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More and more commonly in the seawater of Woods Hole and all over Cape Cod, people are finding a warty, short-stalked ascidian growing attached to docks, floats, and pilings in protected coastal waters. recently it has been collected off MBL floats in Eel Pond, and in Hadley's Harbor on Naushon Island. It has also been found in the Canal and in Cape Cod Bay by collectors from the Cape Cod Museum of Natural History in Brewster.

Styela clava (Herdman, 1881) is gradually invading all the salt waters of the world from what seems to have been an Asiatic origin. The sea squirt was probably introduced into Californian waters in the later 1920's. For a while it was confused with and mis-identified as other native species. It could have come to the east coast on the bottoms of boats that passed through the Panama Canal from California, but this origin would not readily explain its virtually worldide sudden appearance in the north and south temperate zones.

Reportedly common off the coasts of Korea and Japan throughout the 1900s, S. clava , may have spread via the vast tonnage of worldwide military shipping during the Korean War. In 1976 a new record was reported for the southern hemisphere occurance of S. clava in Hobson's Bay, Victoria. In 1978 both an Australian and a Frenchman reported S. clava as a new species for their areas. Records from the south coast of England show S. clava from as early as 1953. In Holland it was found in 1975, in southern Ireland in 1973. It does not seem to like the colder waters of northern New England, Scotland, or Norway. It does however, seem to be able to withstand lowered salinities and can invade brackish bays and marshes.

In 1980 Buzier (in the Bull. Zool. Mus., Univ. Amsterdam) described its development in Holland as explosive. Other writers have shared his amazement at how fast this leathery sea squirt multiplies once it gets into an area.

In 1981 S. clava was reported in Danish waters where it was found attached to ropes and on oyster and mussel shells. Danish investigators theorized that S. clava came into Danish waters attached to ships or to imported oysters planted in local beds. the premetamorphic life expenctancy of the planktonic larva is so short (less than 24 hours) that it probably did not spread in that form.

The ascidian has occasionally been used in embyological research (Willam Jeffery has used S. clava at the MBL) Shellfishermen, however, consider S. clava a pest because it fouls mussels and other shells. While it does not kill shellfish, it makes them very difficult to clean.

A report was filed by Gray Museum assistant Ellie Prosser Armstrong, From the Collecting Net Vol. 4 Number 4 (July 1986), The Marine Biological Laboratory

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David Remsen
Specimen competely covered by Botrylloides, another introduced species. Yellow bushy growth is Bugula.

David Remsen
Whole specimen on dark background.
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