Who,%20What,%20When,%20Where,%20Why,%20and%20How%20of%20Coral%20Reef%20Communities

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Who, What, When, Where, Why, and How of Coral
Reef Communities

• Who (organisms) can be found in a coral reef
  community?
• What is a coral reef community?
• When can you find a coral reef community (is it
  seasonal)?
• Where are coral reef communities found?
• Why are coral reef communities so important?
• How do coral reef communities interact with other
  ecosystems in the ocean?

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Chapter 15 Coral Reef Communities
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• Lets talk about primary productivity in the
  oceans - Photosynthesis by phytoplankton
• Polar oceans are the most productive
• Cold water holds more gases
• Summer brings 24 hours of daylight for
  photosynthesis
• Temperate waters are somewhat productive
• Tropical waters are the least productive
• Thats why there are nice clear, blue water
• Coral reefs are like an oasis in the tropical
  water dessert

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Coral Reef Communities

• Coral reefs are highly productive, but occur in
  nutrient-poor waters
• This is made possible by the symbiotic
  relationship between coral animals and
  zooxanthellae
• These symbionts algae form the basis of the
  community other reef animals depend on these
  organisms

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Organisms That Build Coral Reefs

• Stony (true) corals are the primary organisms
  that 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 and harbor
  zooxanthellae

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Organisms That Build Coral Reefs

• Ahermatypic corals that do not build reefs,
  which can grow in deeper water from the tropics
  to polar seas
• most do not harbor zooxanthellae
• Coralline algae and organisms such as fire coral,
  deposit lesser amounts of calcium carbonate on
  reefs
• fire corals important in Caribbean reefs
• coralline algae important in structure of Pacific
  reefs

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Organisms That Build Coral Reefs

• Coral colonies
• large colonies of small coral polyps, each of
  which secretes a corallite (cup of calcium
  carbonate)
• the coral larva called a planula larva settles
  and attaches
• a polyp develops, and reproduces by budding to
  form a growing colony
• polyps gastrovascular cavities remain
  interconnected
• a thin, usually colorful epidermis overlies the
  colony surface

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Organisms That Build Coral Reefs

• Coral nutrition
• corals have evolved several strategies for
  obtaining food
• symbiotic zooxanthellae
• supply 90 of nutritional needs of stony coral
• zooxanthella provide glucose, glycerol and amino
  acids
• coral polyp provides a suitable habitat and
  nutrients, absorbed directly through the animals
  tissues
• zooxanthellae remove CO2 and produce O2
• need of zooxanthellae for sunlight limits depths
  to which stony corals can grow

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Organisms That Build Coral Reefs

• Coral nutrition (continued)
• corals as predators
• tiny zooplankton or other small animals paralyzed
  by the cnidocytes (stinging cells in tentacles)
  are passed into the digestive cavity

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Organisms That Build Coral Reefs

• Coral nutrition (continued)
• other sources of nutrition
• mesenteric filaments (coiled tubes attached to
  the gut wall) can be extruded from the mouth to
  digest and absorb food outside the body
• corals can feed off bacteria living in their
  tissues, which feed on dissolved organic matter
  directly from the water

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Organisms That Build Coral Reefs

• Reproduction in corals
• Reproduction by fragmentation
• in addition to budding, corals can also reproduce
  asexually by fragmentation
• some branching corals are fragile and tend to
  break during storms
• if they survive the storm, fragments can attach
  and grow into new colonies

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Organisms That Build Coral Reefs

• Reproduction in corals (continued)
• Sexual reproduction in coral
• Many species of coral are hermaphroditic, some
  have separate sexes
• mostly broadcast spawnersrelease both sperm and
  eggs into the surrounding seawater
• some are broodersbroadcast sperm, but retain
  eggs in the gastrovascular cavity
• spawning is usually synchronous among Pacific
  reef species, but nonsynchronous among Caribbean
  species

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Reef Formation

• Involves both constructive and destructive phases
• Bioerosion the destructive phase of reef
  formation
• boring clams or sponges attack exposed surfaces
  on the undersides of large corals
• the coral stand weakens, then topples in a storm
  or ocean surge
• accumulating debris smothers boring organisms,
  cracks are filled with CaCO2 sediments, and
  coralline algae cement it together

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• Types of reefs
• Fringing
• Barrier
• Atoll
• Patch

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Types of Coral Reefs

• Fringing reefs
• develop along shores of tropical/subtropical
  islands or continental landmasses
• Of all reef types, most affected by human
  activities because of their proximity to land,
  develop right next to the land

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Types of Coral Reefs

• Barrier reefs
• similar to fringing reefs but separated from the
  landmass and fringing reef by lagoons or
  deepwater channels
• Great Barrier Reef is the worlds largest barrier
  reef

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Types of Coral Reefs

• Atolls
• usually elliptical, arise out of deep water and
  have a centrally-located lagoon
• Often eroded dead volcano

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• Darwins theory of atoll formation
• corals colonize shallow areas around newly-formed
  volcanic islands to form a fringing reef
• the island sinks and erodes, and a barrier reef
  is formed about the island
• the island sinks completely, leaving an atoll

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Reef
Fringing reef
Reef
Patch reef
Barrier reef
Patch reef
Atoll
Stepped Art
Fig. 15-11, p. 422
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Types of Coral Reefs

• In addition, patch reefs can occur within lagoons
  associated with atolls and barrier reefs

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Reef Structure

• Different reef types share common characteristics
• Reef front or forereef portion of the reef that
  rises from the lower depths of the ocean to a
  level just at or just below the surface of the
  water, on the seaward side
• drop-off a steep reef-front that forms a
  vertical wall
• spur-and-groove formation or buttress zone
  finger-like projections of the reef front that
  protrude seaward disperses wave energy and helps
  prevent damage

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Reef Structure

• Reef crest the highest point on the reef and the
  part that receives the full impact of wave energy
• where wave impact is very strong, it may consist
  of an algal ridge of encrusting coralline algae,
  lacking most other organisms, and penetrated by
  surge channels, grooves of the buttress zone
• Reef flat or back reef portion behind the reef
  crest
• reef flat of fringing reefs ends at the shoreline
• reef flat of atolls and barrier reefs descends
  into the lagoon

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Reef Structure

• Coral populations on reef front are massive
  dome-shaped brain corals and columnar pillar
  corals on intermediate slopes, below this region
  coral species form plate-like formations
• Higher up on reef where wave energy is greatest,
  branching species of coral are found, e.g.,
  elkhorn coral in Caribbean
• In protected areas behind reef front, in shallow
  calm waters, small species of coral occur, e.g.,
  rose, flower and star corals

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Coral Reef Distribution

• Major factors influencing distribution (corals
  are sensitive)
• temperature corals do best at 23-25o C
• light availability photosynthetic zooxanthellae
  need light, corals not found below 60 meters
• sediment accumulation can reduce light and clog
  feeding structures
• salinity, corals absent from areas of massive
  freshwater outflow, e.g., the mouth of the Amazon
• wave action moderate wave action is beneficial,
  brings in oxygenated seawater, removes sediment
  that could smother coral polyps
• heavy wave action during hurricanes can damage
  reef structure
• duration of air exposure can be deadly

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Comparison of Atlantic and Indo-Pacific Reefs

• Pacific reefs are older and have a greater depth
  of reef carbonates
• Buttress zone is deeper on Atlantic reefs and
  coral growth may extend to 100 m down
• Pacific coral growth rarely exceeds 60 m
• Proportion of reef covered by corals may approach
  100 on some Pacific reefs, but usually less than
  60 on Atlantic reefs
• Algal ridges more common in the Pacific because
  of wind and waves

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Comparison of Atlantic and Indo-Pacific Reefs

• Hydrozoan Millipora complanata (fire coral) is
  dominant on Atlantic reefs
• similar species never dominate in the Pacific
• Atlantic corals nocturnal (night) Pacific corals
  diurnal (day)

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Comparison of Atlantic and Indo-Pacific Reefs

• Greater sponge biomass in the Atlantic
• Pacific has giant clams and sea stars that prey
  on corals

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Coral Reef Ecology

• Source of nutrients for coral reefs
• land runoff for reefs close to land
• Thats why too much runoff can bring unwanted
  nutrients
• source of nutrients for atolls unclear (usually
  out in the middle of the ocean)
• possible explanations
• nutrients accumulated over time are efficiently
  recycled
• reef bacteria and filter feeders capitalize on
  nutrients from dissolved/particulate organic
  matter
• nutrients are stored in the biomass of the
  communitys inhabitants

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Coral Reef Ecology

• Photosynthesis on Reefs
• photosynthetic organisms zooxanthellae, benthic
  algae, turf algae, sand algae, phytoplankton,
  seagrasses
• more dense than tropical ocean, with greater
  biomass than reef animals
• associations of producers with other organisms
  assist in efficient recycling, e.g.,
  zooxanthellae with corals, cyanobacteria with
  sponges

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Coral Reef Ecology

• Reef productivity
• ratio of primary production to community
  respiration P-R ratio
• P gross photosynthesis
• C community respiration
• P-R ratio used to measure state of development of
  a biological community

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Coral Reef Ecology

• Reef productivity (continued)
• P-R ratio gt 1 primary production exceeds
  respiratory needs
• biomass increases, excess biomass available for
  growth or harvesting
• P-R ratio 1 steady state (climax)
• little biomass remains available for growth
• P-R ratios for coral reefs are typically close to
  1
• high productivity balanced by high respiration

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Coral Reef Ecology

• Reef productivity
• increases in productivity are often the result of
  eutrophication
• eutrophication nutrient enrichment
• eutrophication typically manifested as a dramatic
  proliferation of algae
• if grazing doesnt increase, algae can grow over
  and smother corals
• This will happen with too much sewage and
  fertilizer runoff

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The Coral Reef Community

• Competition among corals and other reef organisms
• fast-growing, branching corals grow over
  slower-growing, encrusting or massive corals and
  deny them light
• slower-growing corals extend stinging mesenterial
  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

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The Coral Reef Community

• Competition among corals and other reef organisms
  (continued)
• Slower growing corals are more aggressive than
  fast growing corals
• Massive corals are generally more shade tolerant
  and are able to survive at greater depths
• as a result
• fast-growing, branching corals on many reefs
  dominate upper, shallower portions
• larger, slower-growing corals dominate deeper
  portions

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The Coral Reef Community

• Competition among reef fishes
• High diversity
• coral reefs - marine habitats with greatest
  diversity/abundance of fishes
• seems to defy competitive exclusion principle,
  which suggests that no 2 species can occupy the
  same niche
• 60-70 of reef fishes are general carnivores
• about 15 are coral algae grazers or omnivorous

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The Coral Reef Community

• Competition among reef fishes (continued)
• hypotheses proposed to explain this
• competition model factors such as time of day or
  night, size of prey, position in the water
  column, etc. provide each species with a unique
  niche (hence, no competition)
• predation disturbance model assumes competition,
  but suggests that the effect of predation or
  other causes of death keep populations low enough
  to prevent competitive exclusion

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The Coral Reef Community

• Competition among reef fishes (continued)
• hypotheses proposed to explain this
• lottery model assumes competition occurs, but
  suggests that chance determines which species of
  larvae settling from the plankton colonize a
  particular area of the reef
• resource limitation model suggest that available
  larvae are limited and that limitation prevents
  fish population from ever reaching the carrying
  capacity of the habitat

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The Coral Reef Community

• Effect of grazing
• reef is a mosaic of microhabitats with different
  levels of grazing and different algal communities
• grazing of larger, fleshier seaweeds permits
  competitively inferior filamentous forms or
  coralline algae to persist
• herbivory decreases with depth
• damselfish form territories where they exclude
  grazers and permit abundant algal growth
• provides habitat for small invertebrates
• overgrows corals fast-growing, branching corals
  are most successful near damselfish

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The Coral Reef Community

• Effect of predation
• predation of sponges, soft corals and gorgonians
  provides space for competitively inferior reef
  corals
• small invertebrates are almost all well hidden or
  camouflaged, indicating the prevalence of
  predation in the reef

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The Coral Reef Community

• Symbiotic relationships on coral reefs
• cleaning symbioses
• cleaner wrasses, gobies, etc. feed on parasites
  of larger fishes
• cleaning organisms set up a cleaning station
• Other symbiotic relationships
• clownfishes and anemones
• conchfish and the queen conch
• gobies and snapping shrimp
• crustaceans and anemones

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Evolutionary Adaptations of Reef Dwellers

• Adaptive behaviors to avoid predation
• invertebrates hide during the day and forage at
  night
• producing a poisonous coating of mucus
• burying the body in sand to hide
• inflating to appear larger
• hiding at night when nocturnal predators are
  active

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Evolutionary Adaptations of Reef Dwellers

• Structural adaptations for feeding
• cnidocytes (stinging cells) of cnidarians aid in
  prey capture
• radioles (hair-like) appendages of Christmas tree
  worms are used to capture phytoplankton
• non-bivalve mollusks use radula to graze algae
• mantis shrimp have extremely sharp forward
  appendages
• snapping shrimp use sound to defend territory and
  stun prey
• crinoids (feathers stars) use basket of mucus to
  feed

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Evolutionary Adaptations of Reef Dwellers

• Protective body covering
• tough, defensive exteriors help animals avoid
  predation, but can limit mobility and growth
• Role of color in reef organisms
• color for concealment and protection
• Many invertebrates have colors and stripes that
  allow them to blend in with the environment

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Evolutionary Adaptations of Reef Dwellers

• Role of color in reef organisms (continued)
• brilliant color of many fish actually helps them
  to blend in with colorful background of the reef
• other types of camouflage
• body shape
• warning coloration
• e.g., lionfish
• other roles of color
• defending territories
• mating rituals

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Threats to Coral Reef Communities

• Effect of physical changes on the health of coral
  reefs
• hurricanes and typhoons topple and remove coral
  formations
• El Niño Southern Oscillation (ENSO)
• changes winds, ocean currents, temperatures,
  rainfall and atmospheric pressure over large
  areas of tropical and subtropical areas
• can cause massive storms

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Threats to Coral Reef Communities

• Why are coral reefs important?
• protect coast from high surf conditions
• remove large amounts of carbon dioxide from water
  and air
• provide habitat for a huge diversity of
  invertebrates and fish
• economical value, many people earn living by
  collecting and processing reef products
• important place of recreation
• have potential for harvesting pharmaceutical
  products

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Threats to Coral Reef Communities

• Effects of human activities
• Destructive fishing practices
• overfishing, i.e., eliminating grazers, allows
  algae to overgrow reefs
• poisonous chemicals used to capture fish also
  poison corals
• explosives used to stun and capture fish can
  cause massive destruction to coral
• bottom trawling for fish also destroys coral
  structures

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Threats to Coral Reef Communities

• Effects of human activities (continued)
• Coastal development
• produces runoff containing nutrients, pesticides,
  toxic wastes
• increases sedimentation and changes patterns of
  water flow

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Threats to Coral Reef Communities

• Effects of human activities (continued)
• Other human activities
• coral mined for use as bricks, road-fill, cement
  component
• removed to make jewelry
• inexperienced snorkelers and boaters damage reefs

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Threats to Coral Reef Communities

• Effects of human activities (continued)
• effects of human-induced climate change in
  atmosphere
• increased levels of carbon dioxide from burning
  of fossils fuels primary cause of ocean warming
• causes corals to become stressed and more
  susceptible to coral bleaching and disease

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Threats to Coral Reef Communities

• Effects of human activities (continued)
• 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

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Threats to Coral Reef Communities

• Effects of human activities (continued)
• coral diseases
• black band disease a distinct dark band of
  bacteria migrates across the living coral tissue,
  leaving behind a bare white skeleton
• white pox characterized by white lesions and
  caused by Serratia marcescens
• other coral diseases
• white band disease
• white plague
• CYBD (Caribbean yellow band disease) or yellow
  blotch disease

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