Browsing by Author "Hallegraeff, GM"

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    Cyst and radionuclide evidence demonstrate historic Gymnodinium catenatum dinoflagellate populations in Manukau and Hokianga Harbours, New Zealand
    (Elsevier, 2003-03) Irwin, A; Hallegraeff, GM; McMinn, A; Harrison, JJ; Heijnis, H
    Between May 2000 and February 2001, a major bloom of the toxic dinoflagellate Gymnodinium catenatum (a causative organism of Paralytic Shellfish Poisoning, PSP) affected over 1500 km of coastline of New Zealand’s North Island. As this was the first record of this species in New Zealand, we aimed to resolve whether this represented a recent introduction/spreading event or perhaps an indigenous cryptic species stimulated by environmental/climatic change. To answer this question, we analysed for G. catenatum resting cysts in 210Pb dated sediment cores (18–34 cm long; sedimentation rates 0.34–0.69 cm per year) collected by SCUBA divers from Manukau Harbour, where the species was first detected, and from Hokianga Harbour, where the highest shellfish toxicity was recorded, while using Wellington Harbour as a well-monitored control site. The results of this study conclusively demonstrate that abundant G. catenatum has been in northern New Zealand at least since the early 1980s, increasing up to 1200 cysts/g around the year 2000, but with low cyst concentrations possibly present since at least 1937. In contrast, Wellington Harbour cores contained only very sparse G. catenatum cysts (8 cysts/g), present only to a depth of 7 cm (surface mixed layer depth), reflecting an apparent recent range expansion of this dinoflagellate in New Zealand, possibly stimulated by unusual climatic conditions associated with the 2000 La Nina event. The significant increases since the early 1980s also of Protoperidinium cysts at Hokianga Harbour and of Gonyaulax, Protoperidinium and Protoceratium cysts at Manukau Harbour suggest a broad scale environmental change has occurred in Northland, New Zealand. © 2003 Elsevier Science B.V
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    Nuclear detectives - reconstructing histories of toxic dinoflagellates & blue green algae in coastal lakes and estuaries
    (International Atomic Energy Agency, 2004-10-28) Heijnis, H; McMinn, A; Hallegraeff, GM; Srisuksawad, K
    Using isotopic, geochemical and microfossil analyses of sediment cores, it is possible to reconstruct pre and post-colonial environmental conditions of coastal lakes and estuaries and their catchments. This is an important management tool, not only for determining the baseline 'natural' conditions of these ecosystems but also identifying the nature and extent of changes they have experienced through time, including the influx of pollutants and cha nges in sedimentation regimes. Such information is generally not available from historic records. Practical examples includes the following case-studies: 1) Tasmania & South Australia - Over the past couple of decades “alien species” have been introduced to the coastal waters of Australia and of Tasmania in particular, such as the toxic dinoflagellate Gymnodinium Catenatum. Careful dating and reconstruction of sediment archives have revealed the time and nature of this arrival. 2) NSW Blue Green Algae in the Great Lakes Area: The occurrence of blue- green algal blooms in the Great Lakes area of NSW have now been linked with catchment changes and the dynamics of this coastal system, using reconstructed histories from sediment cores. These detailed histories span the last 60 – 80 years, and cover the post World War II coastal population & development expansion.