Coral Reef Ecology

Marine Pollution

Water pollution is the contamination of water bodies such as rivers, lakes, streams, oceans and groundwater. Natural events such as storms and volcanic eruptions have deposited pollutants (such as silt) into water bodies for millenia, however human activities offten exacerbate the effects of these events and pollutants with a human origin often have a more serious and longer lasting effect.

Water pollution produced by human actions, include:

  • Fertilisers from agricultural activities. Increased levels of nutrients such as Nitrogen and Phosphorous in a water body often causes accelerated growth of algae and phytoplankton and may result in a reduction of Oxygen levels and fish kills.
  • Pesticides running into water bodies from agricultural activities kill aquatic organisms such as macro-invertebrates. The loss of these animals has a flow on effect up the food chain as other animals lose their food source or eat contaminated prey.
  • Sewage released into water bodies increases the nutrient load and may introduce dangerous pathogens or disease causing organisms. 
  • Heavy metals, organic toxins, oils, nutrients and solids discharged in large amounts with wastewater from industry.
  • Soil eroded from the land surface due to deforestation, mining and overgrazing of livestock. Sediment added to a water body will increase turbidity (cloudiness) and therefore reduce the depth to which sunlight penetrates the water column. Reduced levels of sunlight in the water effects the depths at which plants can grow. For example, seagrass meadows are no longer able to survive in the deeper parts of Tuggerah Lakes as they did before European settlement due to increased sediment loads from land clearing. The seagrass can now only grow closer to the shore in shallow water resulting in altered habitat for animals that rely on seagrass such as prawns and fish. For more information on Tuggerah Lakes and to find out how you can help improve water quality, visit
  • Litter, including platic bags, bottles and cigarette butts. To discover more about the global problem of plastic pollution, visit

The pie chart below is a rough indication of the percentages of major pollutants which enter the world's oceans annually. As you can see, the three main sources of ocean pollution are air pollution, farm runoff and sewage.

Figure 1: Pollutants Overview

Australia spends more than $1 billion on herbicides, fungicides, insecticides and pesticides which are applied each year. The CSIRO with support from Land and Water Australia now offer a free software package online called The Pesticide Impact Rating Index (PIRI) which can be used to measure the effects of particular pesticides on the aquatic environment. It is a risk indicator for different pesticides and cropping systems. This software can be downloaded from the CSIRO website.

Students learn about threats to coral reefs including
–    overexploitation,
–    destructive fishing techniques
–    pollution
–    global climate change
–    crown of thorn star fish