Marine heatwaves (MHW) occur when ocean temperature is higher than the 90-precentile based on previously recorded temperatures, and this temperature fluctuation should last for more than five days. These events have been known to have destructive effects on the marine environment. Furthermore, MHW have been found to influence the growth and abundance of organisms. Synechococcus and cyanophages are important in the marine environment due to their contribution to primary production and nutrient cycling. However, the effects of their abundance in relation to MHW remain understudied.

This study investigates the effects of MHW on a phycocyanin (PC) rich Synechococcus strain (KAC102) and its associated cyanophage (BSP10), both isolated from the Baltic Sea Proper. To mimic a natural heatwave, cultures were exposed to a temperature based on previous heatwaves registered in the Baltic Sea (27℃). After the heatwave, the post-heatwave growth (18℃) was investigated to see if the cells would be able to recover.

The results from the heat wave indicate that an increase in temperature does not affect the abundance or growth rates of KAC102 nor BSP10. Furthermore, it contradicts previous studies that has found that the abundance of Synechococcus is correlated with temperature, and that higher temperatures would result in more cyanophages being released through lysis. There were also no differences in the post-heatwave recovery for KAC102 as well.

This indicates that KAC102 is resilient to thermal changes, potentially giving the strain an advantage in context of climate change. More studies would be needed to test the abundance of KAC102 and BSP10 in regard to MHW; for instance looking at other strains, expose them to other temperatures or add more stress factors (such as hypoxia or acidification).