Researchers have harnessed the power of the Copernicus Sentinel-2 mission to uncover the remarkable seasonal variations in intertidal seagrass across Western Europe and North Africa. These findings offer crucial insights for the conservation and restoration of these vital seagrass ecosystems, which serve as critical habitats and play a crucial role in coastal protection.
The secrets of seagrass exposed by Sentinel-2
Lush seagrass meadows in the intertidal zone where land and sea meet. Underwater flowering plants operating as nurseries, feeding grounds and shelters for diverse marine biodiversity like birds, fish and invertebrates. In addition to their ecological value, seagrass meadows help stabilize sediments and protect coastlines from erosion.
Until now, global estimates of seagrass importance have significantly underplayed the role that intertidal seagrasses contribute to this food web as assessments failed to distinguish clearly between types of seagrasses – i.e. intertidal and subtidal (fully submerged) —which may have resulted in an over-inflated perception of the health and status of these vital ecosystems globally. Yet, as evidenced in a recent paper led by Wetlands International and Deltares published in Communications Earth & Environment; the incredible potential of the Copernicus Sentinel-2 mission describes it to map intertidal seagrass meadows with high geographic and seasonal detail at continental scales.
Unveiling Seasonal Rhythms
Phone photo of the wilting seagrass (This is from photos sent over by the research), with accompanying study top]The Gloucester’s Water, ecologically known as Halophila ovalis intertidal seagrass, which the researchers believe is probably in its East Asian cousin littoralis being relatively healthy during warmer months when growing temperatures are higher. “Some, but they shifted later and earlier by up to five months—so different peaks in extent can occur,” said Davies.
The satellite imagery helps to illustrate these fluctuations in a stunning way. Seagrass cover in the Cádiz Lagoon, Spain between May 2018 and November 2021. In the bay of Bourgneuf on the western coast of France, a meadow with little live growth in April 2021 grew back abundantly just five months later in September.
Conservation and Restoration Implications
The implications of these results for the conservation and restoration of intertidal seagrass ecosystems are profound. Professor Chris McQuaid, also of UCT’s Marine Research Institute and affiliated to the South African National Biodiversity Institute (SANBI) says: “As with most regions across the world coastal areas are experiencing significant losses in biodiversity. Davies says: “This must be accompanied by effective monitoring to enable land managers to take action before it is too late and ecosystems are lost.
That station-keeping capability is critical for establishing long-term satellite-based monitoring systems and datasets that can support global progress toward the Global Biodiversity Framework. BiCOME project principal investigator Victor Martinez-Vicente agrees: “This study shows how earth observation can be used to monitor variations in the surface area of natural coastal ecosystems, contributing valuable information for indicators within the Global Biodiversity Framework.
It also warns that earlier estimates, which treated intertidal and subtidal seagrasses as a single entity, may have exaggerated the extent of resources available in tidal flats. Intertidal meadows, we now think, work very differently from the kind of seagrass that’s submerged by seawater most of the time,” said study lead author Marie-Helene Rio from ESA. Such research will create a foundation for monitoring and evaluatioon of intertidal seagrass meadows using Sentinel-2 data.
