Effects of Ocean Acidification on the Transcriptome of Larval Atlantic Cod and Impacts of Parental Acclimation
Ocean acidification, caused by the uptake of carbon dioxide (CO2) from the atmosphere, is impacting many marine organisms. This dissertation investigated the effects of direct exposure and parental acclimation to simulated ocean acidification on the larval stages of Atlantic cod (Gadus morhua, L.). For this, ocean acidification levels predicted for the year 2100 were applied on cod eggs from hatch to 36 days post hatch in in vivo laboratory experiments. The direct exposure experiment clearly showed that Atlantic cod larvae were severely affected by simulated ocean acidification on a phenotypic level (chapter 1). Changes in growth, bone and gill development as well as increased frequency of organ damages were observed under predicted ocean acidification levels compared to controls. Then, the underlying molecular phenotype was assessed, using whole transcriptome sequencing (RNA-Seq), to couple transcriptomic mechanisms to the observed phenotypes (chapter 2). Transcriptome analysis revealed 1413 differentially expressed genes in late larval stages, corresponding to the observed changes in growth and developmental patterns, leading to the conclusion that these changes represent an accelerated development under ocean acidification. Surprisingly, only few genes (3 and 16, respectively) were differentially expressed in the early larval stages. An experiment set to address the effects of long-term parental acclimation (5 month) was performed to assess whether or not this kind of acclimation can mediate the identified detrimental direct effects on the larvae (chapter 3). However, none of the previously observed phenotypes under ocean acidification were found in this experiment, making it impossible to draw any conclusion on the effectiveness of parental acclimation on larval susceptibility to simulated ocean acidification. A concluding meta-analysis between experiments shows that the larvae of Atlantic Cod are to be considered vulnerable to simulated ocean acidification.