Ecosystems and Sustainability
Core concepts
Understand food webs (producers, consumers, decomposers), trophic levels, energy transfer (roughly 10% between levels) and biomass pyramids. Know primary productivity drivers: light, nutrients (nitrogen, phosphorus), temperature and upwelling. Study habitat types - coral reefs, seagrass, mangroves, kelp forests, estuaries, rocky shores - and their roles as nurseries and coastal protection. Learn biodiversity, keystone species, carrying capacity and ecological succession.
Sustainability content includes maximum sustainable yield, overfishing and bycatch, marine protected areas, integrated coastal zone management, and pollution (nutrient runoff, plastics, oil, noise). Understand climate change impacts: ocean warming, acidification from dissolved CO₂, sea-level rise, coral bleaching. Know ecosystem services (provisioning, regulating, cultural, supporting) and cumulative impacts.
Traps in questions
- Claiming energy is lost as heat only - it is also lost as respiration and waste; use "reduced transfer efficiency".
- Confusing bioaccumulation (in one organism) with biomagnification (up the food chain).
- Assuming MPAs always ban all fishing; many are multiple-use zones.
- Mixing eutrophication (nutrient enrichment causing algal blooms and hypoxia) with toxic pollution.
- Treating acidification as a direct temperature effect; it is a chemical change from CO₂ dissolution.
Rule of thumb: 10% energy transfer
Only about 10% of energy passes to the next trophic level, so top predators are few and vulnerable.
Worked example: If producers fix 20 000 kJ m⁻² yr⁻¹, primary consumers receive about 2 000 kJ, secondary consumers 200 kJ, and tertiary consumers about 20 kJ. Removing a top predator therefore has disproportionate effects - a keystone concept.
Always justify sustainability claims with a mechanism (stock recruitment, habitat loss, bycatch) and a management response.