6. Human Impacts on Coral Reefs—Sedimentation, Sewage, Tourism, Village Communities and Fishing

Sedimentation

Sedimentation is when a reef gets covered in sediment (soil, sand or mud). Sediment is the small particles of sand and mud floating in the water column. This sand and mud can sometimes be stirred up from the bottom of the sea, but mostly it comes into the sea from the land next to the reef as a result of erosion. Erosion occurs when rain and storms wash away sand, mud and soil from the land.

Why is sedimentation bad for the reef?

  • Corals need sunlight and clear water to be able to make their food to grow and live.
  • When the water is full of sand and mud it will not be clear, and will not let the sunlight down through to the corals below.
  • If the sediment settles on the corals, it can cover them up so that even when the water is clear above them, the sunlight cannot reach them.
Healthy Reef
Healthy Reef		   Sedimented Reef
Sedimented Reef

Why does sedimentation happen?

  • Trees hold the soil together with their roots stopping it from being washed away
  • If these trees are removed then there is nothing left to hold the soil on the land
  • When there is a storm, the rain washes soil from the land down into the sea
  • This causes sedimentation of the reefs (more sand and mud will stay on the reef)

Sewage

Sewage is refuse (rubbish) liquids or solid waste matter. It is often high in nutrients. Nutrients are food for plants and algae.

How can sewage reach the reef?

  • Through improper sewage storage and treatment facilities the sewage can leak out into the soil and then become run-off on to the reef.
  • Through old septic tanks that have not been maintained And cleaned regularly—the sewage can overflow from the tank and find its way on to the reef.

Why is sewage bad for the reef?

Sewage is high in nutrients. Nutrients are compounds (materials) like nitrates and phosphates. Nitrates and phosphates can be found in fertilisers, household cleaning products, and sewage. When there are too many nutrients in the water, the sea plants along with the wrong kind of algae (sea weed) will grow healthy and strong. They will grow bigger and faster than the corals. When this happens, the corals will not be able to receive enough sunlight, and so they will not be able to make food for themselves. The corals will become weak and eventually die.

Brainstorming Session

How can we solve the problems sewage causes?

Tourism

Tourism is the largest contributor to the economy of Fiji (brings a lot of money to the country) It creates a lot of jobs and tourists will also spend their foreign dollars here in the country. The dollars the tourists spend find their way back into the local communities in all sorts of ways: from tourists buying local handicrafts, taking village tours and the hotels buying seafood, locally grown vegetable and other produce and providing employment to many people from the local community.

Tourists come to see the beautiful beaches and colourful coral reefs. This means that here in Fiji, the ocean and coral reefs are used a lot. It is a very valuable resource for all Fijians and for the future of Fiji. Tourism needs to be developed and managed properly to ensure that this resource remains intact and is not overused. MES is dedicated to advancing the adoption of “best practices” through the education of all community and commercial stakeholders (all people involved) in the tourism industry.

Brainstorming Session

What activities related to tourism may be harmful to the reef? What do you think would be the best way to solve these problems?

Village Communities

Tourism has increased dramatically and the population of Fiji has increased over the last 30 years. Village communities have been around in Fiji for a long while however we are now finding because there are more people sharing the same amount of space, there are problems arising due to the ever increasing growth in the population and the demand on the local environment to supply their daily needs. There is more demand on traditional fishing grounds to supply food, inappropriate disposal of sewage through septic tanks which leach out waste from those septic tanks which in turn end up leaking into the sea and inappropriate rubbish disposal all of which threatens the health of the living reefs.

Fishing

Fish are important to us as they are a source of food and income. There are many different ways of catching fish. Some of these methods are better and kinder for the reefs than others. Selective fishing means that we are carefully choosing the fish which are caught. There are some methods of fishing which are harmful and damaging to the environment.

Good Fishing Practise:

  • Not taking more fish than are needed (only take what is enough for your family)
  • Not taking fish below or above a certain size
  • Releasing fish which will not be eaten
  • Not always taking the same species
  • Being careful not to damage the reef
  • Taking home all fishing gear after use

This can be achieved by spear fishing, hand lines, free-diving or snorkel collection. These methods allow the fishermen to see what they are taking and choose whether to take the fish home or set it free.

Poor fishing practices damage the reefs and harm other sea animals. This is also known as destructive fishing. Examples of these include dynamite or blast fishing and cyanide fishing or “duva” fishing, where poison is released into the water to shock the fish so they are easy to collect. The poison however affects all other animals on the reef and kills the little fish that would have grown to maturity.

Another problem is overfishing (catching too many fish). If we take too many of the same fish, this will disturb the ecosystem. For example, parrotfish eat algae (seaweed). If we take all the parrotfish, the algae will grow unchecked and it will choke the coral, which could then die.

It is important that we do not take some fish from the sea before they have had time to have babies (reproduce). Some fish must grow to a certain size before they reproduce. If we take the fish when they are too small there will be no young fish to keep the population going in the future (no fish to increase the number in the sea). In contrast, if we take out all the large fish, there will also be negative effects. Large fish produce more and healthier fish eggs which in turn, will produce more and healthier babies. If we take out all the large fish, there will not be as many eggs and fish babies for the coral reef.

The table below shows the size that some fish must reach before they reproduce, as outlined by the Fiji Government. If we take fish smaller than this, there will gradually be fewer fish in the sea to harvest.

Minimum Catch Sizes:

Fijian Name English Name Size (cm)
Balagi Surgeonfish 20
Ulavi Parrotfish 25
Kawakawa/Donu Grouper/Coral Trout 25
Ta Unicornfish 30
Nuqa Rabbitfish 20
Ogo Barracuda 30
Saga Trevally 30
Damu Snapper 30
Ose Goatfish 15

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