Losing half of tropical fish species as corals disappear

30 06 2021

When snorkelling in a reef, it’s natural to think of coral colonies as a colourful scenography where fish act in a play. But what would happen to the fish if the stage went suddenly empty, as in Peter Brook’s 1971 Midsummer Night’s Dream? Would the fish still be there acting their roles without a backdrop?

This question is not novel in coral-reef science. Ecologists have often compared reef fish diversity and biomass in selected localities before and after severe events of coral mortality. Even a temporary disappearance of corals might have substantial effects on fish communities, sometimes resulting in a local disappearance of more than half of local fish species.

Considering the multiple, complex ways fish interact with — and depend on — corals, this might appear as an obvious outcome. Still, such complexity of interactions makes it difficult to predict how the loss of corals might affect fish diversity in specific contexts, let alone at the global scale.

Focusing on species-specific fish-coral associations reveals an inconsistent picture with local-scale empirical observations. When looking at the fraction of local fish diversity that strictly depends on corals for food and other more generic habitat requirements (such as shelter and reproduction), the global picture suggests that most fish diversity in reef locality might persist in the absence of corals. 

The mismatch between this result and the empirical evidence of a stronger coral dependence suggests the existence of many hidden ecological paths connecting fish to corals, and that those paths might entrap many fish species for which the association to corals is not apparent.

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More species = more resilience

8 01 2014

reef fishWhile still ostensibly ‘on leave’ (side note: Does any scientist really ever take a proper holiday? Perhaps a subject for a future blog post), I cannot resist the temptation to blog about our lab’s latest paper that just came online today. In particular, I am particularly proud of Dr Camille Mellin, lead author of the study and all-round kick-arse quantitative ecologist, who has outdone herself on this one.

Today’s subject is one I’ve touched on before, but to my knowledge, the relationship between ‘diversity’ (simply put, ‘more species’) and ecosystem resilience (i.e., resisting extinction) has never been demonstrated so elegantly. Not only is the study elegant (admission: I am a co-author and therefore my opinion is likely to be biased toward the positive), it demonstrates the biodiversity-stability hypothesis in a natural setting (not experimental) over a range of thousands of kilometres. Finally, there’s an interesting little twist at the end demonstrating yet again that ecology is more complex than rocket science.

Despite a legacy of debate, the so-called diversity-stability hypothesis is now a widely used rule of thumb, and its even implicit in most conservation planning tools (i.e., set aside areas with more species because we assume more is better). Why should ‘more’ be ‘better’? Well, when a lot of species are interacting and competing in an ecosystem, the ‘average’ interactions that any one species experiences are likely to be weaker than in a simpler, less diverse system. When there are a lot of different niches occupied by different species, we also expect different responses to environmental fluctuations among the community, meaning that some species inherently do better than others depending on the specific disturbance. Species-rich systems also tend to have more of what we call ‘functional redundancy‘, meaning that if one species providing an essential ecosystem function (e.g., like predation) goes extinct, there’s another, similar species ready to take its place. Read the rest of this entry »