Coral Reefs

General Characteristics Coral reefs are built from the remains of stony (or hard) corals Reefs cover about 100,000 square miles of the world’s shallow marine areas Located in shallow, tropical waters They grow gradually as the organisms that form their living surfaces multiply, spread, and die, adding their limestone skeletons to the reef.

Types of Reefs The basic Coral Reef classification scheme was first proposed by Charles Darwin There are three main types of reefs: –Fringing –Barrier –Atolls There are two other reef types: –Patch reefs –Bank reefs

Fringing Reefs Occur adjacent to the land, with little or no separation from the shore They develop through upward growth of reef- forming corals on an area of continental shelf. May have a completely shallow lagoon in some areas, or no lagoon at all Most common reef in the Greater Carribbean and Red Sea

Also surround many South Pacific and Indian Ocean Islands Most susceptible to coastal development, agriculture, pollution, and other human activities resulting in sedimentation and freshwater runoff

Barrier Reefs Broader and Separated from land by a lagoon that can be miles wide and at least a dozen yards deep Usually parallel the shore Parts of the reef structure often protrude above sea level as low- lying coral islands. –These develop as wave action deposits coral fragments broken off from the reef itself Largest reefs develop on the edges of continental shelves (called “shelf barrier reefs” –Great barrier reef, Belize barrier reef

Atolls Large, ring-shaped reefs, surrounding a central lagoon found well away from large landmasses, such as in the South Pacific Usually circular or horseshoe-shaped parts of atolls may protrude above the surface forming coral islands as well.

Most common in the Indo-Pacific region (over 300) Rare in Caribbean (only 10-15) –Southern Mexico and Belize Can exceed 100 miles in diameter Central lagoons can be several thousand square miles

Patch Reefs Small reefs found within the lagoons of other reefs Usually small, isolated outcrops of coral surrounded by sand and / or seagrasses Provide refuge and food for may species of animals and fishes

Bank Reefs Reef structures with no obvious link to a coastline

Evolution of the Three Main Reef Types As first proposed by Charles Darwin: Darwin proposed the three main reef types are simply different stages in the geological ‘evolution” of Pacific oceanic islands.

Darwin’s Theory Fringing reefs began to grow near the shorelines of new islands when conditions for growth were ideal

As the island began to gradually subside into the sea, the coral was able to grow at the same rate, and remained in place at the sea surface, but farther from shore. It was now a barrier reef

Eventually, the island disappeared below the sea surface, leaving only the ring of coral surrounding it It was now an atoll

Darwin’s theory of “reef evolution” was verified for the Indo-Pacific reefs in the early 1950’s –After analyses of deep core drilling at Bikini and Eniwetok Atolls –We now know, however, that in some cases, the three types can be formed by different processes as well

Reef Formation Millions of Stony coral polyps are the marine animals responsible for building the hardened coral reefs you see in the ocean Reefs are excretions of calcium carbonate produced by each polyp New polyps secrete reef on top of older polyps

Reef Growth Forms Hard coral colonies generally exhibit one of three basic growth forms: –Massive –Branching –Plate-like

Massive These rely on sheer mass, growing into huge sheet or boulder formations that tend to make up the bulk of a reef

Branching These require a small area to anchor themselves, but branch out into vast, tree- like colonies

Plate-like Form flat expanses that overshadow other corals and monopolize the available light

Reef Formation Some corals grow very slowly Some can grow up to a few inches per year

Zooxanthellae Photosynthetic organisms that live in the tissue of each coral polyp Provide a source of food to the polyps Give corals their color Example of a mutualistic symbiotic relationship This is why corals need sunlight to grow

Organisms Contributions Mollusks and echinoderms add their skeletal remains Grazing and boring organisms break down coral skeletons into sand Coralline Algae bind the sand

Reef Distribution Coral Reefs are found in all three of Earth’s oceans that have portions in the tropics. (Pacific, Atlantic, and Indian). They are scattered randomly, however.

Reef Distribution Grow in clear, sunlit, shallow water Average salinity of 36 ppt Require warmer water temperatures, as seen in tropical and sub-tropical areas Require little or no wave action Little or no sedimentation from river run-off The two main areas of development that meet these criteria are the Indo-Pacific and Greater Carribean Belize – Great Blue Hole

Indo-Pacific Region Central and South Pacific Ocean Greatest number are in an area from southern Phillipines through western New Guinea and Indonesia Red Sea are is cut off from large water flow, so has high number of endemic species

Greater Caribbean Region Tropical, western Atlantic Spans the entire Caribbean Sea, Bahamas, and south Florida

Parts of a Reef

Reef SlopeReef Crest –Narrowest of the reef zones –Massive wall that absorbs the energy of incoming waves (makes water calmer for back reef zone)

Reef Flat and Lagoon Areas AKA “Back Reef” Contains shallow water habitats for reef species Vital role in food web Experiences large temperature and salinity changes, reduced water circulation, and sediment accumulation Main Habitats here: Patch reefs Sand plains Seagrass meadows Mangrove forests

Importance and Human Impacts

Importance of Reefs Provide protective barrier around islands and coasts –Slows down strong currents and waves before it hits the shore –Prevent erosion

Importance of Reefs Create more living biomass than any other marine ecosystem Contribute to local economies Support more species than any other marine environment Possibilities in medicines and science Control carbon dioxide levels in ocean water –The coral polyp turns carbon dioxide in the water into a limestone shell

Did you know… Coral reefs occupy only 2% of the oceans’ area, but are home to ¼ of all known marine species?????????????? To date, about 10% of all reefs have been destroyed?????????????

Coral Reef Threats

Human Impacts on Reefs Coastal and ocean pollution –Oil slicks, pesticides, chemicals, heavy metals, garbage, etc. Poisons coral polyps –Fertilizer and untreated sewage encourages algae growth High concentrations of algae can cover the coral and block sunlight if not kept under control by herbivores Massive oil slick as seen from satellite photos

Human Impacts on Reefs Uncontrolled development of coasts –Deforestation –Dredging and coastal development Hotels Homes harbors Soil run-off - Hawaii Runoff from a pipe in the Virgin Islands, directly near a reef

Human Impacts on Reefs Recreation –Boat anchors crush corals and gouge the reef –Diving tourism Divers and snorklers sit, stand on, or handle corals

Human Impacts on Reefs Collection of corals and organisms –International seashell and aquarium trades have put a strain on coral reef ecosystems –Upsets the balance of the ecosystem Market for coral skeletons, shells, sponges and reef animals for decorations, jewelry, sculptures Tropical fish trade Coral skeletons are are sold as “live rock” –Popular in aquariums because of the living bacteria and algae that acts as a natural biological filter

Human Impacts on Reefs Uncontrolled mining for building materials

Human Impacts on Reefs Destructive fishing practices –Overharvesting of species can lead to the species’ demise –Fishing with dynamite, cyanide, or bleach –Careless handling of nets, lines, and lobster traps can lead to reef damage –Boating / anchors also leads to reef damage Between 1986 – 1991, ½ of the coral reefs in the Philippines were destroyed by this Coca-Cola bottle with slightly burned fuse found around the Capone Islands, Phillipines

Human Impacts on Reefs Natural disturbances: –Hurricanes and tropical storms can strip corals from miles of reef habitat

Human Impact on Reefs Increases in atmospheric carbon dioxide increases the acidity of the ocean Higher ocean acidity makes it harder for reefs to construct their calcium carbonate skeletons –(remember what happened when you added vinegar to your reef in the lab?)

Coral Bleaching Occurs when corals become stressed –They expel the zooxanthellae living in them They lose their color and become whitened Can be caused with warmer surface waters (maybe even by 1-2 degrees) –May have a link to global warming Pollution can also be a cause Full recovery takes decades

Bleaching can be seen in areas of the Great Barrier Reef

Coral Poisoning Very destructive fishing practice A diver sprays sodium cyanide to catch a fish The poison kills all corals in the area

Crown of Thorns Starfish

Coral Reef Diversity Healthy reefs can house thousands of species –Fish –Invertebrates –Sponges –Soft corals Every part of a reef is used by some animal Mutualism – relationship between two different species where they both benefit