Harmful Algal Bloom Toxins in Alaska Seabirds

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Elevated ocean temperatures are linked to the development of harmful algal blooms (HABs). Toxins from these blooms may pose health threats to marine organisms, including seabirds. Since 2015, the USGS has worked with a variety of stakeholders to develop testing methods and research projects to better understand the geographic extent, timing and impacts of algal toxins in Alaska marine ecosystems, including possible links to recent seabird die-offs.

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What are harmful algal blooms (HABs)?

Certain species of phytoplankton produce biotoxins that can injure or kill fish and wildlife. When blooms of these phytoplankton occur, toxins become distributed throughout the food web. These events, termed harmful algal blooms or HABs, are often related to higher seawater temperatures and changes in ocean currents and nutrient levels. There are two primary marine HAB toxins of concern in Alaska: saxitoxin (STX), which is responsible for causing paralytic shellfish poisoning, and domoic acid (DA), which can cause seizures and other neurological distress.

Two birds grabbing fish out of the ocean

Black-legged Kittiwakes forage on Pacific sand lance and capelin near their colony on Gull Island, Cook Inlet on June 28, 2018. 
(Credit: Sarah Schoen, USGS, Alaska Science Center. Public domain.)

Why are we testing birds for algal toxins?

Since 2014, widespread seabird die-off events have been observed annually throughout Alaska; although starvation has been commonly reported, other underlying factors remain unknown. The USGS is the scientific research agency for the Department of the Interior and has developed studies and testing capabilities to address concerns around seabird die-off events. Recent studies in Alaska, including those by USGS, have found STX and DA throughout the marine ecosystem, including in marine mammals, birds, and other wildlife. Increased occurrence of HABs is predicted with changing environmental conditions, including warming ocean temperatures.

What have we learned so far?

We’ve tested nearly twenty Alaska seabird species—including Common Murres, Black-legged Kittiwakes, Northern Fulmars, Short-tailed Shearwaters, and Arctic Terns—for STX and DA. We’ve also tested a variety of forage fish and marine invertebrates. We’ve detected STX commonly in seabird tissues, forage fish, and marine invertebrates throughout Alaska waters, including in the Gulf of Alaska, Bering Sea, and Chukchi Sea. DA has been present less frequently in our samples. In most cases, STX concentrations measured in seabird tissues have been relatively low. We investigated the potential role of HAB toxins in a massive die-off of Common Murres in Alaska in 2015 and 2016 and detected STX in both die-off and healthy birds. However, starvation appeared to be the primary cause of death and the role of HAB toxins is unclear. To date, the highest concentrations of STX have been observed in Northern Fulmars in the Northern Bering Sea and Arctic Terns in Southeast Alaska. Although we don’t know whether STX caused acute mortality in these birds, tissue concentrations were similar to those observed in other bird mortality events attributed to STX, suggesting potentially harmful effects. Within the seabirds we’ve tested, STX has been present in multiple tissues, with the highest concentrations typically found in the gastrointestinal tract.

What do our results mean for seabirds?

Seabirds in Alaska are commonly exposed to STX and DA in the marine environment. How much toxin birds ingest depends on what they eat, where they live, and whether local environmental conditions are suitable for producing HABs. We don’t yet know how sensitive seabirds are to STX but results from a laboratory study of Mallards and Zebra Finches suggests that current levels of exposure in Alaska may be harmful to some species. We are working to address this question for seabirds, which will help us determine the threat of HABs to wild bird populations in Alaska.

What are the implications for human health?

Because humans also consume marine organisms, and in some cases rely heavily on these resources for subsistence, economic, and cultural purposes, HABs have the potential to impact human health. Although our testing and diagnostic tools cannot evaluate food safety, results from seabird research help inform general patterns of HAB occurrence. Our results suggest that bird tissues other than the gastrointestinal tract typically have very low toxin concentrations. Like other recent studies, we have detected algal toxins in wildlife across large geographic areas in Alaska, suggesting that HABs should be considered for any harvesting efforts throughout the state.

What are we doing now?

We work closely with partners and stakeholders to respond to their questions about HABs in Alaska ecosystems. Our current HAB toxin research includes both field and laboratory studies to address the following topics:

  • Experimental trials to determine the effects of STX on seabird behavior and health.
  • Investigating the role of HAB toxins in seabird die-off events to answer the question: Has exposure contributed to bird mortality?
  • Tracking occurrence of STX and DA in seabirds throughout Alaska. Where and in which species do these toxins occur?
  • Understanding food web dynamics of STX and DA. How do algal toxins move from marine invertebrates and forage fish to higher-level consumers like seabirds?

USGS Alaska Science Center biologists are also studying changes in the food web that have contributed to recent seabird die-offs and consequences of marine heat waves for fish and wildlife populations.

Where can I find more information?

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Three Arctic Terns sitting on a log in the water in Prince William Sound

Three Arctic Terns sitting on a log floating in the water in Prince William Sound.
(Credit: Sarah Schoen, USGS. Public domain.)