Spectacular oceanic bloom identified

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Scientists at NIWA have identified the source of the giant plankton bloom featuring in spectacular NASA satellite images.

On 25 October, a NASA satellite recorded a large bloom east of Cook Strait. At the time, NASA suggested that the "especially bright blue areas may indicate the presence of phytoplankton called coccolithophores, which are coated with calcium-carbonate (chalk) scales that are very reflective".

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 ‘collapsing’ 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 favourable light, temperature, and  nutrients are clearly important.

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Bloom identification: Dr Hoe Chang, NIWA. 
Ocean acidification: Dr Cliff Law, NIWA. 

For more information on research to investigate the effects of ocean acidification on plankton in New Zealand waters, see this project:
effects-of-ocean-acidification-on-plankton-in-new-zealand-waters

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Emeritus - Marine Biologist
Principal Scientist-Marine Biogeochemistry
NASA MODIS satellite image showing the bloom as at 25 October [credit: NASA]