Estonian Marine Institute scientists work with macroalgae to improve the Baltic Sea environment

Estonian Marine Institute scientists work with macroalgae to improve the Baltic Sea environment Innovative projects show promising results

Researchers at the University of Tartu’s Estonian Marine Institute are working on a number of projects that seek to address some of the environmental challenges facing the Baltic Sea and, at the same time, to benefi t the aquaculture industry.

Cultivation of Furcellaria lumbricalis under manipulated light conditions in 2 m3 aerated tanks fi lled with natural seawater.

The term algae refers to a large group of mainly photosynthetic organisms ranging from unicellular microalgae species to vast multicellular forms such as kelp. Algae are found in marine environments, in freshwater, and even on land. In the sea they extend down to a depth of about 150 m depending on the transparency of the water and they may be either fi xed to the bottom (benthic species) or fl oat freely in the water column (planktonic species). Marine algae are a source of many nutritionally valuable minerals, trace elements, vitamins, and even of small volumes of fats rich in omega-3 fatty acids. Some species also have a high protein content— up to 47. Cultivating these may off er advantages over traditional high protein crops as they would not need freshwater to grow. Th e divisions and classes that algae are grouped into often refer to the colour of the algae, for example, Cyanophyta are blue-green, Chlorophyta, green, and Rhodophyta, red.

Macroalgae have a variety of uses

Among the most useful products to be extracted from red algae in particular are gelling agents, which are widely used in the food and other industries. Th is property of red algae to thicken products has been known and exploited since the 17th century and is due to the presence of the phycocolloids, agar and carrageenan. In the Baltic Sea few algal species are exploited commercially, but interest in algae is growing—for their nutritional value, their content of commercially useful compounds, and also for their potential to mitigate the impacts on the environment of fi sh farming. At the Estonian Marine Institute, Tiina Paalme has been working to develop intensive land-based

cultivation technologies for the unattached form of the red algae, Furcellaria lumbricalis. Naturally found in the West Estonian Archipelago the species is commercially harvested for its content of furcellaran, a thickening, stabilising, and gelling agent used in the food, pharmaceutical, cosmetics and agriculture industries. F. lumbricalis also contains a red pigment, R-phycoerythrin, a compound that is used in the cosmetics, food, drinks, and paint industries and has potential applications as an anti-cancer drug due to its antioxidative abilities. Th e pigment also has laboratory applications in fl uorescence-based detection, but this calls for a highly purifi ed form for the extraction of which a viable technology is still under development.

F. lumbricalis has two thallus forms: attached and unattached i.e loose-lying. Th e attached form is widespread but is more diffi cult to collect as it grows on stones and removing it from this substrate is time consuming. Th e loose-lying form can be collected much more easily although it is not as pervasive. Dr Paalme’s research sought to establish whether it was possible to use land-based cultivation technologies to enhance the production of the pigment by the algae. To produce furcellaran, the researchers found that production on land could not compete with harvesting naturally growing algae as the volume produced on land was insuffi cient to yield a meaningful quantity of this compound. For land-based cultivation to be economically viable, it was necessary to produce the highervalue R-phycoerythrin for use in the food industry. One of the main objectives of growing F. lumbricalis on land was to try and increase the pigment content of the algae to a higher level than could be achieved naturally. Th e algae were produced in tanks which were fi lled with water pumped from the sea. Diff erent light conditions (irradiance,

Tiina Paalme, Estonian Marine Institute

Furcellaria lumbricalis on the bottom of the cultivation tank illuminated with LED lamps (in the picture is the refl ection of the lamps on the water surface)

spectral composition, day

length) and water temperatures were tested to identify the environment most favourable to boosting the growth of the algae and its pigment content. Th e growth rate of F. lumbricalis in the tanks remained within the same range as observed in nature. Th e technology needs to be further refi ned and diff erent growth conditions need to be evaluated, but Dr Paalme is now using the methods developed and the results from these experiments to cultivate another variety of red algae, Ceramium tenuicorne. Th is species is quite widespread but very diffi cult to collect from the sea, which is why the researchers would like to be able to grow it on land. In their trials the researchers used aquariums fi lled with artifi cial seawater created using a solution of nutrients and salt. Interest in C. tenuicorne is considerable because its structure is diff erent from that of F. lumbricalis, which enables the red pigment it contains to be extracted at analytical grade using existing technologies. However, producing the algae on land is associated with high costs, in particular, for the energy needed to light, aerate, and to drive other processes.

Using algae to clean wastewater from terrestrial fi sh farms

Scientists at the Estonian Marine Institute together with partners from industry are also studying the potential of algae to mitigate the impacts of fi sh farming in the Baltic. Dr Georg Martin has almost completed a project that identifi ed several widely available algae species suitable to be used as biofi lters. In the experiments effl uent water from a terrestrial rainbow trout farm growing the fi sh in water pumped from the sea was used as the growth medium in which algae were cultivated to study their ability to remove nutrients from the water. Th e outcome was quite promising, says Dr Martin, with good results obtained for nutrient removal as well as for the growth of the biomass. In a commercial context it would be an additional benefi t for a fi sh farmer if the wastewater from the production could be used to cultivate a potentially valuable crop. Th e algae produced can be used in several diff erent ways from fertiliser or compost to higher value applications such as the production of biogas or bioethanol. Depending on the species of algae, eff orts are also ongoing to extract compounds that are valuable for diff erent industrial sectors.

Using algae to remove nutrients from fi sh farm wastewater has several benefi ts for the producer. Eutrophication is a particular issue in the Baltic Sea where nutrients (nitrogen and phosphorus) from current and legacy sources contribute to algal blooms. Th ese result in oxygen-free zones with a concomitant reduction in biodiversity, loss of ecosystem services, and increased vulnerability to ocean acidifi cation, according to a 2019 paper by Jonna Kotta and

colleagues published by Elsevier. To reduce eutrophication fi sh farmers are obliged to remove nutrients from the wastewater. Farming fi sh in recirculation aquaculture systems where the water is cleaned and reused is one way of reducing the impact of the production on the environment, but these systems are expensive and highly complex. Using seaweed as a biological fi gure is relatively economic—it grows itself, uses light as an energy source, needs no heating, nor other inputs. Th e project to study the potential of algae to remove nutrients from wastewater will be followed by another that will explore the possibilities of valorising the biomass produced. While applications that use seaweed already exist, they are based on algae that do not grow in Estonian waters. Th e new project will focus on species that grow in the Baltic.

Further studies needed for seaweed to be cultivated in the sea

Another innovative project that Dr Martin is involved in is looking at the potential of marine algae to mitigate the impact of marine fi sh farms. Here the technical issue of how to cultivate the algae in open water is being explored, whether on ropes or on other substrates, and methods to seed the substrate or attach the algae to the ropes are being developed. Once solutions have been identifi ed the seaweed could be grown in the vicinity of fi sh farm cages where it would take up the nutrients released by the fi sh farming operations. Macroalgae (seaweed) take up nutrients from the water in which they grow and by cultivating and harvesting the seaweed these nutrients are removed from the marine environment. According to the Danish Centre for Environment and Energy at Aarhus University, since nutrients are removed directly from the water irrespective of their source, cultivating seaweed can be considered a general method for removing nutrients from the water surrounding a seaweed farm as opposed to a fi lter that absorbs the nutrients from a specifi c source. Th e costs associated with the removal of the nutrients (calculated per kilo of nitrogen and phosphorus removed) can be reduced by removing the maximum quantity of nutrients per unit area of seaweed or by minimising the costs, for example, of labour. However, in Denmark the costs of cultivating seaweed exceed the revenues and paying for ecosystem services would be necessary for economic viability.

Ceramium tenuicorne is interesting for researchers because, unlike F. lumbricalis, its structure allows the red pigment to be extracted at analytical grade with existing technologies. Here, the algae magnifi ed 100 times.

Farming macroalgae has positive and negative impacts

Cultivating seaweed has positive eff ects on ecosystem services, but also a few negative ones. Since seaweed competes with phytoplankton for nutrients in the water, the presence of seaweed may reduce local concentrations of phytoplankton improving visibility in the water and allowing more light to reach benthic vegetation. Forests of macroalgae are sources of food, habitation, and nursery areas for other marine organisms augmenting biodiversity. Autotrophic seaweeds (living from photosynthesis) absorb carbon dioxide which is stored in the biomass. In Denmark, studies of sugar kelp (Laminaria saccharina) show that the carbon amounts to about a third of the dry weight, so growing seaweed can contribute to mitigating global warming. Seaweed has an impact on surface currents, slowing or redirecting them which may contribute to coastal protection, on the other hand this may also result in increased sedimentation. Other negative impacts such as a local reduction in light penetration, increased sedimentation of particulate organic matter (due to slower currents and from the seaweed itself), as well as the potential spread of alien species, parasites or diseases that incubate in the farmed seaweed and then extend further are factors that must be considered by conducting site-specifi c evaluations. Further potential disbenefi ts of seaweed farming include infrastructure that may be unsightly or that can confl ict with fi shers and aquasport practitioners, and broken or damaged structures from the cultivation may get deposited on the coast or pollute the water.

Th e projects carried out by the Estonian Marine Institute in collaboration with the private sector and with support from the Ministry of Agriculture are throwing light on ways to exploit marine macroalgae for the benefi t of industry and the environment. Th e research should lead to the solutions that are sorely needed to improve conditions in the Baltic Sea.