Adaptations to ocean acidification in mesozooplankton

Adaptations to ocean acidification in mesozooplankton (BIOACIDII subproject 1.14) 1

Julia Lange, 3 Rahul Sharma, 2 Susanne I. Schmidt, 2 Klaus Schwenk, 3 Marco Thines, 1 Maarten Boersma Alfred Wegener Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Germany 2Institut für Umweltwissenschaften, Universität Koblenz Landau, Germany 3 Biodiversität und Klima- Forschungszentrum Frankfurt, Germany 1

We investigate the direct and indirect effects of ocean acidification (OA) on mesozooplankton, thereby taking into account both ecological and genetic aspects. Thus looking at changes in population structure of selected copepod species as well as signs of local adaptation in small, large and natural experimental settings. In a first step a study was carried out to investigate the effect of OA on a small scale. The copepod Acartia tonsa was cultured under two different CO2 concentrations (200 and 800 ppm), and fed with algae cultured under the same conditions in a factorial design. Copepods which had been exposed to the higher CO2 concentration developed slower, but the indirect effect of high CO2 (changes in food stoichiometry) was much more important than the direct (pH) effect. During the first mesocosm experiment (Kristineberg) regular plankton samples were taken which were used to perform population genetic studies (community barcoding) to investigate differences in species composition between populations suffering under OA and those exposed to present-day CO2 conditions. First results show no significant effect of higher CO2 conditions on the taxon composition of the micro- and mesoplankton communities within the mesocosms. In contrast to that nutrient availability and temperature had a very strong impact on species composition with a clear succession over time. Additionally we aim for an understanding of the impact of high CO2/lower pH on the fitness of mesozooplankton. Our hypothesis is that organisms can adapt to the changed chemical composition of the water and to the degradation in food quality. To detect those adaptations and furthermore to investigate the heritability as well as the evolutionary effect of OA a longterm CO2 selection study with A. tonsa has been set up and two transplantation experiments were carried out. The first transplantation experiment was designed to investigate potential CO2 adaptation effects on the development on A. tonsa. Individuals showed a much slower development under high CO2 conditions. Under low CO2 concentrations 70% reached the late copepodite stages C4 to C6, whereas under high CO2 conditions only 5% reached those stages. Despite that there was no difference between the selection lines and thus no detectable adaptations to CO2 according the developmental speed. The second transplantation experiment focused on the egg production and hatching rate. There was no difference between the high and low CO2 treatments and selection lines according the amount of produced eggs. Additionally the hatching rate did not vary between the CO2 treatments whereby the nauplii from the high CO2 selection lines hatched significantly faster in the first 24 hours. Transplantation experiments which were carried out one year later showed quite the same results. However individuals with a high CO2 selective history showed a slightly faster development under high CO2 conditions compared to the low CO2 selection line individuals.