Newspaper article The Florida Times Union

A Light under the Dock River Grass Illuminated by Prisms

Newspaper article The Florida Times Union

A Light under the Dock River Grass Illuminated by Prisms

Article excerpt

Scientists trying to save fish populations in the murky St. Johns River have stumbled over a bright idea from a 19th century shipbuilder.

Ultimately, it could end up on scores of new docks in Northeast Florida.

The idea is to harness the light-bending power of glass prisms to illuminate dark areas, including the undersides of docks.

That modest goal could help sustain underwater grass beds that have been dying in the St. Johns for lack of light. The grass beds are the main refuge of tiny crabs and small fish, and are the base of the food chain for the entire river. Manatees also feed off the grass.

The ecological damage is serious enough that federal agencies are experimenting with new grass-protecting regulations that would require many docks to be narrower, taller or more expensive to build. But researchers at the St. Johns River Water Management District want to see whether they can accomplish the same end with less trouble by installing prisms in conventional docks to catch and redirect sunlight.

"The idea was, let's put light under the dock. Let's move the light, not the dock," said John Burns, a water management biologist who got the idea from a prism he saw at a lighthouse souvenir shop in North Carolina.

A study to measure the light's effects on grass under docks started two months ago off Bayard Point in Clay County, said Alicia McKinney, an environmental scientist managing the study. Contractors cut holes about every 18 inches and mounted the glass flush with the deck.

This is the first detailed study of light and grass growth around docks in a dark river like the St. Johns, McKinney said.

Whaling ships, loaded with flammable whale oil, used prisms in the 19th century to steer light below decks without burning lanterns. The palm-sized glass Burns saw was a replica of one from a whaler at Connecticut's Mystic Seaport, a historic tourist attraction. …

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