Harmful algal blooms (HABs) – excessive blooms of phytoplankton that naturally produce biotoxins – have direct negative impacts on marine environments, human health, food security and aquaculture. While previous studies have explored the link between HABs and climate impacts on marine species, examining the relationship between the two – and their combined impacts – is not as widely understood. Understanding how different climate change scenarios can affect HABs is particularly important for future planning.

HABs can occur in freshwater, brackish water and marine water environments. While there are a range of environmental factors determining how habitable an ocean region is to microalgae species, temperature is a main factor. Algal blooms can also grow rapidly when there is an abundance of certain nutrients, particularly nitrogen and phosphorus.

Cawthron Institute senior data scientist Dr Dana Briscoe found under the Intergovernmental Panel on Climate Change’s 2019 RCP 8.5 climate scenario, waters around Aotearoa New Zealand’s North Island and the north region of its South Island could warm by 2C between 2050 and 2099. As such, the researchers predict a greater likelihood of toxic microalgae moving south from tropical waters – where they are traditionally concentrated – and toward New Zealand waters. The scientists plan to use predictive modelling to understand potential impacts under a range of predicted climate scenarios.

Warming water temperatures, driven by climate change, can reduce the natural mixing of water, enabling algae to grow thicker and more rapidly. This can bring about a range of negative impacts including blocked sunlight, the depletion of dissolved oxygen in water and the creation of dead zones.

Phytoplankton including diatoms and dinoflagellates are the most common HAB species found in marine environments. Marine HAB toxins can poison a range of species, resulting in amnesic shellfish poisoning, neurotoxic shellfish poisoning or ciguatera poisoning in fish. More broadly, marine HABs can also directly impact the central nervous system of fish, birds and marine mammals. A HAB played a significant role in the deaths of thousands of crustaceans including lobsters and crabs on parts of England’s north-east coast earlier this year. Elsewhere, a wave of toxic red tide algae blooms was linked to mass fish deaths on Florida’s Gulf Coast last year.

HABs also pose significant risks to fisheries. A separate study from Cawthron Institute recently revealed HABs can impact the health and productivity of shellfish if they come into contact with or ingest the algae. Financially, HABs can pose an even greater impact to farmed fisheries and to wild-caught, reef-based fisheries than any storm insurers have experienced, found another report.

Despite this, there is evidence to suggest a link between aquaculture activity and an increased presence of marine HABs. A study organised by UNESCO’s Intergovernmental Oceanographic Commission found areas with larger expansions of aquaculture developments coincided with areas with greater HAB monitoring efforts.

In the long term, large-scale efforts to reduce CO2 emissions are needed to avoid HAB impacts, as factors including increased temperatures and rainfall will trigger more HABs. On a local scale, the implementation of early warning systems can aid detection and response. Developments in integrating real-time monitoring using artificial intelligence and sensors can boost the effectiveness and deployment of these forecasting systems.

Source: The Fish Site