Cold Water Corals
Little is known about cold water corals (CWC) in diver-inacessible deep waters. Calcification and growth of these scleractinian corals is believed to depend on seawater chemistry, particularly the saturation state of the mineral composing the skeleton, aragonite, which is related to the pH and other chemical constituents. The rising CO2 levels in the atmosphere are predicted to change seawater chemistry and lower the aragonite saturation state, with so far unknown consequences to the deep biota. Because many CWC live at or near aragonite saturation, already slight changes in saturation state may have dire consequences for the calcification and survival of these slow-growing corals.
The Patagonian fjords of southern Chile offer the unique opportunity to study CWC in shallow waters. In Comau Fjord, dense aggregations of the common cosmopolitan cold water coral Desmophyllum dianthus thrive in diver-accessible depths, at just 20 m depth. A well-equipped research station is available providing excellent facilities for study [http://www.fundacionhuinay.cl/]. Aragonite saturation varies both vertically and horizontally, between the fresh surface and marine deep waters and the sheltered inner and exposed outer fjord. So far, it is not known (1) how these natural variations in aragonite saturation state affect coral calcification and growth, (2) what sources and supplies of energies fuel calcification in low-saturation state waters, and (3) how CWC may be affected by the postulated nutrification of fjord waters in the course of salmon farming, and by global CO2 and temperature rise.
An interesting aspect of Desmophyllum dianthus ecology in the twilight zone is its association with cyanobacteria and green algae living on and in the tissue covered part of the coral skeleton. So far, it is not known (1) if the algae are photosynthetically active, (2) if there is an exchange of metabolites between the algae and their coral host, and (3) if this symbiosis may play a role in promoting Desmophyllum dianthus survival in shallow waters - in a way reminiscent of tropical corals living in obligate symbiosis with zooxanthellae.
As with other CWC, the reproductive ecology of D. dianthus is virtually unknown. Larval dispersal can be inferred from communities establishing on artificial substrate, triggering a suite of questions: How do they reproduce? Do they broadcast spawn or brood their larvae? Do corals show any seasonal pattern in reproduction? How does succession proceed? What happens in early settling stages in terms of competition in space? Why can they be found at some sites, but not at others, apparently facing the same environmental conditions?
Focus: time travel to the future - cold water corals from Comau Fjord, Chile [in German language]