North Atlantic Oscillation drives the annual occurrence of an isolated, peripheral population of the brown seaweed Fucus guiryi in the Western Mediterranean Sea

The intertidal brown seaweed Fucus guiryi is distributed in the cold-temperate and warm-temperate coasts of Europe and North Africa. Curiously, an isolated population develops at Punta Calaburras (Alboran Sea, Western Mediterranean) but its presence is not permanent throughout the years, unlike the closest (ca. 80 km), perennial populations at the Strait of Gibraltar. The presence of the alga at Punta Calaburras is supposed to be due to the influence of the permanent Atlantic jet coming from the Atlantic Ocean into the Mediterranean. A twenty six years’ time series (from 1990 to 2015) of occurrence of F. guiryi at Punta Calaburras has been analysed by correlating with oceanographic (sea surface temperature, an estimator of the Atlantic jet power) and climatic factors (air temperature, rainfall, and North Atlantic Oscillation –NAO-, and Arctic Oscillation –AO- indexes). The occurrence of the alga aggregated from 1990-1994 and 1999-2004, with sporadic events in 2006 and 2011. Binary logistic regression showed that the occurrence of the alga at Punta Calaburras is favoured under positive NAO index from April to June. It has been hypothesized that the isolated population of F. guiryi should show greater stress than their congeners of permanent populations, and to this end, two approaches were used to evaluate stress: one based on the integrated response to ontogeny (developmental instability, based on measurements of the fractral pattern of algal thalli) and another based on the photosynthetic response. However, the only significant differences detected were in photosynthetic quantum yield and water loss under emersion conditions. In conclusion, this study demonstrates the teleconnection between atmospheric oscillations and survival and proliferation of marine macroalgae, an aspect practically unknown before.