Tourism, fisheries, aquaculture and energy from the oceans

What marine ecosystems give people

The syllabus lists eight ways in which marine ecosystems are important to humans, and a full-mark answer names the ecosystem as well as the use. Two of the eight are economic - recreation and tourism, and fisheries - and the rest are the services that keep coastal communities fed, employed and protected.

Recreation and tourism. Coral reefs, clear lagoons, mangrove creeks and shipwrecks attract divers, snorkellers, anglers and wildlife watchers, and they support hotels, dive schools, boat operators, restaurants and guides. The income is earned locally, and it also gives the community a reason to protect the reef: nobody pays to dive on a dead one.

Wood and building material. Mangrove trees are cut for timber, poles, fuelwood and charcoal, and coral limestone and reef sand have been quarried for building and for making lime. Coastal protection comes from the same ecosystems: a reef breaks wave energy offshore, mangrove roots and trunks absorb it at the shoreline, and seagrass blades slow the water and bind the sediment, so all three reduce erosion and storm damage.

Food supply and fisheries. Fish, crustaceans, molluscs and seaweeds are the main source of animal protein for many coastal communities, and the fishery is also a livelihood and an export earner. The catch depends on nursery areas: mangrove roots, seagrass beds and the sheltered water of estuaries and lagoons are where the juveniles of commercially and ecologically important species grow before moving out to the reef or the open sea. Damage the nursery and you damage a fishery that is worked somewhere else entirely.

Medicines. Marine organisms make chemicals to defend themselves and to compete for space on a crowded reef, and some of these are used or investigated as medicines - compounds from sponges, soft corals and cone snails, for example - while seaweed products such as agar are used in laboratories and in food. The syllabus adds medicinal plants, which in practice means the seaweeds and mangrove plants used in traditional medicine and as the source of such products.

• Recreation and tourism: reefs, lagoons, wrecks and wildlife attract divers and birdwatchers, generating local income.
• Wood and building material: mangrove timber, poles, fuelwood and charcoal; coral limestone and sand for building and lime.
• Coastal protection: reefs break waves offshore, mangrove roots and seagrass bind the shore, reducing erosion and storm damage.
• Food supply: fish, crustaceans, molluscs and seaweeds provide protein and a livelihood.
• Fisheries: employment from the boat and the processing plant to the market, plus export earnings.
• Nursery areas: mangrove roots, seagrass beds and estuaries shelter the juveniles of commercially and ecologically important species.
• Medicines and medicinal plants: chemicals from sponges, soft corals and cone snails; agar and other products from seaweeds.
• One ecosystem usually provides several of these at once, which is why losing it costs the community more than one benefit.

How human activity damages the sea, endangered species and sustainability

The syllabus names eight impacts, and they fall into three groups: taking organisms out, changing the habitat, and adding something harmful. Sorting an answer into those groups is the quickest way to make sure you cover them.

Recreational activities. Divers and snorkellers knock and break coral, walkers trample organisms on reef flats and rocky shores, and boats and resorts add noise and light pollution that disturb feeding, breeding and navigation - turtle hatchlings, for example, head for the brightest horizon and are misled by lights behind the beach. Litter and plastics are left behind, and organisms are collected and removed as souvenirs: shells, coral, starfish and sea urchins, often taken alive.

Tourist boats and diving. Anchors and chains drag across reef and seagrass, propellers cut through beds and injure slow-moving animals, and boats and swimmers crowd and chase wildlife. Handling, feeding and touching animals change their behaviour, which is why the syllabus lists interaction with organisms and its behavioural consequences as an impact in its own right.

Land reclamation for resorts, and building of infrastructure. Shallow water is filled, sand is pumped or dredged, and reef flat, seagrass and mangrove are buried under hotels, marinas and runways. Roads, jetties and sea walls change currents and sediment movement, so a beach can erode further along the same coast, and the new buildings produce sewage, runoff and litter.

Removal of resources. Sand and mud are dredged from the seabed for building and for beach nourishment, which destroys the bottom community, kills what is buried in the sediment and clouds the water so that light cannot reach the plants. Mangrove trees are logged for timber, charcoal and traps, which removes the nursery and the coastal protection at the same time.

Blast fishing and shrimp farms. Blast fishing uses an explosive, often homemade, to stun or kill everything within range: the catch is indiscriminate and the shock shatters the coral framework itself, so the reef cannot regrow quickly. Shrimp farms are built by clearing mangrove forest, they pump and discharge water carrying waste and chemicals, and they take wild larvae and juveniles from the nursery areas they have replaced. Oil spills are the eighth impact and are dealt with in the last section.

Endangered species. Populations of some marine species are declining, and where the decline continues they may become extinct; species in that position are called endangered species. Over-harvesting, bycatch, habitat loss and pollution usually act together, and a small population is then vulnerable to one more bad year, to disease and to inbreeding, so the decline can carry on even after the original cause is reduced.

Sustainable. A sustainable resource or activity is one that we can continue to use or carry out at the current rate, without causing damage to the environment, and without the resource running out. The definition has three parts - the same rate, no environmental damage, and no depletion - and most answers give only the third.

Tourism and ecotourism: income, definition and impacts

Tourism matters to a coastal area because it is socio-economically important: it provides employment and income to the area, and it leads to improved infrastructure for the local communities. The jobs are direct - hotel staff, dive guides, boat crews, cooks, cleaners, drivers, handicraft sellers - and indirect, through the farmers, fishers and suppliers who sell to the industry.

The income is often foreign currency, which a small island state needs in order to pay for imports, and the infrastructure built for visitors - airports, roads, water supply, sewage treatment, electricity, clinics - is used by the people who live there as well. The weaknesses deserve a sentence: much of the work is seasonal, wages can be low, and in an all-inclusive resort a large share of the money leaves the country with the operator.

Ecotourism is defined in the syllabus as ecologically sustainable tourism with a focus on experiencing natural areas that encourages environmental and cultural understanding, appreciation and conservation. Every part of that definition earns a mark: it must be sustainable, it must be about natural areas, and it must produce understanding, appreciation and conservation rather than just a photograph.

The difference between ecotourism and mass tourism is scale and purpose. Ecotourism uses small groups, local guides and low-impact transport, keeps the accommodation simple, puts part of the fee into conservation and management, and teaches the visitor what they are looking at. Mass tourism brings far more people, needs heavy infrastructure, and is driven by profit rather than by the condition of the reef.

The positive impacts follow from appreciation. Tourists who have seen a reef, a whale or a turtle want it preserved for the future, and that public support is what makes protection politically possible. Tourism revenue funds Marine Protected Areas (MPAs), because visitors pay entry fees, permits and levies, and it brings conservation organisations and volunteers into the area - reef survey programmes, turtle tagging, beach clean-ups. Tourism also gives local people an income that does not depend on fishing or on cutting mangroves, which takes pressure off the ecosystem.

The negative impacts are competition for land or resources, pollution, damage to sensitive ecosystems, removal of organisms to sell, and interaction with organisms together with its behavioural consequences. Resorts take the flat coastal land and the scarce fresh water, and they compete with local people for fish, beach access and fishing grounds.

Limiting the impacts of tourists

The syllabus gives three methods of reducing negative impacts - education, legislation and strategic planning - and four strategies for limiting what tourists consume while they are there. Learn them as two lists and choose the right one for the question.

Education works on behaviour. Dive and snorkel briefings, codes of conduct, signs at the reef, guided walks, school and community programmes and information in hotels teach people not to stand on coral, not to touch or feed animals, not to buy shell and coral souvenirs and not to anchor on the reef. It is cheap, it reaches everyone and it changes attitudes, but it is voluntary: a visitor who was never briefed, or does not care, is not stopped by a leaflet.

Legislation works on everyone, whether they agree or not. Laws and regulations create MPAs and no-take zones, zone the sea for different uses, license dive and boat operators, cap visitor numbers, set speed limits, ban anchoring and spear fishing, protect named species and impose fines. It is the only method that can be enforced, but enforcement costs money - patrol boats, rangers, monitoring, prosecutions - and a rule that is not enforced teaches people that rules are optional.

Strategic planning decides in advance what an area can carry: how many visitors, how many beds, how tall the buildings, how far back from the shore, and where the moorings go. It includes environmental impact assessment before a resort is approved, designated dive sites that are rotated so that others can recover, permanent mooring buoys so that nobody anchors, seasonal closures during spawning or nesting, and sewage and water treatment planned before the hotel is built rather than after.

The four resource strategies are about consumption on site. Use of renewable energy and resources - solar water heating, photovoltaic panels, wind, rainwater collection - cuts the diesel burnt for power and the noise that goes with it. Limiting water use matters because fresh water on a small island is scarce, because desalination and pumping are energy-hungry, and because the waste water has to go somewhere. Banning single-use plastics removes the bottles, bags, straws and cutlery that end up on the reef, and limiting motorised transport - shuttles, electric vehicles, bicycles, walking, sail - cuts exhaust, noise and the disturbance of wildlife, including collisions with turtles and dugongs.

When you evaluate, rank the methods rather than listing them. Strategic planning prevents the damage in the first place, so it is the most effective; legislation is the only method that binds everyone, so it is essential; education is the cheapest and the most popular but the weakest on its own. The areas that succeed use all three, which is why a well-run marine park has a plan, a law and a briefing before anyone gets into the water.

Fishing methods and what each one does to the sea

Social and economic importance. Marine organisms are a source of food and income: fish and shellfish supply protein and micronutrients that are difficult to replace in a coastal diet, and the fishery employs boat owners, crews, processors, traders and repairers. For many communities it is also the culture and the last reliable employer, and for a country it can be an export earner.

Every method can be judged on the same three questions: does it touch the seabed, what does it catch besides the target, and what happens to the part of the catch it cannot sell. Bycatch is the catch that is not the target species, and discards are the part thrown back, usually dead.

Netting and trapping. A cast net is thrown over a shoal in shallow water: it is cheap and selective but it takes juveniles in the nursery areas where it is used. Trawling tows a bag-shaped net. A pelagic trawl fishes in midwater for shoaling fish and barely touches the bottom. A beam trawl holds the net open with a heavy beam and drags tickler chains across the seabed, destroying the bottom community, crushing coral and sponges, resuspending sediment and taking a large bycatch that is discarded.

A purse seine surrounds a shoal with a wall of netting and then closes the bottom like a drawstring purse, so it can take an entire school in one set. It is very efficient and uses little fuel per tonne of fish, but it takes juveniles and bycatch - dolphins, turtles and small tuna - especially when the net is set around a fish aggregating device. Tangle nets catch fish by the gills as they try to pass through: a gill net is set in one place and takes fish of roughly one size, decided by the mesh, while a drift net hangs in the water column, and long drift nets are so indiscriminate that they are banned on the high seas. Nets that are lost or abandoned keep fishing, which is called ghost fishing. Basket traps are baited pots that fish passively, take little bycatch and can be fitted with escape gaps, but they also ghost fish and catch undersized lobsters.

Angling. Trolling tows lures behind a moving boat for fast predators such as tuna and mackerel, with very little bycatch and no contact with the seabed. Longlining sets a main line carrying hundreds or thousands of baited hooks: it is efficient and can be selective by depth, but it catches seabirds as the line is set and turtles and sharks as bycatch. Rod fishing with pole and line uses a rod, a line and a barbless lure, with live bait thrown over the side to hold the school, and takes one fish at a time. Bycatch is almost nil and the catch is landed in prime condition, but it needs many hands and calm water.

Finding the fish. Fishing is also navigation. A chart shows depth, hazards, the nature of the seabed and the position of reefs, banks and wrecks, so the skipper knows where it is safe to tow or anchor. A compass, read against the compass rose on the chart, gives a heading and lets a position be fixed by bearings. GPS gives an exact position, so a shoal, a wreck or a trap can be marked and returned to in fog or at night. Sonar, in an echo sounder or fish finder, sends a pulse down and reads the echo to measure depth and to show a shoal or a dense layer of fish. Radar shows other vessels, land and weather, and the flocks of birds that gather over feeding fish.

The environmental impact of a method is the sum of those three questions, not the size of the boat. A small cast net worked in a nursery can do more lasting damage than a large purse seiner working a mobile school in deep water, and a beam trawl that fishes the same ground every week can flatten a community that takes decades to recover.

Fish aggregating devices, over-harvesting and sustainable harvesting

The principle of a FAD. A fish aggregating device is a floating object - a raft, a bamboo platform, a bundle of nets or a moored buoy - that is anchored in deep water or left to drift, and pelagic fish gather around it. Fish are attracted to floating structures for shelter, shade and the food that grows on them, and the association is strong enough that a boat with GPS can return to the same device and set a purse seine around the whole school. Industrial fleets use drifting FADs, often with sonar and satellite buoys that report how much fish is underneath, while small-scale fishers use anchored FADs close to home.

FAD impacts. The benefits are real: less fuel and time spent searching, more reliable catches for small boats, and food for communities that could not otherwise reach pelagic fish. The ecological costs are real too. A FAD gathers a mixed community, so the net takes juveniles of the target tuna as well as sharks, billfish and turtles, and the catch is often landed as one undifferentiated mass. The netting and ropes of lost FADs drift for years and entangle wildlife, drifting FADs add to marine plastic, and because a FAD concentrates fish, removing them is quick - which makes local depletion more likely and can alter the migration the fish would naturally have made.

Over-harvesting. The syllabus statement is blunt: the increase in human population means fisheries are in danger of being over-harvested and becoming unsustainable. More people want more fish, and better technology - sonar, GPS, refrigeration, stronger nets and engines - means each boat can take far more than its predecessors. A stock is over-harvested when more fish are removed each year than are produced by growth and reproduction, so the breeding stock shrinks, the next year's recruitment shrinks, and the same effort catches less.

Because the largest and oldest fish are taken first, the stock loses its most productive breeders, and because a fishery usually targets a predator, removing it changes the whole food chain beneath. A collapsed stock does not recover quickly, and the people who depended on it lose their income and their protein at the same time.

Sustainable harvesting is a set of limits, and the syllabus gives five. Restricting boat size, net types and mesh size limits how much can be caught and lets small fish escape through the mesh before they are landed. Quotas and licences cap the total catch and the number of boats allowed to fish, so effort is matched to what the stock can produce. Closed seasons protect fish at spawning time, when a school is concentrated and easy to catch. MPAs, especially no-take zones, let fish grow large and spill over into the fished ground around them. International agreements are needed because fish do not stop at a border: shared stocks and highly migratory species such as tuna can only be managed if the countries fishing them agree on the same limits.

Evaluating the strategies means saying what each one cannot do. A mesh size can be checked at the quayside but is useless if the fleet simply switches to another net and another species. A quota needs an accurate estimate of the stock, which is expensive and uncertain, and a quota on landings encourages discarding of fish caught over the limit unless it is paired with a ban on discards. A closed season concentrates the effort into the open season. An MPA only works if it is large enough, old enough and actually enforced, and a no-take zone patrolled only on paper is a line on a map. International agreements fail where illegal fishing, flags of convenience and weak enforcement are tolerated.

Why it matters. Sustainable harvesting keeps the fishery available for future generations and keeps fish stocks at levels that do not affect food chains: enough spawning fish to replenish the stock, enough prey for the predators above, and enough grazers to keep algae from smothering a reef.

• Gear limits - boat size, net type and mesh size: cheap to inspect, but needs enforcement at sea as well as at the quay.
• Quotas and licences - a total allowable catch and a limit on the number of boats: needs good stock data and a ban on discards to work.
• Closed seasons - protect spawning aggregations: effective, but the effort simply moves to the open season.
• MPAs and no-take zones - protect habitat and breeding stock and spill over into fished ground: need size, age and compliance.
• International agreements - the only way to manage shared and migratory stocks, but weak where illegal fishing is tolerated.
• All five work best together, and none of them works without monitoring and enforcement.

Aquaculture: species, systems and methods

Social and economic importance. Aquaculture is the farming of aquatic organisms under controlled conditions, and it is a large and growing part of global food production. It supplies protein and income, employs people in coastal and rural areas, gives a reliable supply of known size and quality all year, and can be sited close to the market, which cuts transport and waste. It can also take pressure off wild stocks, but only where the farmed species does not itself depend on wild fish for feed.

The range of species is limited by the syllabus to five groups. Macroalgae such as kelp are grown on ropes and need no feed at all because they photosynthesise; they are eaten, used as thickeners and used as feed for other farmed animals. Fish such as salmon and grouper are high-value carnivores and the most demanding to feed. Crustaceans such as shrimp are a major export earner but need warm, clean water and careful disease control. Molluscs such as mussels and oysters are filter feeders living on plankton, so they need no feed and they clean the water as they feed. Echinoderms such as sea cucumber are grown on the seabed or in pens, often beneath other cages, where they eat the waste that falls from them.

Open and closed systems. In an open system the farm sits in the sea in cages or nets and water flows through it: the environment supplies the oxygen and carries away the waste, so the farm is cheap, but it discharges nutrients, parasites and escapes straight into the sea. In a closed system the animals are held in tanks or ponds on land and the water is pumped, treated, filtered and often recirculated: conditions are controlled and waste can be treated, but the capital and running costs, especially for pumping and heating, are much higher.

Methods of production. It starts with broodstock, the adults used for breeding: hatchery-reared broodstock avoids taking more fish from the wild, and the fastest-growing individuals are selected as the next broodstock so that the stock improves. The farm must maintain the conditions the species needs - temperature, salinity, light, pH and oxygen - which for a warm-water species means heating and for a cold-water species means cooling, and both cost energy. Food requirements vary by species, because the protein and lipid levels have to be matched to the species and to its stage of growth.

Feed can be pelleted, fresh fish or plant-based protein, and the choice is an environmental decision as well as a nutritional one, because feed made from wild fish takes fish out of the sea in order to feed fish on land. Water quality is maintained by an adequate flow rate of clean water and by filtration of the waste water before discharge, or by moving the cages to a new site so that the old one can recover. Fish are size sorted and fed regularly, because a large fish will eat a small one and cannibalism is a real loss in grouper and shrimp. Low stocking densities, antibiotics where disease occurs and cleaner species such as wrasse that eat sea lice are used to stop parasites, disease and predators entering or spreading.

Restocking endangered species. Aquaculture can rear endangered species for release, or grow them for transplanting, where environmental damage has occurred - the syllabus limits the examples to mangrove forests and coral reefs. Coral fragments can be grown in underwater nurseries and transplanted onto damaged reef, and mangrove propagules can be raised in nurseries and planted out on cleared mudflats. It works best where the cause of the damage has been dealt with: replanting a mangrove forest restores the nursery for fish and the coastal protection, provided the clearing stops, and transplanted coral needs clean water, stable substrate and no further bleaching, anchoring or trampling to survive. The limits are cost, low survival, slow growth, the need for long-term monitoring, and the risk of planting a single genetic strain that the next disease will sweep through.

Oil: a non-renewable fossil fuel from under the seabed

Where it comes from. Oil is found under the seabed. It formed from the remains of plankton that settled into fine sediment on the sea floor, were buried, and were changed by heat and pressure over millions of years into a liquid that migrated upwards until it was trapped beneath an impermeable layer of rock. It is a non-renewable fossil fuel: the process that made it takes millions of years, so it is used far faster than it forms, and once a field is emptied it is gone.

Uses. It is combusted as a fuel in ships, vehicles and power stations, which releases carbon dioxide, and it is made into plastics. Both matter for the sea: the carbon dioxide drives warming and ocean acidification, and the plastics end up in the water.

Extraction and transport. Oil is extracted and transported around the world by offshore platforms, pipelines and tankers, and every one of those stages carries a risk of spillage - a blowout at the wellhead, a pipeline leak, a collision, a grounding, or the illegal washing out of tanks at sea. The risk cannot be removed, only reduced, which is what MARPOL is for.

MARPOL. MARPOL is the International Convention for the Prevention of Pollution from Ships, and modern ships and oil tankers must be built in line with its standards. Double hulls reduce the risk of an oil leak after a collision, because the cargo is held in an inner tank with an empty space between it and the outer hull, so damage to the outer hull does not necessarily reach the oil. Tankers cannot wash out their holds except at special collection sites at ports, so oily washings go to a reception facility instead of overboard. Sewage release must be controlled, and garbage disposal must be controlled, which is why ships separate, store and land their waste.

Impacts of a spill. Oil floats, spreads into a thin slick and is pushed by wind and current onto the shore, where it does the most visible damage. It coats the fur of mammals such as seals and sea otters and the feathers of birds: fur and feathers work by trapping a layer of air, and once that layer is matted with oil the animal loses its insulation and its buoyancy, so it dies of cold or drowns. It poisons organisms that ingest it, because the hydrocarbons are toxic and cannot be digested, and filter feeders and fish larvae take them in with their food.

It disrupts food chains by affecting producers: a slick on the surface blocks light and coats the phytoplankton and algae at the base of the chain, and the toxic fractions kill them, so the animals that graze on them starve even if they were never oiled. Burning the oil at the surface destroys the organisms in the slick and sends smoke and soot into the air.

Energy choices: fossil fuels against wind, wave and tidal

Fossil fuels have four clear advantages. The supply is constant and unaffected by weather, so a power station can be relied on at any hour. Oil is energy dense, so a small mass of fuel releases a large amount of energy and is easy to store and carry in a ship or an aircraft. It is relatively cheap per unit of energy, and it is stable to transport and use, because it does not degrade in a tank and it burns in a simple engine.

The disadvantages are equally clear. It is non-renewable, so the resource is finite. Burning it produces carbon dioxide and other damaging gases, including sulphur dioxide and nitrogen oxides, which drive global warming, acidify the ocean and cause acid rain and smog. Extraction damages the environment, through seabed disturbance, habitat loss, produced water and spills, and the remaining reserves are becoming increasingly difficult to extract, which means deeper water, higher cost and greater risk.

The ocean alternatives. Offshore wind turbines stand on the seabed in shallow water or float in deep water, where the wind is stronger and steadier than on land. Wave devices use the rise and fall of the surface, or the pressure changes beneath it, to drive a generator. Tidal schemes either build a barrage across an estuary and generate from the flow in and out, or, with less habitat damage, anchor tidal stream turbines in a fast current.

Advantages of the renewables. They are an infinite energy source, a source that will not run out; they reduce the production of carbon dioxide while operating, and so reduce global warming; and they reduce reliance on fossil fuels, which improves energy security for a country with no oil of its own. Fuel is free once the device is built, and the resource is local, so there is no import bill and no tanker to spill.

Disadvantages. There are high initial costs, because the structure, the moorings and the connection all have to be built in the sea before any electricity is generated. There are limited locations: a wind farm needs strong steady wind and a workable seabed, a barrage needs a large tidal range in a funnel-shaped estuary, and a tidal stream needs a current fast enough to turn a turbine. Underwater cables have to carry the energy to land, which is expensive and disturbs the seabed, and construction causes damage to the seabed and to the communities that live on it.

Operating problems. Weather damage to turbines - salt corrosion, storms and wave loading - shortens their life and raises insurance costs. Marine life can be caught in turbines, and diving birds, fish and marine mammals can be struck by rotating blades or displaced from a feeding ground. Maintenance costs are high because every repair needs a boat, a crane and calm weather, and access is slow. Finally there can be conflict with tourism if the installations are visible, because a seascape that people pay to look at is changed by a row of turbines on the horizon, and because construction noise disturbs the wildlife the tourists came to see.

The judgement is a comparison of scale and of kind. Fossil fuels are cheap, concentrated and reliable, but they are finite and they cause a global problem that the sea pays for. Ocean renewables are clean, free at the point of use and inexhaustible, but they are capital-hungry, limited to suitable sites and, except for tidal, variable in output, so they need back-up or storage. Tidal is the most predictable of the three because the tide is driven by the Moon, while wind and wave depend on the weather.