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Emma Hartswick. Adaptations in coral reefs. http://www.gefcoral.org/Portals/25/targeted_research/Jord%C3%A1n-Garza%20Photo%201.%20Counting%20corals_web5.jpg. What are coral reefs?. Coral reefs form because of polyps, which are soft bodied organisms related to anemone and jellyfish

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emma hartswick
Emma Hartswick

Adaptations in coral reefs


what are coral reefs
What are coral reefs?
  • Coral reefs form because of polyps, which are soft bodied organisms related to anemone and jellyfish
  • At their base is a hard limestone skeleton known as a calicle
  • Reefs form when a polyp attaches to a rock and divides into thousands of clones
  • What we recognize as coral is the connected calicles of polyps functioning as a single organism
where are they found

Coral gets its varied colors by hosting species of algae called zooanthellae

  • These algae require adequate sunlight for photosynthesis, so coral reefs are found in warm, shallow waters in tropical climates throughout the world
  • The algae transfers needed nutrients to the coral, although at night some corals may ensnare zooplankton or small fish for food
Where are they found?
ecology of a reef

Coral Reefs are like rainforests of coral

  • They contain many layers, each of a differing type of coral structure
  • Coral reefs are only 0.2 % of the world’s oceans but contain 25% of marine life
  • Because of the close proximity of so many species competing for limited resources, organisms have evolved into very specialized niches which build the complex interdependent hierarchy of the reefs
  • Adaptations are key to survival in a reef, separating organisms from each other and creating the diversity that is both distinctive to reefs, and necessary to success in them
Ecology of a reef
types of adaptations

There are many types of adaptations that aid organisms in survival, but those most common in reefs are

  • Symbiotic
  • Defensive
  • Predatory
  • Reproductive
Types of Adaptations

Symbiosis is a relationship between two species in which one or both of the species benefits

  • Symbiotic relationships evolve when species living close to one another become dependent on each other’s functions
  • Overtime, these relationships are refined, further drawing the pair together
  • In coral reefs, the most common form of symbiosis is mutualism, in which both species benefit from the relationship
  • Example: Anemonefish and anemone
  • Example: Giant clams and algae
clown anemonefish
Clown anemonefish
  • “Finding Nemo” fish are really one of many clown fish look a likes
  • Real anemonefish have slightly different shape and habitat
  • Approximately 4.3 inches, live 6 -10 years
  • Live in Indian Ocean, Red Sea and West Pacific
  • “Dance” with anemone, touching it with different body parts to acclimate
  • Layer of mucus makes the fish immune to the lethal sting
  • Fish gains safety and food scraps, in turn, cleans parasites off anemone, drives off intruders and lures in prey
  • Anemone immunity is acquired and can be lost


anemonefish behavior

All anemonefish born are male, and only switch to become the group’s dominant female (which the largest males will mate with)

  • This allows groups to be self sufficient if dominant female dies
  • Creates a functioning hierarchy that increases the stability of the population
  • One of few species that switch from male to female. Sex changes from female to male are much more common in reef
Anemonefish behavior
giant clam
Giant Clam
  • Clam can reach 1.2 m, weigh 500 lbs and live up to 100 years
  • Once they clam attaches early in its development, it cannot move
  • Clam reach this large size by eating the sugars and proteins produced by zooanthellae (algae) on their tissues
  • In return for the food the clam receives, it provides a safe, sun lit home where the algae can photosynthesize


giant clam10

Adult clams are simultaneous hermaphrodites. Born females and mature to into hermaphrodites

  • Release both male and female gametes, but 30 minutes apart to avoid self fertilization
  • First egg release triggers releases in other clams within minutes, beginning chain reaction of fertilization that increases diversity
  • Once established within first weeks, can no longer move – hermaphroditic reproduction a solution to lack of variation
Giant clam
  • Some organisms have evolved special defensive mechanisms including behaviors, colorations and camouflages
  • These techniques may either hide them from predators, antagonize and defend against attackers physically, or warn enemies to stay away
  • Example: Sea cucumbers have evolved unusual ways to frighten off assailants
  • Example: Porcupinefish can inflate themselves to ward off predators
  • Example: Lionfish are brightly colored to warn enemies and are poisonous if attacked
sea cucumbers

Sea cucumbers are related to sea urchins and star fish and live at the bottom of reefs or on the ocean floor in the sand

  • They eat algae, small animals and wastes and function much like earthworms for their aquatic environments
  • Can be 0.75 inches to 6.5 feet long
Sea cucumbers
sea cucumber s defense

When threatened, sea cucumber release sticky threads that trap their predators

  • Others can violently contract their muscles and excrete their internal organs to confuse and frighten their enemies
  • These lost vitals are quickly regenerated
Sea cucumber’s defense


  • Shaped like a short baseball bat approximately 3 feet long
  • Live in weeds or caves/holes of reefs and lagoons
  • Scales of fish form spikes that lie flat against the fish’s body
  • When threatened, fish gulps water and inflates body, reaching double or triple their normal size
  • Spines sick straight out, frightening predators and making the fish extremely difficult to eat
other porcupinefish defenses

Aside from being a prickly lunch, porcupinefish have high levels of poison in their reproductive tissues and livers

  • Toxins accumulate from the types of algae that they ingest when preying on mollusks, snails and sea urchins
  • Would-be predators remember becoming sick after attacking these fish, discouraging them from trying to eat them in the future
  • The combination of the adaptations that the porcupinefish has means that it has very few predators…. Like 1 in adulthood

Porcupinefish also have special beak-like mouths that are well suited to crushing the crunchy critters that they eat

Other Porcupinefish Defenses

Average of 1 foot in length

  • Lionfish have an array of venomous spines on their back
  • They use their poison only for protection, not to hunt their own prey
  • Their brightly colored, vibrantly patterned bodies and showy pectoral fins warn assailants to keep their distance

Some organisms have evolved special hunting techniques that allow them to more efficiently obtain food in the competitive reef environment

  • Example: Geographic Cone Snail is small but venomous to make up for its sluggish movements
  • Example: Carnivorous star fish has evolved into a swift and efficient hunter
geographic cone snail
Geographic Cone snail
  • Approximately 6 inches
  • Has toxic venom that paralyzes fish instantly since creature itself very slow
  • Potent poison containing 100’s of toxins, delivered through harpoon like tooth that shoots out of extendable nose
  • Live on reef edge under dead coral, in sand pocket or on reef
  • Feed at night and capture small fish which they store and eat individually
  • Has caused human deaths

Isolated proteins in venom have painkilling effects for humans more potent and less harmful than morphine.

Intricate shell design prized by collectors.

“tooth” can reach any part of shell, making it unsafe to pick up.

crown of thorns starfish
Crown of thorns starfish
  • Carnivorous starfish that feeds on coral polyps
  • Can grow to a diameter of 40 cm
  • Starfish is extremely mobile for such an organism and is able to move backward and forwards, turn around, and use its 12-19 legs independently from each other
  • They are insensitive to touch or gravity but sense predators through water born chemicals


crown of thorns feeding habits

To feed, they climb onto coral and release digestive enzymes from stomach that liquefy and absorb its tissues

  • Has a significant damaging effect on reefs, which has increased since 70’s
  • Capture of reef fish has allowed Acanthasterplancito proliferate by reducing natural species control
  • Has few predators due to poisonous spines, which cause local paralysis and nausea
Crown of thorns feeding habits
  • Some organisms have developed sexual behaviors that allow them to be better suited to the reef environment
  • Reproductive adaptations allow for more certainty of species survival and increased diversity
  • Example: Coral Trout change sex part way through life
  • Example: Different species of Coral have evolved to reproduce asexually or sexually
coral trout
Coral Trout
  • Coral trout are protogynoushemaphrodites, meaning that the entire species is born female but changes to male as the fish matures
  • Sex change occurs at an average of 42 cm in size, approximately 7 years old
  • Trigger of the sex change is unknown, but may have evolved from fishing pressures
  • Supported by evidence that sex ratios vary in areas open or closed to fishing.
coral trout reproduction

Spawning occurs when water temperature warms

  • Event takes place at dusk and when there is a strong tidal flow to minimize the risk of predators attacking the fertilized eggs
  • To begin courtship, males swim down to the bottom where females are resting and perform an elaborate mating dance
  • If the female consents, the two swim rapidly to the surface and release their gametes as they turn quickly, forming a cloud where the eggs are fertilized
  • The larvae are vulnerable at first and feed off the nutrients of their membranes, but they quickly mature in the water column, are dispersed to different reefs, and soon catch their own prey
Coral trout Reproduction
asexual coral reproduction


  • New polyps bud off of parent polyps when parent reaches a certain size
  • Creates new polyps that are genetically identical to the parents


  • Broken part of original coral may re-establish if it settles in a favorable location, remains identical to the parent colony
Asexual coral reproduction
sexual coral reproduction
Sexual Coral Reproduction
  • Broadcast Spawning:
  • Distributes offspring over a larger area
  • Coral releases both gametes which float to surface and fuse to form planulae
  • Planula float in water column until they find a suitable space to sink and colonize
  • Many produced to compensate for high mortality
  • Only spawn a few days of every year
  • Timing is key and each species synchronizes on same day
  • Timing based on temperature, the length of the day and the lunar cycle
  • Final release occurs at sunset


sexual coral reproduction26


  • Male gametes sink and are taken in by female coral and fertilized
  • Planula released from female at a mature stage
  • Successful but occurs across much smaller distances
Sexual Coral Reproduction

Both forms of sexual reproduction increase Coral diversity and thus, the survival of the species