People of Seagrasses: Dimitris “overlooks” Greek seagrass meadows

Maria Potouroglou and Dimitris Poursanidis

By GRID-Arendal

August 30^th, 2019

The coastal seascape is comprised of the interlinked tidal marshes, mangroves, seagrass meadows and coral reef habitats. They act together like the four musketeers of the coastal zone, protecting and providing multiple ecosystem functions and services. However, these coastal and marine habitats are under pressure by multiple anthropogenic threats currently exacerbated by climate change. Out of the four musketeers, the least famous one is seagrass. The 72 different species of seagrass found within all bioregions worldwide are critical to the health and productivity of our coasts. They create meadows in different forms from patchy systems to extensive meadows. The Mediterranean Sea is home to the longest living seagrass species: the Neptune’s seagrass (Posidonia oceanica), a slow growing plant that forms extensive meadows down to 40 metres below the sea surface.

GRID-Arendal in collaboration with UN Environment convened the International Seagrass Experts Network (ISEN) in June 2018, at the 13th International Seagrass Biology Workshop - the biennial lead event of the World Seagrass Association - in Singapore. ISEN is a consortium of experts and practitioners who want to see seagrasses propelled into wider conservation, appealing decision-makers to invest in advancing seagrass research and management. The first collective output of the Network is a global synthesis report, which aims to highlight the range of values, goods and services provided by seagrasses to people around the world.

The rhizomes of the seagrass. Credit: Dimitris Poursanidis

Anchorage of the leisure boats is a major threat to the shallow part of the meadows. Credit: Dimitris Poursanidis

Dry leafs of the seagrass meadow Posidonia oceanica are exported to the beach during the summer period. Credit: Dimitris Poursanidis

Abandoned fish gear can become home for new dwellers. Credit: Dimitris Poursanidis

In order to put more focus on seagrass in relation to the global synthesis report, the series “People of Seagrasses” has been created where the people featured all contribute in increasing the knowledge about seagrasses and motivating others to enter the field of study. This is the first story in the series.

Dimitris Poursanidis and Dimosthenis Traganos are the coordinating authors of the Mapping and Monitoring chapter of the forthcoming global synthesis report. Below is a reflection from Dimitris on what motivated him to start working on seagrasses and how his research is contributing to seagrass conservation:

Seagrass view. Credit: Dimitris Poursanidis

“My link with the Neptune’s seagrass...

started in my childhood when I visited the beach during the winter for walking and collecting seashells with my parents. As a tradition, every Sunday after family lunch, we would drive to Marathonas bay or the Oropos seaside, where large seagrass banquettes lay on the beach, making the place perfect for exploration. Walking on or next to them, we would collect large bivalves and gastropods that had been stranded during storms.

Later in my life while I was at university, the unknown and dark side of the sea attracted me. With my mask and long fins, I would spend several hours freediving in the ocean in and around seagrass meadows. Some questions have always been on my mind: How extensive are the seagrass meadows? How can we map them? And why do they exist?

The banquette, dead leafs of Posidonia oceanica mixed with sand act a shoreline protection against erosion. Credit: Dimitris Poursanidis

View of a meadow. Credit: Dimitris Poursanidis

With the evolution of technology such as hydroacoustics and satellites, I started to work on the mapping of seagrass meadows at local scales using commercial satellite data and extensive in-situ data. Soon after, with the availability of the Copernicus Sentinel 2 data and the boom of data storage, my colleague Dimosthenis and I developed a methodology to map the seagrass meadows in the Greek territorial waters with a reasonable accuracy.

Almost two years later and many lessons have been learned. Further work includes improving the methods such as becoming better at identifying the limitations of the Earth Observation approach. Most importantly we are talking to the wider audience on the need of spatial data on habitats under a holistic view for concrete monitoring and change detection. With these improvements, data can flow into cumulative impact assessments, and marine and maritime spatial planning at local scales, allowing for the conservation of the vital and vulnerable seagrass meadows.”

The Green and the Blue. Credit: Dimitris Poursanidis

About Dimitris Poursanidis:

Dimitris studied Agriculture Ecosystem Management in the Higher Technological Institute of Crete, Greece and holds a Ph.D. on Marine Ecology and a M.Sc. on Coastal Zone Management from the University of the Aegean, Dept. of Marine Science Greece. He is currently a postdoctoral researcher at the Remote Sensing lab of the Foundation for Research and Technology – Hellas. He uses multimedia tools (photography, videography, audio) to disseminate his work in social media, newspapers, books and popular articles. He is also a member of the global photographic project MeetYourNeighbours.