In the context of the joint project SeaStore, experts from six research institutes are seeking meaningful answers to the five most important questions in seagrass restoration.
The success of seagrass restoration efforts depends on a complex interplay of abiotic and biotic factors at the planned reintroduction sites. In this work package, the experts are laying the groundwork for restoration projects in the southern Baltic by e.g. gathering bathymetric, hydrodynamic and microbial baseline data from native seagrass meadows and comparing it with the baseline data from potential reintroduction sites and previously restored meadows in Scandinavia. All the methods and work steps used will be painstakingly recorded to help ensure optimal data collection, resolution and assessment for future reintroduction projects.
In addition, the experts are developing a growing aid and testing the stability, durability and effectiveness of various prototypes under real-world conditions at Leibniz University Hannover’s 3D wave and current basin. This artificial structure, made of biodegradable material, is to be used especially at sites with comparatively strong wave action – in order to facilitate the germination of sown seeds or the growth of freshly planted seagrasses by protecting them from being swept away or uprooted long enough for the seedlings or young plants to form strong roots of their own.
In the long term, the successful deployment of this growing aid could reduce the number of seeds and seedlings per square meter needed for restoration measures, making the reintroduction of seagrasses feasible on a far larger scale. However, one important prerequisite is that the growing aid be producible in large quantities and as affordably as possible.
The microbiologists participating in the joint project SeaStore are not only using DNA sequencing to investigate the diversity and role of microorganisms in seagrass meadows, but also developing standardized microbiome sampling kits for future reintroduction projects. The kits will include detailed instructions and all the materials needed to collect samples of leaf, root and sediment microbiomes.
To date, the seagrass sprouts used for reintroduction projects have been taken from healthy meadows. But not every seagrass plant is robust or healthy enough to serve as a “donor” plant. Accordingly, choosing the right seagrass to plant is essential to the success of reintroduction efforts.
In this work package, the participating researchers are investigating on the one hand which qualities seagrasses intended for transplantation need to have; these include parameters like root length, plant height and tensile strength. On the other, they’re working to identify which water currents, light and soil conditions a new site has to have in order for the seedlings to have the best chances of survival.
The experts are conducting the corresponding experiments at two test plots in the Baltic, and at Leibniz University Hannover’s twin-flume wave channel. The plots near Kiel and Maasholm are home to over 12,000 freshly planted seagrass plants. Many of them are numbered, allowing the scientists to monitor and document the growth and health of individual plants. In addition, light and flow sensors record the most important environmental parameters. In the first year of the project, the researchers also gathered seed-bearing sprouts; their 14,000 seeds are now overwintering in a seawater aquarium at the GEOMAR Helmholtz Centre for Ocean Research in Kiel and are slated for planting at another test plot in the Baltic in the spring of 2022.
In the 30-meter-long twin-flume wave channel, the experts
will conduct stress tests with actual seagrass plants. By doing so, they hope
to determine the extent to which freshly planted seagrasses can withstand
intensifying currents, and the extent to which the characteristics of
individual plants like leaf length and root length affect their resilience. In
this regard, for every test series, several seagrass plants with varying
characteristics and resting in a bed of sediment will be placed in the wave
channel and their responses to wave action and the force of the water will be
Seagrass meadows are capable of reducing the water’s cloudiness, and improving their own living conditions in the process, by facilitating the sinking of particles floating in the water. In other words, wherever seagrasses grow, they set in motion a feedback process that markedly improves local conditions for their settlement, growth and reproduction.
In this work package, the participating scientists are using restoration test plots in the Baltic and the 3D wave and current basin and twin-flume wave channel at Leibniz University Hannover to determine which reintroduction method is most likely to achieve this natural feedback. This involves e.g. the question of how densely seagrass seedlings need to be planted in order to produce the desired sedimentation effect and what role SeaStore’s newly developed growing aid could play in this regard.
Moreover, the researchers hope to determine whether the health of the seagrasses could be improved by settling musselsclams on the test plots. Clams also filter particulates from seawater, reducing its cloudiness. They will also map the range of influence for individual seagrass meadows: in other words, in which radius they influence the sedimentation rate and therefore water quality. Their findings will subsequently be integrated into a cost-benefit analysis for reintroduction measures.
The restoration plots created in the context of SeaStore will give the project partners the opportunity to explore in detail how quickly restored meadows can provide their natural ecosystem services for human beings and the ocean.
To arrive at an overview of the biodiversity in the newly planted meadows, the scientists will go on check-up dives, collect samples and/or catch local fish and invertebrates on a regular basis. In addition, there will be extensive research into the diversity of microorganisms in the grasses and on the ocean floor. Here, the goal will be to determine how quickly the species composition, i.e., the biodiversity of the biotic communities in the restoration plots, recovers and how quickly the food webs typical of seagrasses can be reestablished. One important question for the project is how soon herring use the newly planted seagrass meadows as a breeding ground and kindergarten.
The researchers also plan to compare the population size and density for selected keystone species in natural seagrass meadows with those in restored plots, and in sites without meadows. In addition to various microorganisms, these species include epiphytes, grazing invertebrates like sea snails, small non-predatory fish and predatory fish. Using this and other field investigations, the project partners hope to determine how tightly bound the food webs in the vicinity of seagrass meadows are, through which channels carbon is passed from one trophic level to the next, and how biomass is recycled in the seagrass meadow system.
This will be supplemented by various comparisons between restoration plots and native seagrass meadows concerning key ecosystem services like slowing currents and accumulating sediments (coastalprotection), as well as carbon binding and sequestration. In this regard, the researchers will collect sediment cores measuring up to one meter long and evaluate their carbon content. The current assumption is that it takes 12 to 18 years before a new seagrass meadow is capable of tapping its full potential, allowing it to bind the maximum amount of carbon and store it below the ocean floor.
Lastly, the SeaStore partners, together with local and regional authorities in Schleswig-Holstein, will monitor the restored seagrass meadows on a regular basis over a timeframe of at least 10 years. In this way, the growth and expansion of the restored plots, as well as their ecosystem services, will be assessed and the long-term effects of reintroduction efforts will be documented, beyond the end of the project.
Successfully implementing seagrass reintroduction measures on a larger scale requires a deeper understanding of not only the natural sciences aspects but also the socioeconomic setting.
In the framework of this work package, the project partners will on the one hand prepare a detailed cost-benefit analysis on seagrass restoration measures, so as to provide a valuable argument for project initiators. On the other, they will use representative online surveys to determine what types of value the German public associates with seagrass meadows and under which conditions coastal communities, tourists and other interest groups would be willing to actively support seagrass reintroduction measures and accept the accompanying limitations on ocean use.
All socioeconomic and natural science research findings will be integrated into the SeaStore guidelines on successfully implementing seagrass restoration projects. These guidelines are intended to enable project initiators and decision-makers to plan and successfully implement cost-effective seagrass restoration efforts in the southern Baltic. Accordingly, they will not only cover aspects like the goals of restoration and selecting the ideal location, but also provide extensive information on potential restoration methods, monitoring freshly planted plots, and getting the local populace people and other important interested groups involved.