01:00 AM EDT on Sunday, June 12, 2005

Our oceans are changing. A few weeks ago, the Woods Hole Oceanographic Institution hosted scientists at the first International Invasive Sea Squirt Conference. The group of species under discussion has invaded New England waters and has, among many other nasty acts, begun growing over our shellfish beds.

Now we find that the worst-on-record bloom of a one-celled organism called "red tide" has expanded throughout the Massachusetts and Cape Cod bays, pushed its way through the Cape Cod Canal and made it over to Martha's Vineyard -- and is possibly heading for Narragansett Bay and Long Island Sound. It has turned clams and mussels poisonous. Fish are dying, shellfish beds are closed and clam diggers are out of work.

"The dominance of one organism is characteristic of disruption," says George Woodwell, founder and director emeritus of the Woods Hole Research Center.

Our poor old ocean! Red tides are somewhat common, but not one this size.

The current plague, which may or may not disappear by July 4th, appears to have several causes.

First, there's too much fresh water in some of our bays, lowering the level of salt in the water and providing a happier home life for the newly born red-tide cells. WHOI scientist Dennis McGillicuddy says that red-tide cells lying on the ocean bottom wake up each spring. When they find lots of fresh water, a perfect ocean temperature, and much nourishment to eat -- they go to town.

So, why are there so many nutrients in the waters? And why is there so much fresh water in our oceans?

For an answer to that mystery, time to move from talking to the scientists to talking to New England housing developers and all those people who have built McMansions on our shorelines. Time to talk to the shoreline homeowners who run their fertilizer-greedy grass lawns down to the shoreline.

Chopping down all the vegetation that nature has grown as a buffer for our rivers, ponds and coasts, and building huge houses with rich-looking green grass running down to the water is a recipe for algae blooms.

Add to those ingredients that many New England sewage plants emit not clean water but only partly purified "gray" water (it's cheaper that way), and it's not hard to figure out why our coastal waters are a mess.

So we know where the nutrients came from, but how did all that fresh water suddenly get here? Scientists aren't certain, but a growing number believe that rising global temperatures resulting in melting polar ice caps may be shifting global ocean currents and playing havoc with our weather systems.

In other words, it's possible that the current massive onslaught of red tide is an unpredicted result of global warming. That scientific debate will probably go on for decades.

But one thing is certain: Nature certainly isn't giving us her Seal of Approval.