Stop 10: Wrack Lines at the Beach
Walk The Trail:
Map of Nature Trail

Tides strand the remains of marine creatures in wrack lines on the beach (see blue arrows).

 
wrack lines on the beach
 

The height of the tide determines the location of the wrack line. This height depends on the gravitational pull of the moon and the sun which is determined by where the tide is in its monthly cycle, the strength of the onshore winds, and the slope of the beach.

 

How many wrack lines can you see in the photograph above? How many can you find in the one below? Both were taken at the beach near the field station.

 
more wrack lines on the beach
 
You can walk along the wrack lines at any beach and look for marine animals and plants. Some of what you'll find here at the field station include:
  • Jingle shells, the remains of a clam (Anomia simplex), so named because they jingle when you drop them on the rocks. When alive, the jingle shell clam attaches by a short stalk to a rock or other hard surface, and eats tiny organisms that it filters from the water. People often place several shells onto a string, since they come in many pretty colors and make a nice sound when the wind stirs them. The lower valve - where the stalk came through - provides a convenient hole for the string!
  • Horsheshoe crabs (Limulus polyphemus), large crustaceans that are considered "living fossils". These invertebrates live in Nantucket Harbor, and come in large numbers to Folger's Marsh to lay eggs in the spring. The bodies of today's horseshoe crabs are nearly the same as the bodies of their ancestors from a million years ago. The largest ones are females; males are smaller and have one pair of legs at the front end (the non-spiky end) that is modified for grasping the female shell during mating.
  • Sediment-dwelling clams, including the kind you find in local restaurants. New England is famous for its seafood, and before European colonists and summer tourists came to Nantucket, native Americans would summer here to enjoy the abundant food in the harbor. Today, we still eat two bivalves that bury themselves deep in the sand and use siphons to strain tiny animals out of the water above them. The thick-shelled clam used by Indians to make wampum is known in New England as a quahog ("ko-hog")(Venus mercenaria); the soft-shelled clam is usually referred to as a steamer ("stee-muh") (Mya arenaria).
  • Egg cases from snails known as whelks. The cases look like a series of parchmentlike plates on a string; plates of the knobbed whelk (Busycon carica) have flat edges and plates of the channeled whelk (Busycon canaliculatum) have sharp edges. If you cut open the plates, you'll find tiny, perfectly formed snail shells inside.

You can see a whole photo album full of sea shells and ocean creatures found at the field station by going here.

 
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Back to the start of the trail Harbor and Barrier Spit Stop 3: Beach Erosion The Ospreys Mowing and Succession Stop 6: How Plants Reproduce The Tangled Web of Vines Plants by the Pond Hidden Treasures at the Pond Wrack Lines at the Beach Folger's Salt Marsh

     The Nantucket Field Station Virtual Nature Trail is a joint effort of the following departments: Biology, Computer Science, Earth & Geographic Sciences, and ECOS. UMass Boston Home Page

     All images are (c) the photographers or UMB and may not be reproduced without permission.