Dietary tracers and stomach contents reveal pronounced alimentary flexibility in the freshwater mullet (Myxus capensis, Mugilidae) concomitant with ontogenetic shifts in habitat use and seasonal food availability
- Authors: Carassou, Laure , Whitfield, Alan K , Moyo, Sydney , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456201 , vital:75493 , xlink:href="https://doi.org/10.1007/s10750-017-3230-3"
- Description: We investigated ontogenetic and seasonal variations in the diet of the freshwater mullet (Myxus capensis) across a river–estuary interface using dietary tracer (stable isotopes and fatty acids) and stomach content analyses. Two hypotheses were tested: (A) the freshwater mullet diet shifts as individuals grow and migrate from the estuary to the river, and (B) the dominant food resources utilized by freshwater mullet vary through time, mainly as a function of the seasonal changes in the availability of preferred food items in each habitat. Both hypotheses were supported, as our results indicated broad dietary flexibility by M. capensis, with utilized food items ranging from benthic microalgae to insects depending on habitat and seasonal patterns in availability of resources. Given the unexpected importance of invertebrate-derived prey, including some of terrestrial origin (i.e. aerial or semi-aquatic insects), during the freshwater phase of the M. capensis life cycle, we also emphasize a need for a re-assessment of the trophic designation of this species (previously designated as a strict detritivore).
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- Date Issued: 2017
Impact of an introduced predator (Micropterus salmoides, Centrarchidae) on native estuarine fish elucidated through fatty acid analyses
- Authors: Carassou, Laure , Magoro, Mandla L , Whitfield, Alan K , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456247 , vital:75496 , xlink:href="https://hal.inrae.fr/hal-04177984/document"
- Description: The introduction of alien fish species can have contrasting impacts on local aquatic communities. The largemouth bass Micropterus salmoides (Centrarchidae; Fig.1) was introduced in 1928 in South Africa for recreational anglers. Concerns about its impact on local indigenous freshwater and estuarine fish populations are raised (Gratwicke and Marshall, 2001; Weyl and Lewis, 2006; Wasserman et al., 2011). In particular, the predatory impact of M. salmoides on estuary-associated juveniles of marine fish species must be elucidated.
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- Date Issued: 2017
Trophic dynamics of the cape stumpnose (Rhabdosargus holubi, Sparidae) across three adjacent aquatic habitats
- Authors: Carassou, Laure , Whitfield, Alan K , Bergamino, Leandro , Moyo, Sydney , Richoux, Nicole B
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456362 , vital:75506 , xlink:href="https://doi.org/10.1007/s12237-016-0075-3"
- Description: Migratory fish species are major vectors of connectivity among aquatic habitats. In this study, conventional stomach contents and stable isotope methods (δ13C and δ15N) were combined to understand how fish of different sizes feed across contrasting aquatic habitats. The Cape stumpnose Rhabdosargus holubi (Sparidae, Perciformes) was selected as an abundant estuarine-dependent species in the permanently open Kowie system, South Africa. Three different habitats were sampled in the region, namely, river, estuary, and sea. Fish entered the estuary as post-larvae from the marine environment, resided in the estuary and lower part of the river as juveniles, and then returned to the sea as sub-adults. The diet varied among habitats, seasons, and fish sizes. “Stable Isotope Analysis with R” (SIAR) Bayesian mixing models mostly supported the results from the stomach content analyses, but also revealed the importance of some prey (e.g., insects) that were underestimated in the consumed diet. Rhabdosargus holubi δ13C values indicated a clear spatial gradient in the origin of food sources assimilated across the habitats, with increasing δ13C along the freshwater-marine continuum. The δ13C ranges of sources and fish also overlapped within each habitat along this continuum, thus illustrating the fidelity of R. holubi to specific habitats at different life stages. By consuming prey in a particular habitat before migrating, either permanently or temporarily to another habitat, R. holubi participates in allochthonous fluxes among riverine, estuarine, and coastal marine environments, with approximately 7 tonnes of Cape stumpnose productivity being exported from the 142-ha Kowie Estuary to the sea each year.
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- Date Issued: 2016
Connectivity through allochthony: Reciprocal links between adjacent aquatic and terrestrial ecosystems in South Africa
- Authors: Richoux, Nicole B , Moyo, Sydney , Chari, Lenin D , Bergamino, Leandro , Carassou, Laure , Dalu, Tatenda , Hean, Jeffrey W , Sikutshwa, Likho , Gininda, Simphiwe , Magoro, Mandla L , Perhar, Gurbir , Ni, Felicity , Villet, Martin H , Whitfield, Alan K , Parker, Daniel M , Froneman, P William , Arhonditsis, George , Craig, Adrian J F K
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , report
- Identifier: http://hdl.handle.net/10962/438363 , vital:73454 , ISBN 978-1-4312-0679-7 , https://wrcwebsite.azurewebsites.net/wp-content/uploads/mdocs/2186-1-15.pdf
- Description: An important aspect of the dynamics of nutrients and pollutants in natural systems is captured in the concept of allochthony, founded on the observation that nutrients and energy in a variety of forms are transferred between adjacent habitats, com-munities and ecosystems that are not routinely considered as connected. Different forms of nutrients and energy move across the conceptual boundaries of habitats via organisms’ activities or physical processes such as wind or water currents, and these transfers can represent important food subsidies. Such cross-partition ecolog-ical subsidies can augment the nutritional condition, biomass and biodiversity of communities, particularly where local production (or autochthony) alone may be inadequate to support local food webs. Furthermore, organic subsidies can influ-ence population dynamics, community interactions and ecosystem processes, and can represent dominant flux inputs in ecosystem budgets. Our intention was to ex-plore organic nutrient fluxes in relation to a primarily lotic (i.e. flowing) aquatic sys-tem at the scale of a hydrological catchment.
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- Date Issued: 2015
Stable isotope evidence of food web connectivity by a top predatory fish (Argyrosomus japonicus: Sciaenidae: Teleostei) in the Kowie Estuary, South Africa
- Authors: Bergamino, Leandro , Dalu, Tatenda , Whitfield, Alan K , Carassou, Laure , Richoux, Nicole B
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457322 , vital:75625 , xlink:href="https://doi.org/10.2989/1814232X.2014.923782"
- Description: 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 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. This dietary diversity may help explain the success of A. japonicus as a dominant top predator in the system, primarily by increasing the energy available to this species.
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- Date Issued: 2014