One of the more interesting marine habitats is found on pilings at docks and piers. Plants and animals exhibit a vertical zonation or distribution on the piling particularly after several years of colonization. There are also several species that are frequently found here, but are absent from other habitats.
Several species of algae can be found attached to a piling. The dominant alga is usually sea lettuce (Ulva lactuca), consisting of large green sheets that often fold along the edges. Sea lettuce is tolerant to changes in salinity and grows abundantly in areas with high nitrogen runoff.
Another common alga growing on pilings on Cape Cod is Irish moss (Chondrus crispus). This has historically been an economically important edible seaweed. Irish moss is a deeply red to purple alga with many flat blades up to four inches long.
Interspersed among the fronds of the seaweed are several interesting animals. A tunicate called a sea vase (Ciona intestinalis) is one of the most common. This vase-shaped filter feeding animal is nearly transparent and grows in large concentrations along the piling. Its body is soft and thin and contains retractable siphons for feeding. This animal also has a notochord, a supportive structure made of cartilage.
Clumps of hydroids called Tubularia spp. are also attached to the pilings. Sometimes these animals are mistakenly believed to be algae, but a close look reveals several stem-like structures capped with pinkish polyps. Underwater they appear to be small colonies of pink flowers. However these polyps have tentacles used to capture prey. This group of animals also attach to the bottom of boats.
Scattered throughout the piling are colonies of rock barnacles (Semibalanus balanoides). The larval stage of this crustacean is planktonic. Once it settles on a surface the adult can grow up to one inch long. These animals are also filter feeders and use their tiny feet to capture food particles while waving through the water.
Feeding on the barnacles are several spider crabs (Libinia emarginata) that scurry up and down the piling. This crab has a brown carapace and long, spindly legs. Spider crabs have excellent camouflage and are often seen with other animals and algae attached to their shell.
A piling may also harbor other species including sponges, sea anemones, mussels, oyster drills, and bryozoans. This habitat is stationary with a relatively constant physical environment. Over time the entire piling will be covered with an impressive assortment of marine species.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.