A massive harmful algal bloom wreaking havoc in waters off Central California appears to be staying out of Southern California waters.
Algal blooms are composed of phytoplankton, most of which are harmless. Some species, however, can be stimulated to produce domoic acid, a neurotoxin that is known to kill sea birds and marine mammals. It is also deadly to humans.
The current bloom was detected by sensors in Monterey Bay in early May. It extends further north, where it necessitated the closure of Washington's Dungeness crab fishery. There are even anecdotal reports of its presence in Alaska.
It's believed to be the largest of its kind ever recorded for the region, according to an official with the National Oceanic and Atmospheric Administration.
“The extent is larger than anything we’ve ever seen before, especially at this time of year,” said Michael Milstein, a spokesman for NOAA Fisheries.
Officials with the California Department of Public Health have issued warnings against eating certain types of seafood caught in Monterey and Santa Cruz counties. Bivalve species, such as mussels, are filter feeders and concentrate the toxin within their flesh.
Not in our water
The toxic marine event is unusual not only for its wide range but also for its duration.
"It's held on longer than these blooms typically do. Often, we will see blooms come in for a week or so. This one kind of looked like it was going to trail off, and then it kind of caught wind again, and it's still quite significant up there," said David Caron, a researcher at the University of Southern California.
Caron oversees projects that aim to better understanding of how the natural phenomenon occurs. Members of his laboratory recently joined a monitoring cruise to sample water off the coast of Southern California.
That trip turned up no significant traces of either Pseudo-nitzxchia or domoic acid. Those findings matched weekly readings from shore monitors.
An algal bloom may not develop in Southern California waters this year, as such occurrences typically stop with the arrival of summer. Caron said that the last major harmful algal bloom in the region happened in 2012 but was short lived and caused no known harm to wildlife.
Though a harmful algal bloom in Central California is no guarantee that one will develop in Southern California, Caron said the sheer magnitude of the Monterey Bay bloom caused him to expect its presence further south.
“We’re a little perplexed as to why we’re not seeing anything down south, and they’re seeing massive amounts of it up to the north. But, you know, that’s something that we’re studying,” said David Caron, a biology professor at the University of Southern California.
He said one possible explanation is the unusually warm water off the coast. Cold, nutrient-rich water may be sitting too far below the surface to support an algal bloom.
"Because of the warm weather, because of the lack of real storms coming through to churn the water up, the surface waters are being kept quite warm in our region, and that may be contributing to the reason we're not seeing any noticeable accumulation of toxin or the algae that produce it," Caron said.