Seeds of Zostera marina (eelgrass) can be used for restoration if they are available. Although the success of establishing adults plants from seeds has been generally low (<10% survival rate), new methods could be investigated to increase the survival rate. In this post, I summarize the techniques that we have tested in the last years and have worked well in Sweden.
The process involves harvesting flowering shoots and storing them in tanks on land until the seeds mature and are released. Then the seeds are collected from the tanks and stored until the seeds are planted in the sea. Seeds can also be collected and used for scientific experiments in the laboratory or mesocosms instead of using them in the field. For example, seeds can be used for germination experiments, animal food choices, seed transport by hydrodynamics, microbiome, genetics, etc.
Shallow coastal habitats play a key role for the overall production and biodiversity of coastal ecosystems and for many commercial species that use them as nurseries. Being located close to human activities, and in many areas targeted by exploitation, coastal habitats have suffered significant and widespread decline on a global scale. However, with the implementation of EU Directives, no further degradation of coastal habitats will be allowed, and potentially costly measures will be needed to restore degraded valuable coastal environments such as seagrass habitats to a good status. Europe is presently not prepared for this challenge since effective measures halt the ongoing decline and restore degraded habitats is largely missing. In contrast to management of rivers and lakes, which have a long history of successful restoration measures, the restoration of marine habitats is still in its infancy.
Seagrass restoration can be performed with seedlings and seeds. Transplantation of seagrass shoots have been used for restoration with differing degrees of success, but this method has been shown to be expensive and labour intensive. As planting represents a large proportion of the costs associated with restoration, developing cost-effective new planting methods would reduce the costs, and seeds are more practical for large-scale restoration. However, seed-based restoration has had variable success (less than 10 % recruitment) because the processes controlling seed establishment and early seedling survival are relatively poorly understood. Unlike terrestrial planting applications where the soil and environmental conditions necessary for successful seed germination and growth are well known, we are only beginning to make progress toward understanding the requirements for successful seed germination of underwater plants.
Zostera marina, L. (also known as eelgrass) is found in Europe from arctic waters along the northern Norwegian coast to the Mediterranean Sea, where it can survive several months of ice cover. The species is very abundant in the Baltic Sea, the North Sea and along the Atlantic coasts down to northern Spain. Seagrass is the dominant macrophyte on soft bottoms along the Swedish west coast and in the Baltic Proper, constituting approximately 20% of all habitats at 0-10 m depth on the Swedish west coast today. Along the Swedish NW coast, almost 60% of the eelgrass has been lost since the 1980’s, representing a loss of approximately 190 km2 of eelgrass. In Sweden, eelgrass is not included in any national environmental monitoring program, and the loss has passed largely unnoticed, and no measures have yet been taken to prevent further loss or to restore the deteriorated habitats. The causes of eelgrass losses are still unclear making it difficult to develop effective management measures and a legal framework to support it. Recent studies suggest that the primary mechanism behind the overall decline is an increased abundance of epiphytic algal mats caused by eutrophication and overfishing, which results in reduced light conditions and increased anoxic events. In order to enhance recovery of eelgrass in this region, it is necessary to understand the basic eelgrass ecological processes as well as to develop new seagrass restoration techniques.
Flowering or reproductive shoots mature first at the base of the plant and on the main axis of the stem, then progresses upward and outward toward terminal inflorescences. Flowering and seed development does not occur equally over the entire shoot and some judgment is required to choose a harvest time that ensures the greatest yield of seeds. Harvesting too early might reduce the yield of seeds collected since many seeds might not fully develop. On the other hand, harvesting after the seeds have matured might not be efficient since many seeds could be already released in the field. Selecting the best harvesting time is currently done by experience personal judgment of the donor site bed, but there is not a standard method to select these dates.
In Sweden, the best time to harvest Zostera marina shoots is in mid-July. In Jun, the spathes are still forming and pollen is released which might be too early for harvesting, since not so many seeds will be matured enough if flower shoots are collected at this date. In contrast, August and September might be too late, since seeds are already starting to be released and many spathes will be already empty, which is not so efficient. In mid-July, most seeds are already formed and ready to be released, which might be the most efficient time for harvesting. These dates could vary between locations and years, for example, in warmer locations, seeds might develop earlier in the summer. Restoration projects should assess the seed maturation time on their locations. More details of this methodology and data in Infantes et al. (2018).
After harvesting, flowering shoots can be stored in tanks on land until seeds naturally drop from the spathes. Flowering shoots were stored for 2 months in tanks until seeds were collected. Seeds will accumulate in the bottom of the tanks until they are collected. We used large tanks of 1500L with seawater flow through to maintain similar temperature and salinity to the sea. Since shoots tend to float, a mess cover was used to keep all the shoot submerged. To keep the water well mixed, air was pumped in the tank bottom using a PVC piping system. Tanks can be filled about 1/3 of their capacity with eelgrass. To collect the seeds from the bottom, the flowering shoots can be removed and the the bottom of the tank is siphoned with a 4-5 cm diameter hose, since smaller hoses can get easily clogged with leaf debris. We used this method during 6 years (2012-2018) and worked very well.
After collecting the seeds from the tanks it is important to separate the good viable seeds from the non-viable seeds and debris. A vertical flume flume can be used for this purpose. The vertical flume is a low cost construction that produce a vertical flow from the bottom of a tube towards the top. The viable seeds which are more dense tend to sink faster to the bottom while the non-viable seeds which are less dense are transported out of the tube. The flow can be controlled with a simple flow meter (Gardena flow meter) installed on the base of the flume. To count the total number of seeds collected, the number of seeds in 1gr could be counted and then multiplied by the total weight of the seeds.
Once seeds are separated from the debris, they can be stored until planting. The best conditions for storing Zostera marina seeds in Sweden is at temperature of 4oC and a salinity of 32. If the temperature is higher or salinity is lower, then seeds will start germinating during storage. For planting at sea, is better to plant them before seeds germinate, since after germination, seeds are less dense and can drift away easily. More details on seed storage in Infantes et al (2016a).
Planting the seeds at sea is one of the most critical steps. In our experience, we had the highest survival when seeds were covered with a 2 cm layer of sand. This method prevented that seeds were transported away from the planting area by hydrodynamics (waves and currents) and that seeds were eaten by other marine species such as the green crab Carcinus maenas. Seeds can be also buried in the sediment by the lugworm Arenicola marina, and areas with high lugworm densities should be avoided if possible. See more details on seed planting on Infantes et al (2016) and seed predation by green crabs in Infantes et al (2016b).
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More information on seagrass seeds
Hej
Can you help me bying some
Danish ( ålegræs ) eel grass seed
Hi Michaeel,
Not sure how you can find seeds for sale. If you want to collect them yourself you probably need to get permits from your local authorities.
Regards, Eduardo
Hi Dr. Infantes,
I am an intern working on seed based restoration of Eelgrass in Massachusetts. I am currently working on constructing our own vertical flume to test the seeds. I was just looking for more information about materials and measurements to inform me on my construction. Any information helps! Thanks so much!
Hi, Glad to hear that you found the vertical flume useful. Most of the information you need can be found in the article here, but feel free to reach out to me directly by email if you have specific questions.
Regards, Eduardo
I am absolutely astonished and grateful for your work as I am doing the same work on Long Island NY with Robert Vasiluth. Thank You
Hi, thanks for your feedback, I am glad that you like it and find it useful.
Eduardo
Hi Eduardo,
I found your articles and research very interesting and promising.
I was wondering if you have encountered any issues on propagation method and what is the survival rate on large scales restoration.
From my experience, some people from Asia encountered huge issues like snails, methods and etc. So, I have developed an eco-friendly material for seagrass propagation from the nursery (in situ & ex situ) to designated areas to drive better success. I will be happy to share, collaborate, and work with you.
Thank you.
Hi, thanks for reaching out, glad to hear that the articles are useful for you.
We initially started to develop eelgrass restoration methods in Sweden by comparing transplants and seeds. We saw that survival of seeds and seedligs in the field was very low (less than 10%) compared to transplants of adult shoots. Since then, for practical and economical reasons, we only suggest transplantation as a restoration method in Sweden. Perhaps in other locations is different.
Perhaps developing a method that increases seed and seedling survival would be very good. Happy to talk directly to you. Send me a direct email if you want to continue discussing.
Regards, Eduardo
Hello Eduardo Infantes…
Really enjoyed your article on Zostra Marina. We at Northern College in Timmins, Ontario, Canada, are looking at a revitalization program along our coastal lowlands, with the assistance of the Indigenous population. Where could we purchase the plants with rhizomes, or the seeds; for this purpose? Thank you.
Bruce Larose CET, P.Eng.
email: [email protected]
Hi Bruce, thanks for your interest. Glad that you found the article interesting and pleased to hear about Northern College’s revitalization program, especially with the involvement of the Indigenous population.!
I am not aware of any way to purchase Z. marina. Usually in restoration projects, donor plants are harvested from nearby locations and then transported and planted in the restoration area. It’s crucial to follow the local guidelines and apply for the right permissions to harvest and plant in the wild since, if its not done propely, it could cause more harm than good.
Having said this, you can check our Z. marina handbook and guidelines and video-guideline that we have produced. Also, please keep in mind that these methods were developed for Sweden and that conditions such as tides, waves, temperatures, sediment, etc, in Ontario might be a bit different.
Good luck! Eduardo
Hello Dr. Infantes,
I’m currently in the process of designing and setting up a nursery tank for Zostera (and other genuses/species) with an emphasis on seed harvesting. I am trying to do this in an inexpensive manner, focusing on main necessities. In your opinion, what are the most essential elements of a nursery tank with seed harvesting in mind?
Best,
Nate
Hi Nate, thanks a lot for your comment.
In my opinion, the most important factors to keep the plants in good shape are water flow and maintaining a temperature around 20°C. I also like to keep the shoots wet at all times by using a net or weights to keep the plants submerged and avoid desiccation. Light does not seem so important, as plants can produce seeds even in a dark environment, such as a crowded tank with shoots.
Hope this helps and wish you good luck, Eduardo
Dear Dr. Infantes,
I found your posts and research really insightful and helpful. I was wondering what method you used to place the 2cm sand layer. In a different field test with shoot transplantation, u used an hydraulic excavator. Was the same method used here or did u you a different method for the smaller scale?
Sincerly,
Anne-May
Hi Anne-May,
I am glad that you found the post interesting. We used 2cm layer of sand during experimental trials to protect seeds against crabs and seed transport by hydrodynamics (Infantes et al 2016). But during large scale planting of 1ha at Askeron bay, a sandcap layer of 10cm was used.
Hope the answer was useful, Eduardo
Hi, Dr. Infantes.
Have you tried in vitro culture or rhizome-mediated propagation?
Thanks.
Saludos desde Alemania!
Hi Romano,
Thanks for your message. I have not tested in vitro culture or rhizome propagation, but I will be glad to test this in the lab. If you want to share your experiences and discuss a possible test contact me directly by email at [email protected].
Saludos, Eduardo
Hi Dr Infantes,
Great post, thank you! It is extremely informative.
Can you envision an operation in which seeds could be harvested and reproduced to create a reliable supply? We are looking at ways to restore seagrass habitat at large scales, and are heavily considering seeding rather than transplanting. Finding enough seeds, however, seems very difficult, so we are looking at ways to control and increase their supply.
Hi Mary,
Glad to hear that the post is useful!
Getting seeds for restoration could be a bottleneck for large-scale planting, specially if the are no donor meadows available nearby. Improving the seed and seedling establishing ratio (eg. number of seeds needed to get 1 adult shoot established) would be a good strategy to make the process more efficient. Right now, you need a lot of seeds to be planted to get few adults shoots (1-10%) in subtidal sites.
Another strategy would be to restore strategic located plots (with seed or transplants) and let nature do their work by spreading naturally to nearby areas.
Hello, Dr.
I would.like.to collaborate to plan sea grass and if possible to buy them and plant them where we would like around where the company operates
I hope we can get In touch on this subject matter as soon as possible
Dear Alaaldeen, I am always glad to collaborate but unfortunately I don’t sell eelgrass seeds. Only use them for research purposes.
Great information, thank you for posting! If growing the seeds in tanks in a lab setting does the 2cm of sand still apply for successful germination? Also is it better to germinate on a petri plate and then transplant to a tank/chamber when in a lab setting? Thanks again!
Hi Gina, If you want to study just germination you can use petri dishes so you can see the germination directly otherwise you need to wait until you see the first leaf coming out of the sediment. But if you want to produce seedlings, I suggest you plant them directly in sediment. In some studies, I used a 2cm layer of sand to cover them but is the same if you just bury them 2cm into the sediment.
Wish you good luck in your experiments!!
Could Saltwater Aquariums use eelgrass?
Like the ones they show off to the public?
Hi Jason, eelgrass plants can be kept in aquariums, but most of the time what you see in public aquariums is artificial plastic plants that look like real plants. Eelgrass in aquariums require quite a bit of light (80-100 PAR) and some water movement. Air bubbling could be good to mix the water. Make sure they have a nice fine/medium sand sediment for the roots to anchor and develop.
Hi Dr. Infantes
Do you know where one can acquire eel grass seeds for decorating a salt water aquarium?
Best regards
Dang Le
Hi, I have not seen eelgrass seeds for sale. You could collect some plants and place them directly in the aquarium. If you want to collect seeds then you need to harvest flowering shoots from a meadow to collect the seeds. Check out the article above on eelgrass harvesting.
https://www.eduardoinfantes.com/pubs/eelgrass-seed-harvesting-coastal-restoration-sweden/
Eduardo
Hi,
Thanks for you reply! I’ll see what I can do, but I guess I have to wait until next year then.
Best regards
Dang
I’m wondering how successful you may have been finding the seed beds and suitable materials for obtaining seeds for eelgrass? What latitude are you interested in propagating the new plants? Best wishes, btw.
Hi Robert, most eelgrass meadows except in some Baltic regions should produce seeds after flowering. Here in Sweden, we harvest them in the summer time (July-Aug) but might be earlier at lower latitudes or later at higher latitudes.