People of seagrasses: Discovering the amazing ecosystem right beneath my fins

I spent a lot of my field time in the Indian Ocean boating or swimming over seagrass meadows to get to the colourful coral reefs beyond. I was always vaguely aware that these green and brown underwater meadows are important and interconnected to their kaleidoscopic neighbours, but I rarely gave them a second glance. The beaches were often awash with thick masses of dead blades, creating large clumps that would appear and disappear with the tides like an ephemeral organic blanket. Seagrass was always in sight, but rarely in mind. Sometimes I would stop and observe a peculiar denizen of these lush meadows – a single branching Acropora coral or a psychedelic echinoderm, surrounded by swaying blades like a pyrotechnic display in the middle of the swaying arms at a rock concert.

But my interest in this ecosystem was piqued by a sad sight I witnessed whilst doing some coral surveys at the invitation of a holiday resort on an Indian Ocean island. I realized that the resort had intentionally smothered and killed all the seagrass in the lagoon using plastic mats ostensibly to ‘protect the tourists walking in the lagoon’ and stop the seagrass leaves from washing up onto the beach. It was sad to see. What should have been a meadow thriving with life and biodiversity had been turned into a sandy, lifeless desert, disfigured by plastic dunes.

Witnessing this loss made me want to learn more about the importance of seagrass, and share this knowledge so that people stop destroying it. As I learned more about seagrass meadows, I realized just how critical they actually are. Small fish start their lives there before moving to the deeper, more dangerous waters of the coral reefs. Fishers all over the world spend their days walking in the intertidal zone or propelling boats through meadows in search for food. Seagrass blades trap nutrients and pollutants to clean our waters. The sediment below the seagrass is so rich with organic carbon that it is recognized as one of the world’s major ‘blue carbon’ sinks!

Understanding the interconnections and mutual reliance among ecosystems opened my mind. The ‘dark water’ in Indian Ocean lagoons suddenly became a rich tapestry of species. Thalassodendron ciliatum, Thalassia hemprichii, Syringodium isoetifolium, and Halodule uninerviswere all living in one small patch that I had previously thought of as a homogenous lawn. A fascinating thing I learned recently is that a Posidonia oceanica seagrass meadow in the Balearic Islands of Spain is believed to be the oldest organism on Earth, having cloned and perpetuated itself for up to 200,000 years!

Now I am a certified seagrass aficionado, and I am proud to be working with the United Nations Environment Programme to help countries around the world protect their seagrass ecosystems. We are currently working with GRID-Arendal on a global report highlighting the importance and plight of seagrasses, which will shed light on an ecosystem that provides us with so much food and stability but that has been ignored for far too long.

Gabriel Grimsditch is programme management officer with the Marine and Coastal Ecosystems Branch of the United Nations Environment Programme, based in Nairobi, Kenya.