Description: Planktonic foraminifera preserved in marine sediments archive the physical and chemical conditions under which they built their shells. To interpret the paleoceanographic information contained in fossil foraminifera, the proxy signals have to be attributed to the habitat of individual species. Much of our knowledge on habitat depth is based on indirect methods, which reconstruct the depth at which the largest portion of the shell has been calcified. However, habitat depth can be best studied by direct observations in stratified plankton nets. Here we present a synthesis of living planktonic foraminifera abundance data in vertically resolved plankton net hauls taken in the eastern North Atlantic during twelve oceanographic campaigns between 1995 and 2012. Live (cytoplasm-bearing) specimens were counted for each depth interval and the vertical habitat at each station was expressed as average living depth (ALD). This allows us to differentiate species showing an ALD consistently above 100 m (e.g. Globigerinoides ruber white and pink), indicating a shallow habitat; species occurring from the surface to the subsurface (e.g. Globigerina bulloides, Globorotalia inflata, Globorotalia truncatulinoides); and species inhabiting the subsurface (e.g. Globorotalia scitula and Globorotalia hirsuta). For 17 species with variable ALD, we assessed whether their depth habitat at a given station could be predicted by mixed layer (ML) depth, temperature in the ML and chlorophyll a concentration in the ML. The influence of seasonal and lunar cycle on the depth habitat was also tested using periodic regression. In 11 out of the 17 tested species, ALD variation appears to have a predictable component. All of the tested parameters were significant at least in one case, with both seasonal and lunar cyclicity as well as the environmental parameters being able to explain up to 〉50% of the variance. Whereas G. truncatulinoides, G. hirsuta and G. scitula appear to deepen their living depth towards the summer, populations of Trilobatus sacculifer appear to descend in the water column towards the new moon. In all other species, properties of the mixed layer explained more of the observed variance. Chlorophyll a concentration seems least important for ALD, whilst shoaling of the habitat with deepening of the ML is observed most frequently. We observe both shoaling and deepening of species habitat with increasing temperature. Further, we observe that temperature and seawater density at the depth of the ALD were not equally variable among the studied species, and their variability showed no consistent relationship with depth habitat. According to our results, depth habitat of individual species changes in response to different environmental and ontogenetic factors and consequently planktonic foraminifera exhibit not only species-specific mean habitat depths but also species-specific changes in habitat depth.

Description: We used carbon and oxygen isotope ratios ( 13 C and 18 O) in otoliths as a tool for identifying the nursery origin of Atlantic bluefin tuna ( Thunnus thynnus ) caught in the eastern North Atlantic Ocean (Bay of Biscay). Juvenile and adult bluefin tuna were collected over three consecutive years (2009—2011) using the regional bait boat fleet. Otolith 13 C and 18 O values of bluefin tuna were measured by mass spectrometry, and values were compared with a reference sample of yearling bluefin tuna from eastern (Mediterranean Sea) and western (Gulf of Mexico) nurseries to determine nursery origin. Maximum likelihood estimates based on otolith 13 C and 18 O values indicated that the overall contribution of western migrants to the Bay of Biscay fishery was 〈1% and varied over the years assessed. A small number of potential western migrants (2.7%) was detected in 2009, and most of these fish appear members of the abundant 2002 and 2003 year classes. In contrast, the Bay of Biscay fishery was composed exclusively (100%) of eastern origin bluefin tuna in 2010 and 2011, suggesting that this fishery is supported almost exclusively by the eastern spawning area but transatlantic western population may contribute to this fishery in a few years.