Thursday, May 18, 2006

Oysters Improve Water Quality

In the late 1800s, oystermen in Connecticut harvested and sold as many as 15 million bushels of oysters a year. New Haven alone had 125 businesses involved in oystering. Long Island’s bays had thriving oyster industries, particularly Manhasset, which was known as Cow Bay.

Nowadays of course the oyster industry is nowhere near what it used to be. In the early to mid 1990s, Connecticut oystermen were producing between five hundred thousand and a million bushels a year; now, because of two diseases, the numbers are down to about 100,000 bushels a year, and 72,000 acres of shellfish beds are open in Connecticut (this is according to the Sound Health report, which does not have similar numbers for New York, probably because New York doesn’t distinguish between the north shore of Long Island and the south shore when keeping track of oyster harvests; if any of my loyal readers from the state DEC can confirm this, please do).

What I don’t know the answer to is how many acres of oysters beds there are in the Sound that are not certified for oystering, or whether there is a significant amount of uncertified oyster beds at all.

I bring this up because of this interesting report, in Environmental Science and Technology Online, about researchers at Woods Hole and the University of Rhode Island who have quantified the amount of nitrogen that oysters filter out of estuaries in the northeast. (The much-maligned zebra mussels prompted their interest by improving water clarity in the Great Lakes.)

The researchers figured out that the amount of nitrogen entering Waquoit Bay, in Massachusetts, increased from 10,900 kilograms a year in 1938 to 24,300 kg/yr now. They also determined that if they plant oysters over 6 percent of the bay’s bottom, the oysters will eliminate half of that increase, or about 6,700 kg/yr.

That’s a significant percentage. Can it work on Long Island Sound, where communities are laying out hundreds of millions of dollars to upgrade sewage plants for nitrogen removal?

I have no way of knowing, of course. I guess part of it depends on how much potential oyster habitat still exists. If there’s none, that means there’s no room for more oysters and you can assume that the oysters that are already here are filtering out as much nitrogen as possible. But if there’s unused habitat, it raises the question of whether there are places where oysters can be planted where they might have a significant affect on nitrogen concentrations, and on the health of the Sound.


Blogger Sam said...

Thanks for the posting, Tom, and you know our family was deeply involved in the Milford-New Haven oyster industry in the 1950's and early 1960's.

I'm no expert here but an oysters job is to filter out algae and other micro-organisms. The algae contains nitogen and phosphorous. What I'm not sure is what form these compounds are when excreted by our oyster - as particulate?

I do know that before DMX and other diseases, the oyster drill, a small crustacean resembling its name, was a big problem. They would borrow right through the shell and eat the oyster. Maybe they're gone now.

Floating aquaculture farms sounds like a good idea, and they release tons of spat (eggs). To start more native oyster neds, one would need oyster sheel or some suitable substrate to grow. I'll leave it to the experts to expand upon this theme.


7:07 PM  

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