Lettuce coral  (Pectinia lactuca)

Classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (2).

One of the most common Pectinia species (3), Pectinia lactuca typically forms conspicuous colonies of large, thick plates, which may grow to over a metre across and are usually a uniform grey, brown or green in colour (1) (3) (4) (5). The colonies are covered in high walls, which may reach several centimetres in height, and elongate, radiating depressions, known as valleys (3) (4) (5) (6). As in other corals, the colonies are formed from numerous tiny, anemone-like polyps, which secrete the hard coral skeleton (3). In Pectinia lactuca, the individual skeletons of the polyps (‘corallites’) are quite widely spaced, and have extensions, known as septocostae, which are continuous between them (4). Each individual polyp bears long, tubular tentacles, which are widely spaced around a central ‘mouth’. In this species, the tentacles are extended only at night, and then only rarely (3) (5) (6).

Pectinia lactuca occurs in the Indian Ocean and western Pacific Ocean, from the east coast of Africa, east to Vanuatu and Fiji, north to Japan, and south to Australia (1) (3) (4) (5) (6).

This species inhabits most reef environments, but particularly lower reef slopes and turbid waters (1) (3) (5). It occurs at depths from around 3 to 20 metres, although it is most commonly seen at 12 to 15 metres (1) (7).

Pectinia lactuca is a zooxanthellate coral, meaning that it obtains most of its nutrients from single-celled algae, known as zooxanthellae, which live within its tissues. The zooxanthellae produce energy-rich nutrients through photosynthesis, and in return receive a protected, stable environment, access to sunlight, and waste nutrients from the coral. This relationship limits the coral to living in relatively clear, shallow, warm waters where photosynthesis can take place, but enables it to grow faster and form large reef structures. The coral may also supplement its diet with tiny zooplankton, caught using stinging cells on the tentacles (3) (8).

Like other coral colonies, Pectinia lactuca can reproduce asexually by a process known as budding, in which polyps divide into one or more new polyps. It can also reproduce sexually, producing sperm and eggs which are released into the water for external fertilisation. The fertilised eggs develop into larvae, which drift in the water column before settling and developing into polyps (3). At the Great Barrier Reef, Australia, this species has been recorded taking part in ‘mass spawning’ events, in which many coral species spawn over just a few nights of the year, in late spring (9). Pectinia lactuca is reported to be hermaphroditic, each polyp producing both eggs and sperm, and the eggs are pink in colour (9).

Although still widespread and common throughout its range, Pectinia lactuca is reported to be particularly susceptible to a number of the threats faced by corals worldwide, including disease and habitat loss, and it is also a common target of the aquarium trade. In addition, the species may be highly susceptible to bleaching, in which a rise in ocean temperatures causes the stressed coral to expel its zooxanthellae, often resulting in death (1).

In addition to localised threats from fisheries, human development, invasive species, pollution and sedimentation, corals around the world are under severe threat from global climate change, which may lead to more severe, frequent storms, and increased sea temperatures. Rising carbon dioxide levels may also increase ocean acidity, affecting the ability of corals to create the hard coral skeleton. These stresses may also make corals more vulnerable to other factors such as disease (1) (8) (10) (11). As a result of these combined threats, around a third of all reef-building corals are now believed to be threatened with extinction (10), and an estimated 20 percent of the world’s coral reefs have already been destroyed (11).

Like all corals, Pectinia lactuca is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES) (2), meaning that international trade in the species should be carefully monitored. This species also occurs in some Marine Protected Areas (1), including the famous Great Barrier Reef, off the coast of Australia, where various coral research and conservation programmes are underway (12). However, enforcement within protected areas is often poor (8), and currently less than half a percent of marine habitats receive official protection (13).

Specific conservation measures recommended for Pectinia lactuca include further research into its populations, ecology, habitats, and its resilience to various threats (1). In particular, population surveys are needed to monitor the effects of collection for the aquarium trade, especially in Indonesia, which is the largest exporter (1). Like many other corals, it would also benefit from the expansion of Marine Protected Areas, reef restoration efforts, collection quotas, and disease and parasite management (1) (8) (11). The IUCN recommends that the conservation status of corals be reassessed in ten years or sooner, in light of the predicted threats from climate change and ocean acidification (1).

For more information on corals and their conservation see:

• Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townsville, Australia.
• Reef Check:
  http://www.reefcheck.org/
• The Coral Reef Alliance:
  http://www.coral.org/