Each species has its own particular requirements in a dynamic and changing system that is influenced by season, tides, and other aspects of the Marshlands environment. In turn, each species has an effect on the habitat in which it lives, for example, by creating shade or increasing the amount of oxygen in the water. Each species is part of one or more food chains that comprise food webs. Interactions among organisms may be complex, as are the links between wetlands and adjacent uplands.
Marshlands inhabitants respond in myriad ways to the seasonal environment found here and each has its own seasonal pattern. There are the well-known migrations of song birds, such as warblers and thrushes, that use the Marshlands as a refueling place as they travel north to nesting grounds in the spring and return to wintering grounds in autumn. However, not all birds nest in spring; Great Horned Owls begin to nest in late January. Insects don’t all appear at the same time; there are early and late butterflies (e.g., Mourning Cloaks and Monarchs) and dragonflies (Jewelwings and Meadowhawks).
Seasonal behavior can also be seen in plants. Flowering is the most conspicuous behavior with species flowering in early spring (e.g., Red Maple, Skunk Cabbage), summer (Buttonbush, Swamp Rose Mallow, milkweeds), autumn (Bur Marigold, asters), or even winter (Witch-hazel). Other plant activities also tend to be seasonal. Seed and fruit production in late summer and autumn corresponds with the intense feeding of blackbirds and other migrants as they prepare for their journey.
Interactions may be local or wider in scope. In the tidal marsh, large quantities of plant material are produced during the growing season. Animals, for example Canada Geese, Muskrats, Red-winged Blackbirds, Wood Ducks, and insects, directly eat some plant material. The rest is partially decomposed; the resulting particles are colonized by fungi and bacteria, and then float away as nutritious detritus. This is the basis of important aquatic food chains that support oysters, clams, and many fish species in the Delaware River and Bay.
At the landscape level, there are intimate links between wetlands and the surrounding uplands. Rainwater from uplands can drain into the wetlands carrying sediment and dissolved nutrients. Water can seasonally moderate the temperature of the surrounding land, because of its ability to absorb or release heat.
There are wetland-upland links. Animals like turtles that live in ponds and tidal areas of the Marshlands need upland habitats to lay eggs. Similarly, Great Blue Herons and Green Herons feed on fish, but build nests in nearby woods, and Kingfishers feed on fish, but dig tunnel nests into the banks of the bluffs along Crosswicks Creek. Crows and robins feed on the mudflats of Watson’s Creek and nest in trees and shrubs. Ground-nesting bees and certain butterflies, important pollinators of wetland plants, also cross boundaries. Ground-nesting bees make their nests in upland soils and Tiger Swallowtail caterpillars feed on Tulip Tree leaves. Mammals also are far ranging. Foxes that prey on frogs have dens in uplands and raccoons that regularly eat mollusks forage seasonally for berries in uplands.
These wetlands also provide important services for nearby human inhabitants. In addition to providing open space for recreation, the Marshlands purify drinking water by removing pollutants. During floods, the marshes, swamps, and floodplains along Crosswicks Creek and the Delaware River temporarily store excess water from their watersheds, as well as from the municipal storm drains of Hamilton Township, Trenton, Bordentown Township, and Bordentown City. The stored water is released slowly, which reduces erosion and minimizes flood damage to nearby residential and business districts. In addition, wetlands help replenish groundwater that supplies local municipalities with drinking water.
Marsh ecology can be considered at the level of individual organisms, populations, communities, ecosystems, and the biosphere. Regardless of how a visitor views or studies the Marshlands, it is an invaluable resource to all. Even a brief walk along Marshlands trails or a canoe trip along Crosswicks Creek can provide a glimpse of the rich tapestry that makes the Marshlands such a vibrant special place.