What are Cold-water corals?
Cold-water corals (CWC) are Cnidarians, biradially symmetrical in their body form and composed of a central mouth with surrounding tentacles (figure 2). These animals contain stringing cnidocytes which are cells which help corals during predation and allow them to capture and kill prey (Roberts et al, 2009).
Actinopharynx is a tube down the coral mouth leading into the main body chamber of the polyp. A polyp is a gastrovascular cavity. Lamellar sheets of tissue (not found in the stylasterid corals) divide the polyp into sections continued with the hollow tentacles which carry digestive cells (spermacysts and oocytes). Octocorals contain eight tentacles and unpaired mesenteries. They also have polyps and branches as part of their structure which contain calcitic calcium carbonate sclerities. Scleractinians (Stony corals) contain variable amount of tentacles, paired mesenteries but always the same amount of each. This species of coral have a aragonitic calcium carbonate exoskeleton and are solitary (Cairns, 2007). Antipatharians (back corals) contain 6, 10 or 12 unpaired mesenteries but maintain 6 tentacles. Their outer skeleton contains spiny like features and are colonial, and gonochoric meaning that fertilisation is most likely external (Roberts et al, 2009). Hydrozoan corals such as lace corals, are made up of calcified, branched skeleton. These corals are visually similar to the stony corals. Lace corals have two types of polyps with specialized functions. One polyp is large which is important for removal of zooplankton in the water, whilst the smaller polyp consists of stinging cells used for to defend themselves (Freiwald et al, 2004).
What makes Cold-water corals so significant ?
CWC are significant, complex structures making them one of the most extreme habitats in the marine environment. They play an important role in providing habitat for various fish species and invertebrates such as Sebastes sp. which were recorded around gorgonian corals by Krieger and Wing (2002). They provide habitat for a variety of fish and invertebrates such as crabs, shrimp, rockfish, sea bass, snapper and grouper species. CWC are important to humans as well as the marine environment. They provide commercial value as they are used for jewellery and art materials.
Coral reef framework
Patches of skeletal remains of reef organisms form hard substrata causing them to rise from the seabed forming biogenic reefs. Organisms such as ‘Serpula vermicularis’ (the tubes of serpulid polychaete worms), the siliceous skeletons of hexactinellid sponges and limestone skeletons of scleractinian corals, all play a role of creating CWC reefs. Reef growth is controlled by levels of bio-erosion which break down reef structures. If bio-erosion exceeds growth of coral reefs, the reefs then increase in growth causing altering in hydrodynamics and sedimentary conditions forming habitats for various species (Roberts et al, 2009). Although both tropical corals and CWCs form reef frameworks, CWCs do not consist of photosynthetic symbiotic algae (Freiwald & Roberts, 2005; Turley et al, 2007).