Spectacular oceanic bloom identified

Published: Mon 9 Nov 2009 03:30 PM
NIWA Media Release: 9 November 2009

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NASA MODIS satellite image showing the bloom as at 25 October [credit: NASA]
Scientists at the National Institute of Water & Atmospheric Research (NIWA) have identified the source of the giant plankton bloom featuring in spectacular NASA satellite images.

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Emiliana Huxleyi, the main species of coccolithophore identified by NIWA scientists from samples of a giant plankton bloom east of New Zealand [credit: NIWA]

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A typical sample found within the bloom, showing the abundance of chalky scales from dead cells [credit: NIWA]
The NIWA deep water research vessel Tangaroa travelled through the bloom last week and collected water samples for analysis. Using a scanning electron microscope, NIWA scientist Dr Hoe Chang has now confirmed the bloom mainly contains two species of coccolithophores. Other microalgae such as diatoms were also present, but were not as abundant as coccolithophores.
These tiny plant cells (coccolithophores) are so small that about 200 of them side by side would fit in one millimetre. Each cell is covered by nine or ten tiny, overlapping scales (or “coccoliths”) of calcium carbonate. They are not toxic.
Hoe Chang says in the sample of water from within the region of the bloom the cell concentration was about 500 000 cells per litre – about 65 times higher in the bloom than outside it. The sample was chock full of scales from dead cells with an astounding 990 million coccoliths (calcium carbonate scales) per litre. That is about 37 000 times more plates inside the bloom than outside it. Dr Hoe Chang says that this means that the population in the bloom was ˜c`llapsing™ releasing the chalky scales from the cells and therefore giving a much brighter image from space.
Coccolithophores are vital food at the base of the marine food web. They are sensitive to the increasing acidity of the ocean, which results from the build-up of carbon dioxide in the atmosphere and makes it harder to form the carbonate scales. For this reason, scientists believe that these and other carbonate-forming marine life may decline in the future as the upper ocean absorbs increasing amounts of carbon dioxide. NIWA Principal Scientist, Dr Cliff Law, says we don™t yet know what caused this appearance of one of the largest recorded coccolithophore blooms in NZ waters, but factors such as ocean currents, favourable light, temperature, and nutrients are clearly important.
For more information on research to investigate the effects of ocean acidification on plankton in New Zealand waters, see:
IMAGES ARE AVAILABLE from in a folder labelled “oceanic bloom”
NASA MODIS satellite image showing the bloom as at 25 October [credit: NASA]
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