Fringe Corals – Wetlands at the Outer Edge

Fringe. It’s the outer edge. Peripheral. Fringe, or fringing, reefs are connected to land and point toward sea; they occur in shallow water along coasts all over the world. Some wetlands are the boundary between land and deep water habitat; fringing corals fall into this group. Corals form in shallow, warm salt water habitats, usually tropical waters. Thousands of hard coral polyps grow together in masses and create a reef, whereas soft corals, like sea fans, do not form reefs. Fringe corals are similar to fringe mangrove ecosystems in that they grow at the edges of the land; sometimes the fringe coral and mangroves are neighbors in a closely-entwined habitat that provides a nursery for many marine animals. What lives in a fringe coral reef? Brittle stars, horseshoe crabs, sea anemone, sea urchins, snails and mollusks inhabit this strange ecosystem.

Darwin asserted that fringe reefs were the first kind of coral reef to form around a landmass in a long-term reef growth process. Until 1753, people did not know that corals were living organisms. Darwin’s Subsidence Theory, which focused on fringing reefs as an explanation for atolls and barrier reefs in the deep ocean, (aka the“coral reef theory”) is still the basis for the understanding of coral reefs today.

Fringe coral communities are unusual. For instance, finger coral (Porites furcata) and coralline algae grow interspersed with sea grasses in less than one foot of water. The two types of coral reefs that are most commonly known—atolls and barrier reefs—live in deep ocean water. Sponges, echinoderms, crustaceans and mollusks may also be found living in the fragile habitat of fringe corals, which are easily damaged by boats that drop anchor or people who walk on them.

Right now marine scientists are calling a “code blue” on coral reefs worldwide. Fringe reefs are threatened by coastal development, dredging and run-off, while all types of corals are stressed by warming sea temperatures as a result of climate change, a phenomenon called “coral bleaching.” The warming sea temperatures kill the algae that give the corals their color. Another problem is acidification of sea water, caused by run-off, certain algae and pollution from dredging or other human activities. Sediment discharge from coastal development can have a very negative impact on coastal wetlands including fringe reefs and mangroves.

In southwest Florida, the Department of Environmental Protection is currently dealing with enforcement issues on a boat lift in a canal, which city developers dredged to build Cape Coral the 1970s. The city developers dredged the canal through fringe mangroves. The original design of the canal allowed the fresh waters to be trapped and prevented that water from flowing into the saltwater estuaries of Matlacha Pass Aquatic Preserve. The preserve is home to four species of sea grasses, three species of mangroves, over 100 species of invertebrates, 200 species of fish and 150 species of shore and wading birds. The barrier lift protected the saltwater mangrove habitat and preserve. In the 2000s, the city developers removed the lift, initially with the intention of replacing it—but several years after-the-fact, there is still no barrier lift protecting the estuary.–votes-being-tallied-on-Cape-spreader-barrier.html?nav=5048

Hawaii’s Conservation Resource Enhancement Program’s strategy involves converting marginal pastureland into native grasses and wetlands. The state seeks to improve water quality and near-shore coral reef (fringe coral) communities by filtering agricultural run-off.
 Additionally the Hawaii Department of Land and Natural Resources has identified a way to use sea urchins to manage invasive algae in coral reefs. State aquatic biologists vacuumed the invasive seaweed off the coral with a “Super Sucker,” and have planted sea urchins to take on the job of eating the seaweed. For pictures, go here: Besides invasive algae, two other threats to coral reefs are hurricanes and overfishing, which have an impact on all types of reefs.

Other interesting links on coral reefs can be found below:

EPA Office of Wetlands & Oceans:

A Return to the Reefs: Smithsonian article by Gordon Chaplin (2006) on the Global Coral Reef Monitoring Network

Coastal Living Habitats:

Wetlands International – Coastal Wetlands (Coral reefs, mangroves, sand dunes, beaches)

Florida DEP coral reefs

Florida’s Coupon Bright Aquatic Preserve

Reef Check (a nonprofit organization)

Code Blue: A possible new coral reef in the Sargasso Sea? – Sylvia Earle’s research (2010),28804,2020806_2020805_2020

NOAA’s Coral Reef Conservation Program

Coral reefs in a climate change context – Climate Change Impacts on the United States
The Potential Consequences of Climate Variability and Change (2000)


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