Restoration of the Rupia (Ruppia maritima) in Lake Atanasovsko - a new approach for the revitalization of coastal ecosystems in Bulgaria.
One of the most challenging activities within the LIFE project "The Lagoon of Life" is the restoration of the sea rupiah. The only aquatic plant in the waters of Lake Atanasovo was considered extinct here for a long time. It is a herbaceous plant with tender leaves, about 15 cm high. It is not by chance that the group of these plants is called seagrasses - they are very similar to terrestrial ones, although they have nothing in common with them. The flowers are small and inconspicuous, and pollination is carried out by water currents and wind. The seeds are spread by water currents.
Discovered in 2015, small and isolated colonies of the species in the northern part of the lagoon piqued our interest and led us to learn more about the reasons for its disappearance. This freshwater species with an amazing resistance to high salinity is widely distributed in freshwater ponds, canals and in the shallow parts of the sea. But in Atanasovsko Lake, the deposits are limited only to the peripheral parts - those that are directly fed by seawater. Apparently, the rupiah is affected by the drying up of the more inland basins, the high water temperature, the strong waves caused by the summer breeze in the shallow basins and the turbidity caused by the movement of the waters and by the waves.
The natural colony of Rupia in North Atanasovsko Lake
But the rupee is a very important species for the ecosystem - although a small and inconspicuous plant, it has an indispensable role in its functioning. First of all, it forms extensive and dense underwater growths, called meadows, which are a habitat for many types of animals that hide or reproduce in the shadows of plants - worms, crustaceans, molluscs, and fish. They attract birds that feed on them, and the rupiah itself is a favorite food for the various species of ducks and geese. It is not by chance that the highest density of these species in Lake Atanasovsko is in the basins in which the rupiah grows. In the scientific literature, there are even data on the feeding of the pink flamingo with rupees, but this has not been observed in Bulgaria.
Other important functions of the rupiah are the purification and enrichment of water and soil with oxygen (the rupiah can grow in a substrate with a complete lack of oxygen, and through the roots it manages to bring into the soil sufficient quantities for its development, as well as for that of other species, living in it), the strengthening of silt and wetland banks and the reduction of wave power.
Perhaps the most valuable function of the plant is the rapid fixation of atmospheric carbon and its conversion into an insoluble form. Seagrasses, and rupia in particular, sequester up to twice as much carbon as tropical forests per year per unit area and do so up to 35 times faster than them. This is due to both the physiology of these plants and the important role of coastal wetlands in carbon sequestration.
Impact of seagrasses on wave strength and height and suspended sediment (source Coastal Resilience: Seagrass restoration triggers rapid ecosystem restoration in Elkhorn Slough, Beheshti, K., UC Santa Cruz, Raimondi Lab, Wasson lab, 2020)
Plant for transplantation
All these indispensable ecosystem functions of the rupiah made us look for opportunities to overcome the causes of its disappearance in Lake Atanasovsko and to create new colonies in basins with suitable conditions to reproduce and spread.
We started in 2019 by researching the specific requirements of the Ruppia to live in Lake Atanasovsko and looking for suitable places to restore. The main requirement for the pools was to have a relatively constant water level, silty substrate, no high waves and good water transparency. The next step was to study the recovery efforts of the species and other seagrasses around the world. This is already a long-standing practice, especially along the Atlantic and Pacific coasts of the United States and in East Asia. In Europe, in recent years, seagrass restoration has also received a lot of attention and is being implemented in many countries - Spain, France, Italy and Greece. In Bulgaria, the use of such a practice is being carried out for the first time, and the challenges we faced were not few.
We tested different methods of transplantation - transferring plants and planting them in the substrate, using biodegradable buckets, transferring tufts with the substrate, and sowing seeds. The first attempts were not very encouraging - the plants could not take hold of the soil and soon after being transferred, they disappeared. Either the substrate was not suitable, or the waves were too strong, or the water was not particularly clear, but more often a combination of all these factors.
The challenges were also increased by the fact that in the period 2019-2021, even the natural colony of the rupiah in Lake Atanasovsko did not develop. The reasons for this were mainly the high turbidity of the waters in the basin, caused by the poor management of the water levels and the supply of the lake with fresh seawater. This made it necessary to look for donor colonies outside the lake, focusing on the localities of the species in Lake Pomorie. There the plant develops very well, favored by the decline of salt extraction, which allows the maintenance of higher water levels, lack of drying and little fluctuation of water temperature and salinity, and above all high transparency as a result of the slow circulation of the waters at the lack of salt extraction. The populations of Ruppia maritima in Atanasovsko and Pomorie lakes have a common origin and are supported by the plants of the species in Burgas lough - the most extensive underwater meadows along our coast. This eliminates the risk of genetic contamination when transporting plants from one place to another.
In 2021, we tested a new methodology called Transplanting Eelgrass Remotely with Frames System - TERFS (transplanting zoster with a frame system). This technique is based on a frame with a net attached to it, to which the plants (in this case Zostera marina) are attached. But in the USA, where it is applied for the first time, plastic frames and metal nets are used, which we consider unsuccessful for application in Lake Atanasovsko in the context of its conservation importance and vulnerability. That's why we adapted the method by using wooden frames and hemp netting, which are completely biodegradable and disappear 1-2 seasons after transplanting. This method allows the transplanted plants to have a stable connection with the soil in the first days after their transfer and favors the strengthening and formation of roots, eliminating the impact of water flow. Thus, in the summer of 2021, we created the first stable colony in South Atanasovsko Lake with an area of approx. 40 m2 which has started to develop, flower and produce seeds. The plants overwintered successfully and the following spring grew again, including well into the basin where their seeds were carried away by the water current. It gave us a lot of hope that we are on the right way and our efforts are worth it.
Preparation of the wooden frames (TERFS method)
Collection of plants for transplantation from the donor colonies
Attaching the plants to the frames
Colony establishment with the TERFS method
The first colony successfully overwintered in South Atanasovsko Lake
In 2022, as a result of the improved circulation and control of the water regime after the reconstruction of the main sea lock in North Atanasovsko Lake, the natural colony of the rupiah developed in its usual place. The reconstruction of the lock (a first for this facility after more than 40 years of operation) was key to the success of all the conservation activities of the Lagoon of Life project. This had a direct effect on the ability to maintain stable water levels, and manage the timing and amount of seawater supply, its transparency, and constant salinity.
In the spring of 2022, we visited the LIFE TRANSFER project in the Po Delta, Italy, which is restoring seagrasses as part of coastal ecosystem restoration. There we learned about the successes of our colleagues in restoration, as well as the used transplantation methodology, which is based on the transfer of chymes (tuffs) with a substrate from the donor colonies to the new colonies.
The conditions in Atanasovsko Lake are not very suitable for this method, because it requires certain structural and quality specifics of the substrate, both in the places from which the reproductive material is obtained and in the places for planting. The success of the method in Italy is also due to the greater depth and constant transparency of the waters in the wetlands there. But also to the perennial nature of the plants – the entire aerial part overwinters there and the transplanted plants quickly start to reproduce the following spring. In Bulgaria, the aerial part dies at the end of autumn and only part of the rhizomes of the transferred plants overwinter, which reduces the success of the transplant. However, we were able to localize in our colonies a suitable substrate structure and composition that favours the extraction of stable chyme and their transport to the transplant sites.
Chim with rupee ready for transplant
Thus, in 2022, we also applied this methodology, together with the TERFS methodology, creating a colony in Northern Lake with a total area of approx. 30 m2. The day after the transplant, the plants must be washed, because when they are planted, particles of mud stick to the leaves, which reduces the possibility of survival - they cannot photosynthesize and grow. The plants in the new colony quickly established themselves and began to spread with their new shoots. After about 2-3 weeks, they began to bloom profusely and form seeds. On the 33rd day after transplantation, the new plants were spread about 5-6 m from the planted ones, and on the 62nd - more than 10 m. Then the new colony already had an area of approx. 400 m2, i.e. increased its area about 13 times! In the first year, the development of the colony is mainly vegetative - through the roots of the plant. The rupee has the ability to form long rhizomes, from the nodes of which new plants grow. The main goal of transplanting is to create a colony that will firmly establish itself and the plants will produce seeds. From them, in the spring, new plants develop quickly and in large quantities, occupying large areas.
Transplantation with chims
The place for the new colony in the north Atanasovsko Lake
The transplanted plants on the day of the transplantation (link - method with wooden frame, right - method with tufas)
New colony on TERFS method on the 33rd day of transplantation - new plants виждат се новите растения, образувани от коренищата на трансплантираните растения
Новата колония по метода с туфи на 33-тия ден от трансплантацията с новите растения
Новата колония на 62-рия ден от трансплантацията