Coral Reefs

What are corals? Invertebrate marine animal A polyp that begins to form an exoskeleton CO2 & Ca in the water to make calcium carbonate (CaCO3) aka limestone Sessile – immobile Form colonies Show examples of corals to class The unit of a coral is the polyp, this is an individual animal that grows and divides to form larger corals. Therefore the corals you see on a reef are rarely an individual animal but colonies of many polyps, all originating from the same first polyp. A colony will begin through sexual reproduction, with microscopic larvae released into the water by existing corals. Wherever these larvae settle a single polyp will form (if conditions are favorable). This polyp then reproduces asexually(budding) , creating new polyps. In this way the colony grows. Once a coral dies it becomes a substrate for a new polyp to settle and grow and replicate. Over countless generations reefs will grow and develop through the continued growth, death and settlement of new corals. When looked at carefully, a coral polyp looks very similar to an anemone, except it sits within a calcium carbonate cup. Not all corals are reef builders, those that do, the hard corals, are knows as Hermatypic, while those that do not form a reef are called soft or Ahermatypic corals .

Coral Reefs Coral reefs are the simplest yet some of the most diverse and beautiful of marine organisms. Coral reefs are called the rainforests of the sea. High % of the ocean’s biodiversity is found at coral reefs Coral Reefs inhabit two main parts of the world: Caribbean – 7.6% Indo-Pacific – 91.9% Coral reef=a wave-resistant structure resulting from cementation processes and the skeletal construction of hermatypic corals, calcareous algae, and other calcium carbonate-secreting organisms Give coral reef handout #19 and #12

The Darwin-Dana-Daly theory of atoll formation. The theory of formation of coral atolls was first proposed by Charles Darwin following his observations during the voyage of HMS Beagle between November 1835 and April 1836. Darwin’s theory was subsequently supported and modified by two geologists, James Daly and Reginald Dana. His theory predicted, that below the thick calcium carbonate cap formed by the reef, there should be volcanic rock-the original island. In the 1950’s is was concluded that Darwin was correct.

The Darwin-Dana-Daly theory of coral atoll formation can be summarized: An oceanic volcano, which emerges from the sea surface and forms an island, becomes colonized by reef building corals. This growth of corals begins to form a fringing reef around the island. The island begins to sink slowly. Coral growth continues. Coral reefs often are divided into atolls and coastal reefs Atoll=a ring of reef, and often islands, surrounding a central lagoon. Common in the Indo-pacific region (tropical Indian and western pacific). Found far land, rising up from depth of thousands of meters or more. No land around-no freshwater runoff=clarity!!!!! Coastal reefs-elongated structures that border a continental coast. Ex Great Barrier Reef. They can be fringing reef or barrier reefs. Fringing reef-most common, seaward from shore. Offshore from land masses where a shallow continental shelf occur you get barrier reef, usually have a lagoon between reef and land Why did coral colonized the oceanic volcano? Basaltic rock-suitable substrate

Fringing Reef How is it able to grow that big? Symbiotic relationship with zooxanthellae

3. The island continues to sink and a barrier reef is formed with a lagoon between the reef and the island. 4. Eventually, the island disappears below the sea surface, leaving an atoll consisting of a ring of small islands with a relatively shallow lagoon in the center. Maldives Atoll Atolls- typically begins as fringing reefs on oceanic islands which is the top of submarine volcano In the Indian ocean by India near Madagascar Outer edge of the reef (away from the land) is the most diverse and pretty portion of it. Why??? Lack of runoff from island

Coral polyps colonized the coast Atoll formation Island begins to sink Fringing reef forms Coral polyps colonized the coast Volcanic island forms

Atoll formation Remaining reef becomes an atoll Islands sinks beneath the surface With lagoon, barrier reef forms As island sinks, lagoon forms

Evidence supporting this theory includes data from deep drilling on coral atolls, for example Bikini Atoll in the Pacific Ocean. The data showed that as the depth of the corals increased, the age of the corals also increased and fossil corals from the base of the drilling were dated to approximately 50 million years old. The corals were found to have grown on underlying volcanic rock. Fossil corals were found at depths of about 1200 meters. Since these corals grow only in shallow water, this provides evidence for the gradual sinking of the volcanic island

Coral Growth The conditions required for the growth of the majority of corals can be summarized as follow: A temperature range between about 16 and 35 °C, with optimum temperatures between 23 and 25 °C. Clear water without silt. Silt reduces light penetration which will inhibit the photosynthesis of the symbiotic algae (zooxanthellae) in coral tissues. A suitable depth. Rapid growth of corals usually occurs within 20 m from the sea surface. In deep water, there is insufficient light for photosynthesis of symbiotic algae. A suitable substrate for attachment, including the basaltic rocks of undersea mountains.

Autotrophy Symbiotic relationship Coral provides protection for Zooxanthellae Zooxanthellae provides food and color “Symbiotic” is defined as “A close, prolonged association between two or more different organisms of different species that may, but does not necessarily, benefit each member”. In the case of corals and zooxanthellae, the relationship is described as “symbiotic mutualism” as both organisms benefit from the relationship. You can clearly see the individual zooxanthellae cells within the tentacle of a coral. This strain of zooxanthellae are orange/brown, which would give the coral itself a similar color. Some pigmentation can come from the coral polyp, but much of it is determined by the zooxanthellae. There are a number of different strains of zooxanthellae, all belonging to the genus Symbiodinium sp. A coral can contain one single strain, but will normally contain a mixture of many different ones. Many other host of animals on coral reefs will host the algae: giant clams, sea slugs, zooanthids, anemones

Benefits of Reefs Coral reefs absorb the energy of waves and so protect the shoreline from erosion. This provides a number of benefits including protection of coastal properties, protection of ecosystems and reducing the cost of providing breakwaters. Reduced wave action also provides safer anchorage for boats. Overall, these benefits have a significant economic advantage. Show video- Coral reefs: their health, our wealth first

Destruction of reefs Predation Crown of Thorn starfish Parrotfish http://www.nationalparkstraveler.com/2013/02/national-park-american-samoa-divers-work-protect-reefs-killing-voracious-starfish22792

Continued with destruction of reefs Storm damage and exposure to the air. Exceptionally low tide Fishing nets, boats running aground, divers Ocean Acidification, Global Warning, Pollution It has been estimated that complete recovery will take between 25 to 100 years Show coral hybrids video from Changing Seas Season 5 – 26 minutes Show Mysterious microbes video from changing seas season 4-26 minutes

Impact of Erosion Reef erosion = shores/coastal properties are exposed to damages from waves Artificial reefs: human-made structures = concrete/stone blocks, sacks filled with sand or shipwrecks (sunken ships) Colonized by algae, corals and fish Used as submerged breakwater Dissipate wave energy If the reef gets eroded away by predation, exposure to low tides, etc—the shoreline gets eroded away http://www.advancedaquarist.com/blog/the-vw-bug-artificial-reef article and video

Artificial Reefs Prevents erosion of land Anchorage/protection for harbors New habitats Increase fishing areas Tourism – snorkeling/diving

Shipwrecks (Artificial Reef) USS Oriskany (2006)

Carbon Dating to Date Coral Reefs Carbon dating (also referred to as radiocarbon dating) can be used to find the age of a sample of coral. As corals grow, carbon, originating from carbon dioxide, is deposited in their skeleton in the form of calcium carbonate. Some of the carbon taken up by corals, in the form of 14C, slowly decays to 12 C. The proportion of 14 C to 12 C in a sample of material is used to estimate the age of the corals. Carbon dating is used on organic remains up to about 50 000 years old. Show video on carbon dating – 3 minutes

Core Drilling to Date Corals Reefs Deep drilling of coral reefs provides cores of material which can be used to identify corals and to estimate the rate of growth of the reef. As corals grow, they produce ‘bands’ which are similar to the annual growth rings of a tree. Interpretation of the bands provides evidence for changes in the growth rate of corals, in response to changes in environmental conditions, such as temperature or nutrient availability.

Growth of coral Growth up to 20m deep Fossil corals found at 1200 m is evidence of subsidence (caving in and sinking of land area) New coral grow on top of old as reef gradually sinks Fossil corals found above sea level Evidence of changes in sea level Mexico – sea level changes between ice ages For homework read and take notes on article: http://earthobservatory.nasa.gov/Features/Paleoclimatology_CloseUp/paleoclimatology_closeup_2.php