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Although coccolithophore physiological responses to CO2-induced changes in seawater carbonate chemistry have been widely studied in the past, there is limited knowledge on the variability of physiological responses between populations. In the present study, we investigated the population-specific responses of growth, particulate organic (POC) and inorganic carbon (PIC) production rates of 17 strains of the coccolithophore Emiliania huxleyi from three regions in the North Atlantic Ocean (Azores, Canary Islands, and Norwegian coast near Bergen) to a CO2 partial pressure (pCO2) range from 120 µatm to 2630 µatm. Physiological rates of each population and individual strain displayed the expected optimum curve responses to the pCO2 gradient. Optimal pCO2 for growth and POC production rates and tolerance to low pH (i.e. high proton concentration) was significantly higher in an E. huxleyi population isolated from a Norwegian fjord than in those isolated near the Azores and Canary Islands. This may be due to the large pCO2 and pH variability in coastal waters off Bergen compared to the rather stable oceanic conditions at the other two sites. Maximum growth and POC production rates of the Azores and Bergen populations were similar and significantly higher than of the Canary Islands population. One of the reasons may be that the chosen incubation temperature (16 °C) is slightly below what strains isolated near the Canary Islands normally experience. Our results indicate adaptation of E. huxleyi to their local environmental conditions. Within each population, different growth, POC and PIC production rates at different pCO2 levels indicated strain-specific phenotypic plasticity. The existence of distinct carbonate chemistry responses between and within populations will likely benefit E. huxleyi to acclimate to rising CO2 levels in the oceans. [ABSTRACT FROM AUTHOR]

The Atlantic herring is a schooling, pelagic species that inhabits both sides of the North Atlantic Ocean. Herring stock identification is usually based on several approaches, including fish meristic characters, population genetic analysis and the use of parasite species composition. A total of 654 Anisakis spp. larvae collected from herring of four fishing grounds in the Norwegian Sea, Baltic Sea, North Sea, and the English Channel off the French coast, was identified to species level using diagnostic allozymes and sequence analysis of EF1 α−1 nDNA and the mtDNA cox2 genes. Population genetic differentiation of Anisakis simplex (s. s.) among the different fishing areas was estimated, at the intraspecific level, on the basis of mtDNA cox2 sequences analysis. Spatial comparison based on molecular variance analysis and F st values was performed for the collected specimens (among regions). Haplotype network construction showed relevant differences in haplotype frequencies between samples of A. simplex (s. s.) from the different geographical areas. Results indicate a genetic sub-structuring of A. simplex (s. s.) obtained from herring in different areas, with the population from the Norwegian Sea being the most differentiated one, and with North Sea and Baltic Sea populations being most similar. The population genetic structure of A. simplex (s. s.) was in accordance with the herring population genetic structure throughout the host’s geographical range in the NE Atlantic. Results suggest that mtDNA cox2 is a suitable genetic marker for A. simplex (s. s.) population genetic structure analysis and a valuable tool to elucidate the herring stock structure in the NE Atlantic Ocean. [ABSTRACT FROM AUTHOR]