Caryophylliidae, Scleractinia, Hexacorallia, Anthozoa, CNIDARIA
Lophelia pertusa is a stony coral (Scleractinia) belonging to the group Hexacorallia. As the name implies this group has six tentacles and septa (body segments), or in multiples of six (compare with Octocorallia that has eight). In contrast to many other stony corals L. pertusa is 'pseudo colonial', i.e. the individual polyps is not interconnected by living tissue. Only the young polyps that recently has emerged on the rim of an adult polyp is still attached to it by living tissues. On the image to the right you can see both an isolated polyp with no attachments to others and an adult polyp with a young bud attached. Lophelia pertusa is capable of building reefs stretching over several kilometers and several meters high.
Reproduction in L. pertusa is both sexual, and by asexual budding (cloning). A single colony is either male or female (gonochoric = separate sexes) and the reproductive cycle begins during spring when the surplus of the phytoplankton spring blooms falls down as 'marine snow' to the deep seafloor and gives energy for investment in gamete development. The cycle is completed almost a year later, and results in synchronized mass spawning during January and February (at least in the NE Atlantic). Eggs and sperm are released to the water and eggs are fertilized externally. The early embryo is called a 'blastula' consisting of a uni-cellular layer resembling a soap bubble. The blastula then goes through a phase of 'gastrulation', i.e. a part of the uni-cellular layer forms an invagination, thus creating the precursor of the gastric cavity and a 'blastopore', the primary mouth opening (stomodeum). The embryo has now become a free-swimming planula larva. After three weeks they get competent for settling and start probing the bottom. Finding a suitable substrate they attach, secrete a skeletal plate and begin metamorphosis into a polyp. The body divides into six septa and the tentacles grow out as extensions of the septa. From this single polyp new individuals will be cloned, and a large colony will grow out. Growth is slow, 4-25 mm/yr, or roughly one polyp length. A large reef thus takes centuries to develop. How dense the colony will become depends on the amount of food available, i.e. a rich food supply can support a denser colony. A large reef consist of many colonies of different sexes. However, in a small reef with just a few colonies, both sexes are not always present and reproduction can be mainly clonal, as is the case at Saekken. The adult polyp is a predator, catching copepods, but also feed on particulate matter.