USGS Research on Atlantic Coral Reefs: Are They Building or Crumbling?

(A) A reef dominated by reef-building elkhorn and brain corals, Great Exuma, Bahamas; (B) one covered by non-reef-building fire coral and fleshy seaweed, St. Thomas, U.S. Virgin Islands. USGS.

Why reefs matter

Coral reefs are massive structures built by living organisms. They protect coasts from hurricanes and tsunamis, supply beach sand as they erode, support tourism and recreation, and provide habitat for fisheries. Their worldwide decline is well documented — and understanding why requires coordinated science on the physical and biological processes at work.

The CREST project

The USGS Coral Reef Ecosystem Studies (CREST) project combines geology, biology and geochemistry to study the processes that decide whether a reef grows or crumbles: calcification, reef accretion (growth) and erosion, sand production and transport, and habitat construction. Its "reefscape" approach focuses on shallow reefs in the U.S. Caribbean, the Gulf of Mexico and the Florida Keys.

Three disciplines together quantify the processes that decide whether a reef grows or crumbles. USGS.

Two questions

1. What controls how fast reefs produce carbonate, erode, move sediment and build?
2. Will reefs stop growing in the near future as oceans warm and acidify and water quality suffers?

How

• Monitoring: in 2009, calcification stations were set up at five outer reef sites from Miami to the Dry Tortugas to measure how fast corals and other organisms build carbonate.
• Comparison: coordinated expeditions study a declining reef (Crocker, Florida Keys) and a healthier one (Pulaski Shoal, Dry Tortugas), across seasons and in three dimensions.
• History: records from living and fossil corals reconstruct past sea-surface temperatures from geochemistry and reef growth through the Holocene, roughly the last 12,000 years.

Left: a calcification station at Molasses Reef in the Florida Keys National Marine Sanctuary. Center: the reefscape approach to field work. Right: drilling a coral core to reconstruct past temperatures. USGS.

Fossil reef cores. The USGS St. Petersburg Coastal and Marine Science Center holds an archive of cores collected over five decades, now being used to map reef growth through the Florida Keys. USGS.

For managers

CREST works with Dry Tortugas, Virgin Islands and Biscayne National Parks and the Florida Keys National Marine Sanctuary. It delivers:

• products and advice for managers in Interior agencies, states, territories and other federal agencies on how reefs function and recover;
• better forecasts of how reefs will change with the climate;
• risk assessments of the chance of losing reef services.

Knowing reefs' natural variability improves the odds of detecting the effects of climate change and poor water quality on reef growth — and whether a reef builds or crumbles determines whether it can keep protecting the communities behind it. More: CREST.

Sources

Based on "USGS Research on Atlantic Coral Reef Ecosystems," U.S. Geological Survey fact sheet, St. Petersburg Coastal and Marine Science Center; a work of the United States government in the public domain. The photographs and diagrams are taken from the fact sheet's PDF; a map on satellite imagery is left out.