Trait combination patterns in reef fish communities across the world’s oceans

In the framework of BiodivScen, the 2017-2018 BiodivERsA – Belmont Forum Joint Action on Scenarios of biodiversity and ecosystem services, 21 research projects were selected for funding, based on their scientific excellence, their involvement of relevant stakeholders and their promising societal impact. The REEF-FUTURES project, funded under BiodivScen and developing scenarios of the impacts of the implementation of Marine Protected Areas on coral reefs services, published new results in the Proceedings of National Academy of Sciences review in March 2021.

On the occasion of this release, Matthew McLean, from the University of Dalhousie, first author of the paper, gave a short interview presenting the stakes of these new findings and summarizing their potential for conservation worldwide.

Can you describe the findings presented in this article? What is the novelty of these findings?

We looked at coral reefs and rocky reefs all around the world (89 regions from Norway to Southern Chile) in terms of fish species’ traits (diet, habitats, size, etc.). These traits give us a better idea of the species’ impacts on their ecosystem than just looking at species names or number. We found similar trait compositions of fish communities, even when those ecosystems were on completely opposite sides of the planet, as long as ecosystems had similar environmental conditions (temperature, nutrients, etc.). In Japan and Chile for instance, there was a very similar composition of traits of fish communities even though the species found in these ecosystems were not the same.

This is the first time that anyone looked at the similarity of functional groups and traits that these fish communities have, highlighting a backbone of 21 trait combinations that fish can have that exist all around the world.

What is the meaning of this ‘backbone’ of 21 trait compositions found in reef fish across the globe?

The fish species studied might be large or small, feed on algae or be predators, live close to the bottom or elsewhere in the water column, live in schools or not, etc. We found that there are 21 different combinations of these traits that the fish could have across all oceans. It tells us that there are some core functional groups of fish that exist on reefs worldwide, no matter whether these are coral reefs or rocky reefs, or in tropical or temperate oceans. It is a very important discovery that tells us there is a selective pressure of the environment resulting in similar functional groups, which are present even if these oceans have different habitats (coral vs. rocky) or if the species are from different families.

Why do you think this type of work on functional traits has never been done before in reef ecosystems?

The main limitation could come from the availability of data. We are fortunate to have used the ‘Reef Life Survey’, a global survey of fish communities’ composition that was made on coral reefs and rocky reefs all around the world. This database has been built very thoroughly over the past 10 years, and interestingly it is not limited to coral reefs but also includes data on reefs that are built on rocks in colder ecosystems. We have been able to combine this recently available data with the different traits species have. Similar research has been done on plant communities and mammal communities, but this is the first time such work is conducted on a global scale for reef communities.

What does this discovery imply for reef fish conservation?

Firstly, our results demonstrate that the fish species and their functional traits are predictable, based on the environmental conditions of their ecosystem. So, we can potentially anticipate how ecosystem functioning might change as the environment changes; for instance how climate change will impact or change fish communities all around the world, because we know there is this link.

Secondly, we can potentially use similar reef management and conservation strategies in completely different places, as long as these have similar environmental conditions. This is important because there are a lot of places with coral reefs where funding or capacities for science-based management are limited. So, we might transfer successful conservation strategies effective in certain parts of the world and apply them in other regions, if these have similar environments.

How will these new findings feed the next steps of the REEF-FUTURES project?    

The next steps for REEF-FUTURES are to develop statistical models that measure very precisely the relationship between the fish trait composition and environmental conditions. Building such models will provide the basis to make predictions on how reef ecosystems will change, based on expected changes in environmental conditions, e.g. temperature. We will also develop our understanding of how exactly the trait composition of fish communities impacts ecosystem functions. We know for instance fish that eat algae have a positive effect for the reef because algae is removed and coral grows. However more work is needed to identify the very specific links between the species’ size, diets, habitat preferences or behavior, and coral ecosystem, or how much fish is produced by the ecosystem. Developing this knowledge will allow to make better predictions on how an ecosystem could change if the fish communities change.

In addition, we will identify places where we see healthy reefs that are in a good functional state, and link this healthy status with the composition and functional traits of fish communities in these places and with local conservation strategies. This could allow to take lessons and best practices from these places, and use them as model approaches for management and conservation strategies in places where reefs are not in a good functional state.  

What do you think is the added value of a global approach used in REEF-FUTURES, and more generally of international research programs such as the BiodivERsA and Belmont Forum?     

One of the main advantages of such an international program is that it brings together experts from all around the world, here from Australia to France to the US and Canada. As mentioned before we could access a global database, but without a team of experts familiar with these different regions we couldn’t have conducted such an exercise successfully. We had begun the project with David Mouillot and Sebastien Villéger in Montpellier in France and could then expand our team to include people with the relevant local expertise around the world to develop that study better. Obviously, the global approach makes possible a complete understanding of how coral reefs work around the world.                   

And what is the added value in terms of supporting and involving early career researchers like yourself?

Being involved in REEF-FUTURES is an amazing research opportunity, and really helped advance my career: I am getting to work with people that are really high profile in my field, and I got to expand my network so much working with these top scientists and learned new things from a variety of mentors. It also generated opportunities for me to be part of multiple new projects. In REEF-FUTURES there are several early-career researchers, and having such a good opportunity to be mentored by great scientists and to produce excellent research is really amazing for all of us.

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