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Summer beach safari: What’s in that brown, dried seaweed on the beach?

Backyard Safari

Wednesday, July 25, 2012

Media contact: Jessica Basham Therriault

What is that dark green or brown stuff all over the beach?

The material, usually in a line where the waves roll in, is known as beach wrack.

When first setting eyes on wrack, you may think it is only dried, dying seaweed. But it is very much alive and filled with sea organisms that are essential to beach life and the creatures that live there.

Marine organisms that wash up with this wrack are an important part of a beach ecosystem. Tiny crabs, sea cucumbers, seeds and pods are only a few of the things you can find in wrack.

Once, while walking the shore at Bahia Honda State Park in the Florida Keys, I found a brown hamburger bean. That’s right, a hamburger bean! It is circular in shape, like a marble, with a thick brown or black line that goes around its center. On each side of the thick line the color is a lighter brown, making it look like a hamburger bun. These little beans are from tropical rain forests and are native to the West Indies and western Africa. Can you believe the things we find on Florida beaches travel that far?

Another neat little treasure I found in beach wrack was on St. Augustine Beach just a few weeks ago. While pushing my toes through the wrack I spotted a purse crab. These crabs get their name because female purse crabs have a purse-like chamber for holding their eggs. The little crabs live in shallow, sandy environments like beaches and are often found washed ashore in wrack.

Beach wrack eventually gets pushed high on shore because of the tides. When the tides go out, the grasses start to dry and die. Dying grasses bring all sorts of life to the beach. As the grasses die, fungi and other organisms attract tiny species like beetles, beach hoppers, ghost crabs and more. These small insects and crabs become food for shorebirds. Dunlin sandpipers and other shorebirds migrate thousands of miles a year and depend on wrack during their journey for food. Without wrack and the organisms that live in it, the birds can die.

Not only can you find neat sea critters, shells, seeds and birds near beach wrack, but wrack is also the first stage in forming sand dunes. Sand dunes are natural barriers against wind and water, and prevent erosion. They form when wrack starts to collect blowing sand. As sand and other plant material collect in the wrack, the plant material can start to sprout and root. This continual process is how dunes form.

So now you know that beach wrack isn’t just icky seaweed that sits on the shore; it is a beautiful ecosystem important to the beach and beach life, as well as a place for unique finds and hours of curiosity. Have fun searching the wrack!



FWC Facts:
Adult white-tailed deer in Florida average 125 lbs. for bucks, 95 lbs. for does. The Key deer subspecies is noticeably smaller, averaging just 27 in. tall and 55-70 lbs.

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