Lesson 15 - Bioherm Communities Through Time

Front 1

Movie - Hike to the Fossil Reef

Front 2

Organosedimentary build-up according to extinction events

Back 2

Community preserved in organosedimentary build-ups can tell us where we are in geological time

OS build-ups are hard hit by extinction events when compared with organisms from other environments.

- lost early in course of extinction, high diversity fauna s can take long time to recover following return of normal environmental conditions.

- long time tom re-establish complex interactions that foster species diversity

Front 3

Identify Precambrian organosedimentary communities and followed mass extinctions.

Back 3

• Stromatolite dominated precambrian mounds
  
• once metazoans with skeleton evolve at base of Cambrian, prevalence of stromatolite mounds decline sharply, because their habitat was disrupted by the evolving Paleozoic Evolutionary Fauna
• When the first herbivores appeared in Early Cambrian, grazed on cyanobacterial mats.
• By middle Ordovician, stromolaite mound were small and restricted to marginal, inner-self environments
• Although stromatolites never dominated reefs after end of Precambrian, there were a few instances where they temporarily regained prominence as a disaster taxa

Middle-late cambrian demise of archaecyathids, earliest silurian, earliest triassic

Front 4

Describe mounds of the Lower Cambrian

Back 4

Archaeocyathids, were the framework of the first ever metazoan mounds in the Early Cambrian

Stromatolites occupied cementing role in these structures, whereas trilobites, brachiopods and sponges lived on the mound's surface

low diversity, and generally homogenous, lacked lateral zonation

limited to tropical paleoaltitude, occupying shallow marine carbonate shelves

Front 5

Lower Ordovician mounds

Back 5

Early Ordovician, siliceous sponges were dominant skeletal component of mounds.

Stromatoporoids and primitive corals, played a much more minor role.

Algae played a imporant cementing role.

Trilobites, brachioposd, and bivavles lives on the surface of the mounds

Front 6

middle ordovician to devonian Stromatoporoid and coral reefs

Back 6

At the base of the Silurian, stromatolite mounds were prevalent

Middle O and Late Devonian reefs, had large sessile benthic organims, such as tabulate corals and colonial rugose corals as well as stromatoporoids

Devonian represents Paleozoic reef growth. Corals did not have complete stability to anchor to substrate.

Sponge Hydnoceras was important framework organism

Structure of MO to D are true reefs in that they exhibit lateral zonation and progress through 4 stages of the Walker-Alberstadt model

brachiopods, bivavles, cephaopods, gastropods and trilobites populated parts of the reef

Front 7

Describe Permain Coral, Brachiopod and sponge mounds

Back 7

In the Permian, most mounds are dominated by algae, include some branching or encrusting organisms such as sponges and corals

Richtofenid brachiopods occur in Permian age mounds

many animals in these communities were decimated by end Permian mass extinction

Front 8

Describe Triassic organosedimentary conditions

Back 8

Midle to upper triasic coral, stromatoporoid and sponge reefs

Triassic -->Stomatolite mounds --> Middle Triassic:

large reefs occurred with colonial scleratininan corals forming the main framework component, whereas stromatoporoid and sponges played a minor role

In these reefs, the corals found in fore reef and reef crest, whereas stromatoporoids and sponges are restricted to more sheltered parts of the reef.

Reefs are the first to show significant erosion from boring bivavles.

Brachiopods, epifaunal vicacles, gastropods, cephalaphods, are present at the reefs of this age

Reefs exhibit lateral zonation, and progress through all stages of Walker-alberstadt model

Front 9

Describe Middle to Upper Jurassic, organosedimentary communtites.

Back 9

Middle to Upper Jurassic Coral, Stromatoporoid, and Sponge Reefs

Reefs took a long time o recover from end-triassic, until middle jurassic

Not like previous refs, limited to deeper water where sponges were dominant.

In nearshore environments, reef ogranisms such as scleractinian corals and stromatoporoids colonized pre-exisitng nearshore mounds

Resulting reef structures were more elaborate and progressed through the Walker-Alberstadt model of reef succession.

Bioerosion was significant as these res were teh first to be impacted by boring sponges.

Decline in spoges was due to scleratinian corals, which had advantage of having zooanthellae.

Front 10

Describe Createacous organosedimentary communtites.

Back 10

Cretaceous Bivalve, Coral, and Stromatoporoid Reefs

During Cretaceous, rudist bivavles were the most important framework component in reefs

Scleractinian corals and stromatoporoids were excluded in more tropical environment by the rudist.

Temperature were 6 to 14 degrees higher, and water was much more saline. may have caused corals to decline.

Cretaceous reef collapsed during end-Cretatceous mass extinction. Rudist became extinct.

Sponges and stromatoporodis sruveve, never to be as diverse or important in reef budling again

Front 11

Describe Cenozoic organosedimentary communtites.

Back 11

Cenozoic Coral Reefs

Cenozoic: reefs dominated by scleractinian corals. Remains the case today.

Successful: basal plate - anchorage to substrate, zooxanthellae, which allowed them to grow quickly and out compete other groups

Clionid sponges are bioeroders

Red Calcerous algae, important cementers

Cenozoic reefs exhibit lateral zonation and progress through all four stages of Walker-Alberstadt model

Reef Crests was dominated by coral accreting at upto 15 m every 1,000 years. Other importnat reef biota, echinoids, bivavles, gastopods, barnacles, and bryozoans

Front 12

Movie - Exploring oceans: Great Barrier Reef

Back 12

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Front 13

Movie - New Species Found at Great Barrier reef

1. What is the "Census of Marine Life"?

2.How are research samples collected from the reef?

3.What are the function of "ARMS" on the reef?

4.How many species can be contained within a single coral head?

5 How many new species have been discovered since the "Census of Marine Life" began several years ago?

Back 13

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Front 14

What are some Modern concerns of coral reefs?

Describe coral bleacing

Back 14

Modern corals stressed by factors of global warming.

changes in water, air temperature, changes in salinity, turbidity, and light levels in ocean

pollution from chemicals, increase in sedimentation due to erosion

Causing corals to expel zooanthellae, or causing zooanthellae to lose some of ther photosynthetic pigments - --> Coral bleaching

Front 15

Movie - Coral Bleaching

1. In what part of the coral do the zooxanthellae live?

2.What is one factor that can stress the coral and affect its relationship to the zooxanthellae?

3.Why are corals without zooxanthellae white?

4.Which two other marine invertebrate groups found in reef environments have resident zooxanthellae?

Back 15

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