Description: Some studies have demonstrated that elevated CO2 concentrations in ocean waters negatively impact metabolism and development of marine fish. Particularly, early developmental stages are probably more susceptible to ocean acidification due to insufficient regulations of their acid-base balance. Transgenerational acclimation can be an important mechanism to mediate impacts of increased CO2 on marine species, yet very little is known about the potential of parental effects in teleosts. Therefore, transgenerational effects were investigated on life history in juvenile three-spined sticklebacks Gasterosteus aculeatus by acclimating parents (collected in April 2012, 55A degrees 03'N, 8A degrees 44'E) and offspring to ambient (similar to 400 A mu atm) and elevated (similar to 1,000 A mu atm) CO2 levels and measured parental fecundity as well as offspring survival, growth and otolith characteristics. Exposure to elevated CO2 concentrations led to an increase in clutch size in adults as well as increased juvenile survival and growth rates between 60 and 90 days post-hatch and enlarged otolith areas compared with fish from ambient CO2 concentrations. Moreover, transgenerational effects were observed in reduced survival and body size 30 days post-hatch as well as in enlarged otoliths at the end of the experiment, when fathers or both parents were acclimated to the high-CO2 environment. These results may suggest that elevated CO2 concentrations had rather positive effects on life-history traits of three-spined sticklebacks, but that parental acclimation can modify these effects without improving offspring fitness. Although the mechanistic basis of such transgenerational acclimation remains unclear, selective gradients within generations seem to determine the direction of transgenerational effects.

Description: With globally growing aquaculture activities, the co-introduction of parasites alongside large-scale movements of commercial species poses an increasing risk for marine ecosystems. Here, we present the first record of the shell-boring polychaete Polydora websteri Hartman in Loosanoff and Engle, 1943 in invasive Pacific oysters Crassostrea (Magallana) gigas (Thunberg, 1793) in the European Atlantic Ocean. In October 2014, mud blisters in the shells of wild Pacific oysters and specimens of a spionid polychaete were observed in close proximity to a commercial oyster farm at the island of Sylt (Germany) in the European Wadden Sea. Subsequent investigations indicated that these blisters only occurred near the farm and that no other mollusc species were affected. Morphological and molecular analysis identified the polychaete as Polydora websteri, a species that nowadays widely occurs around the globe, but likely is native to the Asian Pacific. Later sampling activities detected P. websteri also at other locations around Sylt as well as in the Dutch part of the Wadden Sea at the island of Texel. The number of polychaetes in the oysters was, however, relatively low and mostly below 10 individuals per oyster. Together, this evidence suggests that P. websteri is currently extending its range. As the introduction of P. websteri may have severe ecological and economic implications, this study aims to alert others to look for P. websteri at Western European coasts within farmed or wild Pacific oysters to further document its spread.

Description: Genetic variability of marine fish species is much higher than in most other vertebrates. Nevertheless, some species with large population sizes including flatfish such as European plaice Pleuronectes platessa show signs of population collapse and inbreeding. Taking plaice as a flagship example for fisheries-induced genetic changes also affecting the Wadden Sea, we determined the amount of genetic variability at antigen-presenting genes of the Major Histocompatibility Complex (MHC) and its potential interaction with the microbiota associated to gill tissue using a next-generation parallel tag sequencing approach. Genetic variation at MHC class IIB genes was extremely large, with 97 alleles found in 40 fish from different age cohorts. Although a strong signal of positive selection was present (dN/dS = 4.01) and we found significantly higher allelic diversity in 0+ fish than in older age classes, the amount of genetic variation maintained within the population may not have exceeded neutral expectations derived from mitochondrial markers. Associated microbes revealed significant spatiotemporal structure with 0+ fish displaying the highest microbial diversity as well as the highest diversity of potentially pathogenic genera. Overall the correlation between MHC genotypes and bacterial abundance was weak, and only few alleles significantly correlated with certain bacterial genera. These associations all conferred susceptibility (i.e. presence of an allele correlated to higher number of bacteria), either suggesting age-dependent selection on common alleles or weak selection on resistance against these bacterial genera. Taken together, our data suggest that selection coefficients of balancing selection maintaining immunogenetic diversity may be relatively small in large marine populations. However, if population sizes are further reduced by overharvesting, the response to increasing balancing selection coefficients will be largely unpredictable and may also negatively influence the adaptive potential of populations.