Harmful Algal Bloom Viewer

High Risk Areas

Time Series

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Harmful Algal Bloom Risk
St Helena Bay
St Helena Bay
St Helena Bay
Garden Route
Oyster Bay


The South African west and south coasts suffer from frequent occurrence of Harmful Algal Blooms (HABs). These blooms can have considerable negative impacts on commercial marine concerns such as rock lobster and aquaculture operations, in addition to local marine ecosystems and communities. HAB impacts come about either from the toxicity of some bloom species, or collapse of high biomass blooms through nutrient exhaustion, leading in extreme cases to hypoxia and dramatic mortalities of marine organisms, of which crayfish strandings are the most well known.

The HAB Decision Support Tool provides a capability for monitoring and assessing risk of HAB events, based on quantified understanding of bloom dynamics (Pitcher & Nelson, 2006), hypoxic impacts (Pitcher et al 2014), and earth observation monitoring capabilities (Bernard et al 2006). The example shown below focuses on bloom and hypoxia risk warnings for the St Helena Bay region - there will be broader HAB monitoring capabilities available for the entire national coastal area. Maps of sea surface temperature, ocean winds and ocean colour-derived phytoplankton biomass proxies are used to provide information on the presence and movement of blooms, and extracted time series of these data provide a "virtual buoy" capability giving a multi-parameter risk index.

Earth observation data used here are:

  • Chlorophyll-A derived from 1 km daily MODIS-Aqua nFLH
  • Sea Surface temperature: Synthesised 0.2 degree daily Odyssea Foundational SST
  • Phytoplankton biomass: 1 km daily MODIS-Aqua Normalised Fluorescence Line Height (nFLH) as a proxy for phytoplankton biomass
Sentinel 3/OLCI and/or multi-mission ocean colour and SST products will be used from 2017 onwards. In addition to daily synoptic maps, critical near-coastal 5 – 10 km2 areas, e.g Elands Bay in this example, have time series data extracted as a “virtual buoy” facility. These data are use to produce near real time risk thresholds (as preliminary demonstrators) both for individual and combined variables using appropriate threshold and persistence values. In short, the combined risk is elevated to red=high - indicating imminent danger of a hypoxic event - when the SST is > 13 , the forecast wind for the next three days is low (<5 m s-1), AND there is a persistent high biomass bloom in the critical area. The high risk zones (red stars) can be clearly seen in the figure, prior to a major hypoxic event in Elands Bay around February 6th - 10th 2015.