CPR detects the red-tide dinoflagellate Noctiluca scintillans in the Southern Ocean for the first time

David J. McLeod, Gustaaf M. Hallegraeff, Graham W. Hosie and Anthony J. Richardson

Noctiluca scintillans is a red-tide forming, heterotrophic dinoflagellate that was found for the first time in the Southern Ocean (45°31´S 147°E) in December, 2010. The 'bloom' of Noctiluca extended over 242 km and was detected during a CPR transect conducted between Tasmania and Antarctica as part of the Southern Ocean CPR (SO-CPR) and Australian CPR (AusCPR) Surveys. This record of Noctiluca is the most southerly, oceanic record globally and can be linked to the intensification of the East Australian Current (EAC), a situation apparently caused by altered circulation patterns associated with global warming.

The east coast of Australia has been recognised as a climate change 'hotspot' and poleward migrations of a number of species in the region have already been documented including phytoplankton, zooplankton, invertebrates and coastal fish. On present evidence, the current observation of Noctiluca in the Southern Ocean is an extension of coastal Tasmanian populations. Sea surface height and sea surface temperature data at the time indicated that a warm-water eddy of the EAC extending to Tasmania and beyond provided a potential vector for the transport of Noctiluca offshore into a cool, oceanic environment not generally associated with this organism. Noctiluca is thought to be a neritic species with oceanic occurrences uncommon.

Noctiluca cells found in this study appeared 'healthy' and 'well-fed', seemingly full of mainly diatom prey. This indicates that despite their apparent unplanned venture into the oceanic environment they were able to feed on Southern Ocean productivity. Data from the same CPR transect showed that copepod abundance was apparently limited by the presence of the Noctiluca indicating potential competition for food. If viable populations of Noctiluca become established in the Southern Ocean in the future, there is likely to be additional competition for phytoplankton with copepod grazers, with unknown effects for the food web. Given predictions that the EAC is likely to continue to strengthen and transport more warm water and eddies further south there may be more frequent seeding of Noctiluca into cooler waters in the future and Noctiluca could well become resident in the Southern Ocean.

The results of this finding have recently been published online in the Journal of Plankton Research and can be found at http://plankt.oxfordjournals.org/content/early/2012/02/01/plankt.fbr112.short?rss=1

Apparent range extension of Noctiluca scintillans in the Australian region, comparing distribution records in 1860-1950, 1980-1993 (expansion of blooms in Sydney region), 1994-2005 (range extension into Tasmania), 2008 (first reports in Queensland, Western Australia and South Australia) and 2010 (first report in the Southern Ocean south of Tasmania). The legend shows number of cells per 5 nautical mile segment. Grey circles represent records of Noctiluca from AusCPR samples collected between Melbourne and Adelaide in 2010 (data from www.imos.org.au/emii). Maps are reproduced from Hallegraeff et al. (Hallegraeff et al., 2008).



 

Chl a, sea surface temperature (°C), Noctiluca scintillans abundance and total copepod abundance along a CPR transect conducted south of Tasmania in December 2010.