Tomas Lundälv

Role of cold-water Lophelia pertusa coral reefs as fish habitat in the NE Atlantic

The rate of discovery of reefs of the cold-water coral Lophelia pertusa (Linnaeus, 1758) has been remarkable, and attributable to the increased use of underwater video. These reefs form a major three-dimensional habitat in deeper waters where little other ‘cover’ for fish is available. They are common in the eastern North Atlantic, and occur at least in the western North Atlantic and off central Africa. There are also other non-reef records of Lophelia in the Atlantic, and in Indian and Pacific oceans. Thus, not only are these reefs a significant habitat on a local scale, but they may also provide an important habitat over a very wide geographic scale.

Mapping of Lophelia reefs in Norway: experiences and survey methods

The Institute of Marine Research commenced a program for mapping and assessment of Lophelia reefs in 1997. It was initiated by reports from fishermen claiming that bottom trawling damaged deep-water coral reefs. The strategy was to survey coral sites reported in the literature and by the fishermen. This has provided an extensive database of coral occurrences, both damaged and undamaged sites. A number of major coral reefs have been identified, which has provided a better understanding of the morphology of Lophelia reefs and where they are likely to occur. We are now able to identify potential coral areas by analysing seafloor topography on maps. Fast and reliable ground-truthing methods using simple and inexpensive systems have been developed. Mapping and quantification of corals demand more advanced instrumentation, such as singlebeam and multibeam echo sounders in combination with data processing software allowing coral reefs to be detected in real time. Systems providing real time presentation of multibeam data are especially useful in combination with Remotely Operated Vehicle (ROV) positioned with acoustic navigation systems. We suggest the following mapping procedure: 1) acoustical reef detection followed by multibeam mapping, preferably along with collection of seismic reflection data. 2) ground-truthing with a tethered video camera platform or an ROV. The position of the observation platform is plotted online and draped on the multibeam maps, either in 2D or 3D mode. Examples from the reefs on Sula, Rost, Traena and Fugloy are given.

Compositional variability in a cold‐water scleractinian, Lophelia pertusa: New insights into “vital effects”

We analyzed Sr/Ca and Mg/Ca ratios in the thecal wall of Lophelia pertusa, a cold-water coral, using SIMS ion microprobe techniques. The wall grows by simultaneous upward extension and outward thickening. Compositional variability displays similar trends along the upward and outward growth axes. Sr/Ca and Mg/Ca ratios oscillate systematically and inversely. The sensitivity of Lophelia Sr/Ca ratios to the annual temperature cycle (−0.18 mmol · mol−1/°C) is twice as strong as that exhibited by tropical reef corals, and four times as strong as the temperature dependence of Sr/Ca ratios of abiogenic aragonites precipitated experimentally from seawater. A comparison of the skeletal composition of Lophelia with results from precipitation calculations carried out using experimentally determined partition coefficients suggests that both temperature-dependent element partitioning and seasonal changes in the mass fraction of aragonite precipitated from the calcifying fluid influence the composition of Lophelia skeleton. Results from calculations that combine these effects reproduce both the exaggerated amplitude of the Sr/Ca and Mg/Ca oscillations and the inverse relationship between Sr/Ca and Mg/Ca ratios.

The physical niche of the bathyal Lophelia pertusa in a non-bathyal setting: environmental controls and palaeoecological implications

The habitat-forming scleractinian coral Lophelia pertusa supports an ecosystem that is widely known to occur in the bathyal marine ecologic realm along deep shelves, oceanic banks, seamounts and continental margins. Therefore, L. pertusa is generally considered a ‘deep-water’ or ‘deep-sea’ coral. In contrast, this study analyses the environmental controls of this bathyal ecosystem where it is thriving well in the non-bathyal shallow-water setting of the Swedish Kosterfjord area (NE Skagerrak). This is one of several shallow-water L. pertusa occurrences in Scandinavian waters where saline and temperature stable oceanic waters intrude as topographically-guided underflows onto the inner shelf and adjacent fjords, driven by an estuarine circulation.