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EARTH SCIENCE | BIOLOGICAL CLASSIFICATION | PLANTS | MACROALGAE (SEAWEEDS) | BROWN ALGAE

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  • Kelps are in global decline due to climate change, including ocean warming. To identify vulnerable species, we need to identify their tolerances to increasing temperatures and whether tolerances are altered by co-occurring drivers such as inorganic nutrient levels. This is particularly important for those with restricted distributions, which may already be experiencing thermal stress. To identify thermal tolerance of the range restricted kelp Lessonia corrugata, we conducted a laboratory experiment on juvenile sporophytes to measure performance (growth, photosynthesis) across its thermal range (4 – 22 °C). We found the upper thermal limit for growth and photosynthesis to be ~ 22 – 23 °C, with an optimum of ~ 16 °C. To determine if elevated inorganic nitrogen availability could enhance thermal tolerance, we compared performance of juveniles under low (4.5 µmol/day) and high (90 µmol/day) nitrate conditions at and above the thermal optimum (16 – 23.5 °C). Nitrate enrichment did not enhance thermal performance at temperatures above the optimum but did lead to elevated growth rates at the thermal optimum 16 °C. Our findings indicate L. corrugata is likely to be extremely susceptible to moderate ocean warming and marine heatwaves. Peak sea surface temperatures during summer in eastern and northeastern Tasmania can reach up to 20 – 21 °C and climate projections suggest that L. corrugata’s thermal limit will be regularly exceeded by 2050 as south-eastern Australia is a global ocean-warming hotspot. By identifying the upper thermal limit of L. corrugata we have taken a critical step in predicting the future of the species in a warming climate.

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    An aerial survey was conducted for giant kelp (Macrocystis pyrifera) on the east coast of Tasmania from Eddystone Point to Southeast Cape. This survey represents part of a series of similar surveys, with historic aerial surveys having been conducted in 1986 and 1999. The survey was conducted via light aircraft. Areas of visable Macrocystis pyrifera beds were marked on topographical land tenure maps using landmarks as references, and complimentary photo footage was collected.

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    An aerial survey of giant kelp (Macrocystis pyrifera), was carried out on the east coast of Tasmania from Musselroe Bay to Southeast Cape. This survey represents part of a series of similar surveys, with historic aerial surveys having been conducted in 1986, 1999 and 2009. This survey was conducted via light aircraft in Nov-Dec 2019, and recorded areas of visible surface canopy cover of giant kelp. Canopy areas were scribed in-flight onto 1:50,000 topographic maps (TASMAP 2017), and complimentary photo and video footage was collected. Canopy areas were digitised with reference to photo, video and map data within QGIS 3.4, and boundaries were checked against Seamap Australia seafloor habitats (Lucieer et al. 2017) and bathymetric data (Smith 2016). Each bed was attributed a broad and fine scale location, density and reliability estimate (see attached report for details). This survey was completed with funding from Pennicott Wilderness Journeys, Tassal and IMAS, and equal in-kind support by Marine Solutions and Seacare Inc.

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    This record describes an aggregated data product compiled from a number of different surveys of Macrocystis surface cover in Tasmanian waters, spanning 1950 to 2019. Some surveys represent a statewide census of Macrocystis cover, while others are targeted surveys of smaller regions. Methodology and data quality lso varies between surveys. Please see linked metadata records for specific methodologies and quality statements applying to individual surveys.

  • NESP Marine Biodiversity Hub Project E7. Results from the outplanting of lab-selected and cultivated warm-adapted genotypes of giant kelp (Macrocystis pyrifera), at two trial restoration sites. A third restoration trial site had no surviving kelp, so those data were not included here. Data and details from lab-selection experiments can be found in the associated dataset - "NESP Marine Hub Project E7 - Macrocystis pyrifera thermal tolerance testing" https://metadata.imas.utas.edu.au/geonetwork/srv/eng/catalog.search#/metadata/0b91d7fd-7d29-452f-954a-78cf75151035

  • As a condition of licence for harvesting Macrocystis pyrifera (Linnaeus) C. Agardh 1820, Alginates (Australia) P/L lodged harvest returns to the Tasmanian Lands Department. The harvest returns consisted of what tonnage was harvested from where, when and the length of trip. While Alginates (Australia) P/L harvested from 1964-1973, harvest data for individual sites is only available for the years 1970-71. Here the data is summed for individual sites for the two years 1970-71.

  • A survey of the east Tasmanian coastline from Musselroe Bay to South East Cape revealed a total of 10 km2 of Macrocystis pyrifera (Linnaeus) C. Agardh 1820 kelp forest. Average harvestable quantities based on Alginates (Australia) Company records (1965-72) show that cropping can expect to yield 5 ton/acre or 1.23 kg/m2. This realizes a total of 12,300 tonne available on the East Coast of Tasmania in 1986. Review of past records show fluctuations in total amounts harvested, due possibly to factors such as high oceanic water temperatures with subsequent low nutrient concentrations and storm damage. The survey was conducted from a light aeroplane. Areas of Macrocystis pyrifera beds were marked on 1:100,000 topographical land tenure maps using landmarks as references. Digitising of bed outlines on maps was done using Mapinfo. Weight of Macrocystis per unit area is also estimated from quadrats harvested at a number of sites along the coast.

  • A research program jointly conducted by Alginates (Australia) P/L and C.S.I.R.O. Division of Fisheries and Oceanography was set up to investigate the relationship between kelp: Macrocystis pyrifera (Linnaeus) C. Agardh 1820 and crayfish larvae. Alginates (Australia) P/L, based at Louisville in the Mercury Passage, were harvesting kelp at this time. This study was initiated to address concerns regarding the effect of harvesting on crayfish stocks. The survey results are taken from an unpublished interim report presenting the results of the work at that stage (1965). Apparently an aerial survey was used to determine stock distributions although this is not specified in the report.

  • The results of this survey are based primarily on the first hand experience of Craig Sanderson who was doing his masters thesis at the time on aspects of the biology of Macrocystis pyrifera (Linnaeus) C. Agardh 1820. In need of significant beds of M. pyrifera for research much of the east coast was searched by boat. Significant stands (>1/2 acre) were found at Darlington, Southerly Bottom (East North Bay), Fortesque Bay and George III Rock, (near Actaeon Island). The status of the few areas not visited was determined from anecdotal reports.

  • Surveys were conducted as part of an assessment of the Macrocystis pyrifera (Linnaeus) C. Agardh 1820 beds on the east coast of Tasmania by the Commonwealth Scientific and Industry Research Organization (CSIRO) Division of Fisheries seaweed program in the early 1950's. Surveys were conducted because of interest in the Macrocystis beds as a source of alginates. Surveys were done between 1950 and mid 1953. The paper was published in 1954.