 Cnidarians:  Animals in the phylum  Cnidaria  Radial symmetry  Tissue-level organization  Tentacles with nematocysts  Stinging cells  Life stages:  Polyp: Sessile, sac-like stage, with the mouth and tentacles on top  Medusa: The swimming, bell-like stage, with the mouth and tentacles underneath

 Large variety of marine life  Coral polyps:  Form coral reefs  Lay down CaCO3 skeleton to build reef New generations continue to lay down new layers Grow at rate of 2.5cm per year Will grow up to surface, but not above ocean surface

 Tropical and subtropical regions  Between 30˚N and 30˚S latitude  Oceans are warm and clear in these areas  Each reef is composed of many different types of coral:  Coral creates crevices, depressions, and caves Enable many types of fish to live and hide  2 types of coral: Hard coral: Elkhorn, brain coral Soft coral: sea fan, sea rod  Reefs are highly productive, but fragile:  Some break easily  Touching can damage membrane protecting surface  Shoreline development lead to sedimentation and clouding of water  kills reefs

Brain coral – hard coralFeathery fan  soft coral

 Butterfly fish:  Feed on particular type of reef  Barracuda:  Eats other fish  Parrot fish:  Uses beaklike mouth to eat chunks of coral  Sponges, worms, shrimp, anemones, sea stars, mollusks  Use reef to hide from predators and prey  Camouflage and schooling for protection  Reef fish are very colorful:  Color contrast  patterns of different colors Used to identify members of own species  Disruptive coloration  spots, bars, stripes Obscure the outline of a fish Makes it hard to see and capture

 Made of Calcium carbonate (CaCO 3 )  Limestone deposited by living things  Polyps produce CaCO 3 skeletons Build a massive reef  Most important reef builders  stony or “true” corals  All reefs contain: Zooxanthellae  help coral make CaCO 3 skeletons Corals can produce skeleton without them but very slowly

 Zooxanthellae nourish coral  photosynthesis  Pass some of the organic matter they make onto the coral Feed the coral from the inside Many corals can survive and grow without eating, as long as zooxanthellae have light  Coral still eat on their own  Zooplankton Catch with tentacles

 Particular requirements for development:  Need to settle on hard surfaces  Grow only in shallow waters: Light can penetrate 165ft max found on continental shelves, around islands, or onto of seamounts Clear water Warm water  grow and reproduce above 20˚C (68˚F) Water that is too warm:  30˚ to 35˚C (86˚ to 95˚F)  heat stress Bleaching  coral expels zooxanthellae  Coral turns white Can recover

 Many different species with different relationships  Competition: “the battle for space.” Hard place to anchor themselves, sunlight Different ways to compete: Fast-growing ones  grow upward and then branch out, cutting their neighbors off from sunlight Some attack neighbors  Secrete mucus to digest other corals Most aggressive corals = slow-growing Fish and other organisms compete for food and shelter

 El Niño  Brings unusually warm water  Widespread coral bleaching severe bleaching occurred on many reefs  Scientist are concerned about bleaching:  More frequent  More intense  global climate change  Monitor surface temperatures  Salinity, sediments, and pollution:  Smother coral  Cause disease

 Predation on Corals:  Predation and grazing is important  They eat pieces and allow coral to regrow  Affects both the number and type of coral that live on the reef and how fast the reef as a whole grows Butterfly fish slows the growth of a particular coral that it likes to eat When coral is protected by a cage it grows faster If not for the fish this type of coral would dominate  Crown-of Thorns Sea Star: Feeds by pushing its stomach out through the mouth covering all parts of the coral Digest live coral tissue Prefers certain types of coral Massive invasion Reefs recover in years Attempted to solve problem  failed Solved itself = mystery Occasional outbreaks

 3 main categories:  Fringing reefs  Barrier reefs  atolls

 Fringing reefs:  Simplest and most common  Near shore throughout the tropics Rocky shorelines are the best  Grow in narrow band or fringe along the shore  Longest reef in the world (not with coral area) is a fringing reef about 4,000km (2,500mi) along the coast of the red sea Climate is dry and there are no streams to bring in sediments and freshwater

 Structure of a fringing reef:  Inner reef flat: Widest part of the reef Shallow, sometimes exposed at low tide Slopes very gently toward the sea Strongly affected by sediments and freshwater runoff Seaweeds, seagrasses, soft corals occupy this area  Outer reef slope: Steep Densest cover and the most species of coral Away from shore  away from sediments and freshwater Waves provide good circulation  bring in nutrients  Reef crest: Shallow upper edge of reef slope

 Barrier Reefs:  Lie along the coast  Farther from shore than fringing reef  Separated from the shore  Lagoon forms near here  Scattered coral formations may grow to the surface: Patch reefs Coral knolls Pinnacles

 Structure of a Barrier Reef:  Back-reef slope: May be gentle or steep Protected by waves by the rest of the reef Because of sediment coral growth is not as vigorous Some gentle slopes have luxuriant coral growth  Reef flat: Shallow, nearly flat platform Waves and currents may pile up sand to form small sand islands  sand cays or in the United States  keys  Fore-reef slope: Like the reef-slope on a fringing reef Gentle or nearly vertical Depends on the action of wind and waves Has a reef crest Richest coral growth

 Largest and most famous  2,000km (1,200mi) along the northeastern coast of Australia  Not the longest reef in the world  Covers such a large area and is so complex and well developed  largest reef structure  Not a single reef  System of more than 2,500 smaller reefs, lagoons, channels, islands and sand cays

 Other barrier reefs:  Largest in the Caribbean  off the coast of Belize, Central America.  Florida Reef Tract  New Guinea  Fiji in the Pacific

 Atolls:  Ring of reef  Often islands or sand cays, surrounding a central lagoon  Majority are found in the Indo-West Pacific Region Tropical Indian and Western Pacific oceans.  Rare in the Caribbean and tropical Atlantic Ocean.  Found far from land, rising up from depths of thousands of meters or more  Bathed in pure blue ocean water: Display spectacular coral growth and breathtaking water clarity.

 Structure of Atolls:  Small rings less than a mile across to system over 30km (20mi) in diameter.  Reef flat: Flat, shallow area  Fore-reef and back-reef slope: Outer and inner slopes Extend all the way around the ring-shaped atoll Fore-reef: Vertical, deep  Reef crest: Strongly influenced by wind and waves Lie in the zone of trade winds  wind comes from a constant direction Affects direction of growth  Lagoon: Shallow

 How Atolls formed:  Charles Darwin: Theory of Evolution Theory of atoll formation Reef growth on a subsiding island Start with a deep-sea volcano erupting to build a volcanic island  Corals soon colonize the shores of the new island  Fringing reef develops  Drilled holes through CaCo3 to find volcanic rock = original island  Largest Atoll Reefs:  Two: Suvadiva  Maldive Islands of the Indian Ocean Kwajalein  Marshall Islands in the Central Pacific