Causality
Causes of harmful algal blooms
Nutrients, excess nutrients can fuel algal growth and support the development of harmful algal blooms. Excess nutrients can come from land-based activities as well as natural oceanic processes.
Ocean circulation, ocean circulation patterns, and currents, such as upwelling and mesoscale eddies, can create an environment favorable for the formation of harmful algal blooms.
Water temperature, different types of harmful algal species have distinct temperature preferences. When water temperatures are within a given species ideal range, conditions are more favorable for a bloom of that species to occur.
Biological interactions, interactions between HAB species and other plankton can contribute to bloom formation. For example, grazers can be an important factor that can control the formation of HABs and changes in grazing rates can allow for more harmful algal species to grow.
Linkages between blooms and environmental impacts
The West Coast Ocean Health Dashboard HABs indicator focuses on the impacts of harmful algal blooms rather than the patterns and distribution of HAB species and toxins in the environment. A variety of water sampling efforts to detect HAB species and toxins occur throughout the West Coast, which provide valuable, high-quality environmental data. The limitation of this data is that it is restricted to nearshore areas and may not fully capture offshore HAB events; thus, it is not always correlated to HAB impacts such as shellfishery closures or marine mammal stranding events. For example, water sampling efforts at pier locations in southern California missed much of the bloom associated with a historical marine mammal stranding event caused by domoic acid in 2023.
