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Vertical migration of the toxic dinoflagellate Gymnodinium catenatum under different concentrations of nutrients and humic substances in culture

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Doblin, MA and Thompson, PA and Revill, AT and Bulter, ECV and Blackburn, SI and Hallegraeff, GM (2006) Vertical migration of the toxic dinoflagellate Gymnodinium catenatum under different concentrations of nutrients and humic substances in culture. Harmful Algae, 5 (6). pp. 665-677. ISSN 1568-9883

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Abstract

Vertical migration behaviour by the chainforming dinoflagellate Gymnodinium catenatum Graham was investigated using
vertically-stratified laboratory columns. Under surface nutrient-deplete conditions, with nutrients added only at depth, 100% of
cells underwent vertical migration (VM), starting downwards migration 3 h before the end of the light period and beginning
upwards migration 3 h before the start of the light period. Cells in nutrient-replete columns showed no VM, but they were more
dispersed in the upper layer during the dark compared to the light period. When surface layers (S) were nitrate-deplete (N) and
enriched with humic substances (H) contained in Huon River water and bottom waters (B) were nutrient replete (R) (SHNBR), the
pattern ofVMwas altered—50% of cells underwent migration and 50% remained at the pycnocline. In columns with nitrate-replete
and humic-enriched surface layers (SHRBR), most cells underwent VM, while 30% remained at the surface. Cells in SHNBR
columns showed increased N quotas and intra-cellular nitrate concentrations after 4 days, indicating nitrate uptake by G. catenatum
in bottom layers. The concomitant increase in particulate organic nitrogen (PON) with the decrease in external nitrate
concentrations in bottom layers provide convincing evidence that VM by G. catenatum facilitates nutrient retrieval at depth.
However, addition of humic substances (a potential source of organic nitrogen) to surface layers did not ameliorate G. catenatum N
depletion sufficiently to preclude the need for NO3 uptake at depth. Furthermore, there was no detectable pattern of increasing
carbon (C) quota during the day (photosynthate accumulation) or increasing N quota during the night (nitrate assimilation). Toxic
dinoflagellate G. catenatum blooms are commonly associated with nitrate depletion in surface waters in south-east Tasmanian
waters (Australia). Therefore, vertical migration, facilitating N uptake at depth, could play an important role in this organism’s
ecological strategy, enabling it to exploit environments where light and nutrients are vertically separated

Item Type: Article
Keywords: CDOM; Gymnodinium catenatum; Humic substances; Nitrogen; N-stratified; Vertical migration
Journal or Publication Title: Harmful Algae
Page Range: pp. 665-677
ISSN: 1568-9883
Identification Number - DOI: 10.1016/j.hal.2006.02.002
Additional Information:

The definitive version is available at http://www.sciencedirect.com

Date Deposited: 20 Nov 2007 22:24
Last Modified: 18 Nov 2014 03:25
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