4 results for Atalah, J

  • Temporal variability and intensity of grazing: a mesocosm experiment.

    Costello, Mark; Atalah, J; Anderson, MJ (2007)

    Journal article
    The University of Auckland Library

    Grazing has long been recognised as a structuring force for plant assemblages. Most of this knowledge comes from experiments in which grazers have been excluded or their densities manipulated. However, the intensity of grazing can vary, in space and time. Recently, an increasing number of studies have stressed the importance of the variance around the mean of ecological processes, but the potential effects of temporal variability in grazing in marine systems have not yet been explored. We examined the separate effects of intensity and temporal variability of grazing by the gastropod Cantharidus purpureus (Gemelin, 1931) on algal assemblages in a mesocosm experiment. In replicated experiments, algal assemblages grown on artificial substrata were subject to grazing regimes with mean intensity and temporal variance as crossed factors. In the first experiment, the more variable regimes led to greater reductions in algal cover, regardless of the level of grazing intensity. In the second experiment, variability elicited a similar effect, but this effect was larger for the low-than for the high-intensity treatments. These results indicate that temporally variable grazing regimes may have greater effects on algal assemblages than those anticipated from changes in the mean intensity of grazing alone. Thus, we suggest that temporal variability is a potentially important aspect of grazing processes that should be examined and incorporated into predictive models.

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  • Temporal variance of disturbance did not affect diversity and structure of a marine fouling community in north-eastern New Zealand.

    Atalah, J; Otto, Stefanie; Anderson, M; Costello, Mark; Lenz, M; Wahl, M (2007)

    Journal article
    The University of Auckland Library

    Natural heterogeneity in ecological parameters, like population abundance, is more widely recognized and investigated than variability in the processes that control these parameters. Experimental ecologists have focused mainly on the mean intensity of predictor variables and have largely ignored the potential to manipulate variances in processes, which can be considered explicitly in experimental designs to explore variation in causal mechanisms. In the present study, the effect of the temporal variance of disturbance on the diversity of marine assemblages was tested in a field experiment replicated at two sites on the northeast coast of New Zealand. Fouling communities grown on artificial settlement substrata experienced disturbance regimes that differed in their inherent levels of temporal variability and timing of disturbance events, while disturbance intensity was identical across all levels. Additionally, undisturbed assemblages were used as controls. After 150 days of experimental duration, the assemblages were then compared with regard to their species richness, abundance and structure. The disturbance effectively reduced the average total cover of the assemblages, but no consistent effect of variability in the disturbance regime on the assemblages was detected. The results of this study were corroborated by the outcomes from simultaneous replicate experiments carried out in each of eight different biogeographical regions around the world.

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  • Cladophora ruchingeri (C. Agardh) Kützing, 1845 (Cladophorales, Chlorophyta): a new biofouling pest of green-lipped mussel Perna canaliculus (Gmelin, 1791) farms in New Zealand

    Pochon, Xavier; Atalah, J; Wood, SA; Hopkins, GA; Watts, A; Boedeker, C (2015-01-19)

    Journal article
    The University of Auckland Library

    Cladophora is a genus of branched filamentous green algae (Ulvophyceae). It contains many species that are challenging to differentiate based on morphology because of the scarcity of diagnostic characters and extensive phenotypic plasticity. Within the past five years, Cladophora blooms have been observed on the ropes of green-lipped mussel farms in the Marlborough Sounds, New Zealand. When Cladophora reaches high biomass, it can clog mussel-harvesting equipment; thus, it is considered a nuisance organism in the region. This study used morphological and molecular techniques to identify the species responsible for the blooms, and to investigate whether this might be a recent incursion. Cladophora samples (n = 21) were collected from nine mussel farms, one salmon farm, and a marina. Morphological and phylogenetic analyses (partial large subunit and internally transcribed spacer regions 1 and 2 of the nuclear ribosomal cistron), revealed the identity of the bloom forming species as Cladophora ruchingeri (C.Agardh) Kützing, 1845. This represents the first report of this species in the Southern Hemisphere and Pacific region. Given the distinct morphology of C. ruchingeri (when mature), its absence from previous surveys of macro-algae from this region, and increasing reports of blooms, our findings suggest that this species has only recently been introduced to New Zealand. This study provides a robust taxonomic identification and initial baseline data. Further directed studies on Cladophora are required to advance knowledge on its ecology and distribution in New Zealand, and assist in the development of mitigation strategies.

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  • First evaluation of foraminiferal metabarcoding for monitoring environmental impact from an offshore oil drilling site

    Laroche, O; Wood, SA; Tremblay, Louis; Ellis, JI; Lejzerowicz, F; Pawlowski, J; Lear, Gavin; Atalah, J; Pochon, Xavier (2016-09)

    Journal article
    The University of Auckland Library

    At present, environmental impacts from offshore oil and gas activities are partly determined by measuring changes in macrofauna diversity. Morphological identification of macrofauna is timeconsuming, expensive and dependent on taxonomic expertise. In this study, we evaluated the applicability of using foraminiferal-specific metabarcoding for routine monitoring. Sediment samples were collected along distance gradients from two oil platforms off Taranaki (New Zealand) and their physicochemical properties, foraminiferal environmental DNA/RNA, and macrofaunal composition analyzed. Macrofaunal and foraminiferal assemblages showed similar shifts along impact gradients, but responded differently to environmental perturbations. Macrofauna were affected by hypoxia, whereas sediment grain size appeared to drive shifts in foraminifera. We identified eight foraminiferal molecular operational taxonomic units that have potential to be used as bioindicator taxa. Our results show that metabarcoding represents an effective tool for assessing foraminiferal communities near offshore oil and gas platforms, and that it can be used to complement current monitoring techniques.

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