Northern Star Coral

Astrangia danae

Corals are small animals that attach to each other to form colonies. Each animal takes calcium carbonate from the seawater to form a hard skeleton which is attached to its neighbor. Overtime as the animals died new coral polyps grow on top of the old.

Northern Star Coral is the only species of coral to be found in the mid-atlantic region. It attaches itself to stones, old shells and other smooth objects where it grows to 4 inches in height. The Northern Star Coral does not form massive reefs as many coral species do in subtropical and tropical regions.

Northern Star Coral - Assateaque Island

Northern Star Coral welded to an old shell. The many small holes in the shell are caused by boring sponges. Above right: closeup of coral structure.

Boring Sponge

Cliona Celata

Boring Sponges are animals that tunnel into old shells, limestone and sometime living oysters. They have an appearance of a sulfurous yellow mass up to 6 inches high. Using chemicals produced by their bodies they absorb the calcium containing material leaving the object honeycombed with numerous tunnels 1 - 1.5 mm in diameter.

Shell eroded by a boring sponge - Assateaque Island

Oyster shell showing signs of occupation by a boring sponge.

Carnation Worms

Hydroides dianthus

Carnation worms tubes - Assateaque State Park, MD

Carnation worms affix themselves to shells as well as each other. They feed in much the same way as barnacles using feathery filaments to take passing food.


Layers of sediment trapped by algae became cemented together to form this object.

 - Chincoteaque National Wildlife Refuge

Calcareous Algae

Phymatolithon laevigatum

Calcareous alga on a stone

Calcareous Algae creates a chalky deposit on objects lying on the sea floor such as stones and shells.

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