Distribution of Coralline algae along a salinity and depth gradient in a Patagonian Fjord

Crustose coralline algae (CCA) are susceptible to global change and ocean acidification through changes in seawater carbonate chemistry due to their calcium carbonate cellular structure. In southern Chilean fjords, rainwater and ice melt create a freshwater lens overtop of a marine layer and due to a lack of vertical mixing, these areas remain stratified much of the year. Stratification creates different salinity and carbonate chemistry regimes in the surface and deeper waters. Observations of CCA absence at shallower depths (0-5 m) on the walls of the Comau Fjord and presence at deeper depths (~ 33% cover) lead to questions using field and laboratory analyses to ascertain the effects of freshwater input on CCA distributions within the fjord. Cobbles with Lithothamnion glaciale and other CCA crusts were transplanted from 20 m to 5 m for 9 months to compare pigmentation and physiology of control and transplanted specimens. Transplant experiments revealed tolerance to the surface water conditions in L. glaciale, but near mortality of other CCA species (22% vs. 65% of pigmented areas lost respectively). Water samples taken from 0-20 m in austral autumn and summer and calculated Ωarag levels highlighted stratification within the fjord. While autumn Ωarag levels did not fall below equilibrium at any depth, summer samples were below equilibrium in the surface waters (0.20) creating conditions that negatively affect CCA physiology and their distribution within the Comau Fjord. These results inform us how distributions may vary with global climate change and reduced ocean Ωarag levels