| Summary: | This study investigated the effects of ocean acidification on the genetic diversity of Synechococcus. A mesocosm experiment simulating ocean acidification was carried out by scientists at Plymouth Marine Laboratory at the Large Scale Facility in Bergen, Norway, in May 2006. Mesocosm bags were seeded with C02 to replicate the rise in atmospheriC CO2 concentrations to the level of 700ppm as projected by the IS92a "business as usual" scenario, and were run in conjunction with background bags seeded with air. Changes in Synechococcus microdiversity between these two treatments and a fjord sample at the start of the experiment were assessed using the rpoC1-RFLP method, whereby clone libraries were constructed for three sampling dates. The novel primer pair lpoC1-39F-L4a1lpoC1-462R-L4 was tested for its ability to amplify coastal strains of Synechococcus. Multivariate statistical analyses revealed that there was no significant link between ocean acidification and Synechococcus microdiversity. Moreover, It was not possible to distinguish between treatment and mesocosm effects, with a BIO-ENV analysis revealing that microdiversity was the most highly correlated (p=O.S71) with nutrient concentrations, particulate organic carbon (POC) and particulate organic nitrogen (PON) concentrations within the mesocosm bags. However, the significance level of the sample statistic was low (20%). Therefore, it was found that increasing the number of independent observations by sampling replicate mesocosms is necessary in order to ascertain whether decreasing seawater pH affects Synechococcus microdiversity. However, changes to abundance and occurrence of the 17 RFLP types observed were evident, the most notable being the detection of four novel RFLP types unique to the acidified bag on the 21 st of May. Based upon phylogenetic analysis of the rpoC1 sequences of each RFLP type, it was found that all RFLP types clustered into two putative subclades within the previously defined Synechococcus clade I, which encompasses isolates found in coastal locations. Faculty of Science
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