Blog Post: The Wrack Line
Wrack is the mixture of seaweed, eelgrass and other dead material that washes up on sandy and rocky beaches. This mixture of plant and algae usually marks the high tide line on a beach and is also known as the ‘wrack line’. As this material starts to break down and decompose, it might smell unpleasant for us, but it attracts thousands of small invertebrates like flies and amphipods. The top of the wrack may start to dry in the sun and the eelgrass and algae will turn brittle, but if you lift this top layer you will find that moisture is retained underneath. This creates an important microhabitat for many species of invertebrates to feed and reproduce in. In turn, these invertebrates provide a critical source of food for shorebirds.
Eelgrass and seaweed wrack, Photo by Emily Bodell
In the spring, some species of shorebird, like Black-bellied Plovers, Semipalmated Sandpipers and Ruddy Turnstones, stop on Fishers Island as they migrate from South America to the Arctic to nest. The invertebrates living in the wrack provide an important energy source for these birds making incredibly long journeys. In the fall, some of the same species leave the Arctic and stop on our beaches on their way back to South and Central American for the winter. Many of these shorebirds have brown, gray and black feathers on their backs and wings that make them almost invisible while they forage in the wrack. You might not notice them until you take a closer look! Other species of bird that forage in the wrack line include Song Sparrows, Kingbirds and warblers.
Black-bellied Plover, Pluvialis squatarola Photo by Connor Jones
Ospreys commonly use eelgrass and other wrack materials to line their nests. The male Osprey generally collects the nesting material and delivers it to the nest where the female puts it in place. When you are at the beach or near a nest, keep an eye out for Ospreys and try and spot what they are carrying in their talons! This time of year (June-July) Osprey start hatching, and the adults will be working hard to constantly supply their growing young with fish.
Osprey pair, Pandion haliaetus Photo by Connor Jones
Healthy eelgrass meadows along our shores ensure that there is a constant supply of material for the wrack line. Throughout the year, some of the eelgrass will naturally die off and get washed ashore. Big storms will also deposit eelgrass on the beach as large waves rip some the plants and blades out of the sand. A decrease in the size of eelgrass meadows may lead to a decrease in the amount of wrack on the shore. This in turn can leave many of the birds that visit Fishers Island with a less than abundant supply of food and nesting material.
For more information on the eelgrass that surrounds Fishers Island, contact FISM coordinator Connor Jones at fishersislandseagrass@gmail.com.
