“The Forests of the Sea” Fringe 1/6 th of the world’s coastlines Largest reef is the Great Barrier Reef in Australia (2000km or 1200mi) Member of the Cnidaria phylum Only have a polyp stage Have stinging tentacles and a soft body column, but they also have hard skeletons of calcium carbonate

Coral Growth Start out life as a tiny planktonic larva, floating through the water When it finds a hard substrate it attaches itself and begins secreting a hard skeleton towards the base Coral Parts: Exoskeleton: chalky white skeleton on that is located on the outside Calyx: the cup-shaped depression directly beneath the polyp; the polyp can retreat into it Polyp: the soft tissues on top of the calyx; often very brightly colored

Tentacles Body column

Solitary v. Colony Solitary Corals A single polyp Some secrete a skeleton that produces a vertical column Some produce a skeleton that grows outward (like the Mushroom Coral) Few species are solitary corals

Polyp Skeleton Mouth

Solitary v. Colonial cont’d Colonial Corals Often described as “coral heads” Some grow by budding (the new polyps will form around the original) Some reproduce sexually The new polyps begin secreting skeletal matter and adding to the thickness, diameter, and mass of the coral skeleton All polyps are connected by a thin, often brightly colored layer of surface tissue Classified as Branching or Encrusting corals

Branching v. Encrusting Corals Fig 4-1 Branching Corals Formed by polyps that produce buds at the tips of small branches Forms a complex, branching shape More delicate than the encrusting type Encrusting Corals Formed by polyps that only bud at the edges; forms a “crust” over the base

Encrusting coral Branching Coral

Mutualistic Symbionts Zooxanthellae A single-celled algae that is commonly found in the tissues of most cnidarians 3 major purposes Zooxanthellae photosynthesize, producing oxygen for the coral The coral uses the O2 and produces CO2 and other wastes, which the algal cells use to photosynthesize and nourish themselves Zooxanthellae also stimulate skeletal secretion – they enhance the ability to extract calcium carbonate (CaCO3) from the water *Reef-building corals (generally) only grow and thrive where there’s enough sunlight for the algae to photosynthesize

Reef Formation Reef – a massive deposit of coral skeletons Step 1 – A coral larva floats until it finds a hard substrate Step 2 – The polyp begins to secrete a skeleton under the thin surface of soft tissue Step 3 – The corals bud or sexually reproduce to form “buddies” to help with the growth of the coral head Repeat steps 1-3 several million times… Reefs can be massive! Ex: On the coral islands of Bikini and Enewetak, the researchers drilled through more than 2 km of skeletal matter before they hit the volcanic base!

Reef Formation cont’d Reef Parts Reef Flat The flat upper surface of the reef This is the part that is mostly exposed during low tide Tides limit the height the reef grows Prolonged exposure to air causes the coral to die, producing the skeletons that compose the flat Few corals actually live on the flat Reef Face The outer, seaward surface of the reef The reef grows fastest on this side due to the currents that bring food particles to the living polyps As this part grows, the reef flat is expanded The corals on the shallower outer edges are exposed to high wave energy and the abrasive force of moving sand particles A few hardy corals and coralline algae grow on the face

Reef Formation cont’d Coralline Algae Marine algae that produce large amounts calcium carbonate that forms robust skeletons Better adapted wave action than coral They make up about 90% of the shallow outer reef face Their skeletons resemble coral skeletons, but they don’t have calyces Algal Reef The part of the reef mostly made up of coralline algae Encrusting coralline algae cement parts of the reef together; making it very resistant to heavy wave action

Reef Formation cont’d Think of the reef face as being divided into sections Shallow Outer Reef Face Mostly coralline algae because of the heavy wave action Midwater Outer Reef Face This is where coral growth is excellent There can be as many as 200 species of corals competing with each other Deepwater Outer Reef Face (depths greater than 30m) Coral growth limited by lack of light

Coral Reef Evolution Think back to how reefs form… Fig4-7) Fringing Reef The early stage of the reef It is small and close to shore Barrier Reef The reef has grown as the island has started subsiding Lagoon A region of (usually shallow) water between the reef and the island Coral Atoll Formed when the island sinks below the surface of the ocean and the coral reef grows over it This is all that can be seen at the surface of the water Motu(s) Mounds of coral rubble on the reef face Formed when something like a storm breaks off a large chunk of reef and deposits it on top of the face