The influence of selected environmental parameters on the distribution of the dominant demersal fishes in the Kariega Estuary channel, South Africa

Richardson, Naomi; Whitfield, Alan K.; Paterson, Angus W.

doi:10.1080/15627020.2006.11407339

Cited by 11 publications

(4 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The width of the Kariega Estuary ranges from 40 to 90 m, with a water depth of 1-4 m . Sediment types differ, with the upper reaches comprising mainly coarse material deposited by the river, the middle reaches containing a high proportion of finer sediment particles and the lower reaches closer to the mouth containing large quantities of sand imported from the marine environment (Richardson et al, 2006). The Kariega Estuary is c. 18 km long, with a small catchment area (686 km 2 ) that is impounded by three major dams: Settlers, Moss and Assegai dams (Paterson & Whitfield, 1997).…”

Section: S T U Dy S I T Ementioning

confidence: 99%

River flow, zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary

Mbandzi

Wasserman

Deyzel

et al. 2018

Journal of Fish Biology

View full text Add to dashboard Cite

The possible links between river flow, zooplankton abundance and the responses of zooplanktivorous fishes to physico-chemical and food resource changes are assessed. To this end, the seasonal abundance, distribution and diet of the estuarine round-herring Gilchristella aestuaria and Cape silverside Atherina breviceps were studied in the Kariega Estuary. Spatio-temporal differences were determined for selected physico-chemical variables, zooplankton abundance and zooplanktivorous fish abundance and distribution. Results indicated that, following a river flood event in winter (>30 m s ), altered physico-chemical conditions occurred throughout the estuary and depressed zooplankton stocks. Abundance of G. aestuaria was highest in spring, with this species dominant in the upper and middle zones of the estuary, while A. breviceps was dominant in summer and preferred the middle and lower zones. The catch per unit of effort of both zooplanktivores also declined significantly following the flooding, thus suggesting that these fishes are reliant on zooplankton as a primary food source for healthy populations. Copepods dominated the stomach contents of both fish species, indicating a potential for strong interspecific competition for food, particularly in the middle reaches. Temporal differences were evident in dietary overlap between the two zooplanktivorous fish species and were correlated with river flow, zooplankton availability and fish distribution. The findings of this study emphasize the close trophic linkages between zooplankton and zooplanktivorous fishes under changing estuarine environmental conditions, particularly river flow and provide important baseline information for similar studies elsewhere in South Africa and the rest of the world.

show abstract

Section: S T U Dy S I T Ementioning

confidence: 99%

River flow, zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary

Mbandzi

Wasserman

Deyzel

et al. 2018

Journal of Fish Biology

View full text Add to dashboard Cite

show abstract

“…Comparison of impact derived from use of Catch Per Unit Effort and biomass, whereby CPUE gives a misleading impact assessment of the extralimital predator. CPUE data were taken fromBokhutlo et al (2016) andRichardson et al (2006), with unpublished biomass data from O.L.F Weyl taken fromDick et al (2017c).…”

mentioning

confidence: 99%

On the RIP: using Relative Impact Potential to assess the ecological impacts of invasive alien species

Dickey¹,

Cuthbert²,

South³

et al. 2020

View full text Add to dashboard Cite

Invasive alien species continue to arrive in new locations with no abatement in rate, and thus greater predictive powers surrounding their ecological impacts are required. In particular, we need improved means of quantifying the ecological impacts of new invasive species under different contexts. Here, we develop a suite of metrics based upon the novel Relative Impact Potential (RIP) metric, combining the functional response (consumer per capita effect), with proxies for the numerical response (consumer population response), providing quantification of invasive species ecological impact. These metrics are comparative in relation to the eco-evolutionary baseline of trophically analogous natives, as well as other invasive species and across multiple populations. Crucially, the metrics also reveal how impacts of invasive species change under abiotic and biotic contexts. While studies focused solely on functional responses have been successful in predictive invasion ecology, RIP retains these advantages while adding vital other predictive elements, principally consumer abundance. RIP can also be combined with propagule pressure to quantify overall invasion risk. By highlighting functional response and numerical response proxies, we outline a user-friendly method for assessing the impacts of invaders of all trophic levels and taxonomic groups. We apply the metric to impact assessment in the face of climate change by taking account of both changing predator consumption rates and prey reproduction rates. We proceed to outline the application of RIP to assess biotic resistance against incoming invasive species, the effect of evolution on invasive species impacts, application to interspecific competition, changing spatio-temporal patterns of invasion, and how RIP can inform biological control. We propose that RIP provides scientists and practitioners with a user-friendly, customisable and, crucially, powerful technique to inform invasive species policy and management.

show abstract

“…Although selected physico-chemical variables were correlated with fish distribution, the proportion of variance explained by the uMgeni Estuary was relatively low. Other factors such as vegetation type (Mbande et al, 2005), tidal exchange (Wilson and Sheaves, 2001), sedimentary characteristics (Richardson et al, 2006), habitat variability (Elliott and Dewailly, 1995), nutrient concentrations (Perkin and Bonner, 2014), food resource distribution (Whitfield 1980) or urbanisation (Osborne et al, 2021) may be responsible for the variation in the assemblage patterns. The greater proportion of variance explained in the uMlalazi Estuary suggests that the measured environmental variables more closely explain the assemblage composition, although other unmeasured variables may also be at play.…”

Section: Linking Environmental Variables To Fish Community Patternsmentioning

confidence: 99%

“…Estuaries are highly dynamic, undergoing rapid fluctuations in environmental variables and displaying distinct vertical and longitudinal gradients (Richardson et al, 2006;Medeiros et al, 2018;Connelly et al, 2020). These gradients are often more defined in estuaries with continuous freshwater and marine influences resulting from a permanent connection to the sea (Nicolas et al, 2010b;Taddese and Closs, 2019).…”

Section: Introductionmentioning

confidence: 99%

Decadal changes in land-use, water quality and fish assemblages in a KwaZulu-Natal urban and non-urban estuary.

Van Schoor

View full text Add to dashboard Cite

Globally, estuaries are recognised as highly dynamic environments which support diverse and productive flora and fauna, and provide numerous goods and services for human wellbeing.These systems are under threat from growing coastal populations that demand the transformation of natural land to accommodate urbanisation, agriculture, harbour, and infrastructure developments. Direct and indirect land-use/land-cover (LULC) changes adversely affect estuarine water quality, directly impacting estuarine biota such as fishes.While the short links between these components are known, few studies have attempted to integrate these links, particularly within the South African context. Therefore, this study aimed to integrate different levels of assessment (LULC and estuarine water quality) to describe changes in estuarine fish ecology over space and time. The study compared two permanently open estuaries in KwaZulu-Natal with distinct land-cover types, namely the uMgeni and uMlalazi estuaries. The uMgeni Estuary is surrounded by urban features and is situated in a highly developed catchment, whereas the uMlalazi is near-natural, with some surrounding agricultural areas.Historical land-cover imagery from the estuary to the 20 m topographical contour (inclusive of the Estuary Functional Zone), the estuary catchment land-cover, water quality and ichthyofauna data were collected. Land-cover types were grouped into eight categories and 42 feature classes based on modifications to the South African National Land Cover system, the United States Geological Survey and the Coastal Change Analysis Program. Multivariate statistical analysis identified two distinct groupings of land-cover types, Period 1 (before 1989) and Period 2 (during and after 1989). This period factor was then further used throughout the study to determine associated (temporal) responses in water quality and fish assemblages. Strong negative correlations were observed between dissolved oxygen and artificial land-cover types in the uMgeni Estuary. The results suggested that the uMgeni Estuary receives nutrient inputs from various urban activities, which reduce oxygen levels within the water column. Alterations to the hierarchical ichthyofauna structure in the uMgeni occurred on a year to year basis, relative to these anthropogenic impacts. In contrast, good water quality likely associated with fewer developments within the Estuarine Functional Zone has allowed the hierarchical fish structure in the uMlalazi Estuary to remain the same over time, although minor species level differences have occurred.

show abstract

The influence of selected environmental parameters on the distribution of the dominant demersal fishes in the Kariega Estuary channel, South Africa

Cited by 11 publications

References 0 publications

River flow, zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary

River flow, zooplankton and dominant zooplanktivorous fish dynamics in a warm‐temperate South African estuary

On the RIP: using Relative Impact Potential to assess the ecological impacts of invasive alien species

Decadal changes in land-use, water quality and fish assemblages in a KwaZulu-Natal urban and non-urban estuary.

Contact Info

Product

Resources

About