The cells clear first. The toxin stays behind.

Not every bloom is toxic and not every toxic bloom is visible. Those two facts together are why bloom management is run on assays rather than on photographs, and why a system that only reduces biomass is only doing half of the work.

Three toxin families account for most of the public health and regulatory pressure on the coastlines we work. They behave differently, they are measured differently, and they close different things.

Brevetoxin — the one you breathe

Florida red tide, Karenia brevis, is unusual in that its toxin becomes an air quality problem. Wave action aerosolises brevetoxins and onshore wind carries them inland. What the clinical literature describes is an apparently reversible upper-respiratory syndrome — coughing, throat irritation, chest tightness — and a markedly harder version of it in people who have asthma.

How long it lasts depends on who is standing on the sand. Fleming and colleagues record asthmatic participants reporting symptoms for up to at least five days after a single one-hour beach exposure. A public health authority setting a closure window is setting it around that group, not around the median visitor.

The commercial consequence follows from that, not from the severity. A beach where a proportion of visitors start coughing is a beach that empties, and it stays empty longer than the aerosol does. This is the mechanism behind the tourism losses on the Florida record, and it is why resort groups treat a bloom as a reputational event before an environmental one.

Domoic acid — the one with no antidote

Pseudo-nitzschia blooms produce domoic acid, which causes amnesic shellfish poisoning. At low doses that means nausea, vomiting and diarrhoea. At higher doses it means seizures, coma, irreversible short-term memory loss and death, with elderly people at highest risk.

Two properties make it a regulator's nightmare. There is no antidote. And cooking or freezing does not destroy it, so there is no step downstream of harvest that makes contaminated tissue safe.

That is the whole explanation for why a shellfish closure holds after the water has cleared. It is also why the 2015 West Coast event cost $97.5 million in Dungeness crab landings and roughly $40 million more in razor-clam tourism, against a bloom most people never saw.

Microcystin — the one in the tap

Cyanobacterial blooms in fresh and brackish water produce microcystins, of which microcystin-LR is the most studied. WHO sets the provisional drinking-water guideline at one microgram per litre for lifetime exposure and twelve for the short term, meaning the fortnight a utility takes to get treatment back under control. Which number applies depends entirely on which question is being asked, and answering with the wrong one closes a supply that did not need closing. Human poisoning presents primarily as liver damage, gastrointestinal illness and hepatic toxicity.

Toledo, Ohio, is the case everyone in this field cites, because it was not a fishery or a beach. In 2014 a Lake Erie bloom contaminated the municipal supply and roughly 500,000 residents were advised not to drink the tap water. A city does not recover its confidence in the water system as quickly as it recovers the water system.

The physics, the agency trials and the Florida permit

Bubbles below about a micron behave as a stable suspended phase rather than as something rising to burst, and the measured advantage in how fast gas crosses into water is in the peer-reviewed record. None of that is ours and none of it is contested.

An eight-acre Florida pond in 2018, an ozone nanobubble system, algae gone inside two days with reoxygenation held and no apparent harm to the life in the water, all reported by NOAA's coastal science centres. A separate ballast-water evaluation two years later found no statistically significant adverse residual toxicity downstream. Different equipment, different partners. Those releases say the approach is workable. They say nothing about our hull.

Then the field record, which is one permit. Florida DEP granted Alarivean, Inc. permit FLOA00062 in September 2024, under Chapter 403 of the Florida Statutes and on a five-year window, to trial an ozonated-seawater craft against red tide with live Karenia brevis above 100,000 cells per litre as the gate. The Sarasota Bay Estuary Programme and START logged it independently. The estuary programme supported that application on technical grounds, took no funding for it, and has asked to be the party holding the instruments when open-water measurements finally get taken. An endorsement past the bay would then rest on their readings rather than on ours.

Alarivean also holds a Cooperative Research and Development Agreement with NOAA, and work under it with Dr Peter Moeller established that this treatment neutralises toxins by disabling what makes them toxic rather than precipitating them out of solution. CRADAs are private instruments and none of them is published. That is the company's account of its own research, and a research agreement stops well short of an approval.

Two things stay open, and they are worth stating flatly. Whether the bubbles themselves generate hydroxyl radicals is argued in the literature, so nothing here is planned as though they do. And no open-water result has been published for this class of treatment — ours or anybody else's. The pond and the ballast tank are what exists. Producing a number on your own water, on a bounded area, against parameters agreed before it starts, is what a calibration phase is for.