Coral Reefs

Georgia’s Gray’s Reef Gray's Reef is not a coral reef. It is not built by living hard corals as tropical reefs are. Instead it is a consolidation of marine and terrestrial sediments (sand, shell and mud) which was laid down as loose aggregate between six and two million years ago. At one time, Gray's Reef was dry land!

Coral reefs cover less than 0.2% of the ocean surface yet they are home for ¼ of all marine fish species! S ponges, nudibranchs, fish (like Blacktip Reef Sharks, groupers, clown fish, eels, parrotfish, snapper, and scorpion fish), jellyfish, anemones, sea stars (including the destructive Crown of Thorns), crustaceans (like crabs, shrimp, and lobsters), turtles, sea snakes, snails, and mollusks (like octopuses, nautilus, and clams). Birds also feast on coral reef animals

Types of Coral Two types: Stony (hard) coral Soft coral

Stony Corals Made up of limestone (calcium carbonate) Hard, rocklike Brain coral, staghorn coral, star coral

Soft Coral Made of fibrous protein Flexible Looks like a plant swaying in current Ex. sea fan, sea whip, and sea plume

Coral Animal Polyp (Cnidaria) Mouth, tentacles, digestive cavity, attached to substrate Colonial animals Corals are carnivores that eat zooplankton Attached to one another by thin membrane connecting digestive system coral spawning Can reproduce asexually (budding) and sexually (spawning)

Coral Reef Spawning – YouTube

brain coral releasing eggs

Mutualism (Symbiosis) Zooxanthellae – provides oxygen and food to coral Coral – provides safety and nutrients to algae Zooxanthellae

Coral Reef Formation Built by corals Specialized cells take calcium from the seawater Zooxanthellae (dinoflagellate algae) captured by polyps, collect CO 2 produced by polyps Combine to make calcium carbonate (CaCO 3 ) Polyp secretes CaCO 3 to make new layers of coral reef

Coral Reef Location Tropical areas, shallow waters Warm waters to secrete CaCO 3 skeletons Clear water, free from sediment – need sun to photosynthesize

location of major coral reefs in red

Coral Growth Each generation lays down a layer of reef Massive corals slow growing - a rate of 0.5 to 1 cm/year Branching corals grow faster – a rate of cm/year Provides homes and habitats for other species Large reefs protect nearby coast lines from ocean waves/storms

branchingpillar tableelkhorn

foliase encrusting massivemushroom

Damage to Reefs Ship damage Ecotourism Water pollutants Severe storms Freshwater runoff Sediment High or low water temperature (disturbs algae) Coral bleaching –Living polyp dies off –White skeleton remains

Additional Damage Fishing has degraded reef communities by upsetting the ecological balance Dynamiting (Indonesia, Kenya) has killed hard coral colonies Muro-ami = bouncing rocks tethered to lines off the coral to herd fish has caused serious damage

Formation of coral islands - YouTube

Types of Reefs Fringing reefs Barrier reefs Atolls

Fringing Reefs Connects to shore on leeward side (the direction downwind) of land Water shallow on shore side Water deep on ocean side Grows most rapidly on ocean side due to greater water circulation (more food and oxygen to coral) Florida Keys, Caribbean

Barrier Reefs Approximately 25 km off shore Separated from island by a channel/lagoon Great Barrier Reef –Series of reefs, largest structure made by living organisms –10 to 160 km off northeast coast of Australia –350,000 km 2

Fringing & Barrier Reefs Grow right up to ocean surface May be exposed at low tide Waves and currents break off pieces Accumulate on seafloor Coral pieces pile up to form small islands called keys or cays Florida Keys and Cayman Islands

Atolls String of coral islands forming a circle around a shallow lagoon (1 to 12 km wide) Darwin hypothesized about cause of atoll shape – the final stage in reef evolution Mostly in Pacific

Formation (Darwin’s Theory) 1.Fringing reef appears along shoreline of volcanic island 2.Island begins to sink or erode and reef continues to grow up and out to for barrier reef 3.Island sinks completely below surface leaving an atoll Scientists confirmed Darwin’s theory by drilling through limestone and finding a volcanic foundation beneath the reef