Natural Hazards

Another (surprising) brick in the wall: how seagrass protects coastlines against erosion.

Another (surprising) brick in the wall:  how seagrass protects coastlines against erosion.

Dear readers, today our blog will host Marco Fusi, a postdoctoral fellow working on coastal ecosystems. Together with Marco we will give a twist to our usual geoscientific perspective and mix some ecology in it. Specifically, we will explore the surprising role of seagrass in limiting coastal erosion effects.

Marco Fusi is a Post-Doctoral Researcher at KAUST (Saudi Arabia), since 2014. He graduated at University of Milan (Italy) with a Ph.D. in tropical ecology. His primary interest focuses on ecological connectivity and interactions in coastal ecosystems.

1- Hello Marco, please give us an overview of coastal erosion issues.

When we speak about coasts, we think about beautiful mangrove forests or a dream tropical coastline that harbours beautiful crystal water where to dive in the middle of coral reefs. However, we tend to forget that coasts are inhabited by almost 3 billion of people all over the world and hundreds of kilometres of coastline are heavily constructed. Cities, resorts, villages are expanding along the coast worldwide and often, the risk of coastal erosion is not considered. In the lasts decades, inland anthropogenic management resulted in a limited input of sediment to the sea and therefore the marine current started to erode beaches and rocky shore resulting sometimes in dramatical destruction of buildings.

2-      How does the seagrass fit in all this?

Seagrasses are natural allies that can help to solve this problem. Naturally occurring in the shallow coastal environment all over the world, these meadows are one the most effective barrier against the erosion by trapping sediment among their leaves. For example, in underwater archeological sites like in Denmark where dozens of shipwrecks are discovered, archeologists use a seagrasses-like cover for fast sedimentation and burial of the ship in order to create ideal anoxic condition and conserve the wood from oxidative processes. This is just to give an idea of how fast and efficient seagrasses act as sediment traps (as also shown in the post picture and the one below).

This picture was taken by Dr. Marco Fusi during his fieldwork.

3-      Is this part of your research? What did you do? 

Yes. As an ecologist devoted to understanding the ecological connectivity within and among coastal ecosystem this function is of vital interest for coastal conservation. I took part in an international team of scientist led by Maria Potouroglou from Edinburgh Napier University that wanted to studies the sediment elevation induced by seagrasses. We did a broad range transect involving sites from Scotland to Tanzania where we measured sediment elevation in seagrasses vegetated area and bare sediment area. We did use Surface Elevation Change Pins (SECPs) methods over a period of more than a year. As Post-Doc in Red Sea Marine Center in KAUST University I joined the project measuring the sea bottom surface elevation in the Red Sea, precisely in the KAEC ( King Abdullah Economic City) Lagoon. I installed the SECPs in the seagrasses meadows and in the bare sediment and I monitor the sediment accumulation/erosion along a year.

4-      How much is the seagrass protecting the coast then?

We recorded a positive accumulation of sediment in the meadows and erosion in the bare sediment. The rate of deposition in the seagrasses is dependent by the location and by the ecological settings of the seagrasses studied, but, in every site, we record accumulation of sediment. It varied from 7mm per year in the Red Sea up to 34 mm per year in Kenya. Conversely, erosion in bare sediment did account for a loss of elevation up to 40mm per year in Tanzania followed by Kenya and Saudi Arabia with an average of 30mm per year. This data alone can explain how important seagrasses are to retain the sediment in the coastal area and therefore this highlight the urgency to establish coastal management policies able to protect them.

5-      To conclude, have you had any interesting adventure during your fieldwork?

A lot! Seagrasses did not recall the colours and the magnificence of the coral reef, but they can harbor the same marine biodiversity. With each dive into the seagrass meadow, you make amazing encounters here in the Red Sea. You can bump in some curious blue spotted ray (see picture below), or in a very annoyed mantis shrimp that is scared of all the activity we are carrying on. Octopuses, cuttlefishes and seabream observe you by distance asking themselves why we are actually drilling into the sea bottom a lot of stainless rods.

A blue spotted ray escaping into better shelter place such as the mangrove pneumatophores from the seagrasses meadows. This picture was taken by Dr. Marco Fusi during his fieldwork.



My name is Luigi Lombardo and I am an Assistant Professor at ITC, Faculty Geo-Information Science and Earth Observation since January 2019. My hobby is to do scientific research in the field of geomorphology and statistics. And, my job is to share this knowledge with other people with the same interest and with the public. For this reason, I joined the EGU early career scientists of the Natural Hazard division (NhET) in 2016. Since then I contributed to the activities of the group and now, together with part of the team we will manage the Natural Hazard blog of the EGU. It goes without saying it, but being Italian, I love cooking and has also worked as a sous chef in my youth.

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