Posted by: oikosasa | May 16, 2014

Who eats the sea urchin?

Different factors that effect predation in marine habitats are explored in the Early View paper Differences in predator composition alter the direction of structure-mediated predation risk in macrophyte communities by Simone Farina and co-worker’s. Below is Simone’s short summary of the study as well as a reflection on the history that lead to the study.


Using sea urchins as model prey we examined the role of structural complexity in mediating predator-prey interactions across three bioregions: Western Mediterranean Sea, Eastern Indian Oceanand Northern Gulf of Mexico. As expected biomass of the habitat structure and fish predator abundance were the main determinants of predation intensity. Interestingly though, the direction of structure-mediated effects on predation risk was markedly different between habitats and bioregions. In Spain and Florida, where predation by fish was high, structure served as critical prey refuge, particularly for juvenile sea urchins. In contrast in Western Australia predation was generally higher inside the structure where bottom predators were more abundant.

Gallery 1: Meditarrenean Sea

In this sense, as a Mediterranean student I will never forget the days of field work in WA. We had to look for Heliocidaris erythrogramma, the Australian model prey, the equivalent of Paracentrotus lividus in the Mediterranean Sea, and it was like looking for sparrows in the Amazon rainforest. Kelp was full of huge gastropods. Every time I moved a few shoots I had the impression of seeing any kind of tail run away quickly. It was very easy to get distracted from my search. One time we found a huge Coscinasterias calamaria (sea star) remained attached to a fishing line used to mark one of the sea urchins after having swallowed it entire. In seagrass ecosystems (Amphibolis griffithii and Posidonia sinuosa) we observed many little and coloured sea stars (Patiriella brevispina) approaching day by day to our sea urchins and finish them one after the other. In Australian seagrass ecosystems, working to head down supposed some time to have a look around to check for unexpected arrivals of huge sting ray, as ufos flying over a landscape. Macrophyte communities that we explored in Australia are totally different from the Mediterranean ones, so it does not surprise me that structures works in different ways. It was a really pleasure to carry out this experience and I think I’ll have a good story to tell my grandchildren.

Gallery 2: Australia

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