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2019

43 record(s)
 
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  • Sea urchins have the capacity to destructively overgraze kelp beds and cause a wholesale shift to an alternative and stable ‘urchin barren’ state. However, their destructive grazing behaviour can be highly labile and contingent on behavioural shifts at the individual and local population level. Changes in supply of allochthonous food sources, i.e. availability of drift-kelp, is often suggested as a proximate trigger of change in sea urchin grazing behaviour, yet field tests of this hypothesis are rare. Here we conduct a suite of in situ behavioural surveys and manipulative experiments within kelp beds and on urchin barrens to examine foraging movements and evidence for a behavioural switch to an overgrazing mode by the Australian sea urchin Heliocidaris erythrogramma (Echinometridae). Tracking of urchins using time-lapse photography revealed urchin foraging to broadly conform to a random-walk-model within both kelp beds and on barren grounds, while at the individual level there was a tendency towards local ‘homing’ to proximate crevices. However, consistent with locally observed ‘mobile feeding fronts’ that can develop at the barrens-kelp interface, urchins were experimentally inducible to show directional movement toward newly available kelp. Furthermore, field assays revealed urchin grazing rates to be high on both simulated drift-kelp and attached kelp thalli on barren grounds, however drift-kelp but not attached kelp was consumed at high rates within kelp beds. Time-lapse tracking of urchin foraging before/ after the controlled addition of drift-kelp on barrens revealed a reduction in foraging movement across the reef surface when drift-kelp was captured. Collectively results indicate that the availability of drift-kelp is a pivotal trigger in determining urchin feeding modes, which is demonstrably passive and cryptic in the presence of a ready supply of drift-kelp. Recovery of kelp beds therefore appears possible if a sustained influx of drift-kelp was to inundate urchin barrens, particularly on reefs where local urchin densities and where grazing pressure is close to the threshold enabling kelp bed recovery.

  • The fatty acid content and composition of the Antarctic krill Euphausia superba Dana, 1850 were investigated using samples collected by a commercial fishing vessel. This dataset allowed comparison between seasons, years (2013–2016), and different fishing locations. Quantities of omega 3 fatty acids 20:5n-3 and 22:6n-3 (mg/g dry mass; DM) were highest in autumn and decreased through winter to reach a spring low. Quantities of the flagellate marker 18:4n-3 and diatom marker 16:1n-7c were variable and did not display the same seasonal fluctuations. In summer, krill had high percentages (% total fatty acids) of 20:5n-3 and 22:6n-3, total PUFA, and low 18:1n-9c/18:1n-7c ratios, indicating a more herbivorous diet. Krill became more omnivorous from autumn to spring, indicated by increasing ratios of 18:1n-9c/18:1n-7c and percentages of Σ 20:1 + 22:1 isomers. Bacterial fatty acids (Σ C15 + C17 + C19 isomers) were minor components year-round (0.9–1.8 %). Seasonal levels of herbivory and omnivory differed between years, and levels of specific fatty acid ratios differed between fishing locations. The fatty acid 18:4n-3 was a major driver of variability in krill fatty acid composition, with no obvious seasonal driver. This is the first study to report krill fatty acid data during all four seasons over consecutive years. This large-scale study highlights the value of using fisheries samples to examine seasonal and annual fluctuations in krill diet and condition.

  • This record provides an overview of the scope and research output of NESP Marine Biodiversity Hub Project D5 - "A standardised national assessment of the state of coral and rocky reef biodiversity". For specific data outputs from this project, please see child records associated with this metadata. -------------------- This project will involve integration of a national suite of reef biota Underwater Visual Census (UVC) monitoring datasets (Reef Life Survey (RLS), University of Tasmania (UTAS), Australian Institute for Marine Science (AIMS), Parks Victoria (PV), SA Department of environment, water and natural resources (DEWNR)) to provide a comprehensive update to the state of Australian Reefs report for the next national State of the Environment Report. Maps and indicator trends will show changes in the health of rocky and coral reefs nationally from 2005 to 2020. The update will include addition of a new index which summarises the population trajectories for 600-1000 reef species nationally. Individual species trajectories will provide the only threat status information for the majority of these species, assisting future listing of previously unassessed species if significant declines are detected. Planned Outputs • Maps and trends in SoE indicators • Raw data underlying SoE analyses (data use agreement must be signed with AIMS for access to that data) • Various scientific papers

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    Data accompanying Layton et al. 2019, Resilience and stability of kelp forests: the importance of patch dynamics and environment-engineer feedbacks. PLOS ONE. To explore how resilience and stability of kelp habitats is influenced by this habitat degradation, we created an array of patch reefs of various sizes and supporting adult Ecklonia radiata kelp transplanted at different densities. This enabled testing of how sub-canopy abiotic conditions change with reductions in patch size and adult kelp density, and how this influenced demographic processes of microscopic and macroscopic juvenile kelp.

  • Antarctic krill (Euphausia superba) have a keystone role in the Southern Ocean, as the primary prey of Antarctic predators. Any decreases in krill abundance could result in a major ecological regime shift, but there is currently limited information on how climate change may affect krill. Increasing anthropogenic carbon dioxide (CO2) emissions are causing ocean acidification, as absorption of atmospheric CO2 in seawater alters ocean chemistry. Ocean acidification increases mortality and negatively affects physiological functioning in some marine invertebrates, and is predicted to occur most rapidly at high latitudes. Here we show that, in the laboratory, adult krill are able to survive, grow, store fat, mature, and maintain respiration rates when exposed to near-future ocean acidification (1000 – 2000 μatm pCO2) for one year. Despite differences in seawater pCO2 incubation conditions, adult krill are able to actively maintain the acid-base balance of their body fluids in near-future pCO2, which enhances their resilience to ocean acidification.

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    In support of future science missions, an engineering demonstration was conducted to show the ability of the nupiri muka AUV to be deployed and operated at an ice shelf. The AUV was deployed from Davis Station, Antarctica, to conduct underwater surveys in the vicinity of, and beneath, the Sørsdal ice shelf. The AUV conducted several surface transits from the station to the ice shelf, where dive missions at various depths were conducted. The primary mode of operation was the AUV tracking near the seafloor. In addition, a patch survey was conducted near the stations, where several sediment grabs were taken.

  • Google Earth KMZ files of hammerhead sharks tagged with Wildlife Computers miniPAT archival tags and SPOT6 tags. Files of animals tagged with MiniPAT tags include an MELE polygon, which is the 'Maximum extent of location estimates', that is, a polygon enclosing all position estimates at the maximum error level (100 km). Collectively, movements are restricted within state waters with no hammerheads moving across state or International boundaries.

  • -- Layton et al. Chemical microenvironments within macroalgal assemblages: implications for the inhibition of kelp recruitment by turf algae. Limnology & Oceanography. DOI:10.1002/lno.11138 -- Kelp forests around the world are under increasing pressure from anthropogenic stressors. A widespread consequence is that in many places, complex and highly productive kelp habitats have been replaced by structurally simple and less productive turf algae habitats. Turf algae habitats resist re-establishment of kelp via recruitment inhibition; however little is known about the specific mechanisms involved. One potential factor is the chemical environment within the turf algae and into which kelp propagules settle and develop. Using laboratory trials, we illustrate that the chemical microenvironment (O2 concentration and pH) 0.0–50 mm above the benthos within four multispecies macroalgal assemblages (including a turf-sediment assemblage and an Ecklonia radiata kelp-dominated assemblage) are characterised by elevated O2 and pH relative to the surrounding seawater. Notably however, O2 and pH were significantly higher within turf-sediment assemblages than in kelp-dominated assemblages, and at levels that have previously been demonstrated to impair the photosynthetic or physiological capacity of kelp propagules. Field observations of the experimental assemblages confirmed that recruitment of kelp was significantly lower into treatments with dense turf algae than in the kelp-dominated assemblages. We demonstrate differences between the chemical microenvironments of kelp and turf algae assemblages that correlate with differences in kelp recruitment, highlighting how degradation of kelp habitats might result in the persistence of turf algae habitats and the localised absence of kelp.

  • This record provides an overview of the scope and research output of NESP Marine Biodiversity Hub Project A14 - "Identification of near-shore habitats of juvenile white sharks in Southwestern Australia". For specific data outputs from this project, please see child records associated with this metadata. -------------------- In early 2018, the CSIRO provided the first estimate of abundance for the southern-western adult white shark. Establishing an estimate of total abundance was not possible due to the lack of information of the juvenile life history stage in south-western Australia. The estimate of adult abundance also included trend (essentially zero or slightly negative), however, it was noted that to confirm the trend, a further decade of sampling would be required. This can be reduced if we identify near-shore habitats where juvenile white sharks from the southern-western population can be readily accessed. This pilot project will investigate credible anecdotal evidence of juvenile white sharks using near-shore habitat near the head of the Great Australia Bight, and inform future project development steps. The pilot project will include collaboration and the opportunity for capacity building with the Yatala Land Management group. The outcome of this pilot project will inform whether or not to proceed to future (on-water) activities. Planned Outputs • Spatial maps showing juvenile white-shark aggregation areas that include Australian marine park boundaries and zoning in jpeg format • Shapefile of juvenile white-shark aggregation areas provided to ERIN • High quality and project relevant images (still and video) suitable for communications purposes • Summary (and images) of opportunistic wildlife observations within the Great Australian Bight Marine Park (Commonwealth waters) • Final report

  • This record provides an overview of the scope and research output of NESP Marine Biodiversity Hub project E7 - "Assessing the feasibility of restoring giant kelp beds in eastern Tasmania". For specific data outputs from this project, please see child records associated with this metadata. -------------------- This project will extend an externally funded project conducted through UTAS commencing in 2018 to select for thermally tolerant and low-nutrient-tolerant giant kelp (Macrocystis pyrifera) genotypes, and to examine effects of acclimation of selected genotypes by pre-exposure to warm, nutrient-poor conditions. The proposed project will outplant pre-exposed selected genotypes of giant kelp as micro-sporophytes in an experiment with and without provision of an added source of nutrient. The work is designed to assess the feasibility of this approach as a means to develop minimum patch sizes for giant kelp that can be self-replacing and self-expanding, thus providing restoration and future climate-proofing options for this EPBC-listed marine community. Planned Outputs • Experimental data from macrocystis restoration • Final report