Harmful Algal Blooms

Harmful algal blooms (HABs) are proliferations of aquatic algae that disrupt ecosystems and impair water quality. The environmental impacts of HABs can be sudden, severe and lethal across all levels of aquatic and terrestrial food webs, from stream insects to birds to sea otters. HABs also can contaminate drinking water supplies, kill livestock and dogs, and sicken humans who swim in toxin-filled waters. With HABs expected to become increasingly severe in the coming decades in lockstep with global climate change, California’s water-quality management community is developing a multi-pronged strategy for mitigating ecosystem damage and better protecting humans and wildlife.

SCCWRP is part of a group of researchers working to track the ecosystem impacts of HABs across California’s diverse freshwater and marine environments. Researchers are developing improved techniques for monitoring HABs, building coordinated monitoring programs to track ecological disruptions statewide, and developing models that can predict bloom events. Researchers’ long-term goal is to create effective early-warning systems and other approaches that water-quality managers can use to reduce ecological damage and protect human health.

Water that is being held back by a dam that spans Lake Hodges in San Diego County is tainted a murky green color as a result of a harmful algal bloom.
HABs, which have tainted Lake Hodges Dam in San Diego County green, above, can release toxins poisonous to wildlife and humans. SCCWRP is working to generate strategies for assessing and managing the effects of these toxins.

Managing HAB toxins

In freshwater, estuary and marine environments, HABs can lower dissolved oxygen levels, reduce light penetration, degrade aesthetic condition and produce nuisance odors. Some HABs also produce toxins that can be lethal at all levels of aquatic and terrestrial food webs, from insects to fish to birds. These biological toxins can cause skin rashes for humans who swim in contaminated lakes, and sicken humans who eat contaminated shellfish.

Equally troubling, the toxins produced by HABs can remain viable for many months. Unlike a bloom that might die off in a matter of weeks, HAB toxins can settle into sediment in lakes and coastal marine areas, creating a long-term exposure route for both animals and humans. HAB toxins produced in lakes and rivers also can be transported to the coastal zone, extending their reach across the land-sea interface.

SCCWRP and its partners are working to understand how HABs move through aquatic environments and the short- and long-term ecological effects of HAB toxins. Armed with a foundational understanding of HABs, researchers will be optimally positioned to design monitoring strategies tailored to protect specific resources, including recreational lakes, irrigation water supplies and shellfish harvesting.

A field researcher wades into shallow water at Lake Elsinore to deploy a yellow-colored underwater autonomous vehicle that will monitor cyanobacterial blooms in the lake.
A field crew uses an underwater autonomous vehicle to monitor cyanobacterial blooms in Lake Elsinore in Riverside County. SCCWRP is developing next-generation methods for monitoring HABs and building coordinated monitoring programs to track ecological disruptions statewide.

Ecological disruptions to biogeochemical cycling

HAB events in aquatic environments can have both immediate and long-lasting reverberations through ecosystems. In coastal marine waters, excess algal growth can trigger complex biogeochemical cycling processes that exacerbate a global phenomenon known as ocean acidification. As the algae die, they are decomposed by bacteria that produce carbon dioxide as part of normal respiratory processes. The increased dissolved carbon dioxide levels can alter seawater chemistry so much that the water becomes corrosive to shell-forming organisms.

SCCWRP is part of a network of researchers studying the impacts of ocean acidification on West Coast ecosystems. Researchers are especially interested in understanding the confluence of factors that causes HABs to tip seawater chemistry into corrosive territory.

Types of HABs

HABs encompass multiple types of ecologically disruptive events, including:

  • cyanoHABs: Some freshwater and estuarine varieties of cyanobacterial HABs taint water bodies green and produce toxins poisonous to wildlife and humans.
  • Red tides: Proliferations of certain species of phytoplankton and dinoflagellates can taint water shades of red or brown. Although some red tides are benign, others produce toxins that can contaminate shellfish consumed by humans.
  • Domoic acid: The diatom genus known as Pseudo-nitzschia can produce a neurotoxin that, among other things, leads to short-term memory loss in humans. Domoic acid is the most common marine toxin in Southern California.
Sediment-dwelling organisms, including a small starfish and small hermit crab, are isolated from sediment samples so their tissue can be analyzed for HAB toxins.
When toxins produced by HABs settle into seafloor sediment, they can be absorbed into the tissue of small sediment-dwelling organisms, above. SCCWRP is working to understand both the short- and long-term ecological effects of these toxins on marine life.