Effects of ocean acidification and warming on fertilization success and germling growth in a habitat-forming seaweedResistance, Resilience and Phase Shifts

Alexandra Kinnby¹

¹University of Gothenburg, Sweden

Ocean acidification and warming may impact the early development of marine organisms, including long-lived brown seaweeds. We investigated the effects of high temperature and elevated pCO2 on fertilization success and size of germlings in populations of the brown habitat-forming seaweed Fucus vesiculosus across a coastal salinity gradient. We used a fully crossed design, exposing zygotes to ambient (15°C) or high (18°C) temperature and ambient (400 µatm) or elevated (1100 µatm) pCO2. In general, all populations were affected by the altered environment, although the effects varied between populations. Fertilization success in the two most marine populations was not affected by temperature whereas the low salinity populations had significantly lower fertilization success when exposed to high temperature. In the two most marine populations, elevated pCO2 tended to have a negative effect on fertilization success, while in the remaining four populations it either significantly increased, or tended to increase, fertilization success, although this effect was suppressed by high temperature. In the three populations from the lowest salinity and one from high salinity, germlings grew more under elevated pCO2, but in general high temperature reduced germling growth. Our results suggest that population responses to climate stressors are highly idiosynchratic. In part, this is due to interactions between stressors, but most likely it is also due to differences related to local adaptation. We highlight the importance of not just studying single climate change variables, but also their interactive effects, as well as local adaptation to different environmental conditions in different populations of one species.