Deep-water Coral - Growth and Reproduction

Growth and Reproduction

Corals must attach to a hard surface in order to begin growing. They are often found growing along bathymetric highs such as seamounts, ridges, pinnacles and mounds, on hard surfaces. Corals are sedentary, so they must live near nutrient-rich water currents. Deep-water corals feed on zooplankton and rely on ocean currents to bring food. The currents also aid in cleaning the corals.

Deep-water corals grow more slowly than tropical corals because there are no zooxanthellae to feed them. Lophelia has a linear polyp extension of about 10 millimetres (0.39 in) per year. By contrast, branching shallow-water corals, such as Acropora, may exceed 10–20 cm/yr. Reef structure growth estimates are about 1 millimetre (0.039 in) per year. Scientists have also found Lophelia colonies on oil installations in the North Sea. Using coral age-dating methods, scientists have estimated that some living deep-water corals date back at least 10,000 years.

Deep-water corals use nematocysts on their tentacles to stun prey. Deep-water corals feed on zooplankton, crustaceans and even krill.

Coral can reproduce sexually or asexually. In asexual reproduction (budding) a polyp divides in two genetically identical pieces. Sexual reproduction requires that a sperm fertilize an egg which grows into larva. Currents then disperse the larvae. Growth begins when the larvae attach to a solid substrate. Old/dead coral provides an excellent substrate for this growth, creating ever higher mounds of coral. As new growth surrounds the original, the new coral intercepts both water flow and accompanying nutrients, weakening and eventually killing the older organisms.

Individual Lophelia pertusa colonies are entirely either female or male.

Deep-water coral colonies range in size from small and solitary to large, branching tree-like structures. Larger colonies support many life forms, while nearby areas have much less. The gorgonian, Paragorgia arborea, may grow beyond three meters. However, little is known of their basic biology, including how they feed or their methods and timing of reproduction.