Article Citation: de los Santos, C.B., Krause-Jensen, D., Alcoverro, T., Marbà, N., Duarte, C.M., van Katwijk, M.M., Pérez, M., Romero, J., Sánchez-Lizaso, J.L., Roca, G., Jankowska, E., Pérez-Lloréns, J.L., Fournier, J., Montefalcone, M., Pergent, G., Ruiz, J.M., Cabaço, S., Cook, K., Wilkes, R.J., Moy, F.E., Trayter, G.M-R., Arañó, X.S., de Jong, D.J., Fernández-Torquemada, Y., Auby, I., Vergara, J.J. and R. Santos. 2019. Recent trend reversal for declining European seagrass meadows. Nature Communications, (10) 3356: 1-8 https://doi.org/10.1038/s41467-019-11340-4
A lot of the news we hear these days about the environment is negative. Extreme weather events due to climate change, threatened species, environmental pollution – the list can go on. It’s hard to look around and not see how humans have harshly impacted so many areas of the environment.
The story about seagrasses hasn’t been much different.
Seagrasses are essentially what they sound like – plants with long leaves that live in shallow, salty waters. Not to be mistaken with seaweeds, seagrasses are more like the grass we see on land; they have roots and produce seeds and flowers. For the past several decades, we’ve seen a large decline in seagrasses around the world. The decline can be attributed to human sources such as decreased water quality and coastal modification, as well as natural causes such as chronic wasting disease where plants become infected and die off in large numbers.
Seagrasses = Foundation of Marine Ecosystems
Why is important that our shallow, ocean waters have a healthy covering of seagrass? Seagrasses provide a whole host of ecosystem services. They provide habitat for marine organisms, serve as indicators of ecosystem health, support fisheries, and play a large role in climate change. For example, seagrasses can hold excess carbon. By doing so seagrasses act as a “sink” keeping this carbon out of the atmosphere where it could contribute to global warming. All of these reasons make seagrasses an important global resource.
Many studies have tried to quantify how seagrasses are affected by the negative impacts such as water decreased water quality. At the same time, much work has focused on restoring seagrasses to bring back some of their vital ecosystem services. To understand if the hard work is paying off, one study has quantified the observed changes in seagrasses over the last nearly 150 years.
Increasing or Decreasing?
Researchers examined assessments of change in four seagrass species at 737 sites, in 25 European countries from 1869 – 2016.
In order to gather these data, researchers compiled over 1042 different research studies from different areas of Europe. Most of the sites (56%) were in the Mediterranean Sea. While the studies did not all measure the exact same metrics, the researchers were able to group seagrass results into three different categories: increasing, declining, or exhibiting no change.
Big Losses, Until Recently
Researchers found that the decline from 1869 until 2016 of European coastal seagrasses was substantial. Nearly 30% of the area of seagrasses was lost over this time period. The areas of Europe that saw the greatest losses were the Baltic Sea, with the least amount in the Mediterranean Sea.
However, a more detailed look at the data revealed that the last few decades tell a different story. Seagrass losses peaked in the 1970s and 1980s when sites lost 33% of their areal coverage each decade. Starting in the 1990s and 2000s, seagrasses in many sites have started to recover, and ultimately the net gain of seagrasses during the 2000s reached 20% per decade! These gains included areas such as areal coverage and overall biomass at each site.
Why the sudden swing? Well, while the exact reasons of all the gains isn’t clear, we can point to some management strategies such as reducing nutrient pollution, improving water quality, and protecting habitat areas in different areas across Europe as reasons why seagrasses may have started such a positive recovery.
When seagrasses are healthy, the whole ecosystem benefits. While the fight is not over, the seagrass recovery highlighted in this study is a shiny piece of hope that our efforts to clean up and correct past mistakes are having a positive impact to preserve the important functions our marine ecosystems provide.