Did you know that shells have terrestrial homes?
If we posed the question “Where do mollusks live,” for most interviewees the first habitat that would come to mind is the beach, but many species of mollusks call other environments, like mangrove forests/swamps, home.
Mangroves are shrubs and trees that grow in coastal habitats with a high degree of salinity. The plant life found in mangroves is quite diverse as the vegetation has made physiological adaptations to overcome the high salt content and the frequency, duration, and depth of water reaching the plain of tidal marshes. Mangrove trees are also important because they help make new land.
Florida has some of the world’s largest mangrove forest. It serves as a nursery for billions of young forms of sea creatures which migrate to our offshore waters. Mangrove trees protect the shoreline from erosion caused by storm surges or hurricanes. The immense root system disperses the wave action and slows down the tidal water so that sediment can be deposited, making new land.
The intricate mesh of roots encourages the deposit of silt and mud which gradually builds up to make new land surfaces. These tidewater habitats harbor many forms of sea life, especially larval stages of fish, crustaceans, and mollusks.
In areas of the mangrove forest where roots are submerged all of the time, a habitat is provided for algae, barnacles, oysters, and sponges. These species need hard surfaces to anchor to as they filter water to obtain the nutrients they need to survive. Shrimp and mud lobsters make their home on the muddy bottom of the mangroves. Mangrove crabs actually mulch leaves. This adds nutrients to the mud that are important to the bottom feeders. Angulate periwinkles live on the upper branches.
There are about 110 mangrove species. The three most common species on Sanibel are the red, black, and white mangrove. The long spike-like seeds germinate while still attached to the parent tree. At first seedlings of the red mangrove float horizontally, but later tilt vertically, producing roots and a new tree in soft mud.
Mangrove bark is rich in tanic acid which prevents teredo ship worms, a kind of bivalve mollusk, from attacking the roots.
Some of the larger mollusks found in mangrove areas during low tide are the true and banded tulip, horse conch, crown conch, lightning whelk, and eastern oyster. Kayaking provides an effective means of observing mollusks in mangrove areas. However, please remember that Florida law protects mangrove environments.
Mangroves are important to bird life as well. Shorebirds like plovers and sandpipers feed in the shallow water and mud flats exposed by low tides. Herons, bitterns, egrets, spoonbills, and ibis are wading birds that search for food in the deeper water. Over 20 species of ducks call the mangroves home. Some of these species are year-around residents while others just visit during migration or stay for just the winter. Some birds of prey are permanent visitors while others are seasonal. Bald eagles, osprey, and peregrine falcons are frequent mangrove visitors.
To learn more about the mangroves visit the Shell Museum’s mangrove exhibit.