Primary productivity

  • Image, Primary productivity.

    Phytoplankton are primary producers of biomass (mass of living organisms) and form the main basis of marine food chains. They use a pigment called chlorophyll-a (chl-a) to capture the sun’s energy through the process of photosynthesis. Phytoplankton growth is affected by the availability of nutrients and light, which in turn are affected by the structure of the surface water column. The surface water column structure is affected by oceanographic and climate processes; large-scale changes to climate and oceanographic conditions can lead to changes in phytoplankton growth and chl-a concentrations.

    We measure oceanic chl-a concentrations as an indicator of marine primary productivity. Changes in ocean primary productivity are likely to affect marine food chains and marine biodiversity, including the species we rely on for economic, cultural, or recreational purposes.

    We classified Primary productivity as a national indicator.

    Key findings

     Trend not assessed

    Between 2009 and 2011, primary productivity (levels of chl-a) peaked in the Chatham Rise (a key productive area), but has been falling since.

    From September 1997 to February 2016:

    • the Chatham Rise region had the highest offshore primary productivity of all regions, and the largest-magnitude chl-a variability (anomalies)
    • the Tasman Sea had its highest primary productivity between 2003 and 2011, with negative anomalies at the start of the period (1997–2003) and positive anomalies in the middle (2007–10) 
    • seasonal variations in chl-a in the subtropical waters region were pronounced (approximately 0.35 mg/m3 in spring and 0.1 mg/m3 in autumn) 
    • there appears to be a small increase in chl-a values in the subantarctic waters region between 1997 and 2016.

    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 (Pinkerton, 2016). 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 (Pinkerton, 2016). EEZ – exclusive economic zone; mg/m3 – milligrams chlorophyll-a per cubic metre. The data are smoothed with a 4-year running mean.

    Figure 3

    Note: Data are based on measurements from the SeaWiFS and MODIS-Aqua satellite ocean colour sensors. Anomalies are where chlorophyll-a concentrations deviated from the long-term mean (1997–2016) (Pinkerton, 2016). mg/m3 – milligrams chlorophyll-a per cubic metre.

    Figure 4

    Map. Primary productivity, 2015.

    Note: Annual anomalies show where chlorophyll-a concentrations for 2015 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 (Pinkerton, 2016). EEZ – exclusive economic zone; NM – nautical miles; mg/m3 – milligrams chlorophyll-a per cubic metre (Pinkerton, 2016).

    Definition and methodology

    This indicator provides chlorophyll-a concentrations and anomalies (variability) over time for five selected regions as indicative of changes in ocean primary productivity: the exclusive economic zone as a whole, the Chatham Rise, northern subtropical waters, subantarctic waters, and the Tasman Sea regions within the exclusive economic zone. 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 (Pinkerton 2015, 2016).

    Variation in primary productivity is inferred from observed changes in near-surface concentrations of chlorophyll-a (chl-a). Higher chl-a concentrations indicate higher primary productivity, and vice versa (Pinkerton, 2016).

    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 February 2016. The merged data series between April 2002 and April 2012 was validated using data from a third satellite sensor, MERIS (Pinkerton 2015, 2016).

    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 persistent cloud cover (Pinkerton, 2016).

    Data quality

     Topic Classification Relevance Accuracy
    Marine ecosystems and habitats

    National indicator

     relevance-direct
    Direct

     Image, Medium accuracy.
    Medium

    See Data quality information for more detail.

    References

    Pinkerton, M (2016). Ocean colour satellite observations of phytoplankton in the New Zealand EEZ, 1997–2016. Prepared for the Ministry for the Environment. Wellington: NIWA. – data service link needed

    Archived pages

    See Primary productivity (archived October 2016).

    Updated 27 October 2016

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