New research reveals some seagrasses are resilient to climate change

That’s an important finding because seagrasses and seaweeds make up coastal wetlands, which are among the world’s most efficient carbon sinks: seagrasses sequester more three to five times more carbon from the atmosphere than the equivalent area of tropical forest. The new research, led by Lucy Gwen Gillis, IHE Delft Researcher and Ines G. Viana, Centro Oceanografico de A Coruna,  published in Marine Environmental Research, shows that some seagrasses and seaweeds growing in the Baltic Sea are resilient to marine heatwaves (MHW). This may enable them to continue to provide essential services such as carbon sequestration or as a fisheries habitat despite stresses caused by climate change. 

“Seagrasses and seaweeds are a type of wetland ecosystem, which are key ecosystem engineers providing critical ecosystem services in coastal areas. For example, the huge amounts of carbon and other greenhouse gas emissions they sequester make them essential to the battle against climate change, plus they provide important habitats for fish and crustacean species” – Lucy Gwen Gillis, Researcher in Applied Aquatic Ecology 

Seaweed and seagrass ecosystems face multiple stressors from global warming. Over the next century, average marine temperatures are expected to rise, with marine heatwaves expected to be more intense, occur more frequently and at higher latitudes than in the past. 

The research measured responses in two coastal marine macrophytes, Fucus vesiculosus and Zostera marina, to continuous and consecutive MHWs. Researchers collected the macrophytes in the Baltic Sea and placed them in aerated tanks with seawater to measure their responses to different conditions.

Fucus vesiculosus, which grows in dynamic tidal areas, showed high acclimatization to changes in temperature – the species is used to changing conditions. Zostera marina was more sensitive to the continuous marine heat wave. But results from the photosynthetic performance of the plants showed they were not stressed by the heatwave.

“It would be wrong for us to jump to conclusions on the general resilience of seagrasses in the face of climate change based on this research alone, different ecosystems could face totally different challenges.” - Lucy Gwen Gillis, Researcher in Applied Aquatic Ecology

Macrophytes in different regions may be more sensitive to the rapidly changing conditions, such as temperate giant Kelp forests or tropical seagrass beds. 

The researchers recommend future studies exploring how multi stresses may change wetland resilience. Increased nutrients in coastal ecosystems is a critical issue, the combination of heat waves plus excess nutrients could be disastrous.