Coral Reefs Organisms and Ecology
General Characteristics: Rival tropical rainforests for beauty, richness, complexity Basic structure is made by organisms 3 Dimensional framework home to incredible assortment of organisms
Where found: Particular requirements determine where coral reefs develop Shallow water. Why? Zooxanthellae need light Not deeper than 50 m Found only on continental shelves Around islands Tops of seamounts
Where found: There are corals that grow in deep water, but they do not build reefs (they don t contain zooxanthellae) Reef building Corals are limited to warm waters Tropic of Cancer to Tropic of Capricorn (30ºN to 30ºS) Need to have warm water because calcium carbonate precipitates out of solution much easier in warm water. 19º C is about the minimum
Where found: 85º - 95º is where corals become stressed and become bleached Bleaching is where the corals expel their zooxanthellae Called bleaching because the zooxanthellae give corals their colors and when they are expelled, the corals turn white Some possible sources of water warming are Power plant discharge El Nino Global warming?
General Characteristics: So big they are considered geological structures You can see Great Barrier Reef from space! There are other organisms that can add to the reef, but they play a minor role in production of reef material Subtidal zone
Corals: What phylum do corals belong to? Class? What body style do corals have? One kind of coral that is not an Anthozoan fire coral Hydrozoa Medusa stage Powerful nematocysts
Corals: Not all corals build reefs Soft corals Gorgonians Sea fans Sea whips
Coral Polyp: Reef building corals are colonial Digestive systems of polyps remains connected Some reef building corals are single polyps mushroom corals are an example Polyps lie in a cup-like skeleton of CaCO3 Over years, they build up on each other forming massive structures
Coral Polyp:
Coral Polyp:
Coral Polyp:
Coral Polyp:
Corals:
Massive:
Plate:
Encrusting:
Collumnar:
Branching (Staghorn):
Elkhorn
Symbiotic Zooxanthellae Symbiodinium microadriaticum Dinoflagellates supply 90% of nutritional needs of stony coral
Symbiotic Zooxanthellae zooxanthella provide glucose, glycerol and amino acids coral polyp provides a suitable habitat and nutrients, absorbed directly through the animal s tissues
Zooxanthellae zooxanthellae remove CO2 and produce O2 need of zooxanthellae for sunlight limits depths to which stony corals can grow Helps coral deposit calcium carbonate
Coral nutrition (continued) other sources of nutrition Corals can feed on zooplankton corals can feed off bacteria living in their tissues, which feed on dissolved organic matter directly from the water mesenteric filaments (coiled tubes attached to the gut wall) can be extruded from the mouth to digest and absorb food outside the body
Coral Polyp: Stony (true) corals deposit massive amounts of CaCO3 that compose most of the structure of coral reefs Hermatypic coral species that produce reefs, found in shallow, tropical waters Ahermatypic corals that do not build reefs, which can grow in deeper water from the tropics to polar seas most do not harbor zooxanthellae
Other Reef builders: Most are algaes not animals Some marine biologists think coral reefs should be called biotic reefs Zooxanthellae Other algaes that contribute to the reef material Encrusting coralline algaes grow in sheets over the reefs, deposit lots of calcium carbonate Encrusting coralline algae are the glue that holds the reef together
Other Reef builders: Nearly all the sediment is biogenous Halimeda a green alga that deposits much of the calcium carbonate on a reef Deposits calcium carbonate in its tissues to discourage grazers from eating it Remains accumulate and are bound together by encrusting organisms
Halimeda sp.
Other Reef builders: Other calcium carbonate producing organisms that contribute to the reef materials are Shells of forams Snails Clams Other molluscs Sea urchins Bryozoans Crustaceans Sponges Worms
Other Reef builders: Sponges, hydroids, bryozoans form encrusting growths that help bind the sediment also Nearly all sediment on the reef comes from coral fragments or coral rubble and the shells and skeletons of other organisms
Beginning
After a while
Reef growth.
Sediments, Salinity, and Pollution: Fine sediments (Silt) are very harmful to corals Cuts down light for zooxanthellae Smothers corals Corals use a thin film of mucus to remove sediments, the mucus is sloughed off Corals can only do this a limited amount Reefs tend to be poorly developed near river mouths (large sediment deposits and fresh water influx)
Sediments, Salinity, and Pollution: Corals are sensitive to fresh water Human factors can influence the amount of sediment in the water mining, dredging, logging, construction Can be very harmful to coral reefs Corals also tend to be sensitive to pollution even in low concentrations Larvae are especially sensitive Humans release huge amounts of nutrients in the form of runoff from fertilizers and sewage
Sediments, Salinity, and Pollution: High concentrations of nutrients may affect the coral directly by interfering with skeleton formation Also, high nutrients alter the ecological balance of the reef community Coral reefs usually grow in nutrient-poor water Too much nutrients allow algae to grow rapidly and corals cannot compete for space and light Sometimes grazing fish are removed (surgeon fish, parrot fish, damsels)
Inner reef flat and an outer reef slope: Reef flat widest part Shallow Sometimes exposed at low tide Gentle slope Most strongly affected by sediments Not as many colonies or different kinds as the reef slope
Inner reef flat and an outer reef slope: Reef Slope Quite steep Densest cover of corals Most species Reef crest is the shallow edge of the reef slope Most coral growth of all best of both worlds Lots of light still has lots of water circulation
Inner reef flat and an outer reef slope: Sediments and coral pieces tumble down the reef slope and settle at the base As it builds up, organisms grow on it Bottom is usually flat and covered with sand or mud Coral reefs have an incredible variety of life. Richest and most complex of all marine ecosystems
Darwin s theory of atoll formation:
Darwin s theory of atoll formation: Fringing reefs, barrier reefs, and atolls were stages of island reef development Newly formed volcanic islands and submerged volcanoes are eventually populated by coral larvae The larvae grow near shore and form a fringing reef
Fringing Reef Fringing are simplest and most common develop near shore in tropics hard surface for coral larvae to settle and grow rocky shoreline is best even if there is a small patch of hard bottom they can make their own hard bottom once started Fringing reefs grow in a band along the shore They occur close to landforms borders along shoreline Hawiian reefs are fringing reefs
Darwin s theory of atoll formation: Most rapid growth occurs on the outside of the reef. Why? Good Circulation Zooplankton (Food) Oxygen Brings fine sediments away
Darwin s theory of atoll formation: Waves break pieces off and move them downslope More coral establish on the debris The weight of the reef and volcano depress the ocean floor and sink the island.
Darwin s theory of atoll formation: If the upward growth exceeds the sinking rate, the coral maintains position If not, the reef sinks into darkness and expires.
Darwin s theory of atoll formation: As the island sinks away, large corals die and are covered over. This creates a lagoon. Delicate corals form and survive in the shallow protected lagoon. This is a Barrier Reef
Barrier Reef: Further offshore Separated from shore by lagoon Great Barrier Reef of Australia is the largest single biological feature on earth Smaller barrier reefs are common in the Caribbean sea.
Darwin s theory of atoll formation: Further sinking of the island may leave behind a chain of low lying atoll islands Coral reefs have an incredible variety of life. Richest and most complex of all marine ecosystems
Atolls: - Ring shaped reefs from which a few low islands project above the sea surface
Atolls:
Trophic Structure of Coral Reefs: Tropical waters where coral reefs are found are usually poor in nutrients Very little phytoplankton How can such a rich community exist where there is so little biological production?
Trophic Structure of Coral Reefs: Mutualistic relationship between corals and zooxanthellae Other organisms also have Mutualistic relationships with algae Sponges, sea squirts, giant clams are examples Coral reef communities use nutrients very efficiently
Competition: Space is at a premium Sessile organisms must compete for space and light Competition is in the form of Overgrowing Attacking neighbors Not only with each other, but with other invertebrates or seaweeds
Competition: Corals compete for space with algae Encrusting algae grow slowly because they produce a calcium carbonate skeleton Found in places corals don t do well Herbivores on the reef
Competition: Soft Corals also compete Lack calcium carbonate skeleton Grow faster than hard corals Contain spicules and may produce toxic chemicals or bad tasting Can move slowly
Predation on Corals: Many animals eat corals Most eat individual polyps or pieces of corals The pieces grow back Like grazing by herbivores
Competition among corals: fast-growing, branching corals grow over slowergrowing, encrusting or massive corals and deny them light slower-growing corals extend stinging filaments from their digestive cavity to kill faster-growing corals fast-growing corals can also sting and kill using long sweeper tentacles with powerful nematocysts
Competition among corals (continued) slower-growing corals are more tolerant of shade, and can grow at greater depths as a result fast-growing, branching corals on many reefs dominate upper, shallower portions larger, slower-growing corals dominate deeper portions
Threats to Coral Reefs Coral bleaching a phenomenon by which corals expel their symbiotic zooxanthellae most often associated with warming of the ocean water by ENSO or global warming if the stress is not too severe, corals may regain zooxanthellae and recover if the stress is prolonged, corals may fail to regain zooxanthellae and die
Threats to Coral Reefs Coral diseases black band disease a distinct dark band of bacteria migrates across the living coral tissue, leaving behind a bare white skeleton
Threats to Coral Reefs Coral diseases white pox characterized by white lesions and caused by Serratia marcescens other coral diseases: white band disease white plague yellow blotch disease
Threats to Coral Reefs Human impact on coral reefs overfishing may occur human-sewage bacteria cause white pox nutrient-rich runoff (eutrophication) increases algal growth, which covers and smothers corals e.g. Kane ohe Bay in Hawaii