A Lagoon Damselfish (Hemiglyphidodon plagiometopon) living amongst an arborescent branching coral.

Damselfish (Pomacentridae) live amongst live corals where they establish home territories.  They play important roles in many symbiotic relationships, prevent algae from overgrowing around live corals, and are also an essential prey for other fish living on the reef.

Lagoon damselfish are regularly found living in Acropora branching corals where they are often seen demonstrating strong territorial behaviours towards organisms that attempt to enter their home patch. Individuals engaged in these behaviours often display a rapid change in colour of their face from black to yellow as a communication tool to their opponents whilst defending their coral patches on which their preferred algae grow.

Many damselfish demonstrate a strong dietary preference for specific types of filamentous algae. These fish manage individual territory patches (or gardens), which cultivate their preferred type of food. Damselfish spend much of their time weeding these gardens, removing any unwanted algae species that would otherwise outcompete their favoured crop and spoil future harvests.

Commonly observed by divers, these fish also demonstrate territorial behaviours to other reef species who enter their garden, a behaviour performed to exclude herbivores who may feed off their hard work. Both behaviours mentioned allow Damselfish to cultivate a garden full of their favourite meal.

In addition to their gardening roles, damselfish living in and amongst live corals also provide significant benefits to their host corals. Whilst swimming around the corals, their busy movements help to increase water circulation over the coral polyps. Studies have shown that increased circulation from damselfish swimming has resulted in a higher rate of photosynthesis carried out by zooxanthellae (microscopic algae that live inside corals and provide them with energy from photosynthesis). Productivity in corals has shown to increase with certain damselfish inhabitants as a result of this movement, therefore demonstrating the significant benefit of living with these fish.

Corals provide vital shelter and protection to Damselfish who reside there. Individuals have appeared to show fewer signs of stress when living in live corals compared to dead coral substrates, suggesting live corals may increase the survival and fitness of damselfish. Live corals are therefore important habitats to conserve in order to promote a high abundance and diversity of damselfish. This is essential as they offer a valuable food source to predators living on the reef.

As different species of damselfish reside in and amongst a variety of corals, it is important to promote the abundance and diversity of these corals that provide such important habitats. Marine conservation programs running at Roctopus help to monitor and assess trends in the percentage cover and diversity of important coral types found on the reefs of Koh Tao. This helps to identify any significant loss of specific corals, and therefore habitats to damselfish and other key reef organisms. Information gathered from these project dives is essential for understanding the threats to certain coral types, and important when deciding the most effective conservation methods to promote and conserve the biodiversity of corals.

 -- Click here to see more of Piers' underwater photos of marine organisms. --