BIO 475 Lecture Notes - Lecture 7: Zooxanthellae, Photosystem Ii, Light-Independent Reactions
● Mass bleaching events happening on a global scale
● Back to pack bleaching events in the Pacific
● First bleaching events in the mid 1980’s
○ Usually 5-10 years apart
● Great barrier reef
○ 2014,2015,2016 Mass bleaching events
Terms
● Loss of zooxanthellae OR the loss of pigment from zooxanthellae, OR both!
● Stress response of the host, algae, or both
● Bleaching primarily occurs in response to:
○ Higher than normal temperatures
○ Light
○ Changes in salinity
Zooxanthellae in coral tissues → zooxanthellae expelled from tissue → Dead skeleton covered in
filamentous algae
Water temperature increase → Prolonged temperature stress
Healthy → (days-weeks) → Bleached coral → (Days-weeks) → Dead Coral
Healthy → (Days-weeks) → Bleached coral →( weeks-months) → Healthy
● Can recover, water temperature or other determinate returns to normal
● Without zooxanthellae they cannot photosynthesis
● Sometimes just a colony within the reef will bleach, the rest can be healthy
What causes bleaching
Trigger
Mechanism (how response is manifested)
Heat shock
Damage to photosystem II (light)
Cold Shock
Disruption to Calvin cycle (temp)
High Irradiance
Inhibition of photosystem by Vibrio sp
Sedimentation
Animal cell detachment
Starvation
Programmed cell lysis
Heavy Metals
pathogens
Effects
● Either death in 2-3 weeks or partial recovery in 1-2 months
● Reduction in nitrogen , lipid, protein and carbohydrate content
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● Difficulties in spawning
● Reduced fecundity after recovery from bleaching
○ Producing few juvenile, fewer larvae
● Reduced calcification, growth, and lesion recovery
● Increased susceptibility to disease
○ Corals more vulnerable
● Corals that appear completely bleached have lose 70 to >90% of algal density
Temp
● Temperature is the main driver in coral bleaching
○ Year on x-axis
○ Temperature on Y
■ Above 29.5o , bleaching event (bermuda)
● Bleaching threshold
○ Max temperature varies depending on where the corals are
■ If they are used to warmer temperatures the threshold will be higher
● Predicted that sea surface temperature is going to increase
● Link between bleaching and El nino events
○ Causes spike in summer temperature
● Most severe bleaching events
○ 1998
■ 50% bleached
○ 2002
Mechanism
● Electron Transport
○ Stress affects the rubisco enzyme so the Calvin cycle shuts down. Light driven
electron transport thus exceeds capacity if the Calvin cycle. Damage to the PSII
is secondary
● Protein Turnover
○ D1 protein degradation is higher than re-synthesis results in dysfunction of PSII
● Oxidative stress
○ Photo-inhibition model. Direct damage to the PSII protein by UV light, electron
transport chain breaks down. However, electrons are still being produced as PSII
is excited by light. So water still being split and excess O2 is produced
■ Excess O2 is toxic and will poison coral host
○ Increased seawater temperature
○ Increased UV light
In general, bleaching results from accumulated oxidative stress on the thylakoid membranes of
symbiont chloroplasts as a result of damage to Photosystem II
This damage results in the degradation and eventual expulsion of symbionts from host tissues,
although the exact cellular process involved is unknown.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Mass bleaching events happening on a global scale. Back to pack bleaching events in the pacific. First bleaching events in the mid 1980"s. Loss of zooxanthellae or the loss of pigment from zooxanthellae, or both! Stress response of the host, algae, or both. Zooxanthellae in coral tissues zooxanthellae expelled from tissue dead skeleton covered in filamentous algae. Healthy (days-weeks) bleached coral (days-weeks) dead coral. Healthy (days-weeks) bleached coral ( weeks-months) healthy. Can recover, water temperature or other determinate returns to normal. Sometimes just a colony within the reef will bleach, the rest can be healthy. Either death in 2-3 weeks or partial recovery in 1-2 months. Reduction in nitrogen , lipid, protein and carbohydrate content. Corals that appear completely bleached have lose 70 to >90% of algal density. Temperature is the main driver in coral bleaching. Max temperature varies depending on where the corals are. If they are used to warmer temperatures the threshold will be higher.
