Kleinemonde Estuary was investigated between 2011 and 2013, using geographic information system (GIS) techniques to delineate and quantify land-cover in the whole catchment, in the lower section of the catchment and in the 1 km and 100 m buffer zones surrounding the estuary as mentioned in this paper.
Abstract: Temporarily open/closed estuaries in South Africa are being subjected to varying degrees of catchment land-cover transformation. Natural landscapes and hydrological functions are integral to the functioning of estuaries. The relationship between catchment land-cover and the health of the East Kleinemonde Estuary was investigated between 2011 and 2013, using geographic information system (GIS) techniques to delineate and quantify land-cover in the whole catchment, in the lower section of the catchment, and in the 1 km and 100 m buffer zones surrounding the estuary. Human activities, as outlined by the Department of Water Affairs resource directed measures (RDM) studies, and their associated land-cover classes are described. Possible links between catchment and buffer zone land-cover class composition and the health of the East Kleinemonde Estuary were explored. There was a relationship between catchment land-cover and estuarine health within all assessed catchment delineations. Natural land-cover was deter...
3 citations
TL;DR: In this paper, a decision support system (DSS) is proposed for the management of natural resources in the public domain, where the opinions of how a given resource should be managed are as diverse as the parties themselves.
Abstract: In situations to do with the management of natural resources in the public domain there are often many 'interested and affected parties'. The opinions of how a given resource should be managed are as diverse as the parties themselves. Debates are frequently unproductive. We argue that in these situations the development of a decision support system (DSS) is a constructive way forward towards sound management practices. This approach enables existing knowledge to be integrated into a form that can be used immediately in decision-making. Furthermore, research can be optimally prioritised should greater accuracy or improvement in the initial DSS be required. We illustrate this approach by considering the problem of determining the freshwater requirements of estuaries. The pattern of freshwater flow into estuary of a river that has been impounded is a management decision. This inflow pattern influences the state of an estuary. This in turn affects the fish that use the estuary. In this illustration we focus on these fish in developing a DSS. The DSS is then applied in a case study of the Krom River in the Eastern Cape.
1 citations