Transcript Coral Bleaching 101 - NSTA Learning Center

Coral Bleaching 101
Presented by Mark Eakin
Coordinator, NOAA Coral Reef Watch
What is a coral?
-A “coral” is actually a
“coral colony”
-Rocky limestone
base
-Surface is covered
by thousands of tiny
coral animals, called
“polyps”
-Polyps are filled with
microscopic algae
Anatomy of a coral polyp
-Each polyp looks like
a tiny sea anemone
-Ring of stinging
tentacles around a
central mouth
-Rests in a “cup” on the
surface of the colony
What do corals eat?
-Like a sea anemone,
the polyp can capture
small prey (mostly
zooplankton) with its
tentacles
-Also get nutrition from
a symbiotic relationship
with zooxanthellae….
What are zooxanthellae?
Algae
Fish
Shrimp
What are zooxanthellae?
Photo: Michael ten Lohuis
-Algae that live in the
coral polyp’s surface layer
-Algae get nutrients and a
safe place to grow
-Corals get oxygen and
help with waste removal
-Corals also get most of
their food from the algae
What is coral bleaching?
Healthy
coral
Bleached
coral
Coral bleaching is caused by stress
Poll question: what might be stressful for a
coral? We’ll get back to the answer later….
What turns the coral white?
Healthy
coral
with
algae
Bleached
coral with
no algae
- As a stress response, corals expel the
symbiotic zooxanthellae from their tissues
- The coral tissue is clear, so you see the
white limestone skeleton underneath
What can stress a coral?
-High light or UV levels
-Cold temperatures
-Low salinity and high
turbidity from coastal runoff
events or heavy rain
-Exposure to air during
very low tides
-Major: high water
temperatures
Photos: AIMS and GBRMPA
Thermal stress
-Corals live close to their
thermal maximum limit
-If water gets 1 or 2°C
higher than the summer
average, corals get
stressed and bleach
-NOAA satellites measure
global ocean temperature
and thermal stress
How warm is warm?
How hot do you think the ocean has to get
before corals start to bleach?
Can corals recover?
-Yes, if the stress doesn’t
last too long
-Some corals can eat more
zooplankton to help survive
the lack of zooxanthellae
-Some species are more
resistant to bleaching, and
more able to recover
Photos: AIMS and GBRMPA
Can corals recover?
-Corals may eventually
regain color by repopulating
their zooxanthellae
-Algae may come from the
water column
-Or they may come from
reproduction of the few cells
that remain in the coral
Jeff Miller, National Park Service
Can corals recover?
-Corals can begin to
recover after a few weeks
Jeff Miller, National Park Service
Does bleaching kill corals?
-Yes, if the stress is severe
-Some of the polyps in a
colony might die
-If the bleaching is really
severe, whole colonies
might die
-Bleaching in Puerto Rico
killed an 800-year-old star
coral colony in 2005
What else can stress do to corals?
Photo:
Caroline Rogers, USGS
Question: what is something that happens to
people when they are highly stressed?
Gain weight
Get sick
Turn orange
What else can stress do to corals?
Photo:
Caroline Rogers, USGS
Question: what is something that happens to
people when they are highly stressed?
Answer: more likely to get sick
Bleaching and coral disease
-Coral diseases are
found around the world
-High temperatures
and bleaching can
leave corals more
vulnerable to disease
-Can quickly kill part or
all of the coral colony
Marilyn E. Brandt, University of Miami
Bleaching and bioerosion
-We have seen that
bleaching can kill part
or all of a coral colony
-Areas of dead coral
are more vulnerable to
bioerosion (when
animals wear away the
coral reef’s limestone
structure)
Hurricanes & coral bleaching
2005:
Most named storms
Most hurricanes
Most damage in US
The same warm water that causes corals to
bleach can also lead to strong hurricanes.
Hurricanes : a mixed blessing
-Hurricanes can cause
direct physical damage
to coral reefs
-However, the storms
also cools the water
22 Aug 2005
-Hurricane Katrina led
to less bleaching in the
Florida Keys, 2005
2 Sept 2005
Hurricanes: a mixed blessing
Sombrero Reef , FL
SST (degC)
DHW (degC week)
Dennis
9 July
Katrina
26 Aug
Rita
21 Sept
Wilma
24 Oct
Each passing hurricane in 2005 cooled the
water in the Florida Keys.
Can we protect corals from bleaching?
–
–
–
–
–
Shade reefs
Cool reefs
Improve water quality
Reduce other stress
Reduce overfishing
What Can YOU Do?
1. Learn more about coral reefs.
2. Spread the word.
http://www.publicaffairs.noaa.gov/ 25list.html
http://www.projectaware.org/americas/english/10TYCD.as
Bleaching 101: summary
- Corals are mineral, animal, AND vegetable
- Hot water bleaches corals
- Corals may die after bleaching
- Diseases follow many warming/bleaching
stress events