AQA A-level Geography · 3.1.6

Marine ecosystems and ecosystem case studies

50 exam-style questions with answers for 3.1.6 Marine ecosystems and ecosystem case studies in AQA A-level Geography (spec 7037). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All 50 questions and answers

Question 1 · Spec 3.1.6.5 · Coral reefs
Describe the global distribution of coral reefs. [3 marks]
Answer:
They lie in warm tropical and subtropical seas, between about 30° north and 30° south of the equator (1); the largest areas are in the Indo-Pacific, including the Coral Triangle and the Great Barrier Reef (1); others are in the Caribbean and Red Sea, mainly on the eastern sides of oceans and continents (1).
Question 2 · Spec 3.1.6.5 · Coral reefs
Describe the main characteristics of coral reef ecosystems. [3 marks]
Answer:
Reefs are built by coral polyps, which secrete calcium carbonate skeletons (1); algae called zooxanthellae live inside the polyps, providing food in return for protection (1); they have very high biodiversity, with about a quarter of marine species living on less than 1% of the ocean floor (1).
Question 3 · Spec 3.1.6.5 · Coral reefs
Distinguish between fringing reefs, barrier reefs and atolls. [3 marks]
Answer:
Fringing reefs grow close to the shore (1); barrier reefs are separated from the land by a lagoon (1); atolls are ring-shaped reefs surrounding a lagoon, often on a sunken volcano (1).
Question 4 · Spec 3.1.6.5 · Coral reefs
Describe the environmental conditions needed for coral reef development. [4 marks]
Answer:
Water temperature of about 23–29 °C (1); clear, shallow water, less than about 50 m deep, so sunlight reaches the algae (1); salinity of about 32–40 parts per thousand (1); low sediment and nutrients, and a hard surface to attach to (1).
Question 5 · Spec 3.1.6.5 · Coral reefs
Explain why coral reefs are rare on the west coasts of continents in the tropics. [2 marks]
Answer:
Cold ocean currents, such as the Humboldt Current, bring cool water (1); upwelling cold nutrient-rich water is too cold and too rich in nutrients for corals (1).
Question 6 · Spec 3.1.6.5 · Coral reefs
Explain the benefits that coral reefs provide for people. [3 marks]
Answer:
They provide fish for food and income (1); tourism and diving create jobs and income (1); reefs protect coasts from waves and storms, and they are a source of medicines (1).
Question 7 · Spec 3.1.6.5 · Natural factors
Explain how rising water temperature affects coral reefs. [4 marks]
Answer:
Corals tolerate only a narrow temperature range (1); if the sea is warmer than normal for several weeks, corals expel their zooxanthellae (1); the coral turns white, called bleaching, and loses its main food source (1); prolonged bleaching kills the coral, and recovery can take a decade or more (1).
Question 8 · Spec 3.1.6.5 · Natural factors
Explain how ocean acidification affects coral reefs. [3 marks]
Answer:
The oceans absorb carbon dioxide from the atmosphere, which forms carbonic acid (1); the water becomes more acidic and there are fewer carbonate ions available (1); corals find it harder to build skeletons, so growth slows and reefs become weaker (1).
Question 9 · Spec 3.1.6.5 · Natural factors
Explain how changes in salinity affect coral reefs. [2 marks]
Answer:
Corals need salinity within a narrow range (1); heavy rain and flood water lower salinity, which stresses and kills corals near river mouths (1).
Question 10 · Spec 3.1.6.5 · Natural factors
Explain how algal blooms threaten coral reefs. [2 marks]
Answer:
Nutrients from run-off feed rapid algal growth (1); algae block sunlight and smother coral, and decomposition lowers oxygen (1).
Question 11 · Spec 3.1.6.5 · Natural factors
Explain how cyclones and crown-of-thorns starfish damage coral reefs. [2 marks]
Answer:
Strong waves from cyclones break up coral structures (1); crown-of-thorns starfish eat live coral, and outbreaks are linked to nutrient-rich run-off (1).
Question 12 · Spec 3.1.6.5 · Human activity
Explain how major drainage basin schemes can affect coral reefs. [3 marks]
Answer:
Dams and irrigation reduce the flow of sediment and fresh water to the coast, changing salinity and sediment supply (1); intensive farming in the drainage basin produces run-off containing fertilisers and pesticides (1); clearance of vegetation increases soil erosion, and sediment smothers corals (1).
Question 13 · Spec 3.1.6.5 · Human activity
Explain how onshore development affects coral reefs. [3 marks]
Answer:
Dredging and construction release sediment that smothers coral and blocks light (1); coastal development removes mangroves that filter run-off (1); sewage and urban run-off add nutrients and pollution (1).
Question 14 · Spec 3.1.6.5 · Human activity
Explain how desalination affects coral reefs. [2 marks]
Answer:
Desalination plants release very salty brine into the sea (1); this raises local salinity and may add chemicals and heat that harm corals and other marine life (1).
Question 15 · Spec 3.1.6.5 · Human activity
Describe how pollution damages coral reefs. [3 marks]
Answer:
Sewage and fertiliser run-off cause algal blooms (1); oil spills and chemical pollution poison corals (1); plastic waste and some sunscreen chemicals harm reef life (1).
Question 16 · Spec 3.1.6.5 · Human activity
Explain how tourism can damage coral reefs. [3 marks]
Answer:
Anchors, boats and divers break coral (1); swimmers touch and trample coral in shallow water (1); resorts add sewage, waste and demand for water and sand (1).
Question 17 · Spec 3.1.6.5 · Human activity
Explain how fishing affects coral reefs. [3 marks]
Answer:
Overfishing removes herbivorous fish, so algae overgrow coral (1); destructive methods, such as dynamite and cyanide fishing, kill coral directly (1); nets and trawling damage the reef structure (1).
Question 18 · Spec 3.1.6.5 · Great Barrier Reef
Describe the location and main characteristics of the Great Barrier Reef. [3 marks]
Answer:
It lies off the coast of Queensland, north-east Australia, and stretches for about 2,300 km (1); it is the largest reef system in the world, made up of thousands of reefs and islands (1); it was designated a World Heritage Site in 1981 and has very high biodiversity (1).
Question 19 · Spec 3.1.6.5 · Great Barrier Reef
Describe the evidence of bleaching on the Great Barrier Reef. [3 marks]
Answer:
Mass bleaching events have occurred in 1998, 2002, 2016, 2017, 2020, 2022 and 2024 (1); the events of 2016 and 2017 killed about half of the shallow-water corals in the northern reef (1); events are becoming more frequent, which gives less time for recovery (1).
Question 20 · Spec 3.1.6.5 · Great Barrier Reef
Explain how farming affects the Great Barrier Reef. [3 marks]
Answer:
Sugar cane and cattle farming in the catchments of Queensland produce run-off (1); fertilisers and sediment flow into the lagoon, causing algal growth and cloudy water (1); nutrient-rich water is linked to outbreaks of crown-of-thorns starfish (1).
Question 21 · Spec 3.1.6.5 · Great Barrier Reef
Describe the economic importance of tourism on the Great Barrier Reef. [2 marks]
Answer:
Tourism contributes several billion Australian dollars each year (1); it supports tens of thousands of jobs (1).
Question 22 · Spec 3.1.6.5 · Great Barrier Reef
Describe the measures used to manage the Great Barrier Reef. [4 marks]
Answer:
The Marine Park is zoned, with about a third as no-take areas where fishing is banned (1); the Reef 2050 Plan sets targets for water quality and the control of pollution (1); crown-of-thorns starfish are culled (1); tourism operators need permits and follow rules, and coral restoration projects are being trialled (1).
Question 23 · Spec 3.1.6.5 · Great Barrier Reef
Evaluate the prospects for coral reefs in the future. [4 marks]
Answer:
Climate change is the biggest threat, because warming seas cause more bleaching (1); scientists estimate that 70–90% of reefs could be lost with 1.5 °C of warming, and nearly all at 2 °C (1); local action to improve water quality and reduce fishing can improve resilience (1); recovery depends on global emissions falling, so the future is uncertain (1).
Question 24 · Spec 3.1.6.5 · Great Barrier Reef
Explain how coral restoration and heat-tolerant corals may help reefs. [2 marks]
Answer:
Fragments can be grown in nurseries and planted on damaged reefs (1); heat-tolerant coral could be bred to survive warmer seas, but it cannot be done on a large scale yet (1).
Question 25 · Spec 3.1.6.5 · Great Barrier Reef
A reef had 40% live coral cover in 2010 and 25% in 2020. Calculate the percentage fall in coral cover over the decade. [2 marks]
Answer:
(40 − 25) ÷ 40 × 100 (1); = 37.5% (1).
Question 26 · Spec 3.1.6.5 · Great Barrier Reef
Evaluate the importance of marine protected areas in managing coral reefs. [3 marks]
Answer:
No-take zones allow fish stocks and coral to recover (1); they cannot protect reefs from global warming or acidification (1); they need enforcement and the support of local communities to be effective (1).
Question 27 · Spec 3.1.6.5 · Marine ecosystems
Explain how mangroves and seagrass beds help to protect coral reefs. [2 marks]
Answer:
They trap sediment and filter pollutants from run-off before it reaches the reef (1); they provide nursery habitats for reef fish and protect coasts from waves (1).
Question 28 · Spec 3.1.6.7 · Region case study
Borneo: describe the ecological setting of the region. [3 marks]
Answer:
The third largest island in the world, shared by Indonesia, Malaysia and Brunei (1); it has tropical rainforest with exceptional biodiversity, including orangutans, pygmy elephants and proboscis monkeys (1); it has peat swamp forests that store large amounts of carbon (1).
Question 29 · Spec 3.1.6.7 · Region case study
Borneo: describe the nature of the ecological change. [3 marks]
Answer:
About a third of its forest cover has been lost in the last fifty years (1); lowland forests and peatlands have been replaced by plantations (1); orangutan populations have fallen sharply, with over 100,000 lost between 1999 and 2015 (1).
Question 30 · Spec 3.1.6.7 · Region case study
Borneo: explain the reasons for the ecological change. [4 marks]
Answer:
Land was cleared for oil palm plantations to meet global demand for palm oil (1); commercial and illegal logging, and acacia plantations for paper (1); mining, especially coal in Kalimantan, and road building (1); fires used to clear land, with drained peat burning easily in dry years (1).
Question 31 · Spec 3.1.6.7 · Region case study
Borneo: explain how the economic character of the region reflects its ecological setting. [3 marks]
Answer:
Forests, peat and minerals are the main resources, so the economy depends on logging, palm oil and mining (1); Indonesia and Malaysia together produce most of the world's palm oil, which is a major export (1); communities depend on plantation jobs, and on forest products and fishing in rural areas (1).
Question 32 · Spec 3.1.6.7 · Region case study
Borneo: explain how social and political factors influence the changes. [3 marks]
Answer:
Indigenous Dayak communities have traditionally used forests, but they often have weak legal rights to land (1); governments award concessions to large companies, and corruption and weak enforcement allow illegal clearance (1); migrants and plantation workers have moved in under transmigration and job schemes (1).
Question 33 · Spec 3.1.6.7 · Region case study
Borneo: explain the ecological concerns about the new Indonesian capital, Nusantara. [2 marks]
Answer:
The capital is being built in East Kalimantan, near rainforest and wildlife habitat (1); construction, roads and migration could increase pressure on forests and species such as orangutans (1).
Question 34 · Spec 3.1.6.7 · Region case study
Borneo: describe the impacts of the 2015 fires. [3 marks]
Answer:
Fires on drained peatland burned for weeks in a dry El Niño year (1); smoke haze spread across Indonesia, Malaysia and Singapore, causing health problems and school closures (1); huge amounts of carbon dioxide were released, equal to the annual emissions of a large industrial country (1).
Question 35 · Spec 3.1.6.7 · Region case study
Borneo: describe how the community and governments are responding to change. [4 marks]
Answer:
The Roundtable on Sustainable Palm Oil certifies producers who meet environmental standards (1); Indonesia has a moratorium on new licences in primary forest and peatland (1); the Heart of Borneo initiative aims to protect forest across three countries (1); NGOs run orangutan rehabilitation, and communities map their land, manage community forests and restore peat (1).
Question 36 · Spec 3.1.6.7 · Region case study
Borneo: evaluate certification schemes such as the Roundtable on Sustainable Palm Oil. [3 marks]
Answer:
They provide a market incentive for producers to avoid deforestation (1); only part of the global supply is certified, and enforcement is difficult (1); smallholders may find certification costly (1).
Question 37 · Spec 3.1.6.7 · Local ecosystem
Studland Bay in Dorset: describe the nature and properties of the ecosystem. [3 marks]
Answer:
A coastal dune system that has built up over centuries along about 4 km of sandy beach (1); it has zones of embryo dunes, yellow dunes with marram grass, grey dunes and heath behind, with a freshwater lake, Little Sea (1); it is a National Nature Reserve, owned by the National Trust (1).
Question 38 · Spec 3.1.6.7 · Local ecosystem
Studland Bay in Dorset: describe the wildlife that makes the ecosystem important. [2 marks]
Answer:
All six native British reptiles are found, including the rare sand lizard and smooth snake on the heath (1); seagrass beds in the bay shelter species such as seahorses (1).
Question 39 · Spec 3.1.6.7 · Local ecosystem
Studland Bay in Dorset: describe the human impacts on the ecosystem. [3 marks]
Answer:
Large numbers of visitors trample dunes and vegetation, causing erosion (1); litter, dogs and fires on the heath disturb wildlife (1); boats anchoring in the bay have damaged seagrass beds (1).
Question 40 · Spec 3.1.6.7 · Local ecosystem
Studland Bay in Dorset: describe how the ecosystem is managed. [4 marks]
Answer:
Boardwalks and fenced paths keep people off fragile dunes (1); marram grass is planted and areas are closed to allow recovery (1); heathland is managed by grazing and scrub clearance (1); wardens, information and car park charges manage visitors, and advanced moorings protect seagrass (1).
Question 41 · Spec 3.1.6.7 · Local ecosystem
Studland Bay in Dorset: describe the challenges and opportunities for sustainable development. [3 marks]
Answer:
Challenge: the ecosystem is close to large populations at Bournemouth and Poole, so visitor pressure is high (1); opportunity: tourism provides income and jobs, and funds management (1); opportunity: education and volunteering encourage care for the environment (1).
Question 42 · Spec 3.1.6.7 · Local ecosystem
Describe how the effect of trampling on dune vegetation could be investigated. [3 marks]
Answer:
Use transects across a heavily used path and an area with no path (1); record percentage cover and height of vegetation using quadrats at regular intervals (1); compare the results with a statistical test such as Spearman's rank or a Mann-Whitney U test (1).
Question 43 · Spec 3.1.6.7 · Conflict
Explain why conflicts occur between conservation and local people in ecosystems under stress. [3 marks]
Answer:
Local people may depend on the resources for income, such as farming, fishing or timber (1); protected areas can limit access to land and resources (1); the benefits of conservation are often global or long-term, while the costs fall on local people (1).
Question 44 · Spec 3.1.6.7 · Conflict
Explain how involving local people in conservation can make it more successful. [2 marks]
Answer:
Local knowledge helps to identify problems and appropriate solutions (1); if people benefit through jobs and income, they have an incentive to protect the ecosystem (1).
Question 45 · Spec 3.1.6.5 · Coral reefs
Explain why coral reefs have such high biodiversity. [3 marks]
Answer:
The three-dimensional structure of the reef provides many different habitats and shelters (1); warm, clear, shallow water gives high productivity, as the algae in corals photosynthesise (1); reefs have developed over thousands of years, giving species time to specialise (1).
Question 46 · Spec 3.1.6.5 · Human activity
Explain why coral reef health is a good indicator of the health of the wider marine environment. [2 marks]
Answer:
Corals are sensitive to changes in temperature, water quality and acidity (1); reef decline therefore gives an early warning of wider ocean change (1).
Question 47 · Spec 3.1.6.5 · Natural factors
Explain why El Niño events cause coral bleaching. [2 marks]
Answer:
El Niño raises sea surface temperatures across large areas of the tropical Pacific (1); the heat stress causes corals to expel their algae, so mass bleaching occurs (1).
Question 48 · Spec 3.1.6.5 · Human activity
Explain how reducing greenhouse gas emissions would help coral reefs. [2 marks]
Answer:
Slowing warming would reduce the frequency of marine heatwaves and bleaching (1); lower carbon dioxide levels would reduce ocean acidification, allowing corals to build skeletons (1).
Question 49 · Spec 3.1.6.7 · Region case study
Borneo: explain why the conservation of peat swamp forest is a global concern. [2 marks]
Answer:
Peat swamps store very large amounts of carbon, which is released when they are drained or burned (1); they also support rare species and prevent flooding and haze (1).
Question 50 · Spec 3.1.6.7 · Local ecosystem
Studland Bay in Dorset: explain how the ecosystem shows succession from the shore inland. [2 marks]
Answer:
Vegetation changes from pioneer plants on the beach to marram dunes, then grey dunes and heath further inland (1); the sand becomes more stable and the soil richer in humus with distance from the sea (1).

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