THE CHEMISTRY OF CORAL
BLEACHING
WHAT IS A CORAL?
• CORALS ARE MARINE INVERTEBRATES (ANIMALS)
• THEY CAN TAKE MANY SHAPES!
• THEY USUALLY LIVE IN COLONIES OF TINY POLYPS
• GENETICALLY IDENTICAL
• OF THE SAME PHYLUM AS JELLY FISH AND SEA
ANEMONE (CNIDARIA)
• STINGING CELLS CALLED NEMATOCYSTS
• THERE ARE TWO TYPES OF CORALS
• HERMATYPIC (HARD, STONY CORAL)
• AHERMATYPIC (SOFT CORAL)
ACTIVITY: BUILDING A CORAL POLYP
• ONE 3" X 3" STICKY NOTE
• PENCIL OR PEN
• TRANSPARENT TAPE
• SCISSORS
• 1 EGG CARTON CUP (1/12 OF AN EGG CARTON)
STRUCTURAL AND CHEMICAL MAKE-UP
THE REEF BUILDERS
• POLYPS BUILD HARD LIMESTONE CUPS AROUND THEIR
BASES
• THE CUPS CEMENT TOGETHER TO MAKE A CORAL
COLONY
• REEFS ARE MADE OF HUNDREDS OF HARD CORAL
COLONIES NEXT TO AND ON TOP OF EACH OTHER
• REEF-BUILDING CORALS CAN ONLY SURVIVE IN FAIRLY
SHALLOW AREAS WHERE SUNLIGHT CAN PENETRATE
• REFERRED TO AS THE TROPICAL RAINFOREST OF THE
OCEAN
• REEFS ARE THE LARGEST STRUCTURES MADE BY LIVING
CREATURES!
WHY ARE CORAL REEFS IMPORTANT??
• USED FOR FOOD AND MEDICINE
• ECONOMIC BENEFITS (TOURISM, JOBS AND
FOOD)
- $375 BILLION A YEAR
• BREEDING GROUNDS FOR MARINE ANIMALS
(FISH)
• PROTECTS SHORES FROM WAVES AND STORMS
• HOME & SHELTER TO 25% OF THE FISH IN THE
OCEAN
• SOURCE OF NITROGEN AND OTHER NUTRIENTS ESSENTIAL
FOR THE FOOD CHAIN
PLANT PIGMENT IDENTIFICATION MINI-LAB
The whitening of corals due to the loss of their
symbiotic zooxanthellae or the pigments
associated with the algae.
Adopted from : J. Chem. Educ. 2013, 90, 755−759
WHERE IS THE PIGMENTATION IN CORAL?
SYMBIOSIS
• MANY HARD AND SOFT CORALS (AND SOME
JELLYFISH AND SEA ANEMONES) CONTAIN A
SYMBIOTIC SINGLE-CELLED DINOFLAGELLATE
(ALGAE) CALLED ZOOXANTHELLAE
• THIS IS A MUTUALISTIC SYMBIOSIS
• ZOOXANTHELLAE (LIVING WITHIN CORAL
TISSUES) CONTAIN THE PIGMENTS THAT GIVE
CORALS THEIR COLOR!
FROM THIS…
TO THIS…
DAY 2
CORAL BLEACHING
FROM THIS…
TO THIS…
WHAT IS CORAL BLEACHING?
CORAL BLEACHING IS A STRESS RESPONSE IN CORAL REEFS THAT INVOLVES THE
WHITENING OF CORALS DUE TO THE BREAKDOWN OR LOSS OF THEIR SYMBIOTIC
ZOOXANTHELLAE OR THE PIGMENTS ASSOCIATED WITH ALGAE
IMPORTANCE OF ZOOXANTHELLAE
 THE ZOOXANTHELLAE PROVIDE CORAL WITH THEIR BEAUTIFUL COLORS. WITHOUT THE ALGAE
CORALS ARE CLEAR OR WHITE
 PHENOMENON KNOWN AS CORAL BLEACHING
 ZOOXANTHELLAE THAT LIVES IN CORAL TISSUE PROVIDE NUTRIENTS SUCH AS SUGARS AND
OXYGEN THAT ARE ESSENTIAL FOR THE PRODUCTION OF CALCIUM CARBONATE (CORAL REEF
SKELETON).
 MORE THAN 50% OF THE CORALS’ NUTRIENTS ARE DERIVED FROM PHOTOSYNTHETIC PRODUCTS
PRODUCED BY ZOOXANTHELLAE
 PRODUCTION OF LARGE AMOUNTS OF MOLECULAR OXYGEN (O2) THAT ALLOWS FOR EFFICIENT
RESPIRATION BY THE CORAL HELPS PREVENT INFECTION
PHOTOSYNTHESIS
Photosynthesis is the process by which plants, some bacteria, and some protezoans use the energy from sunlight to produce
sugar. The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green
pigment chlorophyll.
BALANCED PHOTOSYNTHESIS EQUATION
ENVIRONMENTAL FACTORS THAT CAUSE THE RELEASE
OF ZOOXANTHELLAE (SYMBIODINIUM)
TEMPERATURE
FLUCTUATION OF LOW AND HIGH SEA TEMPERATURE ACCOMPANYING INTENSE UPWELLING
 WINTER: CHANGE FROM -3 C TO -5 C FOR 5 TO 10 DAYS
 SUMMER: CHANGE FROM 1 TO 2 C FOR 5 C TO 10 DAYS (MORE COMMON)
OCEAN ACIDIFICATION
ABSORPTION OF CO2 BY SEAWATER IS A CHEMICAL REACTIONS THAT REDUCE THE PH OF
SEAWATER CAUSING THE WATER TO BECOME MORE ACIDIC
UV RADIATION
HIGH LEVELS OF PHOTOSYNTHESIS LEADS TO HIGH AMOUNTS OF NITRIC OXIDE
PRODUCTION BY ZOOXANTHELLAE
SALINITY
ZOOXANTHELLAE ARE SENSITIVE TO LOW SALINITY DUE TO PRECIPITATION AND RUNOFF
NEAR SHALLOW, CLEAR WATERS (NO DEEPER THAN 100M) WITH PLENTY OF SUNLIGHT.
OCEAN ACIDIFICATION
WHEN CO2 DISSOLVES IN SEAWATER, CARBONIC ACID IS
PRODUCED VIA THE REACTION:
CO2 + H2O
H2CO3
THIS CARBONIC ACID DISSOCIATES IN THE WATER, RELEASING
HYDROGEN IONS AND BICARBONATE:
H2CO3
HCO3- + H+
ONE RESULT OF THE RELEASE OF HYDROGEN IONS IS THAT
THEY COMBINE WITH ANY CARBONATE IONS IN THE WATER
TO FORM BICARBONATE (A BASE)
CO32- + H+
HCO3-
CORALS AND CHEMISTRY MINILAB
TEMPERATURE
• CLIMATE CHANGE (GLOBAL WARMING) IS A MAJOR CONCERN:
• IF TEMPERATURES CONTINUE TO INCREASE TO 1-2 C, FOR THE NEXT 20 YEARS THERE WILL
BE MASS CORAL BLEACHING WORLDWIDE.
• THE HIGH SEAWATER TEMPERATURE ELEVATION WILL AFFECT OVER 95% OF THE SPECIES
LIVING WITHIN THE CORAL AND LEAD SPECIES TO BECOME EXTIRPATED OR EXTINCT.
• BLEACHING EVENTS ALSO OCCUR DURING SUDDEN TEMPERATURE DROPS
• -3 C TO –5 C FOR 5-10 DAYS), SEASONAL COLD-AIR OUTBREAKS
FORECASTING BLEACHING
EVENTS MINI-LAB
DOES BLEACHING MEAN DEATH??
IF THE STRESS-CAUSING BLEACHING IS NOT
TOO SEVERE AND IF IT DECREASES IN TIME,
THE AFFECTED CORALS USUALLY REGAIN
THEIR SYMBIOTIC ALGAE WITHIN SEVERAL
WEEKS OR A FEW MONTHS. IF
ZOOXANTHELLAE LOSS IS PROLONGED.
THUS, IF THE STRESS CONTINUES AND
DEPLETED ZOOXANTHELLAE POPULATIONS
DO NOT RECOVER, THE CORAL HOST
EVENTUALLY DIES.
PROTECT THE CORALS THAT
PROTECT YOU!