Coral ReefsMs. Springstroh

Source of information:http://oceanservice.noaa.gov/education/kits/corals/coral01_intro.html

Almost all corals are colonial organisms◦ Composed of hundreds of thousands of individual

polyps Polyps are animals Polyps in a colony are connected by

a thin sheet of tissue (cells aggregated together)

◦ Polyps are sessile

Structure (again)

Reefs form when polyps secrete calcium carbonate skeletons◦ Limestone◦ CaCO3

From polyps to reefs

Calcium carbonate skeleton secreted by the lower portion of the polyp◦ Produces a cup-like structure called a calyx, which

the polyp sits in◦ Bottom of cup is called a basal plate

Every so often, a coral polyp will lift itself up off its basal plate and secrete a new calyx◦ More CaCO3◦ This is how a coral reef grows

When corals are stressed, they retract into their calyx so that no part of the polyp is exposed above its skeleton

Polyps also may extend out of their calyx, especially when they feed

Calyx

Free-swimming coral larva, called a planula, attaches to rocks or other substrates near shallow areas, such as by islands or the edges of continents

Planula metamorphoses (transforms) into a polyp

Polyps divided over and over to form reefs

How Corals Form: Coral Life Cycle

Corals may utilize asexual or sexual reproduction◦ Asexual reproduction: reproduction that does not

require gametes (sex cells) A new polyp– a clone of its parent– “buds” off from

the parent and begins a new colony itself◦ Sexual reproduction: some corals release gametes

(sperm and egg cells) into the water Egg and sperm combine to form planulae

Coral Reproduction

Coral Reproduction

In some reefs, the all the coral species release their sperm and egg at the same time◦ Called broadcast spawning

Influenced by temperature, length of day, lunar cues, time of sunset

Planulae swim toward the light◦ Become part of the waters at the surface of the ocean

Current transports planulae Planulae eventually swim back toward bottom

of ocean◦ Will settle there if conditions are favorable

metamorphose build a colony

Zooxanthellae are photosynthetic algae which live in corals’ tissues

Have a mutualistic symbiotic relationship with corals◦ Symbiosis: close relationship between two

organisms of different species◦ Mutualism: a symbiotic relationship in which both

species benefit (symbolized by + / + )

The “Z” word that nobody can pronounce

Corals provide zooxanthellae with a protected environment in which to live, and with the materials needed for photosynthesis

Zooxanthellae help the coral eliminate waste, provide the coral with oxygen and glucose, & help the coral secrete its skeleton◦ If the coral has enough glucose/ “energy”, it can secrete a calcium

carbonate skeleton and grow!◦ This energy comes from the ‘waste’ molecules produced by the

zooxanthellae during photosynthesis.

Both of these contribute to the “recycling of nutrients”

This mutualistic symbiotic relationship is VERY VALUABLE because tropical waters are nutrient-poor!

Lime (calcium and oxygen) is dissolved in sea water

Corals have carbon and oxygen in their cells◦ Combines with calcium and oxygen from the

water◦ Produces CaCO3

Lab: Building a Coral Skelton

Chalk = contains calcium

Clear liquid from chalk + vinegar (C2H4O2) mixture = dissolved lime = “sea water”

Baking soda = sodium bicarbonate, NaHCO3 = coral’s cells◦ Adding baking soda + water to dissolved calcium

(chalk + vinegar mixture) CaCO3

Pour 250mL of vinegar into a beaker. Break chalk into small pieces. Put into

beaker. Label beaker. Let stand overnight.

Lab Directions: Day 1

Pour off some clear liquid from chalk mixture into cup labeled “dissolved limestone”. Rinse your beaker.

Obtain 240mL of tap water in beaker. Add 3-4 tablespoons baking soda; stir, then let stand for 15 minutes.

Pour off some clear liquid from baking soda beaker into another cup labeled “dissolved baking soda”. Rinse your beaker.

Pour “dissolved baking soda” into “dissolved limestone” beaker. Observe what happens.

Day 2

Mixing of the “dissolved limestone” and the “dissolved baking soda” represents a coral polyp extracting calcium from sea water, combining it with carbon dioxide, and producing CaCO3.

Chalk = contains calcium

Clear liquid from chalk + vinegar (C2H4O2) mixture = dissolved lime = “sea water”

Baking soda = sodium bicarbonate, NaHCO3 = coral’s cells◦ Adding baking soda + water to dissolved calcium (chalk + vinegar

mixture) CaCO3

Source: http://www.usm.edu/marineeducation/old/coralreef/15.pdf

Lab notes

Write a paragraph (using at least four complete sentences) about how a coral builds its skeleton. Try to use as many examples from this lab as possible.◦ Things to think about and include:◦ What does the white precipitate represent?◦ What does the “dissolved limestone” represent?◦ What does the “dissolved baking soda” represent?◦ What does mixing the “dissolved limestone” and

“dissolved baking soda” represent?

Lab

White precipitate= calcium carbonate◦ How does it form?

Coral polyp extracts calcium from sea water (vinegar + chalk mixture, aka dissolved limestone) & combines it with carbon dioxide

Lab Results

Corals can build 3 types of reefs:◦ Fringing: grows very close to or on

shore

◦ Barrier: also grows close to shore but has a lagoon separating it from the shore

◦ Atoll: a ring of coral that surrounds a lagoon, often grows on a submerged mountain or volcano

Types of Coral Reefs

FRINGING

BARRIER

ATOLL

Midway Atoll

Coral Bleaching Zooxanthellae provide coral with greenish-brown

color When under stress, corals expel their

zooxanthellae◦ Coral therefore loses its color and one of its foods sources

Result: coral polyps will die◦ Leave behind white calcium carbonate skeleton

http://www.globalwarmingart.com/images/4/48/Partially_Bleached_Coral.jpg

Types of Coral

ELKHORN CORAL

BRAIN CORAL

TABLE CORAL

Types of Coral

PILLAR CORALSTAGHORN CORAL

Food chains show how living things get their nutrients, and how these nutrients are passed from one organism to another

Producers produce their own nutrients, via photosynthesis

Consumers eat other organisms to obtain nutrients◦ 3 kinds of consumers:

Herbivores: eat only plants Carnivores: eat only animals Omnivores: eat both plants and animals

Coral Reef Food Chains

A trophic level is the position in a food chain an organism occupies

The first trophic level is made up of producers. These producers are called primary producers.◦ Use photosynthesis to create nutrients such as

sugars◦ Examples within a coral reef: seaweed,

zooxanthellae

The next trophic level is made of primary consumers– organisms which consume the primary producers, OR the ‘waste’ products given off by the primary consumers◦ Examples within a coral reef: corals, sponges

Secondary consumers prey on primary consumers◦ Examples within a coral reef: grouper, turtles,

crown-of-thorns sea star

Feeds on corals by pushing its stomach out through its mouth◦ Covers coral colony with its stomach◦ Digests coral tissue

Crown of thorns sea star

Tertiary consumers prey on secondary consumers◦ Examples within a coral reef: gray reef shark (also

considered a top predator: has no natural enemies)

Only about 10% of the energy at one trophic level on a food chain is passed onto the next level.◦ The remaining 90% of energy will be used by the

organism at the lower trophic level to do its normal activities, such as movement & respiration, OR will be lost during the energy transfer.

Food chains are inefficient!