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Reef Check Australia


A set of biologicla indicators was chosen for Reef Check, to serve individually as indicators of specific types of human impacts, and collectively as a proxy for ecosystem health. These indicators fall into the following categories:

  • Anecdotal site description (conducted in the site survey)
  • Coral communities (conducted in the substrate survey and video transect)
  • Macro-invertebrates (conducted in the invertebrate and impact survey)
  • Fish (conducted in the fish survey)
  • Impacts (conducted in the invertebrate and impact survey)

Transect Line

Reef Check surveys are conducted along a transect line marked by a graduated tape measure and laid at a constant depth. The transect line that is surveyed is 80 m. This 80 m length is divided into four 20 m sections or transect replicates. These sections can either be surveyed along a 100m continuous line (an easy option where there is continuous coral reef at a constant depth) or in 20m sections that must each be separated by 5 m or more (where the reef is not continuous, e.g. spur and groove formations or separate bommies. In these circumstances Reef Check transects can be a bit more tricky and time-consuming to set up). This means that Reef Check surveys can only be conducted where there is a minimum of 80 m of coral reef at a constant depth.

Substrate Survey

The substrate survey collects information about the percentage cover of bottom-dwelling (benthic) organisms and substrate on the reef. Each of these indicators of coral reef health has a function on the coral reef. Different codes are used by Reef Check volunteer researchers to quickly record the substrate categories they see underwater.

A 'point sampling' method is used for this survey. The team records the substrate type that is directly below the tape measure every 0.5 m interval along each of the four 20 m sections. To determine which part f the reef is direcly below the line at each 0.5m interval, a weighted line (called a plumb line) is dropped at each interval and the substrate the weight lands on is recorded. This removes bias, which ensures the data represent the real abundance of each substrate category on the reef.

The substrate survey is important because it obtains the percentag cover of hard coral. Hard corals are the reef-builders. Without hard corals, coral reefs and all their associated organisms would not exist. Percentage cover of hard coral is the most commonly used proxy for coral reef health by coral reef managers around the world.

Fish, Invertebrate and Impact Surveys

These surveys are conducted using the same transect line as the substrate survey, however, this time the transect is 5m wide. This is called a belt transect.

Invertebrate and Fish survey

These indicators represent economically or ecologically important invertebrates and fishes. Economically important species are important for fisheries. Ecological indicators are important for the health of the coral reef system. Examples of ecological indicators are Diadema sp. urchins, which are important algae grazers. The absence of algae grazers can cause prolific algae growth and a change in the state of the coral reef from a coral-dominated state to an algae-dominated state. Crown-of-thorns starfish are also ecological indicators and are coral-eating predators. Their presence in large numbers can reduce hard coral cover, providing more space for growth of algae and other invertebrates.

The presence or absence of these indicators does not necessarily mean there is a problem on a reef-by-reef scale. However, providing scientists with an overview of where they occur can help them understand changes to coral reefs over time and analyse the potential cause of threats to coral reef health.

Impact survey

Any visible impact on the reef is recorded during this survey.

Video Survey

This survey provides a permanent record of the coral and substrate on the transect. This information may be important for future, more detailed (species identification) analyses of the data at sites where interesting changes have been recorded by our volunteer researchers.

We also take photographs of the main algae-types we see, as well as any diseased coral, so that we can have these identified by scientists.

For more detailed information on our methods, download Reef Check Australia Survey Methods.

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