Red Tide in the Three Bays
September and October 2001
By Donald E. Schwinn, P.E.
Three Bays Preservation, Inc.
Red-colored water in the northern part of the Three Bays Estuary was first noticed by several North Bay, Prince Cove and Oyster Harbors users in mid-September; it persisted until the first week in October. At times, it turned these waters into a strong rust-red color from shore to shore. At other times, it showed up in wide reddish streaks. When in full bloom, it reduced the Secchi disk transparency of the water from about 6 feet to about 16 inches. Occasionally, it moved under the bridge into the Wianno Yacht Club area.
On September 26, a sample was collected and transported directly to the Woods Hole Oceanographic Institution (WHOI). It was immediately microscopically identified by the laboratory in their Red Tide program as cochlodinium polykrikoides, a member of the dinoflagellate family. This organism has caused many large fish kills in Asia, Canada and Mexico, but only in fish farms where the fish could not escape the toxic effects of the algae. It does not appear to be harmful to humans. No fish kills were noted in the Three Bays area. Town Health officials and WHOI staff knew of only one or two previous occurrences in this area within the last 10 years. WHOI has a web site totally devoted to red tides and harmful aquatic blooms (The Harmful Algae Page).
During daylight hours, the affected areas become a strong rust-red color. Overnight, the growths settle to the bottom. In the morning light, the organisms begin to form what look like red cumulus clouds rising from the bottom. These keep growing until the entire water column is choked with rust-red solids.
It should be noted that our red tide (cochlodinium) is not the dinoflagellate that has had drastic effects on biota in the ocean off New England (alexandrium), nor is it the one that has caused large fish kills and human rashes in North Carolina's Neuse River (pfisteria). However, as it is a member of the dinoflagellate family, it is a matter of concern.
Three Bays Preservation asked Don Anderson, WHOI's expert on red tides and harmful aquatic blooms, to answer a list of questions about this organism's characteristics and what we might expect in the future.
Here are the questions and his verbal replies.
Why did the North Bay bloom happen?
There's no real answer to why it happened. We do have some reports of other occurrences of red tides in the region, and although we don't have samples of those, at least one or two of them appear to have been cochlodinium.
Does the excess nitrogen in our estuary encourage such growths?
Excessive nitrogen is something that this organism would benefit from. Most of those species require higher nitrogen levels to be able to grow well. I am not sure that's the reason those organisms appeared this year because probably your nitrogen levels have been high in past years. I know that about seven or eight years ago we had a bloom of that organism in Cotuit Bay that lasted for a long time, but after that we didn't have anything. And we thought we would see it again the next year, but we didn't. That was in Cotuit Bay, where the oysters are grown, and there was red water and all sorts of problems. We would have expected it to drop cysts and show up again the following year, but it didn't recur. It's more likely than ever to recur in North Bay next year and in years following because of the cyst stage.
As we haven't seen any dead fish and the organism is not toxic to humans, should we be worried?
I think there is good reason to be concerned. It's probably the reason a lot of your fish weren't around. It's also producing harmful effects that you're not even seeing with mortality to some organisms. It's not producing toxins that are directly dangerous to humans, such as pfisteria.
Is there anything that can be done to prevent it?
That's a hard one to answer; we'll have to study it a lot more to figure out just why it's growing there now and where it's originating from. It may be that there's one portion of your waters where all these cysts are accumulating, and one could conceivably monitor that area to see if that's a source. We know that the Koreans use clay sprayed on the water to kill those cells, but the damages would have to be great to get the environmental approvals to spray clay on your bays.
What effects are there on bottom-dwelling organisms?
I don't think anybody really knows that. My guess is that there really aren't any because the toxins that are produced by that organism are produced while it's living, not while it's dead and at the bottom. So the toxic effects are confined to when it's alive and suspended in the water column.
Is there anything WHOI could study in the Three Bays area that would help to understand and predict future blooms of cochlodinium?
We could carry out a monitoring problem that would cost tens of thousands of dollars, but it's not clear what the real benefit would be.