L6 : conservation ecology and marine biodiversity Flashcards
biodiversity and ecosystem resilience
[case study - tropical reefs]
- biodiversity hotspots
- protect coastal habitats and ecosystems
- nursery grounds
- feeding grounds
- carbon sinks
Role of grazers in reef communities
- many grazers are predators (feed on coral polyps)
- many are algal specialists
- many “specialists” are in fact omnivorous
- specialist mouth structure
- specialist digestive structures
grazer importance
- 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
healthy reef
- clear water
- abundant coral
- species diversity
over-fishing
- 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
phase shift
a change in the ecosystem state in response to a persistent change in external environmental conditions,
phase shift - macroalgal dominance
- turbid water
- limited coral
- reduced biodiversity
removing top predators
- removing sharks allows increase in mid-level predators
- these place extra pressure in grazing fishes
- unable to keep up with algal growth
Excess nutrients
- corals prefer low nutrient conditions
- nutrients are captures and recycled within biomass
- high nutrients cause uncontrolled algal growth -> out compete corals -> phase shift
status of world coral reefs
- 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
role of urchins and phase shift
- 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%
Crown of thorns starfish
(Acanthaster planci)
- voracious pred of coral polyps
- can cause permanent damage to reefs
- natural preds have been fished out, larvae are benefiting from eutrophication
k-species
produce offspring that each have a higher probability of survival to maturity
Ecological effects of reserve networks
- 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
- 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