The shoreline of Cape Cod Bay from Sandwich to Provincetown is rich in the diversity of marine plants and animals. Most of these species have washed up on the numerous sandy beaches, but several may live embedded in the hostile intertidal zone, or attached to the many rocks and jetties in front of the beaches. Bring your field guides, a hand lens, and a camera to effectively explore these various habitats. You may be surprised what you will find.
Any exploration starts with the plants, or more accurately in this case, the algae. Commonly called the seaweeds, the marine algae are divided into three main groups based on their pigments: green, brown, and red. Depending on the time of the year, you may encounter several different species that vary in shape and size. Green sea lettuce (Ulva lactuca) may be found in large sheets, or maybe you will see the notorious and invasive green fleece (Codium fragile) which can grow on scallops and other shellfish in large quantities. Attached to rocks and jetties will be the brown rockweed (Fucus vesiculosus), determined by its presence of air bladders along the branches. The red algae may be represented by several bright and attractive species, including the edible Irish moss (Chondrus crispus), or the pervasive filamentous Polysiphonia.
The most common find will be the different sea shells along the shore. Many of these species are recognized because of the economic significance. Others are important ecologically, and frequently wash up in enormous numbers. The popular and edible quahog (Mercenaria mercenaria) can be easily identified by its thick shell and purple coloration on the inside. If you see something squirting at you from the substrate, it could be the soft-shelled clam (Mya arenaria), or steamer. It points its siphon upwards for feeding while remaining firmly attached to the substrate with a strong foot. Long, cylindrical razor clams (Ensis directus) are often found on mud flats. If you examine the banks on the extensive marshes around the bay you will find a group of ribbed mussels (Modiolus demissus) embedded in the mud.
Another common group of animals are the crustaceans which includes crabs and shrimp. Usually you can only find a piece of one of these animals as they are often the victims of larger predators, such as gulls. The perfectly camouflaged spider crab (Libinia emarginata) may be concealed by a colony of algae, bryozoans, and sponges glued to its shell, or carapace. Be careful if you see a live blue crab (Callinectes sapidus). They can pinch, and need to be handled with extreme care. In the salt marsh, you may see the substrate riddled with small holes which are the homes of the important fiddler crab (Uca pugnax). These small animals aerate and fertilize the marsh, and are a major food source for other animals. By the way, the male is the one with the large claw.
Of course one animal that may be seen is commonly mistaken as a crab, and that is the horseshoe crab (Limulus polyphemus). This animal is more closely related to arachnids, such as spiders and ticks. It evolved millions of years ago, and today is known for its contributions to medical science. Harmless to you, it feeds mainly on worms and clams.
Cape Cod Bay is home to many other important plant and animal species as well. Take your time exploring the various habitats, including the sandy beaches, the salt marshes, the mud flats, and the dunes. Look carefully under rocks and clumps of seaweeds. Examine the surfaces of shells and crabs with a hand lens. You will find a fascinating and interesting world of marine life along this valuable shore.