Fire Corals

Fire corals are hydrozoans, and thus have different type of polyps with different functions than anthozoan corals. The polyps of hydrozoans are near microscopic size and are mostly imbedded in the skeleton and connected by a network of minute canals. All that is visible on the smooth surface are pores of two sizes: gastropores and dactylopores. In fact, Millepora means 'many pores'. Dactylopores have long fine hairs that protrude from the skeleton. The hairs possess clusters of stinging cells (nematocysts) that inflict the stings on human skin. These hairs capture prey, which is then engulfed by gastrozooids, or feeding polyps, situated within the gastropores (2). As well as capturing prey, fire corals gain nutrients via their special symbiotic relationship with algae known as zooxanthellae. The zooxanthellae live inside the tissues of the coral, and provide the coral with food, which they produce through photosynthesis, and therefore require sunlight. In return, the coral provides the algae with protection and access to sunlight. Reproduction in fire corals is more complex than in other reef-building corals. The polyps reproduce asexually, producing jellyfish-like medusae, which are released into the water from special cup-like structures known as ampullae. The medusae contain the reproductive organs that release eggs and sperm into the water. Fertilised eggs develop into free-swimming larvae that will eventually settle on the substrate and form new colonies. Fire corals can also reproduce asexually by fragmentation (4) (5).

Fire corals are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which means that trade in these species should be carefully regulated (1). Indonesia and Fiji both have quota systems for corals, monitored though CITES (1). The aim of the quotas are to ensure harvests are kept at a sustainable level, but in reality they are hard to set at the right level due to a lack of knowledge regarding coral biology. Fire corals will form part of the marine community in many Marine Protected Areas (MPAs), which offer coral reefs a degree of protection, and there are many calls from non-governmental organisations for larger MPAs to ensure the persistence of these unique and fascinating ecosystems (6).

Fire corals get their common name from the painful stings they inflict on divers (2). Approximately 50 species of fire coral have been described, which express an array of growth forms. Growth forms range from colonies composed of tree-like branches, solid colonies that are typically dome-shaped, or colonies that adhere closely to the substrate (2). These reef-building (hermatypic) corals can be green, cream or yellow, and those species with branches have hollow cores, containing oxygen, that can be easily broken (2) (3). Other species form thick and sturdy colonies capable of withstanding the strongest wave action (3).

Fire corals form extensive outcrops on projecting parts of the reef where the tidal currents are strong. They are also abundant on upper reef slopes and in lagoons (3), and occur down to depths of 40 metres (4).

Occurs in the Indian and Pacific Oceans (3).

Listed on Appendix II of CITES (1).

Fire corals face the many threats that are impacting coral reefs globally. It is estimated that 20 percent of the world's coral reefs have already been effectively destroyed and show no immediate prospects of recovery, and 24 percent of the world's reefs are under imminent risk of collapse due to human pressures. These human impacts include poor land management practices that are releasing more sediment, nutrients and pollutants into the oceans and stressing the fragile reef ecosystem. Overfishing has 'knock-on' effects that result in the increase of macro-algae that can out-compete and smother corals, and fishing using destructive methods physically devastates the reef. A further potential threat is the increase of coral bleaching events, as a result of global climate change (6). Most fire coral species have brittle skeletons that can easily be broken, for example, during storms, or by divers (2). Divers can easily break the branches of fire corals when diving for leisure, or when collecting fish for the aquarium trade. For instance, the yellowtail damselfish tends to dwell close to the branching fire coral colonies, and retreats into its branches when threatened. In Brazil, fire coral colonies are extensively damaged when harvesting the yellowtail damselfish, as the corals are often deliberately smashed and fishes hiding amongst the branches are 'shaken out' into plastic bags (7).