The Florida Keys are the exposed portions of an ancient coral reef. The northernmost island arising from the ancient reef formation is Elliott Key, in Biscayne National Park. North of Elliott Key are several small transitional keys, composed of sand built up around small areas of exposed ancient reef. Further north, Key Biscayne and places north are barrier islands, built up of sand.
The Florida Keys have taken their present form as the result of the drastic changes in sea level associated with recent glaciations or ice ages. Beginning some 130,000 years ago the Sangamonian Stage raised sea levels to approximately 25 feet (7.5 m) above the current level. All of southern Florida was covered by a shallow sea. Several parallel lines of reef formed along the edge of the submerged Florida plateau, stretching south and then west from the present Miami area to what is now the Dry Tortugas. This reef formed the Key Largo limestone that is exposed on the surface from Soldier Key (midway between Key Biscayne and Elliott Key) to the southeast portion of Big Pine Key and the Newfound Harbor Keys. The types of coral that formed Key Largo limestone can be identified on the exposed surface of these keys.
Starting about 100,000 years ago the Wisconsin glaciation began lowering sea levels, exposing the coral reef and surrounding marine sediments. By 15,000 years ago the sea level had dropped to 300 to 350 feet (110 m) below the contemporary level. The exposed reefs and sediments were heavily eroded. Acidic water, which can result from decaying vegetation, dissolves limestone. Some of the dissolved limestone redeposited as a denser cap rock, which can be seen as outcrops overlying the Key Largo and Miami limestones throughout the Keys. The limestone that eroded from the reef formed oolites in the shallow sea behind the reef, and together with the skeletal remains of bryozoans, formed the Miami limestone that is the current surface bedrock of the lower Florida peninsula and the lower keys from Big Pine Key to Key West. To the west of Key West the ancient reef is covered by recent calcareous sand.
Just offshore of the Florida Keys along the edge of the Florida Straits is the Florida Reef (also known as the Florida Reef Tract). The Florida Reef extends 270 km from Fowey Rocks just east of Soldier Key to just south of the Marquesas Keys. It is the third-largest barrier reef system in the world.
The Florida Keys Coral Reefs have significantly declined since humans first settled the area. In the 1970s, reef degradation accelerated to catastrophic levels. Recent studies (2012) confirm that Reef decline continues to the present day.
Reef decline varies by location – on average, the Conch Republic’s Reefs have lost 90% of their original coral population (in some areas, the loss is over 95%). Reef decline is an ongoing and persistent problem. A recent study found an overall decline of 44% of hard coral over just a 12-year period (44% of the already-depleted coral that was there in 1996 was dead in 2008), with some critical reef-building coral species declining by 73%.3
Millions of tons of plastic waste end up in the ocean every year. And the trash stays there: Whether it's grocery bags or water bottles or kids' toys, plastic is practically indestructible. Now marine scientists have discovered that it's killing coral reefs. A new study based on four years of diving on 159 reefs in the Pacific shows that reefs in four countries — Australia, Thailand, Indonesia and Myanmar — are heavily contaminated with plastic. It clings to the coral, especially branching coral. And where it clings, it sickens or kills. 8 Million Tons Of Plastic Clutter Our Seas "The likelihood of disease increases from 4 percent to 89 percent when corals are in contact with plastic," researchers report in the journal Science. Senior author Drew Harvell at Cornell University says the plastic could be harming coral in at least two ways. First, bacteria and other harmful microorganisms are abundant in the water and on corals; when the coral is abraded, that might invite pathogens into the coral. "It's certainly well known that plastics abrade corals, create new openings," she says. "They basically tear open the skin of the coral and that can allow an infection from anywhere to start." In addition, Harvell says, plastic can block sunlight from reaching coral. https://www.npr.org/sections/thetwo-way/2018/01/25/580227045/plastic-pollution-is-killing-coral-reefs-4-year-study-finds
Prior to logging this cache, email the answers to the following:
- How many kinds of coral can you identify on the rocks below? (If you don't know the names, just describe the shapes of coral you see.)
- When you're there, Is it closer to high or low tide? If low tide can you see the edges of the reef shelf as you look out?
- Can you see any signs of reef degradation at Waypoint 2? In your opinion what is causing this to occur?
- Comparing the different rock formations at 3 and 4, what are some of the differences? Why do you think this is?
| We have earned GSA's highest level: |
 |
