Water Quality Elements in Koh Tao



With every drop of water you drink, every breath you take, you’re connected to the sea. No matter where on Earth you live”  Sylvia Earle

It is difficult to imagine the amount of water that makes up our oceans. Some studies speak of 1,332 million cubic kilometres; however, it is very difficult to know that for sure. What is certain is that the quality of this water has a direct influence on the life quality of its inhabitants.

Innoceana arrived at the coasts of the Gulf of Thailand with a clear idea. We wanted to understand the state of the ocean water by collecting water samples from the surrounding areas of the Island of Koh Tao and analysing them, as well as to try involving more people to continue to do so to create an initial database or “baseline” of the quality of this water. Today, five months later, we have got more than a hundred samples which have been collected from the main diving sites surrounding the island. The analysis of these samples has also allowed us to find two possible “dead zones”. What is more important is that the project has been expanded and today we work alongside different diving centres that have joined our cause. These centres are now buying their own sampling equipment and have begun to analyse the water quality with the purpose of contributing to the database managed by Innoceana and following the methodology that Innoceana created.

There are many parameters that can be measured in water and which are key to the survival of the wonderful living beings that ply the oceans. Temperature, pH, salinity, nitrates, phosphates and oxygen are just some of them. In this blog we are going to try to explain the reason for their importance:

Temperature: Seawater’s temperature (as it happens on land) varies from the equator to the poles where its minima is produced due to solar radiation which has a direct influence on its temperature. The current climate change is generating a dramatic increase in temperatures due to greenhouse gases and the destruction of the ozone layer.

Animal corals are ectothermic, thus leading to them being sensitive to temperature changes. Very low temperatures disable corals from making metabolic reactions necessary for them to survive, however, very high temperatures can also be a threat. When temperatures rise, the coral’s inner body becomes more acidic and toxic to the zooxanthellae, which commence to produce higher amounts of waste in the form of free radicals. The necessity to protect themselves from these free radicals, leave no other alternative to the animal coral but to eject the zooxanthellae in a process called coral bleaching. Bleached corals live only with 5 to 15% of their regular energy levels until environmental conditions return to normal levels and a new zooxanthellae moves into their bodies. However, corals do not often have enough energy to survive this period and die.

Hard corals survive in waters with temperatures ranging from 18 to 36oC, however they are healthiest in temperatures ranging between 22 to 28oC. In temperatures above 30oC, corals struggle to survive and begin to die gradually in most cases. Below 18oC, reef-building corals begin to decline rapidly.

All species of sea turtle are also affected by climate change. An increase in nesting temperature have an impact on sea turtles as they rely on the sand temperature in which the eggs are incubated to determine the gender of the hatchlings. Due to this, 99% of sea hatchlings are turning females resulting in lack of males which in turn affects reproductive rates.

PH: An increase in atmospheric carbon dioxide (CO2) concentrations had led to oceans becoming more acidic, thus, decreasing water pH concentrations from 8.2 to 8.1 units. Studies have shown that corals are more likely to be healthier in seawater with pH levels between 8.0 and 8.3 units, as lowered pH levels lead to reduced calcification rates thus, growth rates. Therefore, pH becomes an indicator of water acidity which can be measured in logarithmic scale bounded between 0 and 14, pH 1 as is the case of hydrochloric acid can kill a human being with a single sip.

Salinity: Corals need salt water in order to survive. They require salinity concentrations in water between 32 to 34ppm as they are highly susceptible to disease leading to rapid coral bleaching in lower salinities which is mainly caused by near river openings, continuous heavy rains, and poor or excessive drainage in coastal areas. Salinity is measured by density or by parts per trillion (ppt) which is usually around 1.023 kg / litre. Salinity also affects other organisms such as fish that use an internal host regulation system. Changes in the salinity not only affect sea life but also produce changes in marine currents.

Nutrients (Nitrates and Phosphates): Coral reefs thrive best in areas with low nutrient levels, also known as oligotrophic waters, due to the fact that nutrient rich waters encourage macro algae growth, which is one of the major threats to corals. Macro algae grow much faster than corals competing with them for space, shading and smothering them. High nutrient concentrations also favour the increase of coral predators such as Drupella snails (Drupella cornus) and Crown of Thorns starfish (Acanthaster planci). The major nutrients of concern are compounds of nitrogen and phosphorous such as nitrates (NO3) and phosphates (PO4) which are present in soil and especially concentrated in human sewage.

When these nutrients reach the sea, a phenomenon called “algae bloom” consisting in an uncontrolled growth of algae occurs resulting in dead zones. To date, Innoceana has located two possible dead zones in the Island of Koh Tao.

O2: Oxygen is fundamental for all life organisms, however, unlike terrestrial species, most underwater creatures use gills to filter dissolved o2 in water. When dissolved o2 levels are too low, underwater breather species must migrate from these areas in order to survive. This is the case of the so-called dead zones. o2 levels below 2 parts per million (ppm) or mg / litre, make survival of most aquatic organisms impossible.

 Source – fondriest.com


Turbidity: Turbidity indicates levels of suspended particles in water which can be directly linked to sea currents, to the type of substrate (muddy substrates lead to high turbidity, thus, blocking the entrance of natural light), or to nutrient levels that promote microalgae formation and growth. In the Island of Koh Tao, it is common to see high turbidity levels after rainy days due to the silt and other particles that the rain drags into the sea. Turbidity can be measured vertically from a boat and horizontally underwater, both by using the Secci disk which is obtained as a result of the refraction and diffraction studied centuries ago by Snell. Areas with high turbidity may be unhealthy specially for corals but also areas with very low turbidity may be a symptom of dead zones.


Innoceana has designed a low-cost measuring kit (150 euros) which can be used to analyse water quality in a very simple way. In addition to this, we have also designed a system to help every diving centre that would like to participate in the collection of data (There are already 10 centres interested on the project and 3 centres have already bought their measuring kit). This system consists of the following:

  1. Cover Letter (pdf): Koh-Tao-WQA
  2. Protocols (pdf): KTWQ Elements Protocol V3
  3. Contract of commitment (pdf): WQEKT-SOU
  4. Measurement kit: