Aice Marine Science - Unit 5

Corals

-invertebrate marine animal

-live individually as a polyp

-grow an exoskeleton from calcium and carbon dioxide to make calcium carbonate

-sessile: mobile and anchored in place

-form colonies of polyps to make a reef

Hermatypic corals

hard corals that build reefs

Ahermatypic corals

soft corals that do not build reefs

ex: fan coral, sea pen, sea feathers

Tropical coral requirements

-warm water: 16-35 degrees Celsius with an optimum range of 23-25 degrees celsius

-clear water

-shallow water: within 200m of the surface

-substrate: solid material such as rocks

-salinity: 34-36 ppt, does not live near freshwater runoff

-pH: basic water, 8.1-8.5

Explain why corals can only live in a pH between 8.1 and 8.5

-lower/higher pH causes stress/coral bleaching

-low pH/acidic water dissolves coral skeleton

-results in death

Coral distribution

30N and 30S of Equator

Atoll Formation

1) an oceanic volcano emerges from the sea surface and forms an island which is colonized by reef building corals

2) growth of corals form a fringing reef around the island

-A fringing reef is a coral structure that is attached to land, either mainland or islands

Island begins to sink slowly (subduction) while coral continues to grow (volcano is dormant

3) island continues to sink, barrier reef forms with a lagoon between the reef and island

-Barrier reef is coral growth separated from the mainland or island shore by a deep channel or lagoon

4) island eventually disappears below the sea surface, atoll forms with a ring of small islands with a shallow lagoon in the center

Coral reef benefits to coast

Protects the shoreline from erosion

-dissipates and/of absorbs energy of the waves

Protects coastal:

-properties, anchorage for boats, ecosystems(habitats)

Bioerosion

-parrotfish, triggerfish, and pufferfish consume corals, including skeletons, and through digestion reduce them to sand

-Crown of thorns starfish

-crustaceans and mollusks

-other consumers include predacious and parasitic worms

Physical erosion causes

-weather

-humans

Weather

-hurricanes and typhoons: heavy wave action and currents break apart corals and carry particles away

-tsunamis

-earthquakes: movement of sea floor break apart reefs and create waves and currents

Humans

-dredging: excavating the sea floor to create channels/passages for boats

-boat traffic and anchorages: trauma to reef from boats and anchors

-dumping of garbage

-chemical effects

Explain how humans caused the reduction of coral cover

1) land clearing such as cutting down trees and plants

2) increased runoff

3) increased turbidity of water, sedimentation

4) sewage or pollution directly killed/caused algae bloom

5) coral bleaching

6) coral erode by wave actions/currents

Explain how a coral reef can be reestablished

-affix farmed coral polyps to existing substrate

-add new substrate such as concrete or metal

-reduce local runoff

Explain why artificial reefs can be beneficial to the native reef community

-increases biodiversity

-provides stable substrate for attachment of primary producers

-increases habitats for shelter/reproduction

-reduces erosion

-increases populations

Radiocarbon Dating

-carbon in the atmosphere exists as carbon-12 and carbon-14

-carbon reacts with oxygen to create carbon dioxide which then dissolves into the ocean

-uptake by producers, such as zooxanthellae, use carbon-14 in carbon dioxide to make organic molecules including their calcium carbonate skeletons

Dead coral skeletons

carbon-14: decays back into nitrogen

carbon-12: stays the same

Carbon-14 (half life)

-carbon-14 decays back into nitrogen-14 over time

-half life of carbon-14 is 5,730 years where half the carbon-14 will decay into nitrogen-14

Half life math

one half life: 1/2 x No = No/2

-If No = 3,000g for one half life

1/2 x 3,000 = 3,000/2 = 1,500g

-If No = 3,000g for two half lives

1/2 x 1/2 x 3,000 = 3,000/4 = 750g

A sample of coral was taken from an atoll. The sample contained 25% of the amount of atmospheric carbon-14. Calculate the age of the sample

2 half lives/75% lost

2 x 5,730 = 11,460

A sample of coral contained 75% of the amount of oceanic carbon-14. Calculate the age of the sample.

1/2 of a half life/25% lost

0.5 x 5,730 = 2,865

A sample of coral was found to be 17,190 years old. Calculate the number of half lives

17,190/5,730 = 3 half lives

Half lives with percentages

100% = 0 half lives

50% = 1 half life

25% = 2 half lives

12.5% = 3 half lives

6.25% = 4 half lives

To date corals in atolls:

-samples are taken and the ages of the layers are determined

-oldest corals are at the bottom, younger corals are found in each layer above

-This is evidence of the atoll formation theory, where subduction is the cause of the coral layers

Sea levels and coral growth

When sea levels are high: corals must grow vertically to remain in the photic zone

-High sea levels occur during warm periods (glaciers melt)

When sea levels are low, corals are

exposed to air and die

-low sea levels occur during glacial periods, this allows for the collection of historical sea level data

Explain the presence of corals found on land in central Florida

-Florida was underwater during periods of high seal level

-corals grew and colonized

-sea levels dropped during glacial period (present day)

Describe the conditions needed for tropical coral growth

-pH of 8.1-8.5

-solid substrate

-shallow water (optimum: 20m)

-salinity of 34-36 ppt

-clear water

-warm water 23-25 degrees celsius

Explain what can cause a growing reef to erode

-Bioerosion (explained)

-example of bioerosion: parrotfish consume corals

-caused by over abundance

-example of over abundance: too many parrotfish

-physical erosion (explained)

-example of physical erosion: dredging

Artificial reef building materials

1) concrete

-most natural for attachment(rough surface)

-easy to obtain (make and recycle)

-can be shaped into any form

-long lasting

-solid substrate

2) metal

-corals and producers can attach

-easy to obtain (recycled objects)

-long lasting

-ships and other vehicles need to be cleaned before becoming a reef

-fixes forms

-often more expensive to deploy than concrete

Deployment of artificial reefs

-requires a location where no natural reefs are present and will not move even in storms

-smaller more numerous and spread out reefs are more productive than one large continuous reef structure