Transcript Coral Reefs - Humble ISD

Coral Reefs
General Characteristics
• Coral reefs are built from the
remains of stony (or hard)
corals
• Reefs cover about 100,000
square miles of the world’s
shallow marine areas
• Located in shallow, tropical
waters
• They grow gradually as the
organisms that form their
living surfaces multiply,
spread, and die, adding their
limestone skeletons to the
reef.
Types of Reefs
• The basic Coral Reef
classification scheme was
first proposed by Charles
Darwin
• There are three main
types of reefs:
– Fringing
– Barrier
– Atolls
• There are two other
reef types:
– Patch reefs
– Bank reefs
Fringing Reefs
• Occur adjacent to the land,
with little or no separation
from the shore
• They develop through
upward growth of reefforming corals on an area of
continental shelf.
• May have a completely
shallow lagoon in some
areas, or no lagoon at all
• Most common reef in the
Greater Carribbean and Red
Sea
• Also surround many South Pacific and
Indian Ocean Islands
• Most susceptible to coastal development,
agriculture, pollution, and other human
activities resulting in sedimentation and
freshwater runoff
Barrier Reefs
• Broader and Separated from land
by a lagoon that can be miles wide
and at least a dozen yards deep
• Usually parallel the shore
• Parts of the reef structure often
protrude above sea level as lowlying coral islands.
– These develop as wave action deposits
coral fragments broken off from the reef
itself
• Largest reefs develop on the edges
of continental shelves (called “shelf
barrier reefs”
– Great barrier reef, Belize barrier reef
Atolls
• Large, ring-shaped reefs,
surrounding a central
lagoon
• found well away from
large landmasses, such
as in the South Pacific
• Usually circular or
horseshoe-shaped
• parts of atolls may
protrude above the
surface forming coral
islands as well.
• Most common in the
Indo-Pacific region
(over 300)
• Rare in Caribbean
(only 10-15)
– Southern Mexico and
Belize
• Can exceed 100
miles in diameter
• Central lagoons can
be several thousand
square miles
Patch Reefs
• Small reefs found
within the lagoons of
other reefs
• Usually small,
isolated outcrops of
coral surrounded by
sand and / or
seagrasses
• Provide refuge and
food for may species
of animals and fishes
Bank Reefs
• Reef structures with no obvious link to a
coastline
Evolution of the Three Main Reef
Types
• As first proposed by Charles Darwin:
• Darwin proposed the three main reef types
are simply different stages in the
geological ‘evolution” of Pacific oceanic
islands.
Darwin’s Theory
• Fringing reefs began
to grow near the
shorelines of new
islands when
conditions for growth
were ideal
• As the island began
to gradually subside
into the sea, the coral
was able to grow at
the same rate, and
remained in place at
the sea surface, but
farther from shore.
• It was now a barrier
reef
• Eventually, the island
disappeared below
the sea surface,
leaving only the ring
of coral surrounding it
• It was now an atoll
• Darwin’s theory of “reef evolution” was
verified for the Indo-Pacific reefs in the
early 1950’s
– After analyses of deep core drilling at Bikini
and Eniwetok Atolls
– We now know, however, that in some cases,
the three types can be formed by different
processes as well
Reef Formation
• Millions of Stony coral polyps are the
marine animals responsible for building
the hardened coral reefs you see in the
ocean
• Reefs are excretions of calcium carbonate
produced by each polyp
• New polyps secrete reef on top of older
polyps
Reef Growth Forms
• Hard coral colonies generally exhibit one
of three basic growth forms:
– Massive
– Branching
– Plate-like
Massive
• These rely on sheer mass, growing into
huge sheet or boulder formations that tend
to make up the bulk of a reef
Branching
• These require a small area to anchor
themselves, but branch out into vast, treelike colonies
Plate-like
• Form flat expanses that overshadow other
corals and monopolize the available light
Reef Formation
• Some
corals grow
very slowly
• Some can
grow up to
a few
inches per
year
Zooxanthellae
• Photosynthetic organisms
that live in the tissue of
each coral polyp
• Provide a source of food
to the polyps
• Give corals their color
• Example of a mutualistic
symbiotic relationship
• This is why corals need
sunlight to grow
Organisms Contributions
• Mollusks and
echinoderms add
their skeletal remains
• Grazing and boring
organisms break
down coral skeletons
into sand
• Coralline Algae bind
the sand
Reef Distribution
Coral Reefs are found in all three of Earth’s oceans that have
portions in the tropics. (Pacific, Atlantic, and Indian). They are
scattered randomly, however.
Reef Distribution
• Grow in clear, sunlit,
shallow water
• Average salinity of 36 ppt
• Require warmer water
temperatures, as seen in
tropical and sub-tropical
areas
• Require little or no wave
action
• Little or no sedimentation
from river run-off
• The two main areas of
development that meet
these criteria are the
Indo-Pacific and Greater
Carribean
Belize – Great Blue Hole
Indo-Pacific Region
• Central and South
Pacific Ocean
• Greatest number are
in an area from
southern Phillipines
through western New
Guinea and Indonesia
• Red Sea are is cut off
from large water flow,
so has high number
of endemic species
Greater Caribbean Region
• Tropical, western
Atlantic
• Spans the entire
Caribbean Sea,
Bahamas, and south
Florida
Parts of a Reef
Parts of a Reef
• Reef Slope
• Reef Crest
– Narrowest of the reef
zones
– Massive wall that
absorbs the energy of
incoming waves
(makes water calmer
for back reef zone)
Reef Flat and Lagoon Areas
AKA “Back Reef”
• Contains shallow water
habitats for reef species
• Vital role in food web
• Experiences large
temperature and salinity
changes, reduced water
circulation, and
sediment accumulation
•
•
•
•
•
Main Habitats here:
Patch reefs
Sand plains
Seagrass meadows
Mangrove forests
Importance and Human
Impacts
Importance of Reefs
• Provide protective barrier around islands
and coasts
– Slows down strong currents and waves before
it hits the shore
– Prevent erosion
Importance of Reefs
• Create more living biomass than any other
marine ecosystem
• Contribute to local economies
• Support more species than any other marine
environment
• Possibilities in medicines and science
• Control carbon dioxide levels in ocean water
– The coral polyp turns carbon dioxide in the water into
a limestone shell
Did you know…
• Coral reefs occupy only 2% of the oceans’
area, but are home to ¼ of all known
marine species??????????????
• To date, about 10% of all reefs have been
destroyed?????????????
Coral Reef Threats
Human Impacts on Reefs
• Coastal and ocean
pollution
– Oil slicks, pesticides,
chemicals, heavy metals,
garbage, etc.
• Poisons coral polyps
– Fertilizer and untreated
sewage encourages
algae growth
• High concentrations of
algae can cover the coral
and block sunlight if not
kept under control by
herbivores
Massive oil slick as seen from satellite photos
Human Impacts on Reefs
• Uncontrolled development of
coasts
– Deforestation
– Dredging and coastal development
• Hotels
• Homes
• harbors
Soil run-off - Hawaii
Runoff from a pipe in
the Virgin Islands,
directly near a reef
Human Impacts on Reefs
• Recreation
– Boat anchors crush
corals and gouge the
reef
– Diving tourism
• Divers and snorklers sit,
stand on, or handle
corals
Human Impacts on Reefs
• Collection of corals and organisms
– International seashell and aquarium trades
have put a strain on coral reef ecosystems
– Upsets the balance of the ecosystem
• Market for coral skeletons, shells, sponges and
reef animals for decorations, jewelry, sculptures
• Tropical fish trade
• Coral skeletons are are sold as “live rock”
– Popular in aquariums because of the living bacteria and
algae that acts as a natural biological filter
Human Impacts on Reefs
• Uncontrolled mining for building materials
Human Impacts on Reefs
• Destructive fishing
practices
– Overharvesting of species
can lead to the species’
demise
– Fishing with dynamite,
cyanide, or bleach
– Careless handling of nets,
lines, and lobster traps can
lead to reef damage
– Boating / anchors also
leads to reef damage
• Between 1986 – 1991, ½
of the coral reefs in the
Philippines were
destroyed by this
Coca-Cola bottle with slightly burned
fuse found around the Capone Islands,
Phillipines
Human Impacts on Reefs
• Natural disturbances:
– Hurricanes and tropical storms can strip
corals from miles of reef habitat
Human Impact on Reefs
• Increases in atmospheric carbon dioxide
increases the acidity of the ocean
• Higher ocean acidity makes it harder for
reefs to construct their calcium carbonate
skeletons
– (remember what happened when you added
vinegar to your reef in the lab?)
Coral Bleaching
• Occurs when corals become
stressed
– They expel the zooxanthellae
living in them
• They lose their color and
become whitened
• Can be caused with warmer
surface waters (maybe even
by 1-2 degrees)
– May have a link to global
warming
• Pollution can also be a cause
• Full recovery takes decades
Bleaching can be seen in areas of the Great Barrier Reef
Coral Poisoning
• Very destructive
fishing practice
• A diver sprays sodium
cyanide to catch a
fish
• The poison kills all
corals in the area
Crown of
Thorns
Starfish
Coral Reef Diversity
• Healthy reefs can
house thousands of
species
–
–
–
–
Fish
Invertebrates
Sponges
Soft corals
• Every part of a reef is
used by some animal
• Mutualism –
relationship between
two different species
where they both
benefit