Sandbox at bottom of ocean is an ecological playground


A great deal of research has been done on coral reef ecosystems, but there have been few studies on the sandy bottoms they cover — until now.

scocking@ MiamiHerald.com

For years, Florida resources managers have touted natural and artificial reefs as ecological powerhouses while treating the sand bottom surrounding them like poop. The assumption is that reefs — both coral and manmade — are complex structures while sand is basically worthless since it comes from the waste products of fish.

But a scientist at Nova Southeastern University Oceanographic Center is challenging that premise in a first-of-its-kind, two-year study in the ocean off Fort Lauderdale.

Adjunct professor Amy Hirons and four of her graduate students, assisted by Ken Banks of Broward County’s natural resources planning and management division, are looking into the role that sand bottom plays in the food chain of reefs. What they learn could help guide the placement of future artificial reefs, such as ships and boulders, intended as havens for fish and other marine creatures.

“A lot of money is spent constructing artificial reefs,” Hirons said. “You’re changing an environment. These items are being placed in a sandy environment on the assumption out of sight, out of mind. But there’s all kinds of invertebrates living there. This is our first real stab at figuring out what kind of community artificial reefs are creating.”

The researchers are collecting samples of bottom-dwelling invertebrates such as worms and crustaceans and counting fish at eight different sites. Four are piles of limestone boulders that were deployed about 45 feet deep on sandy bottom in 2009.

The other four sites are split between the inshore reef tract about 20 feet deep and the middle reef in about 45 feet of water.

Hirons said she would like to get a permit to collect fish at each site and study the gut contents.

“We’re trying to figure out who’s eating who,” she said.

Finding the answer is important because reef fish don’t necessarily eat the other creatures that live on the sunken ship or coral patch. For example, recreationally and commercially important species such as mutton snapper and hogfish forage in the sandy bottom outside the reef structure. So putting an artificial reef there might not be beneficial.

“We may be creating surface areas for [bottom] organisms, but if the target is recreational fishing, it may not be productive,” Hirons said. “It may not be habitat.”

Banks, who heads Broward’s artificial reef program, is looking forward to the study’s outcome as a tool to help determine where to sink ships and other structures.

In mitigation projects where artificial reefs are deployed to compensate for damage done to the marine environment, Banks said the aim is to create something that functions the same way ecologically as the natural habitat.

“While [artificial reefs] may attract more fish than natural reefs, you’re not trying to attract more fish,” he said. “You’re trying to make it as similar to the damaged reef as you can. For mitigation, we might find instead of acres of artificial reefs, you may need patches of sand.”

As for structures deployed as fishing and diving havens to ease pressure on coral reefs, Banks said “if you put the ship too close to the reef, you could be stealing resources from the reef. This helps us on where we’re going to put them.”

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