In the In Depth section of the March newsletter we interviewed the jellyfish expert and oceanographer Ainara Ballesteros, who is in the final phase of her PhD at the ICM.
Today we interview Ainara Ballesteros, PhD student at the Institut de Ciències del Mar (ICM-CSIC) and an expert in jellyfish. Ainara is in the final stage of her PhD, which she has carried out in the framework of an industrial project in partnership with the pharmaceutical company ISDIN. She landed at the Institut in 2017 to carry out her Master's Thesis, thanks to which she had the opportunity to know in depth the Aquaria and Experimental Chambers (ZAE) of the ICM-CSIC and to specialize in the culture of jellyfish and their stinging cells, the cnidocytes. Today, the researcher will talk to us about her research and, more specifically, about a prototype of aquariums for the raising of the first stages of the life cycle of jellyfish that she has developed together with her group. This is something certainly innovative, as it has allowed them to cultivate jellyfish from the early stages of life in open system, that is, in water tanks where water renewal occurs automatically, thus favoring the growth of these invertebrates and reducing the maintenance time of the cultures.
How did the idea of introducing this improvement in aquariums for jellyfish culture arise?
In our research group we have been cultivating jellyfish for many years, both for research and for the development of industrial applications. Currently, we are working with the jellyfish Pelagia noctiluca, the most important jellyfish in the Mediterranean considering the severity of its sting and its abundance. The life cycle of this species has a peculiarity: it lacks the polyp phase, which means that the males and females expel the oocytes and sperm into the aquatic environment and, after fertilization and the metamorphosis process, the ephyra, that is, the small jellyfish, are generated directly. The first stages of the cycle are the most complex to maintain in culture, so we generally work in tanks with manual water changes to keep the individuals under control. However, this system requires a lot of maintenance, so we decided to work on an aquarium prototype that would allow us to cultivate jellyfish in open system.
How do you manage to work with something so small?
Since ephyrae are so small and delicate, they are usually grown in jars or glass balls with continuous water changes. Proper maintenance involves daily water changes and cleaning the receptables to prevent the accumulation of organic matter from the food. These maintenance tasks are based on the removal of the small ephyrae one by one, for which a lot of time is required, since in a five-liter jar there can be more than 300 ephyrae. In addition, in the case of the Pelagia noctiluca species, the ephyrae are, during the first two weeks of life, transparent, which makes their capture even more difficult and requires the use of flashlights and a black background to be able to see them.
What is the main danger of open system?
Before introducing the improvement, it was much safer to work with containers such as jars and to renew the water manually, because if we moved the ephyrae to conventional kreisels -the rounded aquariums typically used for jellyfish breeding- to work in open system, in which water renewal is automatic, the suction of the drain dragged them to the mesh net and they were trapped. This caused us to lose individuals daily, and there was the danger that, as the net became clogged with individuals, the system would not drain properly and the tank would end up overflowing.
What are the advantages of open system?
Working in an open system makes cultivation easier. The inflow and outflow of water allows us to feed the jellyfish more frequently. In addition, it reduces the amount of organic matter deposited on the bottom and, with this, its decomposition, which can end up affecting the quality of the water. This is important because jellyfish may eat many times a day, but the water parameters must remain stable. The open system reduces the time we used to spend on continuous water changes to maintain water quality. In fact, we used to do daily or every three days cleaning routines, while now we clean the systems deeply once a week or every 10 days.
Which modifications have allowed you to grow the jellyfish in open system?
We have made structural changes to the kreisels. Specifically, we have introduced an air inlet and added a long, narrow mesh net. In this way, the bubble runs through the entire net and expels the ephyrae back into the tank, preventing them from being retained in the net. In addition, this mesh net is interchangeable, which allows us to clean the system more easily and to change the size of the net according to the growth of the jellyfish, which is faster during the first weeks of life in the same aquarium. This allows us to add larger prey, while facilitating the outflow of water with organic matter.
Could this improvement be used in the growing of other species?
Yes, we have tested it with Rhizostoma pulmo, Phyllorhiza punctata and Aurelia aurita species. In addition, we have conducted experiments with snail and crab larvae, which has allowed us to see that, in general, the improvement works for any planktonic species, which are those that live suspended in the water column. Finally, we have been able to see that the enhancement is also effective for the culture of Pelagia noctiluca eggs and planulae, which also need to be kept suspended in the water column. In fact, these eggs metamorphose directly in the tanks, so during the experiments we avoided once again transferring the new ephyrae to other aquaria.
What is the use of jellyfish culture?
It is useful for both basic and applied research. Thanks to the existence of the Experimental Aquarium Zone of the ICM-CSIC, in our group, whenever we have needed to do research with jellyfish because the experiment required it, we have been able to culture them. We have also been able to supply individuals to aquariums and even companies. Jellyfish have a great biotechnological potential, since they provide services and natural products of great interest for numerous applications, as is the case of collagen. Therefore, advances in the field of jellyfish aquaculture such as our improvement of aquariums or others related to feeding regimes or cycle closure have a lot of potential. It is a field in full development, this is just the beginning.
How does climate change affect jellyfish in the sea?
The increase in sea temperature due to climate change has an impact on the size, abundance and frequency of blooms or jellyfish proliferations, which are increasingly recurrent. To some extent, the increase in temperature accelerates the metabolism and favors the reproduction of these individuals. But it is not only climate change, there are also other factors of anthropogenic origin that are affecting jellyfish proliferations, such as overfishing or the construction of breakwaters or ports, which offer new places for the settlement of polyps, the benthic phase - which is in contact with the seabed - of the life cycle of jellyfish.
What are the advantages of being able to cultivate jellyfish in the laboratory?
Wild jellyfish are an unpredictable resource for the industry, since the life cycles of most species are seasonality, that is, adult individuals are not always available for capture at sea. In addition, sometimes, environmental conditions can make it difficult to catch them, so you may need them at a given time and not be able to get them. Therefore, being able to breed them in captivity allows us to have a permanent stock. Furthermore, in research, working with cultures allows us to observe every detail. Thanks to this, for example, we have been able to describe for the first time the cnidome -a set of stinging cells throughout the life cycle- of the Pelagia noctiluca species. For things like these, aquaculture is a fundamental tool in basic and applied research.