Cape Cod’s landscape is characterized by dozens of small kettle ponds formed by the receding glaciers thousands of years ago. In some instances the ocean has broken through creating a salt pond and allowing a salt marsh environment to form a ring around the pond. These ponds are subject to tidal changes and vary in salinity depending on their proximity to the ocean.
Some salt ponds, such as the one at Dowses Beach in Osterville, are connected by a narrow culvert to a bay or estuary. Others like the salt pond at the Cape Cod National Seashore Visitors Center in Eastham, are part of a large salt marsh system, in this case Nauset Marsh. In both of these examples salt marsh grasses (Spartina) support a large diversity of life in and outside the pond. When the grasses break apart and decompose into smaller detritus particles, these provide essential nutrients to many species of animals.
Mollusks are present throughout the system and are able to attach to the muddy substrate or the banks of the salt marsh. The surface of the sediments are populated by an army of mud snails (Ilyanassa obsoleta) that are feeding on bits of food. Ribbed mussels (Modiolus demissus) form dense clusters along the edges of the marsh. Quahogs (Mercenaria mercenaria) flourish in this environment and there are aquacultural rafts of quahogs growing in the Eastham salt pond. Moon snails (Lunatia heros) are common predators on clams attacking them with their sharp radula.
Many crab species can be found in this ecosystem also. Blue crabs (Callinectes sapidus) congregate near the entrance to the salt pond at Dowses Beach. Spider crabs (Libinia emarginata) favor the muddy substrate as an effective environment for camouflage. And the omnipresent green crab (Carcinus maenas) has invasive tendencies and is a significant predator of commercial shellfish.
Because many salt ponds are shallow and are located near highways and developed areas, they tend to concentrate nutrients from runoff and other sources. Consequently algae blooms can form where nitrogen loading is an issue. This can have a negative effect on any eel grass (Zostera marina) or animal populations. A salt pond can quickly become eutrophied particularly during the warm summer months.
Salt ponds represent a successional change in which a freshwater system becomes marine after a breakthrough or change in the dynamic coastal environment. Fluctuations in the physical environment are accompanied by changes in species structure and diversity.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.