Ensemble prediction distribution maps of macroalgae for current conditions and four climate change scenarios and high resultion bathymetry for Potter Cove, WAP, Antarctica

Species distribution models (SDM) predict species occurrence based on statistical relationships with environmental conditions. The R-package biomod2 which includes 10 different SDM techniques and 10 different evaluation methods was used in this study. Macroalgae are the main biomass producers in Potter Cove, King George Island (Isla 25 de Mayo), Antarctica, and they are sensitive to climate change factors such as suspended particulate matter (SPM). Macroalgae presence and absence data were used to test SDMs suitability and, simultaneously, to assess the environmental response of macroalgae as well as to model four scenarios of distribution shifts by varying SPM conditions due to climate change. According to the averaged evaluation scores of Relative Operating Characteristics (ROC) and True scale statistics (TSS) by models, those methods based on a multitude of decision trees such as Random Forest and Classification Tree Analysis, reached the highest predictive power followed by generalized boosted models (GBM) and maximum-entropy approaches (Maxent). The final ensemble model used 135 of 200 calculated models (TSS > 0.7) and identified hard substrate and SPM as the most influencing parameters followed by distance to glacier, total organic carbon (TOC), bathymetry and slope. The climate change scenarios show an invasive reaction of the macroalgae in case of less SPM and a retreat of the macroalgae in case of higher assumed SPM values.

Direct linkage between dimethyl sulfide production and microzooplankton grazing, resulting from prey composition change under high partial pressure of carbon dioxide conditions

Oceanic dimethyl sulfide (DMS) is the enzymatic cleavage product of the algal metabolite dimethylsulfoniopropionate (DMSP) and is the most abundant form of sulfur released into the atmosphere. To investigate the effects of two emerging environmental threats (ocean acidification and warming) on marine DMS production, we performed a large-scale perturbation experiment in a coastal environment. At both ambient temperature and 2 °C warmer, an increase in partial pressure of carbon dioxide (pCO2) in seawater (160-830 ppmv pCO2) favored the growth of large diatoms, which outcompeted other phytoplankton species in a natural phytoplankton assemblage and reduced the growth rate of smaller, DMSP-rich phototrophic dinoflagellates. This decreased the grazing rate of heterotrophic dinoflagellates (ubiquitous micrograzers), resulting in reduced DMS production via grazing activity. Both the magnitude and sign of the effect of pCO2 on possible future oceanic DMS production were strongly linked to pCO2-induced alterations to the phytoplankton community and the cellular DMSP content of the dominant species and its association with micrograzers.