Tidal Wetland Ecology of
Long Island Sound (Part 3)
(Part 1)
(Part 2)
Tidal Wetland Ecology of
Long Island Sound (Part 3)
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High Marsh - The Salt Meadow Cord-grass and Black Grass Belts
Moving up the intertidal slope, the Smooth Cord-grass gets a little shorter as elevation approaches mean high water. At or a
bit above this point, Smooth Cord-grass generally is replaced by the much shorter, fine stemmed Salt Meadow Cord-grass
(Spartina patens) on what is called the high marsh. Smooth Cord-grass often persists along the frequent mosquito ditches
dissecting the high marsh.. Shoots of Salt Meadow Cord-grass are often 30 to 50 centimeters long, but a weak spot at the
base of the stems lets them fall down, often forming large characteristic "cowlicks" by mid season (See front cover photo). Its
roots and rhizomes form a dense turf, out competing the intertidal Smooth Cord-grass at these higher, less frequently flooded,
elevations.
On natural levees which form along creeks and bay fronts, Salt Meadow Cord-grass may mix with or be replaced by Blackgrass (Juncus gerardii), which also is often found as a belt along the upper border. This grass-like rush, with a characteristically darker green color than Salt Meadow Grass, is also usually a bit taller and has less of a tendency to form cowlicks. One might say Blackgrass is "on the fast track." It starts spring growth in May, before the other high marsh plants, flowers in June and by the beginning of August is beginning to turn brown. The end of August finds most Blackgrass shoots dead or dying. On some marshes the Blackgrass belt near the upland has decreased in abundance over the last few decades, often being replaced by bare, algae-covered peat with occasional patches of Arrow-grass (Triglochin maritima) and other broad-leaved plants (see below). This phenomenon may be related to the recent increase in the rate of sea level rise, which is favoring marsh development landward.
A short form of Smooth Cord-grass frequently occurs in relatively pure stands in depressions on the high marsh. This stunted growth form is due to a complex of incompletely understood factors. Oxygen levels in the root zone of these stands are very low, and the soil salinities in such sites are high, often reaching up to 40 to 60 ppt by the end of August. These factors probably contribute to the distribution of Short Smooth Cord-grass on the high marsh as well as to its stunted condition.
Wiry, stiff, Spikegrass (Distichlis spicata) with its light green leaves is usually scattered within the high marsh meadow, but occasionally may occur in pure stands. It is the last of the grasses to flower in late summer, and is easily recognized by its terminal flowering spike. Spikegrass has a relatively high salt tolerance and can be found mixed with Short Smooth Cord-grass; it is also frequently found in patches or belts near the upland, often in wetter depressions.
Forbs, a group of plants which have more showy flowers and usually broader leaves than the grasses, frequently occur in slight depressions or pannes on the high marsh. They include Sea Lavender (Limonium nashii), Pink Gerardia (Gerardia maritima), Arrow-grass (Triglochin maritima), Seaside Plantain (Plantago maritima), and Saltmarsh Aster (Aster tenuifolius). Arrow-grass is not a grass but has long, grass-like leaves as does seaside plantain. These forbs may exhibit wide variation in their size and vigor depending upon site conditions. They are found both as occasional scattered plants within the expanses of dominant grasses or in relatively pure patches. When dominant, they indicate the site may have been subjected to disturbance.
It is not uncommon for the high marsh grasses to be killed in places by flotsam (floating debris) or other causes. Jointed Glasswort (Salicornia europaea) is often the first plant to colonize the newly opened sites. Two other species of Glassworts may be found on Connecticut salt marshes - Salicornia bigelovii, an annual, and S. virginica, a perennial. These succulent, cactus-like plants turn a brilliant red in autumn. Such open, annual dominated areas are usually colonized by Spikegrass or Stunted Smooth Cord-grass.
The high marsh is basically a terrestrial environment much of the time, but it is more or less regularly flooded by spring tides. Among the most characteristic invertebrates of the high marsh are the Saltmarsh Snail (Melampus bidentatus), the Saltmarsh Isopod (Philoscia vittata), and the Saltmarsh Amphipods (Orchestia grillus and O. uhler)(Fig. 6). These tiny animals are deposit feeders which ingest partly decomposed marsh grasses, algae and other material.
The Saltmarsh Snail is frequently a dominant member of the high marsh community and may occur at densities exceeding 1000/square meter. This is a pulmonate snail which has a lung-like respiratory organ adapted for aerial respiration. It is somewhat unique in that while leading a largely terrestrial existence, it possesses an aquatic larval stage. Egg-laying, hatching of the larvae into the water column, and subsequent settling of the larvae back onto the marsh occur during spring tides when at least portions of the high marsh are flooded. The larvae spend two or more weeks in the adjacent estuary where they feed on phytoplankton. Another pulmonate snail, Succinea wilsoni, may occur at the upland border of the marsh, as well as in brackish marsh. The isopods and amphipods of the high marsh are typically less abundant than the Saltmarsh Snail. Adult Philoscia and Orchestia grillus may reach densities of 20 to 100/square meter.
Other important invertebrates of the high marsh community are mites, spiders and insects. Spiders such as the Wolf Spider (Pardosa sp.), which are abundant on the marsh, are predators. Common insects of the marsh include Meadow Grasshoppers (Conocephalus sp.), Ground Crickets (Nemobius sp.), planthoppers, leafhoppers, aphids, Plant Bugs (Trigonotylus sp.), beetles, Greenhead Flies (Tabanus sp.) and Saltmarsh Mosquitoes (Aedes sollicitans). Of these, Plant Bugs are the only insect that is typically most abundant in the tall Cord-grass of the low marsh. The grasshoppers and crickets graze directly on the grasses of the high marsh meadows. Leafhoppers, planthoppers, aphids and Plant Bugs suck plant juices. Although these insects may be abundant, they consume relatively little plant material. Some beetles are plant or detritus feeders, whereas others prey on other insects. Greenhead Fly larvae, which are voracious predators, are found throughout the marsh. The Saltmarsh Mosquito breeds on the high marsh in shallow depressions which dry out and then reflood. Dragonflies and Praying Mantis are predatory insects that may also be present on the marsh.
The Meadow Vole (Microtus pennsylvanicus) is a frequent high marsh resident during the warmer months. This rodent feeds primarily on the stems of Salt Meadow Cord-grass and Spikegrass, but also on grass seeds during the dry summer. Voles cut down entire plants in order to eat the stems. Portions of the plants that are unconsumed enter the detrital cycle sooner than they would if voles were absent from the marsh. The voles make runways that crisscross the high marsh. Progressive deepening of the runways may contribute to the hummocky nature of some marshes.
Upper Border - The Marsh Elder/Switchgrass Belt
At the upland-marsh interface, Marsh Elder (Iva frutescens), a shrub typically 0.5 to 1.5 meters tall, may form a distinctive
belt (Fig. 1). Marsh Elder also grows on the locally elevated areas of the high marsh, especially along the banks of mosquito
ditches. Groundsel Tree (Baccharis halimifolia), when present, is found landward of Marsh Elder. It is really a shrub
growing from two to three meters in height.
Switchgrass (Panicum virgatum), an attractive grass from one to two meters tall, is also a resident of the upper border. Its clumps or tussocks sometimes form its own distinctive belt of vegetation. Another important plant in the upper border is Phragmites or Common Reed (Phragmites australis), a very tall (two to four meters) grass that forms dense, nearly pure stands. Its establishment is favored by disturbance or by fresh water runoff. Landward of the upper border, true upland soils and vegetation are present. A few high marsh animals, such as the Saltmarsh Snail, may also be found in the upper border; but species not usually found on the high marsh are also present. These include the snail, Succinea wilsoni, and the isopod, Porcellio sp.
Salt Marsh Birds
Birds are the most conspicuous animals of tidal marshes. Salt marsh birds include Ospreys, Herons, Egrets, Rails, Swans and
Ducks, to name a few. Some of these birds may nest in or near the marsh, whereas others visit the marsh primarily in search
of food.
The Osprey or Fish Hawk (Pandion haliaetus) hunts while in flight and dives feet first into the water to capture prey. It is able to plunge only about a meter below the surface of the water and therefore takes surface fish and those that occur in shallow water. Ospreys generally feed on fish that are between 25 and 35 centimeters in length. Winter Flounder constitutes about half of their diet during the breeding season, but almost any accessible fish of appropriate size may be eaten. Herring (Alosa aestivalis) and Menhaden (Brevoortia tyrannus) are taken in substantial quantities. Ospreys nest near the water on the tops of solitary trees, utility poles, nesting platforms erected in the marsh, and other similar structures.
Herons and Egrets are long-legged, long-necked wading birds that possess a long tapering bill. The Great Blue Heron (Ardea herodias), the Green-backed Heron (Butorides striatus), the Black-crowned Night Heron (Nycticorax nycticorax) and the Snowy Egret (Egretta thula) are common on southern New England marshes. These birds feed extensively on small fish but also prey on crabs and a variety of other animals. They employ several hunting strategies; 1) wait motionless and ready to strike at prey that comes within range; 2) stealthily stalk prey by slowly walking or wading with little disturbance of the water; and 3) make a disturbance and then actively pursue potential prey that are aroused. The Herons normally use the first two methods, whereas Snowy Egrets often employ the third as well. The Great Blue and Green-backed Herons are usually solitary feeders; Snowy Egrets and Black-crowned Night Herons sometimes feed in flocks. As the name implies, the Black-crowned Night Heron is a nocturnal forager, except during the breeding season when it hunts for food both day and night to feed its young. Green-backed Herons often nest in trees along the upland border of the marsh.
The Clapper Rail (Rallus longirostris) is a true marsh bird, being restricted to the salt marsh habitat. Its diet includes snails, small crabs and fish. Fiddler Crabs are a major food item. This rail may nest almost anywhere in the marsh, frequently on an elevated platform. Its grass and reed nests are occasionally washed away when storm tides flood the marsh to exceptional depths. Other marsh specialists include Marsh Wrens (Cistothorus palustris), Seaside Sparrows (Ammodramus maritimus) and Sharp-tailed Sparrows (Ammodramus caudacutus). Mute Swans (Cygnus olor), a European introduction, and ducks such as Mallards (Anas platyrhynchos), often feed in shallow water at the edge of the marsh. These birds may also nest in the marsh.
The Tidal Brackish Marsh Community
As previously mentioned, extensive tidal brackish and freshwater communities occur along major river systems like the
Connecticut (Fig. 7) and Housatonic where tidal action is still present despite low to undetectable salinities.
Fig. 7 Click on figure to see map of Connecticut River Tidal Wetlands (328K)
Smaller areas of brackish marsh are also common at the upper reaches of many smaller tidal rivers and inlets. As with salt marshes, each has characteristic zones defined by marsh elevation in relation to tidal inundation. In locations where average salinity is below 18 ppt, one can distinguish several tidal brackish communities, such as the short-meadow grass type and the taller reed marshes. The short-grass meadows of brackish high marshes are characterized by Smooth Cord-grass, Salt Meadow Cord-grass and Blackgrass (Fig 8). Common associates are Seaside Goldenrod (Solidago sempervirens), and Silverweed (Potentilla anserina) . Patches of Bulrushes such as Common Threesquare (Scirpus pungens) and Olney Threesquare (S. americanus) maybe present in addition to a diversity of other fresher water species including Bent Grass (Agrostis stolonifera v. palustris), Spike Rushes (Eleocharis palustris, E. rostellata), Straw Sedge (Carex straminea) Mock Bishop Weed (Ptilimnium capillaceum, a member of the carrot family), New York Aster (Aster novi-belgii) and Saltmarsh Fleabane (Pluchea purpurascens).
As salinity falls, taller reed marshes dominated by Narrow-leaved Cattail and Phragmites can form extensive stands with the latter growing several meters in height (Fig. 8).
Fig.8 A brackish marsh with a short-meadow grass community in front of a tall reed community
(Narrow-leaved Cattail with some Phragmites to the rear). (R. Rozsa). (109K)
Two colony forming sedges, Salt Marsh Bulrush (Scirpus robustus) and Olney Threesquare may also be associated with this community type. The low marsh zone is still dominated by Smooth Cord-grass, but that is gradually replaced by Common Three Square and Rough or Prairie Cord-grass (Spartina pectinata) as the salinity decreases. Several rare or uncommon plants may be found on the intertidal mud flat, including Mudwort (Limosella subulata, a member of the Snapdragon family) and a diminutive member of the carrot family, Lilaeopsis chinensis. Both of these plants have linear, grass-like leaves and grow less than 15 centimeters (six inches) in height. The showy and rare Golden Club (Orontium aquaticum), a relative of Jack-in-the-pulpit, also occurs here.
Since the late 1950s or early 1960s, Phragmites has been spreading into tidal wetlands of the lower Connecticut River system at an alarming rate (1 to 2 percent per year), converting the diverse natural plant communities into monocultures. The decline in plant species diversity and the possible loss of habitat for typical wetland animals are major concerns of wetland ecologists. Recent studies by Connecticut College faculty and students suggest that Phragmites dominated brackish marshes may be performing some of the same basic ecological functions as the uninvaded marshes. Rapid breakdown of Phragmites foliage yields detritus that apparently is consumed by the many marsh detritus feeders. These marshes support populations of typical invertebrates and birds, and provide foraging areas for fish (primarily Mummichogs) when the marsh surface is flooded by high tides.
It is important to note that those marshes studied are well flushed by tides. Marshes situated behind impoundments that restrict tidal flow may not be functioning in the same way. Furthermore, Phragmites on the marshes of the lower Connecticut River tends to form relatively narrow and somewhat discontinuous fringes along creek and river banks. Large expanses of continuous Phragmites marshland may provide less favorable habitat for many animals, including large marsh birds (herons, egrets and waterfowl). Generalizations about the effects of Phragmites invasion cannot be made with confidence based on our present state of knowledge. More studies are needed.
THE TIDAL FRESHWATER MARSH COMMUNITY
As the salinity decreases below the measurable level, one enters the very species rich tidal fresh water communities. Over 100 different kinds of higher plants have been recorded in this community compared to only about 36 in the brackish marsh and only 17 in salt marshes. This elevated species richness is primarily related to salt stress, which continues to decrease up river until salt is hardly detectable ( less than 0.5 ppt) in the tidal freshwater marsh. However, tidal action still operates and serves in a positive manner by helping to keep nutrients and oxygen available throughout the system. On the Connecticut River, freshwater tidal marshes are located north of Joshua Cover in Lyme and Post Cove in Essex.
Wild Rice (Zizania aquatica), a tall annual grass, is the indicator species on the lowest marsh sites, and its many associates include both grass-like and more showy broad-leaved flowering plants (Fig. 9).
Fig.9 A tidal freshwater marsh dominated by wild rice. (R. Rozsa) (104K)
The diversity of plants provides an interesting sequence of flowering activity with the perennials Pickerel Weed (Pontederia cordata), Water Arum (Peltandra virginica) and Bullhead-lily (Nuphar variegatum, a water-lily) especially showy in the low marsh during the early part of the growing season and the annuals Jewel Weed (Impatiens capensis), Common Bur-marigold (Bidens frondosa) and Smartweeds (Polygonum spp.) flowering in the summer. Other species on the high marsh are Reed Canary-grass (Phalaris arundinaceum) and Purple Loosestrife (Lythrum salicaria), a beautiful invasive introduced species which is rapidly increasing in many of our freshwater wetlands and crowding out our native flora. The tall River Bulrush (Scirpus fluviatilis) is a distinctive sedge found between the high and mid-marsh zones.
Animals of the Brackish and Freshwater Marsh Communities
These less salty tidal wetlands also support a diversity of animal life. Many invertebrates typical of salt marshes extend up
estuaries into brackish regions. For example, the Marsh Amphipod (Orchestia) and Marsh Isopod (Philoscia) occur in
marshes where the salinity of the water flooding the marsh is in the range of 1-13 ppt, but these crustaceans are not present in
freshwater tidal marshes. Although the Marsh Snail may exist in brackish marshes, its numbers rapidly decline with decreasing
salinity and it is progressively replaced by another pulmonate snail, Succinea. In freshwater tidal marshes, Oxyloma, a snail
closely related to Succinea, may be common, together with Limacid Slugs (Agriolimax laevis). In addition, small
pomatiopsid snails often are present in large numbers. Earthworms (lumbricid oligochaetes) may also occur in these
marshes. As in salt marshes, spiders and insects are important components of the high marsh community.
The Ribbed Mussel occurs along the lower edges of slightly brackish marshes, but generally is not found where the salinity of the water at high tide drops much below 10 ppt. Also, as the salinity declines, the Black Fiddler Crab becomes less abundant and is replaced by the larger Red-jointed Fiddler (Uca minax).
Some of the common salt marsh fishes, including Mummichogs and Silversides, occur in waters of low salinity, and Mummichogs are even present in fresh water. However, other species, such as the Striped Killifish, disappear as salinity declines, and still others, the Banded Killifish (Fundulus diaphanus), Pumpkinseed (Lepomis gibbosus), and Spottail Shiner (Notropis hudsonius) become more abundant. The latter two species are typical of brackish and freshwater marshes.
Bird studies in brackish and freshwater marshes along the Atlantic coast reveal that 280 species frequent these wetlands. This group includes 44 species of waterfowl, 35 rails and shore birds, 23 birds of prey and 15 species of waders. Wild Rice can cover extensive areas of the low marsh, and in the autumn its seeds are an important food source for neotropical migrants such as Red-winged Blackbirds (Agelaius phoeniceus) and other birds that travel to wintering grounds in Central and South America. Historically, these marshes also attracted large numbers of Sora Rail (Porzana carolina) in the autumn. In addition to most of the previously mentioned tidal marsh bird species, brackish and freshwater marshes are home to the Swamp Sparrow (Melospiza georgiana), the Belted Kingfisher (Megaceryle alcyon) and the Wood Duck (Aix sponsa).
SUGGESTED READING
Bertness, M.D. 1992. The Ecology of a New England Salt Marsh. American Scientist 80: 260-268.
Gleason, H.A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, NY. 910 pgs.
Kneib, R.T. 1986. The Role of Fundulus heteroclitus in Salt Marsh Trophic Dynamics. American Zoologist 26: 259-269.
Nichols, G.E. 1920. The Vegetation of Connecticut. VII. The Plant Associations of Depositing Areas Along the Seacoast. Bulletin of the Torrey Botanical Club 47:511-548.
Niering, W.A. and Warren, R.S. 1980. Vegetation Patterns and Processes in New England Salt Marshes. Bioscience 30(5):301-306.
Metzler, K.J. and R.W. Tiner, 1992. Wetlands of Connecticut. Connecticut Geologic and Natural History Survey, Report of Investigations No. 13. 114 pgs.
Birds of Connecticut Salt Marshes. Connecticut Arboretum Bulletin No. 27.
Plants and Animals of the Estuary. Connecticut Arboretum Bulletin No. 23.
Salt Marsh Plants of Connecticut . Connecticut Arboretum Bulletin No. 25.
Tidal Marsh Invertebrates of Connecticut. Connecticut Arboretum Bulletin No. 20.
A complete listing of Arboretum publications is located at the end of this Bulletin.
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