Grasshopper, the Underwater Robot That Will Help Restore Posidonia Meadows in the Mediterranean

Robots to the Rescue of the Mediterranean’s Underwater Meadows

Beneath the Mediterranean’s surface lies one of the planet’s oldest ecosystems. Seagrass meadows, particularly those formed by Posidonia oceanica, extend to depths of 45 metres and cover approximately 2 million hectares along Mediterranean coastlines. Although they are often mistaken for algae, seagrasses are true flowering plants, with roots, stems, leaves, flowers and fruit. They produce oxygen, provide shelter for juvenile fish and numerous other marine organisms, and help protect coastlines from waves and erosion. They are also an important carbon sink: despite covering only around 0.1% of the seafloor, they are estimated to store up to 18% of the world’s oceanic carbon.

A Habitat in Decline

Seagrass meadows are nevertheless retreating. Researchers estimate that 34% of Posidonia meadows along Mediterranean coastlines have been lost over the past 50 years, mainly as a result of climate change, pollution and boat anchoring. Between 30% and 50% of meadows may potentially be affected by unregulated anchoring. In 2024 alone, an estimated 180,000 boats dropped anchor on seagrass. A damaged meadow can take approximately 100 years to recover.

The first line of defence is passive restoration, which involves protecting existing meadows through marine protected areas, no-anchoring zones and mooring buoy fields in environmentally sensitive locations. Where meadows have already deteriorated, active restoration becomes necessary. Teams of specialised operators, effectively “sea gardeners”, monitor and select suitable sites, collect shoots and rhizomes from donor meadows, test sustainable materials to secure them to the substrate, prepare and transplant the plants, and subsequently monitor their growth and health.

Enter the Robots

This is where underwater robotics can change operational methods. Robots can map the seabed, collect data and images from difficult-to-access locations and perform tasks previously carried out entirely by humans, reducing operating time, resource requirements and risks for researchers.

ROVs, or Remotely Operated Vehicles, are tethered underwater robots controlled from the surface. They can follow predefined routes above the seabed, conduct observations using cameras and sensors, collect water or sediment samples, and gather information to map habitats, count organisms and assess ecosystem health. One example is SuBastian, an ROV that enables scientists to explore some of the deepest parts of the oceans.

Grasshopper, the Robotic Gardener

If ROVs are the eyes and hands of oceanographic research, Grasshopper takes on the role of gardener. Developed by the US startup ReefGen, this underwater robot is designed to restore seagrass meadows, coral formations and other coastal habitats. Traditionally, these operations have relied on divers planting small sections of seabed by hand.

Grasshopper is remotely operated. It travels to a previously selected site and positions itself on the seabed. It then inserts seagrass seeds or cuttings directly into the sediment, automatically repeating the operation across large areas. Its reported performance includes an operating depth of up to 10 metres, planting speeds 8 to 10 times faster than manual methods, and the capacity to restore one hectare of seabed in five days.

Oysters as Natural Filters

Planting is only one part of the restoration process, as young plants require favourable environmental conditions to survive. For this purpose, filter cages containing live oysters are installed on the seabed in restoration areas. As filter-feeding bivalves, oysters help clean the surrounding water, improving its quality and creating more favourable conditions for plant growth.

This approach combines technology with natural processes: the robot handles planting, while oysters help improve water conditions so that the new plants can establish themselves. It reflects a broader principle of environmental restoration: successful ecosystem recovery requires support for the entire habitat, rather than a single species.

From Wales to the Adriatic

The results achieved so far are encouraging. In Wales, Grasshopper distributed 25,000 Zostera marina seeds across 200 square metres of seabed. Within 18 months, a new meadow covering more than 100 square metres had developed.

The first Mediterranean trial is scheduled for 2027 in the Gulf of Trieste, in collaboration with researchers from the Miramare Marine Protected Area.

Robots cannot replace protective measures, which remain the most effective means of safeguarding seagrass meadows. However, they can make it possible to extend restoration operations over larger areas and within timeframes that would be difficult to achieve through divers’ work alone.

Rebecca Gabbi