Tropical Coastal Seas

Tropical Coastal Seas - Tropical Coastal Seas The most...

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Unformatted text preview: Tropical Coastal Seas The most famous and important tropical coastal marine ecosystem is the coral reef: The term coral is given to many species of cnidarians but only a few are HERMATYPIC or reef builders The polyps of hermatypic corals produce a CaCO 3 skeleton in a great variety of sizes and shapes. The most important reef builders are SCLERACTINIAN corals Figure 14.02 Coral structure - recap Figure 14.06 Nutrients in tropical waters Due to high intensity sunlight year round, a permanent thermocline forms in tropical waters Nutrients in this warm surface layer of water are soon used up and cannot be replenished by bottom waters due to the stratification of the water column Therefore tropical waters are typically OLIGOTROPHIC (low in nutrients) Lack of nutrients and consequently phytoplankton, means that tropical waters are unusually clear good light penetration Nearly all reef-building corals contain a symbiotic (mutualistic) ZOOXANTHELLAE These are typically single-celled dinoflagellates These provide photosynthetic products to the coral to aid in its survival and growth. The zooxanthellae pass nutrients to the coral polyp which adds to nutrients gained by filter feeding by the polyp Carbon dioxide produced by the respiration of the polyp helps fuels photosynthesis for the zooxanthellae (which in turn is aided by the clear tropical waters) The zooxanthellae make up for the low nutrient levels in tropical waters Exchange of materials between zooxanthellae and their coral host. Forms of Coral Other reef builders In addition to the symbiotic algae in coral, other algae are important for reef production e.g. encrusting CORALLINE ALGAE lay down calcium carbonate sheets that add to reef growth This algae is especially important in the Pacific The algae forms a stony pavement that protects the reef against wave action The algae can form a ridge around the reef ALGAL RIDGE that absorbs the force of waves and prevents erosion Algae & sediment Coral fragments ( CORAL RUBBLE ), skeletal material, foraminifera shells, gastropod, bivalve and urchin shells waste of grazing parrot fish & sea urchins Burrowing and boring polychaetes & sponges form sediment (= BIOGENOUS CALCAREOUS SEDIMENT ) that accumulates around the base of corals Grazing and boring that wear away reef material = BIOEROSION Algae & sediment Loose sediment can damage coral if it lands on them smothering the colony Encrusting algae grow over layers of sediment, consolidating it and cementing it in place like asphalt over the gravel of a road Bryozoans and sponges also help to consolidate this sediment This helps to build up the reef and prevent it from being worn away by bioeroders Figure 14.08a Figure 14.08b Figure 14.08c Coral Distribution Living coral reefs usually are located within 30 latitude of the equator in water that averages at least 20C (but usually lower than 30-35C or bleaching...
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Tropical Coastal Seas - Tropical Coastal Seas The most...

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