March 26, 2010

Technical Question of the Month: Why are turf algae not counted in Reef Check surveys?


Each month, Reef Check will answer a technical question regarding the monitoring protocol of our coral reef or rocky reef programs. If you have a question you would like answered, please email

Reef Check Tropical — Why are turf algae not counted in Reef Check surveys?

Algae (also known as seaweed) are a normal component of healthy coral reefs. Turf algae are cropped algae only a few centimeters in height, typically growing on rock, rubble or sand. They are important ecological indicators because they indicate a healthy population of algae-consuming fish and invertebrates, the herbivores, therefore many ecologists include turf algae in coral reef surveys. So why isn’t this important indicator part of Reef Check surveys?

Although Reef Check is an ecological survey protocol, it is primarily designed to track human impacts. If turf algae are allowed to grow, due to a combination of high nutrients (fertilizer) and low herbivory (algae eating), then the algae can become an important indicator of human impacts – mainly sewage pollution and runoff from agriculture. It is the unbalanced ecological condition of unchecked algal growth that is of interest to Reef Check, because this is the indicator of human impacts. So rather than monitoring the normal balanced condition of turf algae – Reef Check tracks out-of-control algal growth – which we call Nutrient Indicator Algae (NIA). In other words, presence of turf algae is the normal condition so is not counted. When it grows above 2.5 cm then it is counted to indicate the above problems (NIA). As such, it is an indicator of high inputs of the nutrients phosphorus and nitrogen and low numbers of herbivores.