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Biological oceanography

A toxic toasty blob: warm water in the Pacific provides a happy home for poisonous algae

Original article: McCabe, R. M., B. M. Hickey, R. M. Kudela, K. A. Lefebvre, N. G. Adams, B. D. Bill, F. M. D. Gulland, R. E. Thomson, W. P. Cochlan, and V. L. Trainer (2016), An unprecedented coastwide toxic algal bloom linked to anomalous ocean conditions, Geophysical Research Letters, 43(19), 10,366–10,376, doi:10.1002/2016GL070023.

2015 was an unusual year along the western coast of the US and Canada. Ocean surface temperatures had been much warmer than average over a large area of the northeast Pacific since late 2013, and by 2015 they were being credited for causing the drought in California, warm air temperatures in the Pacific Northwest, and the deaths of countless fish and marine mammals. Whales, otters, and sea lions were stranding on shorelines in numbers far exceeding ordinary, often with signs of distress. Some were found having spasms and convulsions on beaches, symptoms that indicate exposure to a neurotoxin called domoic acid, which was also showing up in mussels and clams along the coast. Shellfish fisheries were closed for months while managers waited for concentrations of the toxin to return to normal.

Domoic acid periodically becomes concentrated in the surface ocean off the west coast when a certain type of algae, called Pseudo-nitzchia proliferates, but it had been several years since the algae spread as much as it did in 2015. Pseudo-nitzchia loves warm temperatures, so it’s more often found farther south. It is consumed by mussels, clams, crabs, sardines, and anchovies and, while the domoic acid it produces doesn’t harm shellfish, it is toxic to humans and marine mammals, causing illness, seizures, and even death. For this reason, state Fish and Wildlife departments have monitored concentrations of domoic acid in shellfish for decades and there are thresholds above which fisheries are mandated to close.

Pseudo-nitzschia, a species of diatom that produces the neurotoxin domoic acid. (Wikipedia)

Pseudo-nitzschia, a species of diatom that produces the neurotoxin domoic acid. (Wikipedia)

In 2015, concentrations of domoic acid were elevated almost everywhere along the coast from California to Alaska. The Dungeness crab fishery, an industry worth $170 million was closed for almost a year beginning in May 2015. Razor clams weren’t fished for almost as long. This economic loss and human health issue led to some important questions: How did this happen? Is this the new normal? Will we be able to predict toxic blooms this large in the future? The Northwest Fisheries Science Center added additional scientists to a fisheries survey cruise that took place in the summer of 2015. Researchers from multiple institutions on the west coast of the US and Canada, led by Dr. Ryan McCabe from the University of Washington, reported on results from that cruise and on additional observations in an article published in Geophysical Research Letters in September 2016. They described the timeline of events that led to the uninhibited growth of toxic algae along the entire west coast and how it affected the animals that live there.

Map and timeline of fishery closures caused by high levels of domoic acid (Figure 1 in the paper.)

Map and timeline of fishery closures caused by high levels of domoic acid (Figure 1 in the paper.)

The process that led to the pseudo-nitzschia bloom began late in the fall of 2013. A high pressure system in the atmosphere expanded over the northeast Pacific causing weaker winds than were usual for that time of year. Without strong wind mixing, the surface of the ocean did not overturn and mix with the cooler waters below, so it remained warm. Thus, “the blob” was born. This area of warm water persisted throughout the following two years, sometimes moving offshore and then back towards the coast, sometimes shrinking and eventually spreading from California to Alaska, but always maintaining its warm blobby structure.

The blob’s movement on and offshore was determined by the direction of the predominant winds. The Coriolis force, an effect of the Earth’s rotation, causes surface water to be pushed to the right of the direction of the wind. During winter, winds tend to blow from south to north, so the blob was pushed in eastward toward the coast. During summer, the wind direction switches along the entire coast. It blows from the north, pushing surface water offshore and forcing deep water to come up at the coast to replace the displaced surface water, in a process called upwelling.

Map of sea surface temperature anomalies in April, May, and June of 2015. Blue arrows show upwelling bringing deep nutrients to the warm surface ocean, creating the perfect environment for pseudo-nitzchia to bloom. (Figure 2b in the paper.)

Map of sea surface temperature anomalies in April, May, and June of 2015. Blue arrows show upwelling bringing deep nutrients to the warm surface ocean, creating the perfect environment for pseudo-nitzchia to bloom. (Figure 2b in the paper.)

Throughout 2014, the warm blob was made up of water with temperatures 2-3˚C above normal. Pseudo-nitzchia, the warm-water-loving, toxin-producing algae began pushing its northern boundary, content to float around in the now balmy Oregon and Washington waters. Newly upwelled nutrients from the deep ocean supported the budding algae population and by early 2015, domoic acid was detected in zooplankton samples.

By the time of the spring upwelling season in 2015, pseudo-nitszchia were proliferating in the offshore blob. Domoic acid was prevalent, but it was concentrated in waters far from the coastal habitats of shellfish. The bloom may never have become a public health issue were it not for a series of northward-moving storms that swept along the coast that spring. Each storm pushed the warm, algae-laden water toward the coast where it fed shellfish and small fish that were themselves consumed by seabirds and mammals. Concentrations of domoic acid in in fishery species spiked and the harvest of those animals stopped abruptly.

The National Ocean and Atmosphere Association (NOAA) conducts bi-weekly surveys during which they usually bring up swarms of healthy krill in their nets. During 2015, they were pulling up soupy algae and jellyfish instead. Not only do the algae produce toxins, but they are poor substitutes for heartier krill in the diets of many fish and other marine animals. Many fish unaffected by domoic acid still died of starvation in 2015.

Timeseries of domoic acid concentrations in razor clams in Oregon since 1990. Concentrations as high as those seen in 2015 were only seen a few times before, usually during El Nino years (grey bars) or soon after. (Figure 6c in the paper.)

Timeseries of domoic acid concentrations in razor clams in Oregon since 1990. Concentrations as high as those seen in 2015 were only seen a few times before, usually during El Nino years (grey bars) or soon after. (Figure 6c in the paper.)

Water temperatures in 2015 were unusually high over a large portion of the Pacific. These temperatures coincided with El Nino conditions, which have led to similarly high levels of domoic acid in the past. The blob is not a permanent feature, but the ocean is warming, and Pseudo-nitzschia does do well in warm temperatures. It’s excellent at taking up nutrients from the surrounding water, so as long as the temperature is warm enough, it outcompetes a lot of other species leading to blooms like we saw in 2015. We can be sure that warm events like this will occur in the future and domoic acid will be back to poison marine animals. It may become more and more normal, so it’s critical that we continue to monitor the toxin and be prepared to react quickly to times when it exceeds healthy levels.

 

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