Harmful Algal Bloom Decision Support Tool

The South African west and south coasts suffer from the 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. Examples of typical rock lobster loss for large events range from 200 to 2000 tonnes, with an estimated direct economic loss of ± 8 USD to 80 million USD per event, in addition to the indirect ecosystem and sustainability impacts. In Feb 2015, 200 tonnes of cape rock lobster suffered from hypoxia and exited the ocean with 80% mortality. The economic value of the event was estimated at R114 million.

HAB impacts come about through either the toxicity (to humans and animals) of some bloom species (e.g. red tides), 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 on the West Coast are the most well-known. HABs are expected to become more common as the oceans warm as the climate changes, with earlier onset and longer durations of HAB “seasons”.

The HAB Decision Support Tool (DeST) provides a capability for monitoring and assessing risk of HAB events for the South African coastal area to approximately 50 km offshore. Risk assessment and monitoring is 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). Maps of various ocean colour-derived phytoplankton biomass proxies, sea surface temperature, and ocean state (wind, current, sea state) 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.

This science and relevant datasets are translated and digested into this simplified DeST via a set of computational processing chains and data management systems that present an interactive map based dashboard to end users. In addition, a HAB bulletin is occasionally issued by Council for Scientific and Industrial Research (CSIR) when noteworthy HAB-related events occur. This bulletin is distributed to members of government departments (Department of Environmental Affairs and Department of Agriculture, Forestry and Fisheries), Provincial Disaster Management Centres and various mariculture companies.

The HAB DeST utilises i) South African scientific knowledge about marine ecosystem function and oceanographic patterns to create ii) localised algorithms that extract regionally relevant information out of globally available earth observation datasets and numerical models running on iii) automated analytical processing chains to produce iv) open standards compliant datasets and data services that are composed into this Web applications which is specifically tailored to support South African socio-economic activities and protect natural resources.

Relevant datasets include:

~ 1 km2 daily Phytoplankton biomass derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Normalised Fluorescence Line Height and Chlorophyll-A products

~ 1 km2 Phytoplankton biomass derived from Sentinel 3 Ocean and Land Colour Instrument (OLCI) instrument Chlorophyll-A product

~ 2 km2 daily ODYSSEA Merged Foundational Sea Surface Temperature (SST) product

Related news articles:

Red Tide Along the West Coast – http://www.capenature.co.za/warning-red-tide-along-west-coast/

Lobsters Crawl Out of Elands Bay – https://www.enca.com/life/lobsters-crawl-out-elands-bay

Tons of Lobster Die After Red Tide – http://www.iol.co.za/scitech/science/environment/tons-of-lobster-die-after-red-tide-1816954

Cape Crayfish Stage Another Walkout – http://www.iol.co.za/news/south-africa/cape-crayfish-stage-another-walkout-82610