Global warming and ocean acidification: effects on Australian seagrass ecosystems

As concentrations of atmospheric CO2 increase, mean temperatures across the globe rise, the carbon system equilibrium in the ocean shifts, and pH is reduced in a process termed Ocean Acidification (OA). These changes can dramatically alter seagrass meadows as both temperature and pH fundamentally influence biochemistry and physiology of plants. Seagrass responses to climate change are species-specific and dependent on interactions with other factors such as light intensity, nutrient availability and competition. The majority of seagrasses appear limited by the availability of dissolved inorganic carbon at current ocean pH, suggesting that rates of photosynthesis and growth are likely to increase with OA. Short- and intermediate term laboratory experiments have shown an increase in photosynthetic rates to increased pCO2. Longer-term studies (>1 year) indicate enhanced shoot proliferation resulting in meadows with high shoot density. Studies utilizing natural gradients in pCO2 that exist near shallow volcanic CO2 vents have shown that, overall, seagrasses appear to benefit from OA. Seagrasses photosynthesize across a range in temperatures, but rapidly decline above thermal optima. Respiration rates increase with warming at a faster rate than photosynthesis and reduces the overall photosynthesis-to-respiration ratio, and thus growth. While seagrasses can recover from moderate temperature stress, extreme temperatures result in mortality. Future changes in seagrass species distributions are predicted as sensitive species shift poleward. Foundation species, like seagrasses, have a large influence on their environment and their loss can significantly impact the functioning of the whole ecosystem. Despite a recent increase in climate-change research, we lack an understanding of how seagrass meadows are going to respond to the combined pressures of warming and OA. It is particularly difficult to predict longer-term responses and possible adaptation, and efforts should be focused in this area to determine how we can manage seagrasses to maximize resilience to climate change.

Olsen Y. S., Collier C., Ow Y. X. & Kendrick G. A., 2018. Global warming and ocean acidification: effects on Australian seagrass ecosystems. In: Larkum A. W. D., Kendrick P. J. R. & Ralph P. J. (Eds.), Seagrasses of Australia, pp 705-742. Springer, Cham. Chapter (restricted access).

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