Rising ocean temperatures reduce the natural carbon storage capacity of seagrass meadows

A recent study in Communications Earth & Environment reveals that rising water temperatures significantly diminish the capacity of seagrass meadows to store carbon over the long term. Researchers from Spain and Germany examined how increased water temperatures impact the dissolved organic carbon released by seagrasses and marine algae.

Their findings demonstrate that as temperatures rise, the proportion of carbon that remains stable in the ocean for extended periods, contributing to long-term carbon storage, decreases notably. Conducted in a controlled aquarium setting by Alba Yamuza-Magdaleno, Pedro Beca-Carretero, and Hauke Reuter from the Leibniz Centre for Tropical Marine Research (ZMT), the study simulated various temperature conditions in Bremen, Germany.

The results indicate that even a slight increase in water temperature alters the chemical composition of the carbon released by seagrasses and algae. While seagrasses and algae uptake carbon dioxide for growth, some of this carbon solidifies into structural components that can remain in the seafloor for centuries. However, a considerable portion is released into the water as dissolved organic carbon, which can be broken down by microorganisms or persist for weeks, years, or even centuries.

The study found that a 4-degree Celsius temperature rise led to a 28% reduction in the carbon that is difficult to decompose, while significantly increasing the proportion of easily degradable carbon. This more readily degradable carbon was largely consumed within 60 days. Seagrass beds and kelp forests are recognized as natural carbon sinks, absorbing and storing substantial amounts of carbon dioxide from the atmosphere.

However, the study highlights that if ocean temperatures continue to rise, these coastal ecosystems may sequester significantly less carbon in the future than previously estimated. The researchers also note that both the storage of carbon in the seafloor and dissolved organic carbon play crucial roles, with similar storage rates.

Most studies have focused on carbon stored permanently in marine sediments, but this research underscores the importance of dissolved organic carbon. The invasive seagrass species studied had minimal impact on the carbon balance, while temperature emerged as the dominant factor affecting carbon storage. The findings suggest that existing climate models may underestimate the effects of rising temperatures on carbon sequestration, potentially underestimating the actual capacity of coastal ecosystems to absorb and store carbon.

As ocean temperatures continue to climb, further long-term observations in natural coastal areas are necessary to accurately assess the impact of warming on coastal carbon storage and inform more effective climate mitigation strategies.