EVSC20004 Lecture Notes - Lecture 15: Fringing Reef, Coral Triangle, Intertidal Zone
21 Jun 2018
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Coral Reef Ecosystems:
1) What is a coral reef?
Coral reefs are geomorphologic structures formed by accretion and accumulation of
aragonite, produced primarily (but not exclusively) by hermatypic corals
There are 2 types of corals:
a) Hermatypic- produce CaCO3 skeleton (provide the vast majority of the coral
reef’s structure); hard corals (Made CaCO3 whilst also secreting it)
b) Ahermatypic- do not produce CaCO3 skeleton; soft corals
Reef building corals are known as scleractinian corals and are categorised as phylum
cnidarian Class anthozoa Subclass zoantharia Order scleractinia (=madreporaria)
Mega-biodiverse (most diverse marine system with 32/34 phyla in them)
Complex and diverse biological associations
Topographically complex (‘Trees of the ocean’)
Physically stable (Has existed for millions of years)
2) Coral symbiosis:
Corals are animals that are made up zooxanthellae (algal endosymbionts which
provide photosynthesis, takes in energy and is used by the coral to grow).
oZooxanthellae are also found in anemones, nudibranchs and clams
They have other feeding methods- tentacles, mucus sheets on surface,
mesenterial filaments, and by absorbing dissolved organic matter (DOM).
Necessary for reef building
3) Coral Reefs- Structure and Distribution:
Aside from corals, the following organisms also contribute to the overall structure and
distribution of coral reefs:
Coralline algae are major depositers of CaCO3 and acts as buffers for corals and
other organisms within the coral reef from wave activity
Sponges and Bryozoans trap and cement sediment within the coral reef
4) Importance of reef ecosystem
Economics- Worth over US$30 billion each year in goods and services
oFisheries:
Nurseries for 25% of ocean’s fish
Seafood- 1 billion people depend on coral reefs for food and
income (15 tonnes of seafood per km2 per annum)
oTourism
Great Barrier Reef generates US$1 billion per year, Florida Keys
~US$3 billion per year
Alternative income for coastal communities in developing
countries (A lot of coral reefs found in developing countries)
Coastal protection- form a barrier against wave energy, absorb breaking waves
during storms and protect against coastal erosion
Medical opportunities/prospects- anti-viral, cancer and HIV
Intrinsic cultural value- Cultural traditions, biophysical beauty
5) Brief geologic history
First corals were found 500 million years ago (Simple, solitary organisms) and
have gone through a number of extinction events
find more resources at oneclass.com
find more resources at oneclass.com
First reef building corals were found 250 million years ago
Corals we know today are only ~10,000 years old
Modern corals are building upon the first corals
6) Types of reefs
Darwin proposed that the many types of reef structures that exist today had come from
a volcanic event in which the volcano itself had formed the structure of reefs.
Main types of reef structures are:
Fringing reefs (Close to land)
oAdjacent, attached or nearshore (Found along the coast)
oNo lagoon
oInfluenced heavily by the land- explains why there are high non-
carbonate sediments, rainfall (Other types of reefs are more influenced
by the ocean)
Barrier reefs (further from shore)
oOff-shore structures (Larger than fringing reef)
oHave lagoons separating shorelines
oOceanic controlled (e.g. Wave-resistant consolidated limestone)
oHold the highest biodiversity as opposed to fringing reefs
Atolls (encircling lagoon)
oOften ring-shaped
oHave a central lagoon
oOff-shore
oChannels connect to open ocean
oOften submerged
Patch reefs (subsiding)
oVery common
oSmaller reef structures
oOften in ‘deep’ lagoons (10-14m)
oIsolated
Bank reefs (e.g. Hawaii)
oOften offshore
oOften deep
oNo clearly associated lagoon
These reef structures don’t just exist individually and separately, they often flow in each
other).
There are many factors driving the structure of these reefs, and these are:
Horizontal zonation- Wind and waves
oOn an island, you can spot the windward side of the island (branching
corals- fast growing) and the landward side of the island (massive corals-
older)
oCurrents
oTides
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find more resources at oneclass.com
*Front reef, back reef refers to what the wave creates (Front is where the waves hit
first)
Vertical zonation
oDepth
oWave and current strength (Top- front reef is more affected by waves
and currents; wave energy decreases down the water column)
oLight penetration (Less light, less photosynthesis)
oSuspended sediment
7) Modern distribution and regional patterns- Areas where corals are found
Coral Triangle in Asia is where you find most of the coral
Hot water corals near the tropics; there are also cold water corals
Warm water corals Cold water corals
Optimum temperature (~23-25C) Can be as low as 4C
Zooxanthellae No zooxanthellae (influences the
way they feed)
Capture particles Capture particles but have larger
polyps to compensate for not
getting energy from
zooxanthellae
Shallower sea Deep sea
Many species Few species
Reef forming Reef forming
High biodiversity Lower biodiversity
Species richness follows the same pattern as coral
8) Limiting factors
Corals have physical and biotic controls
Physical controls:
oTectonics (Darwin’s subsidence)
Found primarily in Hawaii (Volcanoes produce new land)
oSea level (keep up, catch up, or give up)
oTemperature (Optimal temperature because of the algal symbionts)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Coral reefs are geomorphologic structures formed by accretion and accumulation of aragonite, produced primarily (but not exclusively) by hermatypic corals. There are 2 types of corals: hermatypic- produce caco3 skeleton (provide the vast majority of the coral reef"s structure); hard corals (made caco3 whilst also secreting it, ahermatypic- do not produce caco3 skeleton; soft corals. Reef building corals are known as scleractinian corals and are categorised as phylum cnidarian class anthozoa subclass zoantharia order scleractinia (=madreporaria) Mega-biodiverse (most diverse marine system with 32/34 phyla in them) Physically stable (has existed for millions of years: coral symbiosis: Corals are animals that are made up zooxanthellae (algal endosymbionts which provide photosynthesis, takes in energy and is used by the coral to grow): zooxanthellae are also found in anemones, nudibranchs and clams. They have other feeding methods- tentacles, mucus sheets on surface, mesenterial filaments, and by absorbing dissolved organic matter (dom). Necessary for reef building: coral reefs- structure and distribution:
