Sea change: A screenshot of an ocean-colour map, developed by the Council for Scientific and Industrial Research, on the Fisheries and Aquaculture Decision Support Tool, which uses satellite data to help farmers predict the scale and movement of harmful algal blooms. Photos: Supplied
In 2017, Abagold, an aquaculture facility in Walker Bay, Hermanus, was hit by an algal bloom that it was not prepared for.
Millions of abalone in the Walker Bay area were killed as numbers of phytoplankton — microscopic marine algae — grew out of control, producing toxins that caused a harmful “red tide” throughout nearby bays.
“We had mortalities of about 40% in that year,” said chief operating officer Marius Hugo.
Since then, the abalone farm has learnt to manage harmful algal blooms far better, he said. “We’ve learned to anticipate with systems like Ocims [the National Oceans and Coastal Information Management System] and if we weren’t prepared, it would take us years to rebuild that biological asset and the losses that we incurred.”
Satellite data can provide early warnings to help protect the aquaculture industry along South Africa’s coastline against these harmful algal blooms, or red tides, according to the Council for Scientific and Industrial Research (CSIR).
Its scientists have developed ocean colour and temperature data from satellites that is easy to access as an online tool. The free tool interprets ocean colour and temperature data from the Copernicus Sentinel-3 polar-orbiting satellite so that abalone farmers can track approaching harmful red tides in near real time before they harm their export molluscs. Abalone can be sensitive to certain species of bloom-forming algae.
Abagold’s aquaculture facility has a standing stock of between 600 tonnes and 650 tonnes of the pearlescent molluscs, which grow through their various stages of life in seawater,” Hugo said. The roughly 400 staff tend to about 15 million of these animals: intake pipes fill 5 000 tanks directly from the ocean below.
The environmental conditions around South Africa’s coast can be challenging, said Marié Smith, a marine earth observation expert at the CSIR, who is lead expert behind the Fisheries and Aquaculture Decision Support Tool of the Ocims.
“We have a lot of upwelling that happens; we have marine heatwaves coming past. We have a very productive environment that has lots of microscopic algae that can be very beneficial but also some of them can cause harm and it’s important for us to be able to monitor the environment on an operational scale,” Smith said.
“The satellite data that we provide to the aquaculture farms comes from polar orbiting earth observation environmental satellites so they look at things like the colour of the ocean and the temperature of the ocean and we can derive certain variables from that.”
From this data, scientists can glean how much phytoplankton biomass is in the water, how many algae are in the water potentially and what harm they are going to cause.
“The nice thing about satellite information is that it provides you with a much larger spatial scale of information than you could get with simply taking a single sample at the intake pipe,” Smith added.
“If they detect algae at the farm, or a high concentration of algae, the tool will then be able to tell them how far does that bloom of algae extend into the bay. Is it only a couple of hundred metres or is there a bloom of tens of hundreds of square kilometres up the coast? That will allow them to make decisions accordingly on the farm based on that information.”
Smith noted that had the satellite imagery and tool been available in 2017, abalone farmers would have had more time to take protective measures to preserve the water quality for their animals.
Sarah Halse, Abagold’s research and sustainability manager, said there are different mechanisms of harmful algal blooms. “Some cause toxins and some toxins are harmful to certain species but not to others. Some blooms are harmful in that they cause mechanical damage – they might be spiky and stick in fish gills, for instance.”
According to a 2020 study by Smith and Stewart Bernard, of the University of Cape Town’s oceanography department, the global marine aquaculture sector faces environmental threats from harmful algal blooms, with impacts from these events amounting to about $8 billion a year. Ocean colour remote sensing provides a cost-effective and valuable tool in the detection and monitoring of various types of phytoplankton blooms, they said.
On a larger environmental scale, some non-toxic dinoflagellate blooms can cause marine mortalities and anoxia following the collapse of blooms with very high biomass. Harmful algal blooms have the potential to cause devastating economic losses in the aquaculture and fisheries industries.
The study noted that in 2015 farms were closed 13 times because of the presence of bio-toxins in shellfish flesh above acceptable regulatory limits.
“Harmful algal blooms can also pose a threat to the physical condition of sardines and associated fisheries . The decay of high biomass dinoflagellate blooms have often led to marine mortalities and mass rock-lobster strandings in the St Helena Bay region with losses valued up to $50 million in some cases.”
According to Hugo, Abagold is the largest employer in the entire Overstrand region, second only to the municipality. “The aquaculture industry is really integrated into the community. It’s a large provider, a driver of the economy and the small local economy.
“Within the larger context, a lot of the jobs that were dependent on the fisheries and the ocean, have transferred to the aquaculture sector so the government is very supportive of this sector through [Operation] Phakisa … to make sure that the jobs that the industry creates are sustainable. One of those tools that keeps us sustainable is the CSIR tool that manages our algal blooms for us. It’s all connected and keeps the industry on its feet.”
Smith said that in terms of climate change adaptation and being able to prepare for climate impacts, satellite data is “very valuable because the satellites have been up there for a long time so we have a track record of what the conditions were many years ago”.
“We know what the conditions are now and there’s several missions planned into the future so we can track how the conditions like the ocean colour and the temperatures have been changing. We can see if there’s more variable conditions or if the red tides have been increasing.”
Smith and Bernard warned in their study that the occurrence and frequency of harmful algal blooms are thought to be increasing worldwide. Within the context of a changing climate, the global distribution and occurrence of different harmful algal blooms species are likely to change in the future. This holds “inherently diverse threats” to industries and humans relying on these systems.
“These concepts support the notion that the southern Benguela aquaculture industries require adaptable and robust harmful algal blooms monitoring strategies to safeguard the economic viability of these facilities,” they said.
Smith said South Africa and the rest of the continent “still has a lot of room to grow” in the marine aquaculture sector. “Having a tool that helps to safeguard that sector helps to promote the economy, promote jobs in that sector and helps to grow the GDP of the country.”