ABSTRACT
The cold-water scleractinian coral Lophelia pertusa (Linneaus 1758) is the main ecosystem engineer in the northeast Atlantic (Freiwald et al. 2004) building important habitats for fish and invertebrates (Costello et al. 2005, Mortensen et al. 1995, Reed 2002, Ross and Nizinski 2007). Coral presence increases diversity threefold compared to surrounding soft-sediment habitat (Gage and Roberts 2003, Henry and Roberts 2007, Husebø et al. 2002, Jensen and Frederiksen 1992, Jonsson et al. 2004, Jonsson and Lundälv 2006), and loss of coral habitat adversely affects local fisheries (Fosså et al. 2002, Koenig et al. 2000). It is estimated that 30% to 50% of the Norwegian reefs have been damaged by bottom-trawling (Fosså et al. 2002). Likewise, the coral coverage and habitat complexity of the L. pertusa reefs in the Skagerrak have been severely reduced. In the Swedish part of Skagerrak, only one small live reef, consisting of small detached and scattered colonies, remains, whereas six hitherto known reefs are extinct and consist only of dead coral rubble. Rubble fields are known to give a poor substrate for recolonization, with little or no recovery in both high and low wave-energy environments, and, rather than recovery, a further deterioration has been the case (Brooke et al. 2006, Clark and Edwards 1994). Furthermore, due to geographic isolation of reef sites in the area, the natural recolonization by coral larva from neighboring reefs is unlikely. For example, dispersion probabilities using a Lagrangian model shows a mere 4–9% probability of larval recruits from the nearest Norwegian reef (Tisler) reaching Saekken (Ericson and Ljunghager 2006). These results are corroborated by genetic data showing high genetic differentiation between reefs in Skagerrak (Broberg 2006) and high levels of clonality within reefs (Dahl 2006). Hence, it seems that rehabilitation efforts by means of deployment of artificial reefs with coral transplants are necessary to restore cold-water coral cover in the area.
