Depth

graph of coral depth

graph showing coral depth in the pacific ocean (Freiwald et al 2004)

Depth is one of the main factors that governs where an animal or plant can live in the world’s oceans. Vertebrates such as whales and fish are limited by hydrostatic pressure as to how deep they can go, the deeper an animal dives the more pressure it has on its body. Many species such as whales have evolved to dive to great depths. Plants are governed by depth as they need light for photosynthesis and the light can only penetrate to a certain depth depending on the water conditions, this is called the photic zone and it is where tropical coral reefs are found.

Records and observations of cold-water coral ecosystems prove that hydrostatic pressure is not an issue for them as Lophelia pertusa has been found as shallow as 39m in Norwegian fjords (Freiwald et al. 2004), however, L.pertusa abundance has been recorded to be at its highest in between 200-400m (Dons 1944). Most species of corals are most abundant around 40-1000m deep (Freiwald 2002; Freiwald et al. 2004; Roberts et al. 2006; Wheeler et al. 2007; Roberts et al. 2009) but they have been observed at depths around 5500m (Davies 2010). In colder environments such as those at higher latitudes (e.g. North Atlantic) cold-water corals tend to be found in shallower water as the temperature stays reasonably constant with depth, this as appose to lower latitude where they are found in deeper water as the surface water is warmer (Freiwald et al. 2004).

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