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Reefs are large-scale, organically constructed, wave resistant structures
One of the rarest ecosystems on Earth
The marine ecosystem that as the highest diversity of life
Because of the fine environmental partitioning, reefs are fragile ecosystems
They are highly vulnerable to mass extinction

Reef Construction

Framework building organisms-corals
Internal sediment-sediment is shed into pockets

Reef Construction

Patch reefs are small structures-SUV sized dive or take
Barrier reefs fringe islands or continents and can be thousands of km long

Factors that promote reef formation

Warm water-makes it easier to form Calcium Carbonate skeletons
Clear water-mud is bad for organisms that live on reefs, clogs breathing apparatus, harder for them to feed
Light-many organisms have symbiotic algae-helps make CaCO3 skeletons
they typically form in tropical, shallow water

Pre-Cambrian reef systems

Dominated by microbial build-ups called stromatolites
These can be very large-scale or small patch reefs
Downfall of microbial reefs by the Cambrian largely blamed on grazing organisms(snails)

Cambrian reef systems

Formed from early group of sponges called arochaeocyathids
Reefs were bound by microbial buildups between the sponges
Reef system collapsed by end of Early Cambrian

Ordovician reefs

Small microbial/aglal mounds abound
No large-scale reef communities

Silurian-Devonian reefs

So-called strom-tabulate reefs
Tabulate corals provide framework
Binding by sponges called stromatoporoids
Reef system collapsed by end of Devonian


Reef systems absent
Some large buildups lacking skeletal framework-so called mud mounds

Permian reefs

Return of sponge algal reefs
Large reef tracts built up notably in Texas and China
Collapses of the reef ecosystem at the end of the Permian-mass extinction

Cretaceous reefs

Reefs built by a group of clams called rudists
Forms large reef trends throughout the tropical Earth
Reef system collapses at the end of the Cretaceous-mass extinction

Paleogene reefs

Sponge algal reefs return again
Reefs are not of large scale
Replaced by modern reefs

Modern reefs

Modern reefs are coral algal reefs
Found in tropical seas across the globe
Very fragile environments

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