Coastal bacterioplankton communities show resilience to climate change under varying nutrient regimes

Bacterial communities are essential in coastal marine ecosystems, recycling nutrients as part of the microbial loop, and influencing energy and carbon flow up the food web. As atmospheric concentrations of CO₂ increase, ocean temperatures are increasing and pH is decreasing. In the open oceans, these changes have been shown to have insignificant effects on bacterial diversity and overall community function. However, the effects on coastal waters have received less attention, despite the economic, recreational and cultural significance of coastal marine ecosystems.

Bacterial diversity and changes to the community were measured during three 18-21 day mesocosm experiments using coastal water in Wellington, New Zealand. The experimental treatments compared current conditions with the projected pCO₂ and temperature levels for 2100 and 2150. The three experiments received differing nutrient additions: none, irregularly and daily. The prokaryotic community was determined by sampling the 16S rRNA gene periodically throughout each experiment.

The results show no significant treatment effect of warming or ocean acidification on bacterioplankton diversity during any of the three experiments. Only minor succession between bacterioplankton groups occurred over the experiments, despite the development of blooms and shifts in phytoplankton community composition in the latter experiment. Bacterioplankton resilience was demonstrated by maintenance of high diversity with stability of the main groups sustained during changes in pCO₂, temperature, nutrients and eukaryotic phytoplankton across the three experiments.