Primary productivity

  • Image, Primary productivity.

    Archived 27 October 2016

    Phytoplankton are primary producers of biomass and form the basis of the oceans’ food chains. They use a pigment called chlorophyll-a (chl-a) to create their own food through photosynthesis. We study concentrations of chl-a in phytoplankton to assess primary productivity in our oceans. Changes in ocean primary productivity are likely to affect food chains and, ultimately, marine biodiversity, including the species we rely on for economic, cultural, or recreational purposes.

    We classified Primary productivity as a national indicator.

    Key findings

     Indeterminate trend

    In 2010, primary productivity (levels of chl-a) increased markedly in subtropical waters and the Chatham Rise, but has been falling since. For the period 1997–2014, chl-a anomalies were highest in the Tasman Sea between 2006 and 2009, and productivity was highest between 2009 and 2011 in the Chatham Rise.

    In addition, from 1997 to 2014:

    • the Chatham Rise region had the highest offshore primary productivity in the New Zealand exclusive economic zone (EEZ) and the highest monthly chl-a variability (anomalies)
    • seasonal variations in chl-a in the northern subtropical waters region were pronounced (approximately 0.35 mg/m3 in spring and 0.1 mg/m3 in autumn)
    • no clear pattern was evident for the subantarctic waters region

    Figure 1

    Note: Data are based on measurements from the SeaWiFS and MODIS-Aqua satellite ocean colour sensors. Data are not shown for the territorial sea. EEZ – exclusive economic zone; NM – nautical miles; mg/m3 – milligrams per cubic metre.

    Figure 2

    Note: Data are based on measurements from the SeaWiFS and MODIS-Aqua satellite ocean colour sensors. mg/m3 – milligrams per cubic metre.

    Figure 3

    Note: Data are based on measurements from the SeaWiFS and MODIS-Aqua satellite ocean colour sensors. Anomalies are where primary productivity deviated from the long-term mean (1997–2014). mg/m3 – milligrams per cubic metre.

    Figure 4

    Note: Chlorophyll-a levels show where primary productivity was highest and lowest in 2014. Data are based on measurements from the SeaWiFS and MODIS-Aqua satellite ocean colour sensors, and are not shown for the territorial sea. EEZ – exclusive economic zone; NM – nautical miles; mg/m3 – milligrams per cubic metre.

    Figure 5

    Note: Annual anomalies show where primary productivity for 2014 deviated from the long-term mean (1997–2014). Data are based on measurements from the SeaWiFS and MODIS-Aqua satellite ocean colour sensors, and are not shown for the territorial sea. EEZ – exclusive economic zone; NM – nautical miles; mg/m3 – milligrams per cubic metre.

    Definition and methodology

    This indicator provides primary productivity and primary productivity anomalies (variability) over time for five selected regions: the exclusive economic zone as a whole, the Chatham Rise, northern subtropical waters, subantarctic waters, and the Tasman Sea. This approach aims to give a better understanding of areas of high primary productivity in New Zealand waters, as well as identifying long-term geographical variation in primary productivity.

    Variation in primary productivity is measured from observed changes in concentrations of chlorophyll-a (chl-a). Higher chl-a levels indicate higher primary productivity, and vice versa.

    The time series is derived by combining measurements from two satellite ocean colour sensors, SeaWiFS and MODIS-Aqua. The satellite data covered the whole New Zealand region at 9km spatial resolution from September 1997 to December 2014. The merged data series between April 2002 and April 2012 was validated using data from a third satellite sensor, MERIS3.

    The lack of longer-term variability in the monthly chl-a anomalies in the subantarctic waters region may be partly due to poor data availability: no ocean colour data are available for winter in this region, because of high cloud cover.

    Data quality

    We classified Primary productivity as a national indicator.

    Relevance

    relevance-direct This national indicator is a direct measure of the ‘Ability of marine ecosystems to function effectively’ topic.

    Accuracy

    accuracy-high The accuracy of the data source is of high quality.

    See Data quality information for more detail.

     

    Published 21 October 2015

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