Transcript threats to coral reefs from increasing concentrations of dissolved

• Coral reefs are diverse underwater ecosystems held together by calcium
carbonate exoskeletons secreted by corals, which support and protect the coral
polyps.
• Most coral reefs are built from stony corals, which in turn consist of polyps that
cluster in groups.
- “polyps” are tiny marine animals that stay fixed in one place and are the main
structure of a coral reef. Each polyp is connected by living tissue to form a
community.
Each polyp has a ring of tentacles shaped
like a cup around a central opening.
The tentacles are like long arms with tips
that can sting. They are used either for
defense or to capture zooplankton for food.
• Reefs grow best in warm, shallow, clear,
sunny and agitated waters.
• They are therefore most commonly
found at shallow depths in tropical
waters
Close up of polyps arrayed on a coral
• Coral reefs occupy less than 0.1% of the world's ocean surface, yet
they provide a habitat for 25% of all marine species, including fish,
molluscs, worms, crustaceans, echinoderms sponges, tunicates and
other cnidarians.
• The Great Barrier Reef is the largest coral reef. It is made up of over 2
900 individual reefs and 900
Islands stretching for over 2 600
kilometres off the northeast coast
of Australia. It is home to more
than 1,600 types of fish, 133 types
of shark and ray and 30 species of
whale and dolphin tart.
• The Great Barrier Reef provides the pockets of space for small fish to spawn
(release eggs into the water) away from larger predators.
• The vibrancy of the reef provokes awe from its visitors who are used to less
exotic wildlife.
• Coral reefs deliver ecosystem services to tourism, fisheries and coastline
protection. The global economic value of coral reefs has been estimated to
be between US $29.8 billion[5] and $375 billion per year.
• Coral reefs protect shorelines by absorbing wave energy, and many small
islands would not exist without their reefs to protect them.
• Coral reefs are a source of medication: some painkillers come from coral
reefs and the marine aniamls as do drugs used for arthritis, Alzheimer's
disease, heart disease and viruses. Research is still in process
• Cold, deep-water reefs, are home to marine organisms that produce potent
molecules that might inspire new anti-cancer therapies
Coral reefs are sites of two important processes: the organic carbon
metabolism (photosynthesis & respiration) and the inorganic carbon
metabolism (calcification & dissolution of calcium carbonate).
Because of their high rates of calcification, coral reefs fix about half of
all the calcium entering the sea into calcium carbonate. Calcification
releases carbon dioxide as it involves the precipitation of calcium
carbonate from bicarbonate and calcium in seawater.
In addition, while coral reefs absorb large amounts of carbon dioxide
(per unit area) during photosynthesis, they generally release almost
equivalent amounts via respiration, resulting in little net storage.
• Cyanide fishing for aquarium fish
(spraying a sodium cyanide mixture in
order to stun the fish)
-Cyanide concentration slows
photosynthesis in zooxanthellae, which
results in coral reefs losing colour as well as eliminating one of their
major food sources
• Sunscreen use- Some commonly used chemical sunscreen
ingredients cause coral bleaching
• overuse of reef resources
e.g. overfishing disrupting the natural
food chains
• Blast fishing(using explosives) =
destroys coral reefs
Harmful land-use practices, including urban (e.g. sewage) and
agricultural runoff (fertilizers) and water pollution, which can harm reefs
by encouraging excess algal growth which blocks out sunlight for coral
reef (can’t photosynthesize so it dies)
• Coral Mining- humans use the first layer of coral reefs as road-fill or
cement which causes long-term physical damages
• Climate Change-makes the water warmer and coral can’t live in
water temperatures that are not within 26-27°C
-When coral is subjected to higher temperatures than it is used to, the
symbiosis between it and algae that powers it breaks down, leaving the
coral reef as a chalky, brittle ghost of what it once was. Once the coral
bleaches and dies, so does its wildlife
The Great Barrier Reef specifically has been affected by diver’s fins
slapping against the coral, anchors scraping the reef, and the rampant
scavenging of shellfish disturbing its food chain.
• Ocean acidification is the ongoing decrease in the pH of the Earth's oceans,
caused by the uptake of carbon dioxide from the earth’s atmosphere.
• Over 500 billion tonnes of CO2 released by humans since the start of the
industrial revolution have been dissolved in the oceans.
• pH of surface layers of the earth’s oceans
in the late 18th century ≈ 8.1179 currently ≈ 8.069, which represents
30% acidification.
• Reef-building corals deposit calcium carbonate un their exoskeletons do
they need to absorb carbonate ions from seawater.
• The concentration of carbonate ions is low in seawater because they are
not very soluble.
• Dissolved CO2 makes the carbonate concentration even lower as a result f
some interrelated chemical reactions:
CO2 + H2O -> H2CO3 -> H+ + HCO3−
H+ + CO32 –
• If the carbonate ions concentrations drop it is more difficult for reef-building
corals to absorb them to make their exoskeletons
• Also, if seawater ceases to be a saturated solution of carbonate ions, existing
calcium carbonate tends to dissolve, so existing exoskeletons of reef-building
corals are threatened.
• Volcanic vents in the Gulf of Naples have been releasing carbon dioxide into
the water for thousands of years, reducing the pH of the seawater. In this
area of acidified water there are no corals, sea urchins or other animals that
make their exoskeletons from calcium carbonate. In their place other
organisms like invasive algae and sea grasses flourish. Unfortunately this
could be the disheartening future for coral reefs around the world if carbon
dioxide emissions continue to rise…
• Loss of tropical coral reefs to acidification could cost $1 trillion by 2100 in
terms of lost shoreline protection and lost revenues for the tourism and food
industries.