Human Pressures
What does anthropogenic mean?
Caused by human activities.
What is coral bleaching?
Loss of zooxanthellae or their pigments, exposing the pale skeleton through translucent tissue.
Which atmospheric gas drives ocean acidification when absorbed?
Carbon dioxide, CO2.
Does colder or warmer water generally dissolve more CO2 at equilibrium?
Colder water, with other conditions held constant.
What information can coral cores preserve?
Growth bands and chemical signals that provide evidence of past growth and environmental conditions.
Name two human activities that can physically damage reefs.
Examples: dredging, coral mining, destructive fishing or ship grounding.
Does bleaching always mean a coral is dead?
No. A bleached coral can survive and recover if stress is relieved in time.
Which two mineral forms of calcium carbonate are important in the ocean?
Calcite and aragonite.
What is the biological carbon pump?
Photosynthesis fixes carbon; sinking organic material transfers some carbon into deeper ocean waters.
How can acidification affect coral-dependent fish?
Reduced reef growth and structural complexity can remove shelter and food-web resources.
How can nutrient-rich runoff harm a reef?
It can stimulate algal growth and alter food webs, increasing competition with corals and degrading water quality.
How does Shelford’s law of tolerance explain bleaching?
Corals tolerate a limited environmental range; conditions beyond their tolerance cause stress and bleaching.
Why does dissolved CO2 reduce carbonate availability?
CO2 forms carbonic acid, releasing hydrogen ions that react with carbonate ions to form bicarbonate.
What is the carbonate compensation depth?
The depth at which carbonate supply is balanced by dissolution; below it carbonate generally does not accumulate in sediments.
Why compare laboratory and field acidification experiments?
Laboratories isolate variables; field studies test responses in complex natural environments. Together they improve interpretation.
How can ballast water affect a marine ecosystem?
It can introduce non-native organisms that disrupt local ecosystems.
Reef A has 2 degree heating weeks and Reef B has 8. Which has greater accumulated heat stress?
Reef B. Its larger degree heating week value indicates greater accumulated thermal stress and higher bleaching risk.
If ocean pH falls from 8.2 to 8.1, has the water necessarily become acidic?
No. It has become less alkaline; both values are above pH 7. Acidification means decreasing pH.
How can upwelling influence surface pH?
It can bring CO2-rich deep water to the surface, increasing dissolved CO2 and lowering pH.
In an illustrative dataset, coral cover falls from 40% to 25%. What is the change in percentage points?
A decrease of 15 percentage points. Relative decline is 15/40 x 100 = 37.5%.
Why can overfishing and nutrient runoff together promote an algal-dominated reef?
Fewer herbivores reduce grazing while nutrients stimulate algae; together they increase competition against corals.
What conditions support recovery after bleaching?
Stress returns to tolerable levels, surviving corals regain symbionts, water quality is good, herbivory persists and larvae can recruit.
If [Ca2+] x [CO3 2-] = 6 x 10^-7 and Ksp = 3 x 10^-7, calculate omega and interpret it.
Omega = 2. Water is supersaturated with respect to aragonite; precipitation is thermodynamically favoured, though biological and kinetic factors matter.
Why does carbonate buffering not prevent all ocean acidification?
The buffer moderates pH change but has finite capacity. Continuing CO2 input shifts equilibria and reduces carbonate availability.
Why does reducing local pollution improve resilience without eliminating climate threats?
It reduces additional stress and supports recovery, but does not stop global warming or atmospheric CO2-driven acidification.