What are the main drivers of Lophelia pertusa reefs and why are they so influential?
Surprisingly, there are more types of corals (66% of known coral species) found in the deep water below 50m, called cold-water corals, than shallow corals that we more commonly associate with tropical coral reefs (Cairns, 2007). Cold-water corals and shallow-water corals have similar anatomy making comparisons commonplace (fig 1), though cold-water corals feed exclusively on suspended food particles that float by. Coral skeleton is made up of calcium carbonate secreted by the mesoglea (fig 1). Scleractinian
corals secrete their skeleton on their outer surface called a corallite. Some types of scleractinian corals are responsible for the framework of reefs and are known as reef builders (fig 2). In the deep water environment only six types of hard corals are known reef builders; Enallopsammia rostrata, Goniocorella dumosa, Lophelia pertusa, Madrepora oculata, Oculina varicosa and Solenosmilia variabilis (Freiwald, 2004). L. pertusa has been extensively researched, respectively, due to its abundance and wide distribution and is the focus of this blog. L. pertusa can create reefs reaching kms in length, particularly in the North East Atlantic (fig 3); creating an important habitat for organisms including commercially important fish (Costello et al., 2005; Henry et al., 2007).
Cold-water corals are sessile organisms and cannot move to areas with optimal conditions. They are at the mercy of the environment and depend on stable repetitive conditions for growth and for food supply. Variables associated with depth such as pressure and light appear to have no effect on Lophelia pertusa (Davies, personal communication; Shelton, 1980). As a result L. pertusa can occur as shallow as 25m in sediment laden fjords where light attenuation reduces light utilising organism abundances, and thus competition. At the other end of the scale, they may be found as deep as 3, 383m (Squires, 1959). Therefore the depth and location at which L. pertusa is found depends on salinity, temperature, competition, dissolved oxygen content, aragonite saturation, food supply, current velocity and water density amongst others. Through understanding the limits of the parameters that L. pertusa can tolerate, we can predict the global distribution of L. pertusa by modelling the habitat suitability (Davies et al., 2008, 2011; fig. 3.). This blog will look at why some of these parameters are considered important for habitat suitability and investigate what are the most important physical environmental drivers. Furthermore this blog will briefly explore how these conditions are changing with climate change and determine what will become the most influential variables in the future.
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