Hump coral  (Porites annae)

Porites annae is classified as Near Threatened (NT) on the IUCN Red List (1) and is listed on Appendix II of CITES (2).

Extremely long-lived due to their remarkably slow growth rates, with some colonies growing at just nine millimetres a year, Porites corals often form giant colonies which are among some of the oldest living forms of life on earth (3).

Like other colony-forming corals, colonies of Porites annae are composed of numerous small polyps. The polyps secrete a hard calcareous skeleton, called a ‘corallite’, which contributes to the formation of a coral reef over successive generations (3) (4).

Porites annae colonies typically have knobbly, elongate branches, which join together to form one larger branch or column. The branches have a characteristically irregular appearance, and are usually pale or dark green, yellow, purple or brown (3) (4) (5).

Porites annae occurs in the northern Indian Ocean, including the Arabian Sea, the central Indo-Pacific, Australia, Japan and the South China Sea and the oceanic West Pacific (1).

Usually found on reef slopes, Porites annae occurs in both clear and murky, turbid waters. It generally inhabits depths down to 30 metres (1) (3) (4) (5).

Like other reef-building corals, Porites annae has many microscopic photosynthetic algae, called zooxanthellae, living within the polyp tissues. Both the coral and its zooxanthellae are sensitive to changes in water temperature and acidity, and any increase in the water temperature greater than one or two degrees Celsius above the average may stress the coral and cause ‘bleaching’, a phenomenon in which the coral expels it zooxanthellae and turns white (3) (4).

The coral and the algae have a mutually beneficial relationship; the coral provides protection for the algae, which in return provide energy and nutrients for the coral through photosynthesis (3) (4). Porites annae is also able to supplement this with a diet of minute zooplankton, which it catches using stinging cells on tentacles that extend from the coral polyp (3). The tentacles of Porites annae are generally only extended at night (4).  

Porites corals have separate male and female colonies. Instead of releasing bundles of eggs into the water, most Porites species brood the larvae inside their body cavity. Fertilisation is generally internal and therefore depends on free-swimming sperm from male colonies reaching the polyps of female colonies (3). When released, the larvae quickly settle close to the parent colony. Whilst this means that, unlike spawning corals, the coral is not easily dispersed, brooding corals have the advantage of their young settling in an environment that has already proved suitable for successful reproduction (4).

Although less susceptible to bleaching than many coral genera, the Porites genus is much more prone to disease than many other corals. An emerging threat to coral reefs worldwide, coral disease is a major cause of reef deterioration (1).

The major threat to all corals is global climate change, which is expected to cause rising sea surface temperatures and ocean acidification, and more frequent, severe storms, which can damage reefs. Climate change will also increase the risk, frequency and duration of coral bleaching, and corals will be more susceptible to disease, parasites and predators, such as the crown of thorns starfish (Acanthaster planci) (1) (6) (7) (8).

Worldwide there is increasing pressure on coastal resources resulting from human population growth and development. There has been a significant increase in domestic and agricultural waste in the oceans, pollution, poor land-use practices that result in an increase in sediment running on to the reefs, and over-fishing, which can all have knock-on effects on the reef (6). Porites species are also heavily collected for the aquarium trade (1).

Porites annae is listed on Appendix II of CITES, meaning that all trade in this species should be carefully monitored. Parts of this species’ distribution falls within Marine Protected Areas (1).  

Recommended conservation measures for Porites annae include research on its population trends, abundance, ecology and habitat. There is a need to identify how resilient this species is to existing threats, and to identify any unknown threats it may face currently and in future. Protected areas are likely to be beneficial to this species and so should be effectively managed and expanded, and potential new sites for protected areas should also be identified (1).

Porites annae is targeted by collectors for the aquarium trade. Population surveys should be carried out to monitor the effects of harvesting on this species, and fisheries management needs to be carefully considered, including setting catch quotas, size-limits and no-take zones, especially within Marine Protected Areas (1).

Further information on the conservation of coral reefs:

• Reef Check:
  
  http://www.reefcheck.org
• The Coral Reef Alliance:
  
  http://www.coralreefalliance.org