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Coral reefs are productive and important ecosystems for marine life and people around the world. All reefs contain a broad spectrum of sheltered and wave exposed habitats, which in their turn influence the many species of reef living animals and plants. Herbivorous fishes, that graze down algae and are essential for maintaining productive and healthy coral reefs and ecosystem services, are no exception.

This aspect of coral reef ecology was recently analysed by Sonia Bejarano from the Leibniz Centre for Tropical Marine Research in Bremen, Germany and GEDB researcher Jean-Baptiste Jouffray. Their work, which also included contributions from colleagues from Australia, Germany, Oman, UK and USA was recently published in the journal Functional Ecology.

Their study was conducted in the eastern barrier reef of the Palau archipelago and investigated how differences in wave exposure influence herbivorous fishes, which have effects on the whole reef’s functioning.

The results showed that the feeding capacity of certain species was limited under high wave exposure, but also that others were either unaffected or increased their feeding frequencies under the same conditions. Streamlined herbivorous fish species seemed to be better at eating under strong swell compared to laterally-compressed fishes.

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“It is surprising how widespread the notion is that two species that have similar functions can replace each other fully, if one of them disappears,” says lead author Sonia Bejarano.

Knowledge important beyond coral reefs

The team of researchers also learned three things that are useful beyond the world of coral reefs and fishes. First, animals that do different jobs in an ecosystem also tend to be different in the way they cope with environmental stress, making them even more complementary than people usually think. Second, animals that do similar jobs in an ecosystem may also respond in subtly differently ways to environmental stress thus ensuring that the job gets done across a broad range of environmental conditions (something that is called response diversity). Third and last, some species go and others come as environmental stress increases, but because of this response diversity, vital ecosystem functions can be preserved even under harsh conditions.

"The results of the study challenge the way biodiversity is often perceived and confirm that species presence does not imply their complete functionality, especially under harsh environmental conditions," says Jean-Baptiste Jouffray.

Next step is to assess whether applies also to man-made environmental stresses and to what extent human impacts cab disrupt the resilience provided by response diversity in coral reefs and other ecosystems.

With coral reefs being increasingly stressed by global human-made stresses like climate change and ocean acidification, this kind of knowledge is more important than ever before to inform local and regional management efforts to strengthen reef resilience.

Read more and methodology

Bejarano, S., Jouffray, J.-B., Chollett, I., Allen, R., Roff, G., Marshell, A., Steneck, R., Ferse, S. C. A. and Mumby, P. J. 2017. The shape of success in a turbulent world: wave exposure filtering of coral reef herbivory.. Functional Ecology 31, 1312–1324