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Survey Methodologies

Water quality measurements

Aim: To measure the quality of the water each time we go to Salang by measuring the pH, dissolved oxygen content, mineral content, temperature and transparency (visibility).

What does measuring these properties of the reef water tell us about the health of the reef? The table below highlights each property we will measure. The significance of the measurement and the optimal range are also listed. Further details are available in the appendix.

Properties Why How Optimal Range
pH Rise and fall related to atmospheric CO2. Lower pH inhibits coral growth. pH probe, 4 corners 8.1-8.4 pH
Temperature Increased temperature inhibits coral growth, decreases oxygen. Depth-gauge, everywhere 21-29 Celsius
Oxygen Fish and coral die without it. Algae and bacteria reduce oxygen. Linked to temperature. O2 test-kit, 4 corners 2-5ppm
Solids Linked to conductivity. Ion movement. TDS probe, 4 corners
Conductivity Linked to solids. Ion movement. EC probe, 4 corners
Salinity Affects coral metabolism. Refractometer, 4 corners 32–40ppm or 1.022–1.025sg
Visibility Sunlight is required for photosynthesis. Secchi-disc, 4 corners High visibility
Nitrites Algae growth indicator. Test-kit, 4 corners Less than 2ppm
Phosphates Bacterial growth indicator. Test-kit, 4 corners 0.03ppm
Sediment Settles on corals, affects metabolism. Sediment trap, 2 Low
ORP Redox potential breaks down elements in water. ORP-probe, 4 corners High
Alkalinity Magnesium and carbonate indicator. Test-kit, 4 corners 8.1-8.4 pH

How: A water sample will be collected at depth from all four corners of the survey site. These water samples will be brought to the surface and analysed. By measuring the data at all four corners of the site we will be able to see if there are variations in water quality due to depth and/or coral cover.

In addition to the results obtained from analysing the water we will also record the weather, public holidays and number of tourists visiting the reef. Over the years we can correlate this data to the water quality to look for trends.

 

Hard coral growth and health

Aim: To take a closer look and build up a complete map of the site documenting which corals are where, their health and monitor their growth rates.

The types of coral found and their growth rates will give us a good indication of the health of the reef at Salang. Over time we can correlate this data to the weather, public holidays, water quality and fish populations to look for trends and therefore to develop a better understanding of the health of the reef


Coral Mapping

This is going to be a massive undertaking. We will photograph each colony in the site; taking a photo of the entire colony and a macro shot of the polyps to aid identification. The location will be recorded to create an accurate and detailed map of the site. Working on 1m transects of the site, we aim to complete this task over the first season.


Coral growth

We observed how quickly the corals grew during 2012. Two branching colonies grew and completely intertwined the line in only five months. We would now like to quantify how quickly the coral is growing, so we will tag and measure a representative sample of branching and massive corals.

There are two types of coral we will measure; branching corals and massive corals.

Branching corals grow rapidly, up to 10cm a year. A few different colonies will be selected and three branches on each colony will be marked using a cable tie. The distance from the cable tie to the tip of the branch will be measured every month.

Massive corals grow more slowly, often just a few mm a year. A few different colonies will be selected and marked with a nail driven into the coral head. The distance between the surface of the coral and the end of the nail will be measured at the beginning and end of each season.


Hard coral damage/bleaching/disease

During regular visits to the reef we will record any damage we observe to the coral. For cases of coral bleaching and disease a photograph will be taken of the colony and an estimate of the percentage of the colony affected will be recorded. After identification, the colonies will be monitored monthly to see if the condition is improving or not.


Coral recruitment

Coral recruitment is the measure of the number of juveniles entering adulthood – the supply of new individuals. The greater the supply of new individuals the greater chance the reef has to recover from any damage. For example for a reef to recover from bleaching it is reliant on a number of new individuals repopulating the damaged area.

However, new colonies can’t grow on algae so if algae growth is high, the number of new colonies would be low. Once established, new colonies can also be smothered if the sedimentation rates are high.

Therefore we plan on measuring the number of new colonies that grow on clay tiles placed near the reef every 6 months. This combined with information from sedimentation experiments will give us an idea of whether the reef could recover from damage or has the optimal conditions to grow.

 

Fish populations

Aim: To conduct a fish census using videos and diver counting to monitor the rise or fall in fish populations during the season and over the years.

As we can see from the chemistry of a coral reef, the ecosystem is highly complex; however fish abundance and diversity can be used to reflect the condition of the reef. Reef fish are mobile and if conditions deteriorate they are free to leave. Through monitoring the population of fish and the number of species present, we would be able to get a better understanding of the health of the entire ecosystem.  Over time we can correlate this data to the weather, public holidays, water quality and coral growth to look for trends and therefore to develop a better understanding of the health of the reef.


Video

Several different locations will be selected and a permanent stake put in place. A camera will be mounted to the stake and set to record for 10 minutes while the divers leave the area. Once we have returned to dry land we can identify the species observed in the filmed area. By filming several different locations in the site, we can record which fish are found where. By recording without the divers present we hope to be able to record those fish that are disturbed by our presence.


Diver counting

This will be a two part process. Initially we want to photograph and identify all the species living at Salang, so we will be able to compile a catalogue of all the fish present.

Once we know what fish are present, we can train divers in fish identification to conduct the fish abundance surveys. The greater number of people who would like to help in this the better, as greater numbers reduces the statistical error (especially as we aren’t experts in fish ID). Divers will record which species they observe each weekend. We can track the sighting frequency of each fish species and monitor the changes over the season and years.

1)       Pattengill-Semmens, C.V. and B.X. Semmens. 1998. J. Gulf Mexico Sci (2): 196-207.

 

Other Organisms

Aim: To conduct a census of all other organisms found on the reef.

It is not only fish who inhabit Salang, there are plenty of other organisms too; soft corals, invertebrates, sponges etc. Each one will be affected by the overall condition of the ecosystem. In a similar way to the fish census we aim to photograph all life found on the reef, and to monitor any changes observed over time.


Diver counting

We will use a similar method to the fish counting. Initially we will photograph and identify all the other organisms living at Salang. We compile a catalogue of all the other organisms present.

Once this database has been established, we will be able to train the divers in what they can expect to see specifically at Salang. Then divers will record what they see during a dive to generate a sighting frequency for the organisms. We will be able to track changes during the season and over the years.

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