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Surfrider's Coastal Science Manager Mark Rauscher replies:

There doesn't seem to be any specific resource for when red tides occur. When large blooms occur it usually makes it into the local papers and the blooms usually at least several days.

The other option would be to watch for the right conditions. They seem to occur in the late summer or early fall when we've had a long period of warm water followed by a cold water upwelling event. If you surf often you know that the water temperature dropped precipitously a couple weeks ago following a strong NW wind. This cold water is rich in nutrients and combined with the strong sunlight that we still have this time of year provides ideal conditions for a red tide (or other algae) bloom.

Fortunately it seems that most of the red tides in Southern California are not toxic, while Florida has had major problems with large toxic red tides in the last few years. It got to the point where your lungs would burn if there was a strong onshore breeze.

These red tides that cause illnesses are technically called "Harmful Algal Blooms" and some ocean researchers spend many hours trying to determine why they occur in such high numbers and how they might be avoided.

See here for more info than you could ever want.

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Now, Peter J.S. Franks, Professor of Biological Oceanography at the Scripps Institution of Oceanography adds his two cents in mid September '03:

Okay, our nearshore, relatively shallow waters.

As you might have noticed, the waters are a dark brownish purple. This is caused by dense accumulations near the surface of dinoflagellates (think: tiny cellulose-covered balls with two little whips for propulsion). As luck would have it, today's bloom (as opposed to the one last month) is dominated by our friend Lingulodinium polyedrum. This dinoflagellate is photosynthetic (makes sugars from light and carbon dioxide), and bioluminescent (makes its own light). Each cell is about 30-40 microns across (there are 1000 microns in a millimeter, which is about the thickness of a dime). The cells have tiny sacs of enzymes that react when the cell is jostled (for example by the breaking surf). When the enzymes react, they give off a bluish flash of light. So our waves (and your footsteps on the beach; your hands and feet when you swim) will be adorned with gorgeous flashes of light at night.

The bioluminescence of these cells is on a circadian rhythm -- they don't bother making light during the day 'cause no one could see it. So here's what you do to amaze your friends, astound your children, and be the toast of your neighborhood: Get a clear jar or bottle, and fill it with some water from the surfzone (ask a friendly neighborhood surfer to fill it for you in deeper water, to get less sand in it). Take your bottle home, and wait until after the sun has gone down. Then take your bottle into a dark room (bathroom or closet with no windows). Wait for your eyes to adjust to the darkness (a minute or so), and then give your bottle a swirl. You should see a really amazing light show.

For extra added excitement, add some vinegar to the bottle. You'll get a particularly bright flash (but then all the cells will die, so it only works once). The acid of the vinegar makes the enzymes react inside the cell, even without stirring.

Some frequently asked questions (that I mostly cannot answer):

Why is there a red tide?
I don't know. Red tides are natural occurrences; the plankton community becomes dominated by one or a few species at extraordinarily high concentrations. The only thing I can say for certain is that the net growth rate of the cells (including accumulation by swimming) is higher than their net loss rate (due to grazing, etc.). It's certainly possible that the growth of the cells is fueled by nutrients brought to the surface by upwelling (the water temperature dropped suddenly back in August).

Why are red tides so dense?
The organisms that make red tides (at least around here) tend to be able to swi
m. They might be swimming upward to photosynthesize, and downward to take up nutrients. If they are all doing the same thing, then they can form dense layers that are visible from the surface (like today). It's possible that the total amount of nutrients in the red-tide organisms is higher than the nutrients that were in the water before the bloom. This means that the cells must have moved relative to the water, in order to accumulate nutrients.

Why are the cells bioluminescent?
Two thoughts on this (Mike Latz is the expert...): One is that the organisms eating the red-tide cells don't like lights flashing in their face, and so don't graze on the flashing cells. The other thought is that the cell's flashing acts like a burglar alarm: an organism eating a red-tide cell causes it to flash, attracting the notice of a visual predator (the police) who then eats the grazer (burglar). Swift justice.

Why don't you so-called experts know anything about where the red tides come from?
It's embarrassing, isn't it? To really know why we have a red tide off the Scripps Pier right now, we would have had to do dense and continuous sampling all up and down the Southern California Bight for several months prior to the bloom. We would have had to measure the growth rates of the red-tide organisms, their swimming behaviors, and all their sources of mortality.

Furthermore (and this is the easy part), we would have had to measure all the water velocities, since the water motions move the blooms around. It's quite likely that our present bloom is the same one that was off Huntington beach a couple of weeks ago. On the upside, there are plans afoot to put observation networks in place all along the US coast, that would help generate data that might give us some clues about how and why these blooms form. Get back to me in about 15-20 years. From a scientific point of view, these red tides are a wonderful examples of physical-biological interactions leading to a massive perturbation of the marine ecosystem. I think that if we could understand why they occur, we'd learn a lot about how the planktonic ecosystem works the rest of the time.

And what the heck was that foam on the beach?
Probably degradation products and exudates from a different phytoplankton bloom (maybe the "green tide" of August). According to Lihini Aluwihare, the foam was mostly protein (a lot like egg whites). I'll defer all foam questions to her.

Is the water toxic?
No. You'll die from salt water before any phytoplankton toxins kill you.

Then why do I get skin rashes/ear/nose/throat infections/and-or eye irritations?
Don't know. Try bathing more.