Nature Notes

LARRY PENNY

"Seawater covers two-thirds of the earth's surface" is the first pronouncement of every text on the subject of oceanography.

The seas are bountiful. They contain members of every major plant and animal group, as many as 100,000 different species (many in abundance), a good many of the microscopic ones, and several of the macroscopic ones, yet to be identified and described.

The oceans have more crustaceans, fish, mollusks, jellyfishes, starfishes, anemones, segmented worms, sponges, phytoplankton, and seaweeds - thus the name - than any other habitat. They hold their own in mammals and birds, and have a score or so of reptiles.

Seagrasses

On the debit side, they host no amphibians, very few insects, and even fewer flowering plants.

Inasmuch as the paucity of flowering plants is the criterion by which we define the expanses of the great deserts, it might be said that the world ocean is also a great desert. It ranks right up there with the Sahara and the Gobi in terms of coverage by flowering plants.

There may be fewer than 20 species of marine flowering plants worldwide, and they inhabit a very small amount of sea bottom, only where the water is very shallow, not more than 40 or 50 feet, in most cases less than 20 feet. They need sunlight to photosynthesize.

Collectively, they are called "seagrasses," and most of them are in one family, Zosteracea, the eelgrasses. Along our coast and most of the Pacific coast across from us, the predominate eelgrass species is Zostera marina.

The Staff Of Life

Call them what you will, seagrasses are the staff of life for shallow marine habitats. According to the botanists Robert K. Godrey and Jean W. Wooten, "Zostera marina is considered to be the food at the base of a pyramid of living things, 25 million tons of which are required to produce eventually five million tons of birds, 5,000 tons of halibut, flounder, and plaice, and 6,000 tons of cod."

Some us have had the props on our outboards clogged by eelgrass leaves. Eelgrass can wash up in unsightly and foul-smelling masses and snag fish hooks and fishing lures, but in general, there are very few among us who wouldn't call eelgrass a blessing, if not a boon.

Aside from the handful of declaimers, most fishermen and scientists alike recognize eelgrass as an essential ingredient, probably the most essential ingredient, of estuarine and near-shore habitats.

Eelgrass Vanishes

When it virtually disappeared in the '30s because of a widespread wasting disease that devastated stocks on both sides of the Atlantic, it was soon sorely missed.

Scallop stocks plummeted, scaup and brant had little winter food and went elsewhere, several species of fish that were in one way or another dependent upon eelgrass bottoms lost vigor and numbers.

In many East Coast areas from Florida to Nova Scotia where eelgrass once thrived it has yet to come back. In other areas, say the Chesapeake, where it did come back, it has been on the wane since the '60s and '70s.

At this time, in most places up and down the coast, stocks of eelgrass are not much better off than they were at the height of the blight during the Great Depression.

Peconic Estuary

Its status locally has been of great interest during this decade, particularly so because of two events, the brown tide visitations, which decimated stocks out in the bays, and the designation of the Peconic-Gardiner's Bays system as a national estuary.

As a result of that designation the Peconic Estuary has been the subject of a vigorous five-year study, a focus of which has been the depleting stocks of eelgrasses. In 1995, Cashen Associates assessed the stocks of eelgrass, the first time such a baywide assessment had ever been done.

Hog Creek in Springs turns out to have the most eelgrass. Northwest Creek, almost chockablock full in the mid-'70s, has none now.

Cashen biologists found an interesting thing, something we may have suspected at the time. Stocks of eelgrass were minimal. There were a few places extensive eelgrass meadows thrived - on the west sides of Shelter Island and Gardiner's Island, off Hedges Banks and off Northwest Creek, to cite a few examples - but in general, much less than 5 percent of the estuary bottom was covered with eelgrass.

It turns out, then, that in this respect, the Peconic Estuary is quite comparable to Chesapeake Bay.

What Was Up?

Moreover, Cashen found that the situation in the tributaries leading into the outer bays was not much different. Only a few of them had sizable collections of eelgrass; many were completely devoid of eelgrass.

What was up?

It wasn't that the existing eelgrass plants weren't fertile or reproducing. Jerry Churchill of Adelphi University and Sandy Wyllie-Echeverria of the University of Washington assessed fruiting in Northwest Harbor stocks and found that seed production was ample.

They were able to readily germinate seed that they collected, demonstrating that it had the capacity to produce new eelgrass plants. Nothing was wrong with the seed.

Suddenly Inhospitable

Eelgrass seed can be so plentiful, in fact, that Mr. Churchill is of the belief it can be considered analogous to the fall acorn crop and its relationship to blue jays, squirrels, deer, wild turkeys, and other species.

It rains down and supports a large number of crabs, waterfowl, and other animals that scarf it up and come to depend on it.

Transplantings of eelgrass plugs into different water bodies, carried out by the Cornell Cooperative Extension, Environmental and Energy Analysis, a Water Mill company, and East Hampton Town's natural resources department indicated that some areas formerly occupied by eelgrass were no longer hospitable to its growth.

Something was up. What was it?

Annual Mappings

These agencies searched for the answers. In successive years beginning in 1995, eelgrass stocks in various East Hampton Town tidal embayments were mapped.

At the same time, a historical assessment was made, by interviewing people who knew local waters and remembered something about their eelgrass beds in past years, and by using aerial photographs taken over the last 45 years.

Based on these interviews and the photos, the recreation of historical eelgrass maps was possible. These maps, however sketchy, proved to be quite useful.

The Most Eelgrass

The most recent eelgrass mapping of East Hampton Harbors has just been completed by natural resources. It is not so different from the first one made in 1995.

Hog Creek in Springs turns out to have the most eelgrass. About 50 percent of its bottom is covered. Northwest Creek, almost chockablock full of eelgrass in the mid-70s, has none now. Lake Montauk and Napeague Harbor are holding steady. About 10 to 15 percent of their bottoms are covered with eelgrass meadows.

As far as we can tell, Napeague Harbor wasn't so different prior to 1980. Neither was Hog Creek, but Lake Montauk had a lot more eelgrass back in those times.

Turbidity

We could only find 10 very small patches of eelgrass in Accabonac Harbor, a far cry from its relative abundance in that harbor 20 years ago, when it literally covered very large sections of bottom - for example, almost all of East Harbor.

Fresh Pond in Amagansett doesn't have any eelgrass.

It's hard to pin the whole thing on brown tide. There are some things we know that eelgrass doesn't like besides brown tide. It doesn't like turbidity, that is, particles suspended in the water column.

These particles can be plankton cells, silt kicked up off the bottom, or silt and clay washed in by runoff generated by precipitation.

Contributing Factors

Eelgrass is sensitive to nutrients; it can't handle a lot of nitrates. Of course, it doesn't like herbicides.

Eelgrass doesn't do well when there is little or no tidal flushing, such as at Fresh Pond. Eelgrass can't tolerate long periods of hot summer temperatures that elevate the water temperature above normal levels.

Crabs can havoc eelgrass beds. Various waterfowl, including swans, can pillage eelgrass. Clammers can do a lot of damage when they pull rakes through eelgrass beds, dislodging the rhizomes.

We see this happening in Napeague Harbor.

Entire Beds Killed Off

When we look at the situation in East Hampton, some things become obvious.

We have observed the feeding waterfowl, the goldeneyes, mallards, canvasbacks, scaup, the geese and the swans. Some of these may be keeping down eelgrass numbers, but they certainly don't account for the bulk of the depletion.

The same goes for crabs and clammers.

We've had some hot water times during this decade, but not to the extent that entire beds of eelgrass would be killed off. During such sieges the shallow-water harbors would suffer the most, yet Hog Creek, which is one of the shallowest, is thriving.

Turbidity

We probably don't get much herbicide washing into our harbors, though it remains to be determined. We may get a lot more chlorine and some of the harmful products of chlorination.

E.E.A., the environmental agency, has deployed turbidity meters in various estuary harbors and found that some have very high turbidity levels throughout the summer, while others, such as Napeague Harbor, are mostly clear.

We think turbidity has something to do with the spotty distribution of eelgrass. Some of this turbidity, no doubt, relates to boat traffic.

Runoff can also account for a lot of this turbidity. It can also bring in nutrients such as nitrates.

Runoff

Street runoff has almost been eliminated in the Three Mile Harbor, Accabonac Harbor, and Hog Creek watersheds. However, stream runoff hasn't been.

Pussy's Pond and other small streams contribute a lot of suspended particulates to Accabonac Harbor. Soak Hides and streamlets contribute a lot to Three Mile Harbor. Northwest Creek gets a lot of stream input as well.

Those harbors with elaborate grids of mosquito ditching, such as Northwest Creek and Accabonac, also get a lot of particulate runoff.

Lake Montauk gets a lot of street runoff, plus a lot of runoff from streams. The oceanside drain contributes the most stream runoff; it pours into the south end of the lake. There is no eelgrass in the south end of the lake.

Underflow

Groundwater can bring nutrients and other pollutants into contact with eelgrass roots. Preliminary results from sampling test wells situated around all of the above-named harbors indicate that the groundwater entering their waters is not all that pure.

It can contain relatively high amounts of nitrogenous substances, not to mention other things. Harbors such as Three Mile Harbor, with extensive groundwater feed, called underflow, stand to suffer more in this regard than those with minor groundwater flows, such as Napeague Harbor.

Three Mile Harbor has a sprinkling of eelgrass, but only one spot where it is flourishing, immediately off Boys Harbor south of Hand's Creek, in the lee of the southwesterlies and northwesterlies, and where the underflow should be reasonably clean.

Why Hog Creek?

Having said all this, why is Hog Creek perennially the harbor with the richest eelgrass resources, not just in East Hampton but throughout the East End of Long Island?

It's a hard question to answer. Its shores are ringed by houses. It must get some fertilizers and particulates in the runoff from lawns and other landscaped surfaces.

On the other hand, it has very little groundwater feed, no streams running into it, very little boat traffic inside the creek, very little street runoff, no vector ditching, and a well-maintained inlet.

If we get to know Hog Creek more completely, we may just uncover the golden rule to good eelgrass production.