New Zealand Journal of Marine and Freshwater Research abstracts

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Seasonal changes in factors controlling phytoplankton growth in Beatrix Bay, New Zealand

M. M. GIBBS
W. N. VANT

National Institute of Water & Atmospheric
Research Ltd
P. O. Box 11-115
Hamilton, New Zealand

Abstract  Phytoplankton biomass and growth rates were measured in Beatrix Bay, Marlborough Sounds, during 1994-95. In spring and summer, nitrate and chlorophyll a concentrations in the mixed layer were low (typically < 1 mg N m^-3 and < 1 to 3 mg Chl. a m^-3, respectively), and phytoplankton growth rates were moderate (average 0.3 d^-1). Growth rates increased several-fold in response to the experimental addition of inorganic N (but not to inorganic phosphorus). Higher nitrate concentrations were found below the pycnocline. During autumn and winter, nitrate concentrations in the mixed layer were high (up to 60 mg m^-3), but phytoplankton growth rates were lower than in summer (average 0.2 d^-1), and did not respond to added nutrients. Chlorophyll a concentrations, however, were highest during the winter (typically 3-6 mg m^-3). Even so, low light levels meant integral photosynthesis per unit chlorophyll a was low in winter. Phytoplankton growth appears to be controlled by the availability of nitrogen in summer and by light in winter.

Keywords  phytoplankton; algal growth; photosynthesis; nutrients; light; aquaculture; Pelorus Sound

New Zealand Journal of Marine and Freshwater Research, 1997, Vol. 31: 237-248

0028-8330/97/3102-0237 $7.00/0 (c) The Royal Society of New Zealand 1997

PDF file of entire paper: medium quality (1009K); (scanned from paper original: notes about this process)

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