Coral Reefs

-Are produced by the organisms that live on them-Are produced by a soft bodied polyp similar to and related to

an anemone-Very diverse ecosystem

Coral Anatomy & Growth-Reef forming corals secrete CaCO3-Are members of the Phylum Coelenterata, Class Anthozoa-Are radially symmetrical

-Subclasses:-Soft Corals- sea fans, sea pens, sea whips-Hard Corals- stony corals (make the reefs)-Are carnivores, tentacles have nematocysts to capture prey and bring it into the digestive cavity

-Most corals live in colonies-Each polyp sits in a hard limestone cup called a corallite-Which is made by their epidermis-The polyp grows by drawing itself up a secreting a new layer in the bottom of the cup-All the polyps are connected over the top of the calcium cup by a thin tissue layer called a cenosarc, so touching and tearing this tissue can injure the coral and let infections in.

Corals have a symbiotic relationship with a unicellular algae, zooxanthellae

Corals give off carbon dioxide which is taken in by the algae and is converted to sugar and oxygen is given

off.

RESPIRATIONin coral polyp

PHOTOSYNTHESISIn zooxanthellae

CO2

H2O

Sugar

O2

Stony corals are found in many varieties. The rate of growth will depend on the type of coral. Branching corals grow faster than massive corals (brain). Corals will show growth in the rate of growth is more than the rate at which they are broken down.

The growth rate of coral reefs is affected by:

Light intensityWater motionWater depthTurbiditySedimentationLength of dayWater temperaturePlankton concentrationPredators (sea urchins, parrot fish, some algae)

Coral Distribution

-non-reef forming corals are found in deep oceans and in temperate zones-reef forming corals are found in tropical and subtropical waters-reef forming corals are usually found on the eastern side of continents more so than on the west-reef forming coral are found in normal salinity seawater {exception is near the Amazon River where a large amount of freshwater flows into the Atlantic}-reef forming coral are found within 25-70 m of the surface of the water -corals need warm water to deposit the calcium carbonate easily

http://www.oceanservice.noaa.gov/education/corals/media/supp_coral04a.html

Coral Reef Formation

Two general types of reefs:1.Shelf Reefs- form off the continental margin (shelf) also a fringing reef- a coral

reef that closely borders the shoreline2. Oceanic Reefs- form around islands

- three types of oceanic reefs:a. fringing reef- ex. thru/out the Red Seab. barrier reef- are further offshore and are separated from the

shoreline by a lagoonEx. Great Barrier Reef- Australia

c. atoll- a ring shaped chain of coral reefs from which a few low islands may project above the surface of the waterex. Marshall Islands

It has be theorized that each of the types of reefs are actually an evolutionary

process.Newly formed volcanic islands become populated with coral polyps which as they grow from a fringing reef along the shoreline waves cause pieces of the reef to break loose and move down the

sides of the volcano where more corals now develop upward toward the waters

surface the weight of the growing coral reef and the cooling of the volcano causes the island to sink creating a barrier reef further sinking of the island below the water’s surface which leaves a lagoon ringed by a group of islands that are

supported by coral reefs called atolls

See pg 273 Figure 10.7 of text

Reef Zones

Algal ridge- a low jagged coral ridge on the windward side of the reef- affected by wave action

Buttress- seaward side of a reef, no deeper than 20 m- affected by continuous heavy wave action

Reef Flat- the portion of the reef that extends behind the algal ridge to the island- nearly flat, level surface barely covered by water

Coral Reproduction

Corals can reproduce asexually or sexuallyAsexual reproduction can be from:

a. budding where a smaller version of the adult breaks off from the polyp

b. fragmentation where a section of coral reef breaks off from the rest of the colony- could be beneficial if the type of coral has a fast growth rate- one type of coral could dominate a reef- reduces the chances of altering the species as with sexual reproduction (the gene make-up of an organism)

Sexual reproduction- eggs can be fertilized internally where they are held in the digestive cavity until motile sperm cells fertilize the eggs and they can stay there and develop before being released into the water can be released right away

or fertilized externally where the eggs & sperm are released in the water to fertilize and develop in the open ocean

Corals spawn synchronously (at the same time) right after a full moon, but it is not true for all corals in all areas. This could cause problems if a rainstorm and drop in salinity occurs at the same time. It could wipe out a whole reproductive season in that species of coral.

Coral Reef FishFish use the reefs for protection, prey on plants, algae, and animals living there. Some will even eat the reef. Fish are an important part of the reef community because they bring in nutrients from other areas through waste material.

Symbiotic Relationships on the Coral Reef

1. Mutualism- remoras and sharks also called inquilinism which is a benefit of protection from the relationship.

2. Cleaning Symbiosis is a form of mutualism

3. Commensalism- shrimpfish face down among the spines of a sea urchin, where the shrimpfish benefits but the urchin doesn’t.

4. Parasitism

Animals that rapidly change their skin coloration to match their environment do so by expanding and contracting pigmented cells in their skin called chromatophores.Iridocytes are cells that contain reflecting crystals which can produce a wide variety of colors.

Disruptive coloration, contrasting lines, false eye spots are all used to distract and disguise predators.

Bright colors can be used to attract potential mates or warn others that a fish of animal may be poisonous.

Purposes of different color patterns:

Concealment

Disguise

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Mimicry –to look like a friendly fish or one that may be dangerous

Mimicry –to look like a friendly fish or one that may be dangerous

Coral Reef diversity rivals that of tropical rainforests. This many be in part to constant attack from natural agents ie. storm waves; therefore, there is a constant changing of the ecosystem with a constant changing of primary species

1. Predators to Coral Reefs: Parrot fish2. Crown of Thorn Sea Stars- if allowed to overpopulate because their natural

predator (a snail) is removed will damage reefs or large amounts of larva are swept in to the region

3. Sea Urchins that graze on algae are suddenly killed and then the algae is allowed to overgrow, it competes for space on the reef.

4. Blackband Disease- a cyanobacterium that grows ina dense matt and separates the cenosarc from the skeleton allowing other pathogens to come in a kill the coral polyp. It appears as a black band of dead tissue as it moves over the reef.

5. Bleaching- stressed corals get rid of their zooxanthellae causing the coral to turn white. It can be caused by temperature changes, excess ultraviolet radiation may cause this.

6. Sedimentation7. Nutrification- excess nutrients in the water will enhance algae growth, this can

occur when fertilizers run off into the rivers and reach the nearby coral reefs

Coral Reef Mortality

Blackband Disease

Yellowband Disease