Maine has significant wetland resources, but like other New England states is limited in tidal marsh acreage because it is, geologically speaking, a recent shoreline. At the center of Mt. Desert Island is a small tidal marsh that we visit each year. Known colloquially by the teaching staff as: Dave's Marsh, it is fed by Kittredge Brook, a cool, rocky stream which drains the surrounding hills and an extensive upland area called Long Heath.Kendall Kittredge arrived in 1799 and was the first doctor on the island. Locals are quick to point out the small vintage house that overlooks the marsh as the "new Kittredge place" (the first one burned down in the 1800's). This was a perfect location for Dr. Kittredge's home since his rounds included the 107.7 square miles of eastern America's third largest island, Mt. Desert, and towns across Blue Hill Bay to the west.

Responding in all seasons to strategically placed signal fires, by horseback and by boat, the charitable and rugged doctor tended the sick and injured, but only after he and his horse were provided with a hearty meal, offered as a portion of his payment.

Dave's Marsh is an excellent location to study the ecology of a northern New England marsh. It covers approximately 25 acres, which is typical of the small marshes that are sandwiched into coves and steep valleys along the Maine coast. It is divided by a wide central creek (The Doctor's Brook) that ranges from fresh water where it tumbles into the marsh, to water nearly as salty as neighboring Somes Sound at its mouth. Here it is funneled over a sill that was created where it flows under a roadway.

Several creeks like this in the area are said to have been the sites of tidal mills a century ago. I've never gotten a firm answer that one existed here, although it's quite possible since its narrow mouth makes it a good site for one, and Somesville is the oldest permanent settlement on the island.

Like most marshes here, it is a picturesque spot that thousands of visitors pass, but few stop to appreciate as they travel to Acadia National Park. If I have a favorite marsh in Maine, and there are lots of candidates; I think this is it; surrounded by mountains and forest, near the sea, and rich in wildlife.

The upstream portion of the creek is fast, ankle-deep, and rocky. Polished stones form a slippery carpet across the bottom and living among the film of algae coating them is a multitude of scuds, that ubiquitous shrimp-like crustacean that is found in both fresh and salt water. Elvers that have traveled all the way from the Sargasso Sea arrive here in the warmer months and also hide between the rocks. Killifishes and sticklebacks roam the creek on flood tides, but tend to stay downstream in the deeper brackish water at low tide.

A minute tidal wedge forms in the shallow creek as fresh water flows over the denser brackish water. These two layers of water, the top one clear and the bottom one muddy, are usually visible during the tidal exchange. Detritus and algae sometimes collect at the interface between but the fishes and other creatures living here seem to move through it without hesitation.

At low tide most of the marsh is accessible. There are some mud flats which are too soft for walking, but there are also many acres of firm high and low marsh that can easily be explored. The upland perimeter of the marsh is northern forest typical of the island: white pine, spruce, paper birch, sugar maple and lots of ferns, mosses, blueberries, and bunchberry dogwood on the forest fringe. The high water mark from spring tides is indicated by a skirt of lichen covering the tops of the larger pieces of glacial till that line the marsh and forest border .

Plants in the marsh itself segregate themselves according to salt tolerance. Upstream and along the higher marsh fringe where flooding by the tides is infrequent, dense stands of black grass dominate. Interspersed with it are patches of rushes, reed grass, seaside goldenrod, freshwater cordgrass and silverweed. Where tongues of freshwater from forest runoff permeate the upper marsh soil, cattails and rushes extend sizable colonies across the marsh.

Downstream and along the tidal creeks, wide cowlicks of salt hay and redtop grass
crowd out everything else except at the seaward edge of the creeks. There the salt -tolerant tall cordgrass dominates. In the creeks, eel grass thrives below the reach of the tides.

Many animals utilize the upper marsh. Mosquitoes, gnats, and greenhead flies are present but tolerable, especially in the cool Maine air where it isn't a burden for us to wear extra layers of clothing. The bugs' sluggishness also provides us with some additional defense against them, and for the most part, annoying insects are relatively scarce on the island. Legions of inoffensive grasshoppers, dragonflies, wolf spiders, and an occasional vole hop, glide, and scurry through the marsh when we blunder across it. All are potential food for the many birds that regularly visit the marsh.

Crossbills were especially common this year, flying across the marsh at treetop level to raid the spruce cones at the marsh fringe. Apparently a short food supply forced them south in greater numbers this summer. Bluejays, always a regular feature in the trees, dart out over the marsh to snatch flying insects in midair or investigate a variety of items to scavenge. Our activities chase wary kingfishers from their perches, and they complain loudly as they are forced downstream to less desirable fishing spots.
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Bald eagles and osprey are not uncommon here and regularly perch on dead treetops to survey the waters for prey. Usually they are so still that they are not noticed by visitors in all the cars that pass. There is a herring run in a neighboring stream, and some wander into this creek too, attracting the attention of these raptors and divers like mergansers that are usually fishing in the deeper waters.

The firm soil of the upper marsh is crisscrossed with the tracks of deer and raccoons, documenting their nocturnal wanderings here. Herons leave their marks too, wherever there is a pool of water. In the spring it is not unusual to find a fawn lying hidden in the tall grass where it was left earlier in the day by its mother

In the winter, ice damages the marsh as frozen sections of it are lifted out with the rising tides. Occasionally these patches, named appropriately, marsh rollers and often as large as a hay bale, establish new grass colonies where they are stranded by the tides. The depressions left by their removal, which can be over a foot deep, are called pannes. These remain empty for a time but are eventually colonized by an assortment of very hardy plants and animals. Over the years they fill back in with sediments and finally, halophytes.

Pannes are fascinating environments that demonstrate how vigorously living organisms strive to colonize even the most inhospitable places. They teem with life just like the rest of the marsh. In fact if I have a favorite marsh spot, this is it.

Conditions in the pannes are much different than elsewhere in the marsh. In the winter they may freeze and at other times dry out. In the summer their shallow waters have temperature ranges that are much greater than the stable brook or brackish waters in the neighboring creeks; exceeding them on sunny days and cooling off rapidly at night and in the fall.

We even have detected vertical stratification (thermoclines and haloclines) in some of them from the heating and evaporation that occurs in the warm months. The salinity of the pannes also varies greatly, depending on the season, weather, precipitation, and the nearness of individual pannes to freshwater runoff from the forest. The most isolated pannes, those that are only flooded during the spring tides, may lose enough water through evaporation to become saltier than ocean water. Sometimes their salinities exceed 40 parts-per-thousand, however most of them here are closer to estuarine waters, about half ocean salinity. Dried pannes can be identified at a distance by a thin crust of brine on top of the cracked mud.

The amount of dissolved oxygen in the water determines what type of organisms can live in most aquatic environments. During the day we have recorded dissolved oxygen levels of 16 parts-per-million in the pannes, twice the concentration of adjacent estuarine water. These levels may plunge to between two and three parts-per-million at night, a strenuous situation for most aquatic creatures. This type of stress excludes most types of marsh inhabitants from the pannes, but the puddles swarm with aquatic life nonetheless.

Animals that thrive in spite of the stress include familiar producers like diatoms and dinoflagellates, which form a living, oxygen-generating film atop a thick carpet of detritus. During the day, countless bubbles of oxygen emanate from the brown biological film and lift pieces of it to the surface. Other microbes in the layer include a host of protozoa and bacteria which feed on the detritus and are in turn eaten by larger creatures like insects. This is an area of the marsh with some of the softest sediments and even the feet of featherweight shorebirds sink into the mayonnaise-textured muck. However, it is easy enough to kneel on the firm, grassy edge of a panne and get close enough to observe its inner workings. If you stir the clear waters of a pool they are transformed into a dark and odiferous broth. Toxic hydrogen sulfide released from the anaerobic bacteria in the dark bottom sediments is responsible for the rotten egg smell and the black color.

Many of the resident animals would suffocate during periods of oxygen depletion if they had to obtain all of their oxygen from the water, so many use snorkel-like appendages to stick above the surface and gulp air, or carry bubbles with them when they dive into the panne water.

Seemingly immune to all this and moving feverishly though the detritus and the water column are mosquito larva and water boatmen, the hardiest and most visible aquatic insects in the marsh. Bright scarlet water mites, the most striking of the marsh arthropods and perhaps the sturdiest of all the animals here, plod steadily underwater through the detritus and on the mud surface. Like the mosquito larva and boatmen, they seem impervious to the temperature and salinity differences and move freely about in search of food. Only one species of snail, Hydrobia, and fry of the killifish were found in samples taken from the pannes; an indication of how stressed an environment this can be, especially to higher organisms.

At the panne's edge, and if shallow enough in the center, halophytic plants take hold. Here some of the plants that are directly useful to people are found. These include spike grass, seaside plantain, samphire, and sea lavender. Samphire, or pickleweed, is edible and tasty because of its high salt content. Sea lavender is used in dried flower arrangements, and was also used like moth balls by the colonists.

Over time pannes fill in enough to be nearly level with the rest of the marsh and can support marsh grass. However, more will be created elsewhere each winter from continued ice damage to the marsh surface.

For me, the pannes are the most interesting part of the most fascinating ecosystem because of the extremes found in them. Surprisingly full of life in spite of harsh conditions, they attract many beautiful creatures like herons and egrets that feast on the stranded fishes in the pools. Shorebirds like the wary killdeer and yellowlegs also visit the pannes regularly to probe the mud for food.

On my visits here during the quiet autumn months when the summer crowds have departed, I've had migrating dowitchers and peeps land beside me to share the spots where I am puttering around, taking samples and staring into the water. This always gets me wondering if perhaps on their first flight south from the far north, they have never seen a human and to them I'm just another large, but harmless creature visiting the marsh to feed. Certainly that's not a bad way to spend time or be remembered by those creatures that need odd little places like this to survive.

Grant was Education Director at the Acadia Institute of Oceanography in Seal Harbor, Maine; and is now Director of Brookdale College's Ocean Institute at Sandy Hook, NJ..