Red Tide

Image: Red tide in our bay.

It’s definitely been a summer for unusual events. Harmful algal blooms, often called HABs or red tides, have been one of these.

Beginning in May, and extending throughout the summer, there has been a massive toxic bloom of the marine diatom Pseudo-nitzschia, stretching from central California to the Alaska Peninsula. Pseudo-nitzschia produces a potent neurotoxin, domoic acid, which can accumulate in shellfish, other invertebrates, and sometimes fish, leading to illness and death in a variety of seabirds and marine mammals. Human consumption of shellfish contaminated with domoic acid can result in Amnesic Shellfish Poisoning, which can be life threatening. This bloom was the largest and longest-lasting in at least the past 15 years. Concentrations of domoic acid in seawater, some forage fish, and crab samples were among the highest ever reported for this region. In the U.S., shellfish, Dungeness crab, anchovy and sardine fishery closures were put in place to protect human health. This HAB event was also suspected of playing a role in sea lion strandings and the mortality of 30 large whales. While the exact causes of this massive bloom are not yet known, the unusually warm surface water in the Pacific is considered a factor. So this bloom was potentially yet another outcome of global warming.

In our little bay at the end of Port Neville Inlet, we also experienced very intense phytoplankton blooms during the summer. Initially, during the same time period as the big HAB was occurring along the outer coast, we also had a thick, murky-yellow bloom, most likely caused by a diatom. Although I did not have my microscope set up to check the species, I wouldn’t have been surprised to find that it was Pseudo-nitzschia. As this bloom intensified, we started seeing cockles dying on our beach, either from oxygen depletion (one of the problems associated with HABs) or the toxins produced by the bloom. Interesting, there were no warnings issued by DFO regarding the potential toxicity of this bloom. Was the bloom seen here different from the Pseudo-nitzschia bloom seen on the outer coast, either less intense and less toxic, or a different non-toxic species entirely, or was DFO simply unaware or unconcerned about what was happening? Hopefully, next time, I will have my microscope ready and be able to identify the culprit!

Later, in early September, we got a second algal bloom. Unlike the earlier one, this one was intensely red in color, and thus truly deserved the name “red tide”. It was concentrated in the surface water, and the wind blew it in furrows along our beach. This bloom was most certainly composed of dinoflagellates, although again the species remained a mystery to me, as my microscope was still buried deep in the Moody Blue’s hold. I suspect that it may have been a Noctiluca bloom, a relatively harmless and non-toxic species. Next time, I hope to know for sure!

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