Start of the Underwater Planting Season

Eleven divers in black diving suits get ready for their underwater gardening mission on this early summer morning on the beach at Wackerballig in Geltinger Bay. The planting material is stored in bright blue net bags: seagrass sprouts taken from a nearby healthy donor meadow. These are to grow together here, a few metres from the beach, to form a new seagrass meadow. The divers slowly wade into the water, where a rubber dinghy then pulls them to the planting site. Once there, they dive down. On the seabed, sprout after sprout is now placed in the soft sediment, eight sprouts per square metre.

With a net bag and neoprene: Underwater gardening for nature and climate protection

The method is called single-shoot transplantation and is currently considered the most effective technique for reintroducing seagrass. It requires many hands. This summer, five non-governmental organisations (NGOs) and numerous volunteer divers are taking on seagrass restoration on a larger scale for the first time.

"The pilot phase is over – now we are moving into the field," says Prof. Dr. Thorsten Reusch, Head of the Marine Ecology research department at GEOMAR. "The fact that the NGOs are now independently restoring seagrass meadows with the help of trained divers is great news for biodiversity in the Baltic Sea’s coastal areas and for natural climate protection."

Seagrass - the underestimated natural CO₂ sink

Seagrass is a true all-rounder underwater: it provides important habitats for fish and other creatures, stabilizes sediment, calms waves, and filters pathogens from the water. Most importantly, it binds carbon very effectively and over the long term. This makes seagrass meadows one of the most important natural CO₂ sinks in our coastal waters.

This is precisely where the ZOBLUC project, which is funded by the Federal Ministry for the Environment and started this year under the leadership of GEOMAR, comes in. ZOBLUC stands for "Zostera marina as a blue carbon sink in the Baltic Sea" and combines research, protection, and restoration of seagrass meadows. The focus is on the extent to which these ecosystems act as natural carbon reservoirs – and how they can be specifically strengthened. The project is part of the Natural Climate Protection Action Programme (ANK) and is funded by the federal government and the state of Schleswig-Holstein.

“Seagrass meadows are like undersea moors,” explains Reusch. “They store carbon in the oxygen-poor sediment for centuries – this makes them an underestimated but effective weapon in the fight against climate change.”

But seagrass meadows are under threat. Excessive nutrient inputs and the resulting excessive growth of algae, mechanical disturbances such as anchors, and rising water temperatures have led to the disappearance of seagrass in many places in recent decades. However, according to GEOMAR data, conditions have improved again on some stretches of coast. “In order to jump-start the slow natural colonisation, it makes sense to renaturalise seagrass in carefully selected areas.”

Citizen science for marine conservation

The involvement of citizens in renaturalisation as part of the citizen science approach is a central element of ZOBLUC. The training formats required for this were developed over several years and gradually expanded: in 2023, GEOMAR researchers developed an eight-part pilot course and offered it in cooperation with Sea Shepherd for a small group of experienced “citizen divers.” In the following year, 2024, the training courses were extended to diving instructors and diving club leaders.

2025 now marks the transition to the area: the members of five NGOs – Sea Shepherd Germany, Mission Förde, Lake Divers (Just1Ocean), Seagrass Conservation e.V. (SeaGCon, in formation) and Greenpeace – will be trained. They will then look after nine scientifically selected areas in the Baltic Sea, from Holnis to Fehmarn, where seagrass has either completely disappeared or is only present in small remnants. Targeted planting is intended to fill these gaps and create a long-term network. The suitable renaturalisation areas and donor species are selected by GEOMAR and approved in close consultation with the Schleswig-Holstein Ministry of the Environment (MEKUN). The measures are scientifically accompanied by a monitoring programme that documents environmental conditions and planting successes.

Nine areas, five NGOs, one common goal

For Christin Otto from Sea Shepherd, who is coordinating the training courses, this mission is a central concern: “We are thus consistently continuing our long-standing commitment to protecting the Baltic Sea – with direct, effective marine protection. Thanks to the cooperation with GEOMAR, we are able to further expand our conservation efforts and make a sustainable contribution to the preservation of important habitats.” “We offer nature conservation that you can take part in,” says biologist and research diver Christian Lieberum. He is the full-time coordinator of the Citizen Science programme. “The response has been huge,” he says. Not all those interested could be offered a training course. “But we’re only just getting started. This success story will hopefully continue for a long time to come.”