Browsing by Author "Williams, RJ"

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    Comparisons of fish catches using fyke nets and buoyant pop nets in a vegetated shallow water saltmarsh flat at Towra Point, NSW
    (Coast and Wetlands Society, 2005) Mazumder, D; Saintilan, N; Williams, RJ
    The selection of appropriate sampling methods is a prerequisite for the design of any survey detailing nekton assemblages. In the present study two commonly used saltmarsh fish sampling methods, the fyke net and the buoyant pop net, were used to compare the assemblages of fish caught in a saltmarsh flat during monthly spring tides over a twelve month period. Both nets were made of 2mm mesh. A total of 3514 fish and crustaceans of 21 species were captured by 48 fyke net sets and 818 fish of 16 species were captured by 48 pop net releases. Fyke and pop nets recorded significantly different (ANOSIM: P<0.001) assemblages, with higher proportions of Pseudomugil signifer caught in the fyke nets and Ambassis jacksoniensis in the pop nets. Five species, Sillago cilliata, Rhabdosargus sarba, Redigobius macrostoma, Taeniodes mordax and Metapenaeus macleayi, were caught in the fyke nets only. Significant differences in the size of fish caught were recorded for two species, Gobiopterus semivestitus and Gerres subfasciatus, with larger fish on average caught in the pop nets. The result suggested that pop nets are less efficient at catching smaller fish. © The Authors, CC-BY-ND 3.0
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    Evaluating trophic linkages in mangrove-based food webs using stable isotopes of carbon and nitrogen
    (Rosenstiel School of Marine and Atmospheric Science University of Miami, 2006-04-19) Mazumder, D; Szymczak, R; Saintilan, N; Williams, RJ
    An understanding of the energy flow pathways and trophic linkages in estuarine food webs is essential for managing estuaries and their ecosystems sustainably. These pathways are complex, given the dynamics in physico-chemical processes, variety and area of habitats. Carbon and nitrogen stable isotope ratios (δ13C and δ15N) were measured for a variety of fish, invertebrate, and crustacean species collected from saltmarsh and mangrove habitats in Botany Bay and Homebush Bay, NSW, Australia. The work is on-going, however, initial observations indicate specific prey-predator linkages evident within a complex trophic structure. Results also advocate the role of certain non-commercial estuarine species as important conduits of energy and nutrition to higher trophic-order commercially valuable species, linking these with specific estuarine habitats. This work seeks to model the source of energy and nutrition in mangrove and saltmarsh-based food webs and to determine the chemical linkages between high trophic order species and different habitat resources. © The Authors.
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    Evaluating trophic linkages in mangrove-based food webs using stable isotopes of carbon and nitrogen
    (Ingenta, 2006-04-19) Mazumder, D; Szymczak, R; Saintilan, N; Williams, RJ
    An understanding of the energy flow pathways and trophic linkages in estuarine food webs is essential for managing estuaries and their ecosystems sustainably. These pathways are complex, given the dynamics in physico-chemical processes, variety and area of habitats. Carbon and nitrogen stable isotope ratios (δ13C and δ15N) were measured for a variety of fish, invertebrate, and crustacean species collected from saltmarsh and mangrove habitats in Botany Bay and Homebush Bay, NSW, Australia. The work is on-going, however, initial observations indicate specific prey-predator linkages evident within a complex trophic structure. Results also advocate the role of certain non-commercial estuarine species as important conduits of energy and nutrition to higher trophic order commercially valuable species, linking these with specific estuarine habitats. This work seeks to model the source of energy and nutrition in mangrove and saltmarsh-based food webs and to determine the chemical linkages between high trophic order species and different habitat resources. © 2007 Rosenstiel School of Marine and Atmospheric Science
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    Fish assemblages in three tidal saltmarsh and mangrove flats in temperate NSW, Australia: a comparison based on species diversity and abundance
    (Springer Nature Limited, 2006-06) Mazumder, D; Saintilan, N; Williams, RJ
    Fish assemblages in three geographically distinct saltmarsh meadows and mangrove forests in the Sydney region were examined using fyke nets over three common sampling periods. The saltmarshes at Towra Point and Allens Creek, though of contrasting geomorphic setting, showed similar fish assemblages during spring tides, with relatively high diversity and abundance. The saltmarsh at Bicentennial Park, reclaimed from dredge spoil in the early 1960’s, showed significantly lower diversity and abundance. Fish assemblages in the three mangrove settings were each distinct, though with no significant differences in diversity and abundance between sites. The result raises questions about the efficacy of created saltmarsh as a compensatory habitat for fish. © 2006 Springer Nature Switzerland AG
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    Impoundment constraint of fish niche diversity in a temperate Australian river
    (Springer, 2016-02-02) Mazumder, D; Williams, RJ; Wals, C; Wen, L; Saintilan, N
    Dams constitute a major threat to aquatic ecosystems world-wide by modifying habitat and impairing opportunities for many freshwater fish. Subsequently, there can be a loss in fish diversity and change in the species distributions and population structure that ultimately contribute to changes in trophic structure and ecosystem function. In this study, stable isotope analysis (SIA) was used to compare trophic interaction and niche space of five fish species residing upstream and downstream of a significant barrier (Tallowa Dam) on the Shoalhaven River in south-eastern Australia. Significant reduction in niche space was found among predator/prey species residing in upstream habitat, implying limited dietary opportunity. Mixing calculations for Macquaria novemaculeata confirmed ontogenetic differences upstream and downstream of the dam. Causal mechanisms for this variability in trophic structure include habitat modification and/or discontinuity in river connectivity. SIA provides a useful tool for demonstrating the effect of barriers and/or impoundments on aquatic ecosystems, and for developing future monitoring programmes to evaluate restoration strategies.
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    Stable isotope (δ13C and δ15N) studies in aquatic ecosystems: response to different conditions
    (The University of Western Australia, 2013-07-10) Mazumder, D; Walsh, C; Williams, RJ; Jenkins, K; Sives, C; Hollins, SE; Meredith, KT; Doyle, T
    Rivers and wetlands are complex ecosystems with numerous relationships between water, earth, air, plants and animals. The stable isotopes 13C and 15N were investigated in river and wetland ecosystems to evaluate food web structure complexity, with particular emphasis on their response to changing hydrological conditions. A study developed on the Shoalhaven River focused on assessing the differences in trophic conditions of fish populations found above and below Tallowa Dam. Some species displayed little variation in C or N signatures over the two years sampling period suggesting a preferential dietary niche, regardless of hydrological or density-dependent conditions. The variable diet sources between Australian bass revealed by source mixing calculation also indicated trophic discontinuity within these restricted environments. We found variable trophic levels and sources for the same species of invertebrate and fish between habitats in wetlands show the effect of divergent ecological conditions and landuse practices. For example, in the Macquarie Marshes we found that an extended inter-flood interval caused the decline of riparian vegetation communities including river red gum signalling a shift from aquatic floodplain ecosystems to terrestrial ecosystems where grasses and chenopod shrubs dominate as an organic carbon source. Results provide insights into stable isotope use to better understand potential impacts of future climate variation on river and wetland systems.
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    Temporal variations in rish catch using pop nets in mangrove and saltmarsh flats at Towra Point, NSW, Australia
    (Springer Nature Limited, 2005-08) Mazumder, D; Saintilan, N; Williams, RJ
    Fish assemblages utilising saltmarsh and mangrove during spring tides were surveyed over a 12-month period using buoyant pop nets. A total of 48 net releases in the saltmarsh identified 16 species, at a density of 0.56 fish m−2, with six species being of commercial importance. The same number of releases within the mangrove collected a total of 23 species at a density of 0.76 fish m−2. However, fish density was higher within the saltmarsh than the adjacent mangrove when corrected for water volume. Multidimensional scaling revealed different assemblages of fish in the two habitats, with higher numbers of Ambassis jacksoniensis and Pseudomugil sp. in the saltmarsh and higher numbers of Mugilogobius sp. and Acanthopagrus australis in the mangrove. The result suggests a potentially significant role for saltmarsh as a fish habitat in the estuaries of southeast Australia. © 2005 Springer Nature Switzerland AG
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    Trophic importance of a temperate intertidal wetland to resident and itinerant taxa: evidence from multiple stable isotope analyses
    (CSIRO Publishing, 2011-01-18) Mazumder, D; Saintilan, N; Williams, RJ; Szymczak, R
    Juveniles of commercially important fish species congregate in shallow vegetated estuarine habitats during high tides. Considerable debate has centred on whether the significance of these habitats lies in their provision of greater feeding opportunities, or shelter from predation afforded by greater structural complexity. We tested the hypothesis that an inundated mangrove and saltmarsh wetland provided feeding opportunities for itinerant species, and that the contribution of wetland primary producers and grazing herbivores could be identified in their diet, using stable isotopes of carbon and nitrogen. Potential sources of dietary carbon included mangrove, saltmarsh, seagrass, seagrass epiphytic material and benthic organic material. Saltmarsh plants (mostly Sporobolus virginicus and Juncus kraussii) and fine benthic organic material appeared to be the primary sources of dietary carbon for the resident grazing herbivores in the wetlands, based on IsoSource mixing models. During high tide, species of itinerant fish enter the mangrove and, when inundated, the saltmarsh, and feed primarily on crab larvae and copepods. Fine benthic organic matter, seagrass epiphyte, and C3 and C4 plant materials also supplement the diet of some fish. The crab larvae therefore provide a significant source of nutrition and an important link between the intertidal wetlands and the adjacent estuarine ecosystem. The carnivorous fish Acanthopagrus australis, at the highest trophic level, hunted within or adjacent to the mangrove–saltmarsh wetland and fed on several lower-order consumers within the wetland. The present study highlights the significance of mangrove and saltmarsh wetlands as a feeding habitat for resident grazers and itinerant nekton. © 2011, CSIRO Publishing
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    Trophic relationships between itinerant fish and crab larvae in a temperate Australian saltmarsh
    (CSIRO Publishing, 2006-02-23) Mazumder, D; Saintilan, N; Williams, RJ
    Comparisons of zooplankton inputs and outputs for a temperate Australian saltmarsh demonstrate a substantial contribution of crab larvae to the ebbing tide water, particularly during the cooler months. Few crab larvae were present in the incoming tide (mean abundance 4 m−3), whereas many crab larvae were present in the outgoing water (mean abundance 2124.63 m−3). Stomach content analysis of itinerant fish exiting the saltmarsh with the ebbing tide demonstrated extremely high proportions of crab larvae in the gut of glassfish (Ambassis jacksoniensis), as well as flat tail mullet (Liza argentea) and blue eye (Pseudomugil signifer). The results suggest a direct trophic link between secondary production of saltmarsh and itinerant fish, and a significant ecological role for burrowing crabs occupying saltmarshes in temperate Australia in the trophic food web of saltmarsh–estuarine systems. © CSIRO 2006
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    Variability of stable isotope ratios of glassfish (Ambassis jacksoniensis) from mangrove/saltmarsh environments in Southeast Australia and implications for choosing sample size
    (Taylor & Francis, 2008-04) Mazumder, D; Williams, RJ; Reid, D; Saintilan, N; Szymczak, R
    Stable isotopes offer an accurate and cost-effective way to understand critical pathways of energy, and their use has application where aquatic habitats have been degraded. Isotope ratios can offer insights into appropriate conservation and rehabilitation techniques to manage these valuable resources. To date, the literature shows little attention to spatial and temporal variation in isotope signatures of samples taken from estuarine environments. This study reports on an investigation of sample size by which to determine isotopic signatures within a single species of fish, Ambassis jacksoniensis. Provided are two ways by which to determine how many samples are needed, and the results imply that care may be needed in interpreting previous studies based on small sample size. A minimum of five individuals would appear necessary in some cases. © 2008, Taylor & Francis Ltd.
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    Variability of stable isotope ratios of mangrove glassfish (Ambassis Jacksoniensis) from southeast Australia and the implications for ecosystem studies
    (Ingenta, 2007-05-03) Mazumder, D; Williams, RJ; Szymczak, R; Reid, D; Saintilan, N
    Scientists concerned with organic matter flow and food web structures in aquatic ecosystems are increasingly realizing the potential of stable isotope ratios as natural tracers. Stable isotopes offer an accurate and cost effective way to understanding critical pathways of energy and pollutant transfer. Further, many aquatic habitats have been degraded and isotope ratios offer insights into appropriate conservation and rehabilitation techniques to manage these valuable resources. So far, the literature shows little attention has been paid to spatial and temporal variations in isotope signatures of samples taken from saltmarsh and mangrove environments. This study reports on investigations into the differences in isotopic signatures within a single species, Ambassis jacksoniensis, surveyed from two locations at two different times. The results suggest significant variation in δ13C between different season and location for glassfish, but not for δ15N. The results also suggest that care is needed in interpreting previously published results. © 2007 Rosenstiel School of Marine and Atmospheric Science
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    Zooplankton inputs and outputs in the saltmarsh at Towra Point, Australia
    (Springer, 2009-06) Mazumder, D; Saintilan, N; Williams, RJ
    The contribution made by saltmarsh to the production of estuarine zooplankton was examined through a comparison of inputs and outputs of tidal water at a site on Towra Point, NSW, Australia. Saltmarsh proved to be a net exporter of crab and gastropod larvae, although it functioned as a sink for copepods and amphipods. Further, the highest density of zooplankton in estuarine nearshore habitats (saltmarsh, mangrove, seagrass, and open water) during a high tide event was found in the saltmarsh. The presence of high concentrations of zooplankton, predominantly crab and gastropod larvae, in the saltmarsh and lesser extent in the mangrove represents a source of food for estuarine fish. © 2009, Springer. The original publication is available at www.springerlink.com