Human influences on the marine environment
Evaluate how tourism, fishing, aquaculture, energy, plastics, nutrient pollution and climate change affect marine systems, and compare conservation responses.
Section 6 · Human influences on the marine environment
Exam scope and assessment notes
This original lesson maps Cambridge IGCSE Marine Science 0697 syllabus sections 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 for examinations in 2024–2029. These are original StudyForA explanations and practice, not Cambridge questions, mark schemes or official grades. Paper 2 assesses practical skills in both familiar and unfamiliar contexts. This course can rehearse planning, measurement, data handling and evaluation, but it cannot provide real laboratory or coastal-field experience, verify equipment use, certify safety, or award a practical mark. Follow teacher supervision, local safety rules and environmental permissions for all practical work.
Before you begin
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Before you start: What is a useful basis for evaluating a marine conservation strategy?
What you will learn
- Connect marine ecosystems to human benefits, impacts and sustainability
- Evaluate tourism, fisheries and aquaculture trade-offs
- Explain pollution, energy and climate-change processes affecting oceans
- Compare conservation strategies using ecological, social and economic evidence
Benefits, tourism, fisheries and aquaculture
Marine ecosystems support recreation and tourism, food, materials, medicines, fisheries, coastal protection and nursery habitats. Human pressures include litter, plastics, disturbance, habitat conversion, resource removal and destructive methods. Endangered species face declining populations; sustainable use must avoid environmental damage and resource exhaustion.
Tourism can provide jobs and income while increasing noise, light, litter, trampling, souvenir collection, boating impacts and coastal construction. Fisheries can supply food and livelihoods but overharvesting and damaging methods can reduce populations. Aquaculture can reduce pressure on wild fisheries yet cause habitat loss, pollution, disease or escaped organisms. Evaluate conditions and trade-offs, not labels alone.
Energy, plastics and eutrophication
Oil is a non-renewable fuel extracted and transported with spill risks. Spills can coat mammals and birds, poison organisms and disrupt food chains; booms, skimmers, dispersants and burning each have limits. Ocean energy can be renewable but its social, economic and environmental effects depend on the technology and site.
Plastics persist, fragment and can release toxins; microplastics enter food chains and larger items can be swallowed or entangle animals. Gyres concentrate floating debris. Nutrient-rich fertiliser run-off and untreated sewage can drive eutrophication: nutrients rise, algal growth increases, decomposition and aerobic respiration consume oxygen, dissolved oxygen falls, and oxygen-dependent organisms may die.
Climate change and conservation
Increasing greenhouse gases enhance warming. Oceans absorb heat and carbon dioxide; warming expands seawater and lower pH indicates acidification. Potential marine impacts include sea-level rise, habitat loss, coral bleaching, reduced dissolved oxygen, shifting distributions, species loss and extreme weather. Compare thermal expansion with land-ice melt; floating ice melt is not the same source of sea-level rise.
Conservation strategies include sustainable harvesting, aquaculture, marine protected areas and targeted projects such as coral restoration, turtle nesting protection and management of invasive species. Evaluate goals, evidence, timescale, enforcement, local livelihoods and unintended effects. Measure species richness as the number of different species in an area; it is not the same as total abundance.
Sources for this lesson
Pause and explain
Which sequence best describes eutrophication after excess nutrients enter water?
Worked example
A coastal town proposes a marine protected area to rebuild a fish population while maintaining tourism. Identify a benefit, a possible cost and evidence to evaluate the plan.
Show the worked solution
- A protected area may reduce extraction and allow populations or habitat to recover.
- Fishing restrictions can affect local income; tourism can also disturb wildlife if poorly managed.
- Compare repeated population, habitat, compliance and livelihood data inside and outside the protected area.
Answer The area could support recovery, but outcomes depend on boundaries, enforcement and ecological conditions. Repeated ecological and livelihood evidence, including a suitable comparison site, is needed to evaluate the policy fairly.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
After heavy rain, a bay receives fertiliser run-off. Explain how this can lead to low dissolved oxygen and one measurement that could test the explanation.
Give me a hint
Trace nutrients through algal growth, decomposition and respiration.
Compare my reasoning
- Explain that added nutrients can increase producer growth.
- Describe how dead biomass is decomposed and aerobic respiration uses oxygen.
- Measure dissolved oxygen over time alongside nutrients or algal abundance.
Extra nutrients can stimulate algal growth; when biomass dies, decomposers respire aerobically and consume dissolved oxygen. Repeated oxygen measurements, together with nutrient or algal data, can test the sequence. Other oxygen sources and water movement should also be considered.
Look for these in your work
- Explains the causal sequence
- Uses respiration correctly
- Proposes repeated linked measurements
Compare a plastic-bag charge with a coastal clean-up as strategies for reducing marine plastic impacts.
Give me a hint
Compare prevention and removal, costs, reach and what each cannot address.
Compare my reasoning
- Explain how a charge may reduce single-use bag demand at source.
- Explain how clean-ups remove some existing litter but may miss small or offshore debris.
- Identify outcome data for both and avoid claiming either solves all plastic pollution.
A charge may prevent some single-use bags from entering waste streams; a clean-up removes accessible existing litter. The charge needs monitoring of use and substitutions, while clean-ups need collected mass and habitat-impact checks. Neither alone addresses all plastic sources or microplastics.
Look for these in your work
- Distinguishes prevention from removal
- Identifies limitations
- Suggests measurable outcomes
A fishery reports more catch after a protected area opens. What evidence is needed before concluding that the protected area caused the increase?
Give me a hint
Use a comparison over time and consider other changes in effort or environment.
Compare my reasoning
- Compare population or catch data before and after implementation.
- Include a suitable comparison area and record fishing effort, rules and environmental conditions.
- Check that the measured increase is not due only to greater effort, reporting or movement from nearby areas.
A before-and-after comparison with a similar unprotected area, population measures and fishing-effort data would strengthen the case. Increased catch alone could reflect more effort or displaced fishers rather than population recovery.
Look for these in your work
- Uses a comparison
- Accounts for effort and other factors
- Distinguishes catch from population size
Common mistakes
- Assuming an activity is sustainable because it is labelled eco-friendly
- Confusing eutrophication with simple water warming
- Treating all ocean energy technologies as impact-free
- Claiming a conservation intervention worked without before-and-after evidence
What can you explain now?
Which sequence best describes eutrophication after excess nutrients enter water?
Compare with the explanation
Algal growth rises, decomposition increases, oxygen falls and some organisms die
Use the scientific relationship, relevant evidence and correct units. State the limit of any conclusion when the evidence does not support a universal claim.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How can marine scientists distinguish evidence that a conservation strategy worked from evidence that happened after it was introduced?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.