L6 : conservation ecology and marine biodiversity

Question 1

biodiversity and ecosystem resilience
[case study - tropical reefs]

Answer 1

• biodiversity hotspots
• protect coastal habitats and ecosystems
• nursery grounds
• feeding grounds
• carbon sinks

Question 2

Role of grazers in reef communities

Answer 2

1. many grazers are predators (feed on coral polyps)
2. many are algal specialists
3. many “specialists” are in fact omnivorous
   - specialist mouth structure
   - specialist digestive structures

Question 3

grazer importance

Answer 3

• highest grazing rates (removal of 1^degree prod) of any habitat on earth
• important role of space clearing
• clear coral rock of algae to provide space for settlement, and maintain low standing crop of algae that would otherwise overgrow corals

Question 4

healthy reef

Answer 4

• clear water
• abundant coral
• species diversity

Question 5

over-fishing

Answer 5

• shift from subsistence to cash economies - increased pressure on reef fish populations
• reef fish species have crucial role in maintaining balance between algae and coral
• overfishing removes biological limits on algal growth -> algae dominate -> phase shift

Question 6

phase shift

Answer 6

a change in the ecosystem state in response to a persistent change in external environmental conditions,

Question 7

phase shift - macroalgal dominance

Answer 7

• turbid water
• limited coral
• reduced biodiversity

Question 8

removing top predators

Answer 8

• removing sharks allows increase in mid-level predators
• these place extra pressure in grazing fishes
• unable to keep up with algal growth

Question 9

Excess nutrients

Answer 9

• corals prefer low nutrient conditions
• nutrients are captures and recycled within biomass
• high nutrients cause uncontrolled algal growth -> out compete corals -> phase shift

Question 10

status of world coral reefs

Answer 10

• 20% destroyed
• 24% at imminent risk of collapse under human pressure
• 26% under long-term threat
• most damages in SE Asia, Indian ocean and Caribbean

Question 11

role of urchins and phase shift

Answer 11

• disease in urchin species (Diadema antillarium) in the Caribbean
• increased algal cover
• decline in reef biodiversity
• recovery of urchin has reduced algal cover 65% to 5%

Question 12

Crown of thorns starfish

Answer 12

(Acanthaster planci)
- voracious pred of coral polyps
- can cause permanent damage to reefs
- natural preds have been fished out, larvae are benefiting from eutrophication

Question 13

k-species

Answer 13

produce offspring that each have a higher probability of survival to maturity

Question 14

Ecological effects of reserve networks

Answer 14

1. increasing evidence that a network of reserve buffers against the vagaries of environmental variability and provides significantly greater protection for marine communities that a single reserve
2. effective network needs to span large geographic distance and encompass a substantial area to protect against catastrophes and provide a stable platform for the long-term persistance of marine communities