Down in the cold waters of Smitty's Cove, a concrete paradise is being built for some of Alaska's most unusual creatures. It took less than 24 hours before some of them started checking out the new real estate _ the state's first artificial reef.

"There were two sunstars ... already glommed onto the structure, just checking them out I'm sure. And there were a couple of copper rockfish swimming among them," said Brian Lance, a federal fisheries biologist.

The reef was installed this week to provide a haven for small plants and fish near Whittier, where barges stacked high with containers bring everything from road graders to toilet paper into one of Alaska's busiest ports.

The federal government required Alaska Marine Lines to mitigate damage the shipping company caused to marine habitat when it filled in tidal waters as part of its container facility expansion last year.

The expansion, which disturbed a little less than an acre (0.4 hectares), forced baby fish into deeper water where they are more vulnerable to being eaten.

The roughly US$100,000 (£á77,000) reef project involves two types of structures _ one built with about 100 concrete pyramids and the other with about 100 concrete balls said Lance.

The reef balls are hollow so small fish can use them to hide from larger fish. They have holes that create mini-whirlpools to help mix the water column, and are thick on the bottom and thin at the top so they won't tip in stormy seas. A rough exterior encourages algae growth.

The pyramid fish havens work on the same premise.

A crane was used to lift the reef balls and fish havens off a barge and submerge them 50 feet (15 meters) down in the cove.

The two reef styles were installed side-by-side so researchers can compare how well each works in coastal Alaska waters. Both the balls and the pyramids have been used successfully in more southern waters, but it is uncertain how well they will work off Alaska's coast.

Lance is optimistic. "Fish and invertebrates will start using it pretty quick," he said.

Reef balls have been used successfully all over the world, including cold Canadian waters, said Todd Barber, chairman of the Reef Ball Foundation, an Athens, Georgia-based nonprofit group.

Barber said the structures typically fill in two weeks with fish that normally show up to fight. Once their territorial disputes are settled, the fish leave, with the winners returning later.

"After a full season of growth, whoever won the fight before takes it over as its new home," Barber said.

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On the Net:

http://www.reefball.org

http://www.artificialreefs.com