Welcome to the inaugural edition of our EuroMarine Researchers in the Spotlight series, where we engage in captivating conversations with prominent researchers within our network.

We had the opportunity to interview Daniel Martin, a Scientific Researcher of CSIC in the Marine Ecology Department of the CEAB, working in the Research Group “Molecular Ecology of the Marine Benthos”. His research focuses especially on the study of inter-specific interactions involving Polychaetes, such as symbiosis. In this interview, we talked to him about his research studying the behaviour of this group of marine worms and how they can serve as indicators for Ecosystem Health and Climate change.


Daniel started his career with a Doctorate in Biological Sciences (Ecology) from the Universitat de Barcelona. Today he works as a Scientific Researcher of CSIC in the Marine Ecology Department of the CEAB. With expertise in taxonomy, ecology and biology of marine benthic invertebrates, his research focuses especially on the study of inter-specific interactions involving Polychaetes (e.g. symbiosis).

He has been Vice-director of the CEAB from 2001 to 2002 and director from 2003 to 2014. His CV includes more than 160 scientific papers and collaborations in more than 52 research projects. He edited two books, one on Polychaeta and the other one on deep-water submarine canyons. He also belongs to the editorial committee of Scientia Marina and Invertebrate Zoology and is Review Editor for Annelida in the section Marine Systematics and Taxonomy of Frontiers in Marine Science and Section Editor for the Bulletin of Marine Sciences. Last but not least, he is is also a member of the International Polychaete Association, The International Society for Invertebrate Morphology and the Systematics Association of UK, and Professional Member of the Marine Biology Association of UK.

EuroMarine: Could you briefly explain your current position within CSIC and the CEAB? What initially sparked your interest in marine research, and how did you embark on this career path?

I have had a position in the public research system of Spain since in 1992, so for quite a long time. In recent years, I have been moving and progressing to my actual position as Research Scientist.

I started working on marine research because during my university career I decided to start a diving course and then I fell in love with marine creatures and with marine life. But my dedication to polychaetes was just a matter of chance. Being a student, I went to the Department of Invertebrates in the university and I said, well, I'm here and I would like to do something. Then, they told me: “There are some samples of little worms waiting for somebody to study them; there is only one other person doing this kind of studies here, and it will be nice if you can help him”. So I started with this, and I was getting in love with polychaetes to the extreme that I have been working with them since then.

EuroMarine: What are your primary research interests and areas of focus within marine sciences?

First of all, polychaetes, for those non-familiar with taxonomic words, is a group of marine worms that are close relatives of earth worms. Like them they are, let's say, a series of rings joined in some way, with an anterior end containing the head and a posterior end containing the annus. They have many, many different forms, colors, and life strategies, and they play really a very important roles in the marine ecosystems. For example, they serve as food for many other organisms, like fish, crabs or birds. They interact among them and with other organisms in many different ways, being predators, filter feeders, deposit feeders.

Virtually all possible feeding strategies are present in this group and they occur in almost all types of marine environments. This makes this group very particular because, as we know their life strategies, if we are able to know which species inhabit a given ecosystem, we can use them as indicators of its heath status. Having a list of the species of polychaetes, we can know if an ecosystem has been polluted or if it is pristine, and how it can evolve through time. Most of my research thus addresses knowing how the ecosystems are based on their polychaete inhabitants.

However there is second more attractive part, at least for me, which is finding animals that have not been found by any other people to describe them and show their existence to the world. That is the basic idea leading the taxonomic work and so I am basically a taxonomist. One of my main tasks is to describe species new to science, illustrating them to show the morphological characters that allow them to be distinguished from any previous lifeform, which are now complemented molecular tools.

Finally, there is a third part that focus on studying interactions. I am particularly interested in studying the polychaetes that are living in symbiosis with other organisms, no matter what. They could be sponges, crabs, starfish, other polychaetes, etc. Knowing these interactions and the species that live in these way is certainly one of my passions in science.

The size range of polychaetes is incredible wide. You can find species so tiny that may be less than one millimeter in length, while some can be three meters in length, but most of them are between one and fifteen centimeters. They can be found in the in any ocean, even when the conditions of the ecosystem are too hard. For instance, they can still be found wen there is almost no oxygen. They inhabit the shallowest bottoms until thousands of meters deep, on rocky bottoms or inside the sediments, but there are swimming species inhabiting the water column and, interestingly, some species are adapted to live in fresh waters, like rivers or lakes, and a few leave in terrestrial environments, either in wet substrate dot in trees, inside the water reservoirs of saprophytic plants.

EuroMarine: Could you highlight any major findings or breakthroughs that you have achieved in your research? How has your research contributed to advancing knowledge and understanding in your specific field of study?

Well, probably one of the most amazing things I have been doing with polychaetes is to be able to work with symbiotic species alive, to be able to study their behavior. The Mediterranean is not specially rich in these kind of associations. Thus, I have been forced to move to other seas with more tropical conditions like the China Sea facing Vietnam, where in collaboration with a Russian colleague that has working there for a long time, we succeeded in making fantastic experiments to see how these animals interact among them.

One of the most interesting discovering dealing with the Vietnamese symbiotic polychaete was its very complex and aggressive territorial behavior shown when defending its host against the intrusion of other polychaetes of the same species. This particular species have very strong jaws, which it uses to really bite each other. The attacks can be so strong that one of the embattled specimens may even be divided into two parts. This may appear as an extreme behavior, we you must take into account that these animals are able to fragment themselves naturally as a defense. For instance, they can separate the posterior part of their body if they feel they are attacked. This posterior part moves fast to attract the possible predator, while the anterior end is able to survive and then regenerate again the posterior end. These complex biological and behavioral interactions resulting in highly specific life strategies are precisely what allow them to live in symbiosis.

Our most recent discovery has been the finding of some species of polychaetes living in anchialine caves (underground cavities that are separated from the sea by several hundreds of meters, but contain seawater reservoirs covered by an upper layer of fresh water). There are some organisms specifically adapted to these conditions, with the most well-known being usually crustaceans, but we have been able to find polychaetes living in this extreme environment, two of them being new species. We are really lucky as we have just started a four-year project to study these troglobiont (i.e., cave inhabitant) organisms in the complex network of caves existing tin the Balearic Islands, in cooperation with scientists from the Universitat de les Illes Balears and other international research institutions.

EuroMarine: What are the priority areas for marine research that could have a significant impact on policy development and sustainable marine management? How can EuroMarine engage with policymakers and stakeholders to ensure that scientific findings are effectively communicated and utilized in decision-making processes?

Certainly, there are priority areas in marine research that could significantly impact policy development and sustainable marine management. One of them is the study of benthic organisms (i.e., the species living at the sea bottom), including polychaetes. Benthic organisms are highly responsive to environmental conditions, not only present conditions, but they are also able to reflect past influences on the ecosystem.

When collecting these organisms for study, we are essentially documenting the environmental conditions that have shaped the community over time. By understanding the biology and characteristics of polychaetes and other benthic organisms, we can thus infer past conditions that lead the ecosystem to the present status. This knowledge is widely recognized, and numerous private and public organizations, including governments, use it to assess the environmental health status.

Private companies may use these organisms as indicators when, for example, exploring areas for gas or oil extraction. Usually they collect samples and rely on experts to analyze the organisms to monitor environmental impacts and eventually predict its evolution in time. Similarly, governments employ these organisms to monitor environmental conditions and implement regulations to protect ecosystems.

In Europe, legislation has incorporated findings from such research to develop specific rules, which are subsequently adopted by each European country. Therefore, research in this area plays a vital role in providing valuable tools and insights that directly influence policies and regulations related to marine management and conservation.

EuroMarine: Can polychaetes be an indicator of climate change?

Indeed, polychaetes and other benthic organisms can serve as indicators of climate change, although there have not been numerous studies specifically examining the impact of temperature on polychaete life cycles. However, researchers have developed a deep understanding of the environments these organisms inhabit. Therefore, when studying specific communities, scientists can predict what species should be present based on historical data or they can also infer which changes may contribute to explain why some species have disappeared or have recently apeared.

Discovering species that were not previously found in a given area, raises questions about their origin and survival. Recent findings indicate an increase of introduced species that are able to survive thanks to the changing conditions. This is particularly relevant in small closed seas like the Mediterranean, where sea temperatures have risen by one or two degrees, allowing the presence of species with tropical affinities whose permanence suggests a sustained change in the ecosystem.

These species are often Introduced via ballast water or through the exchange of small individuals that is habitual shellfish in aquaculture (such as oysters or mussels). Once introduced, if these species find suitable conditions due to changing environmental factors like temperature, they can expand and even become invasive, posing a significant challenge to local ecosystems.

EuroMarine: You mentioned that symbiotic polychaetes are hard to find in the Mediterranean. What are some of the main challenges or obstacles you have encountered in your research, and how have you addressed them?

My primary focus is on taxonomy, particularly discovering and describing new species. This usually requires exploring areas where finding unknown species could be relatively easier. The Mediterranean, while previously and extensively explored, still presents opportunities, but it can be challenging as you need to venture into specific, often difficult-to-reach ecosystems to find these new species.

On the other hand, tropical areas or less-explored regions can yield unknown species more readily, but accessing these places is not always straightforward. To address these challenges, collaboration is key. There is a global network of scientists working on polychaetes, covering various aspects, including taxonomy. When someone encounters specific problems or needs expertise in a particular area, one can connect with specialists through this network, to establish effective collaborations.

A recent example my ongoing collaboration with a Japanese and a Russian scientists to work in the description of an unknown species. I realized that we had specimens of the same species after the Japanese researcher sent a picture to the network, we from Vietnam and he from Japan. This initiated our collaboration, and we are now in the process of describing this species, which not only appears to be new to science but potentially a new genus of polychaete. What's particularly fascinating about this species is its mimicry strategy.

Symbiotic species may have two mimicry strategies: some mimic their host, attempting to blend in, while others adopt a pale coloring to remain hidden within the host's tubes or galleries. This new species, contrary, employs a unique strategy. It exhibits striking colors – yellow, withe, and blue – and mimics a type of mollusk known as a nudibranch, which also inhabits the same environment. Nudibranchs consume their hosts and accumulate urticant cells from them in their appendages so that they are protected. Their sticking coloring is an indication to potential predators that it would not be a good idea to try to feed on them.

By mimicking the nudibranch body shape and coloring, this new species of polychaete gains protection against predation even if it does not accumulate urticant cells in their appendages and, thus, feeding on it could not harm any predator. This complex mimicry situation is a fascinating discovery, and as far as I know, it is the first such case described among polychaetes.

EuroMarine: What are your future research plans and directions? Are there any specific goals or projects you are currently working on or planning to pursue?

Among others, I am currently engaged in two exciting research projects. One of them deals with the anchialine caves of the Balearic Islands. As I have already explained, we have been fortunate to make intriguing discoveries even before the official project commencement, and we have now the next four years to explore the Balearic cave system.

Two initial dives into only one cave yielded the remarkable finding of three different species of polychaetes. These include a new genus and species, a new species, and one that seems not to be new, but is intriguingly present in a cave isolated from the sea and also in marine caves with wide connections with the open sea. I anticipate that, as we explore more caves in the Balearic Islands, we will uncover even more fascinating insights. The Balearic Islands resemble Swiss cheese, riddled with holes, so the exploration promises to be truly captivating.

The second project, led by two chemical researchers of the Universitat de les Illes Balears, has a focus on the potential use of artificial structures as regeneration systems for marine environments, with an emphasis on sponges and polychaetes. Both these groups of organisms are exceptional filter feeders. Our concept involves deploying artificial structures in areas with polluted waters, facilitating the growth of sponges and polychaetes. Subsequently, we aim to study the impact of these organisms on the water quality in the vicinity of these structures. This project is highly interdisciplinary and promises to yield intriguing results, so I am excited to see where it leads.

EuroMarine: How has being a member of EuroMarine network supported your research and career development?

Being a member of the EuroMarine network has been incredibly valuable for my research and career development. Firstly, it has provided me with access to a forum of researchers who study marine systems from various perspectives.

This has been intellectually stimulating and allowed for the exchange of ideas. I have had the opportunity to engage with experts in different marine science fields, and these interactions have enriched my own research.

On a personal level, being part of EuroMarine has been a source of satisfaction. It is fulfilling to collaborate with scientists with highly diverse backgrounds, all united by their dedication to marine science. The network has fostered a sense of community among researchers who share a passion for the marine environment.

Additionally, I have the privilege of representing my institution, the CSIC, in the EuroMarine General Assembly and serving on the Steering Committee. It has been rewarding to see that I have been able to engage researchers from my institution and that many of them are actively interested in participating in EuroMarine initiatives. Young researchers, in particular, have shown enthusiasm for EuroMarine's activities, such as Foresight Workshps, the Individual Grant Fellowships, more recently, the Collaborative Projects that allow them to lead true research projects.

One of the significant benefits I personally experienced was the opportunity to participate in a Foresight Workshop held in Ravenna, Italy. The outcomes of this workshop were highly satisfactory, resulting in a paper published in a high impact journal and in a well stablished networking that allows to actively seeking funding for a European project related to the workshop's topic. In summary, EuroMarine has provided a platform for collaboration, knowledge exchange, and professional growth. It is akin to being in a dynamic environment where good ideas constantly emerge, having the potential to develop into meaningful projects.

EuroMarine: What advice would you give to early-career researchers who are aspiring to make an impact in marine sciences?

To make a meaningful mark in marine sciences, early-career researchers should immerse themselves in the scientific community, attending conferences and workshops while actively networking with peers. Be present in the spaces where science is being made. Seize opportunities through grants and training programs, such as EuroMarine's OYSTER initiatives. Set ambitious goals and pursue them diligently, even when faced with challenges. The OYSTER Collaborative Projects provide flexibility and innovation, so I strongly advice to consider them. Perseverance is vital, as setbacks are part of the journey. Stay informed about the latest developments, think globally, and embrace international collaborations. With determination, ambition, and engagement, aspiring marine scientists can navigate this dynamic field and contribute significantly to its advancement while building the bases of the required personal and career stability.