Corals fuel sponge engine in tropical and deep-sea reefs
In 2013 an international research team, including Jasper de Goeij from the University of Amsterdam's Institute for Biodiversity and Ecosystem Dynamics, found an answer to Darwin's reef paradox: how one of the world’s most diverse ecosystems can thrive in the marine equivalent of a desert. The discovery was a link in the food web between corals and sponges. Recent findings show that this linkage not only exists in tropical, shallow warm-water reefs, but also in deep-sea cold-water reefs.
The recent discoveries were published in the multidisciplinary journal Scientific Reports. The results are particularly important because food and nutrients are very scarce on both warm- and cold-water coral reefs. Coral reefs cover less than 0.1% of the surface of world’s ocean, yet they support over one-quarter of all marine species. The food web link between the two key coral reef organisms thereby supports the functioning of entire reef ecosystems.
Sponges bring life to coral reefs
The team of scientists made this discovery by carrying out a series of parallel experiments at research stations in Jordan at the Red Sea and in Sweden at the North Atlantic. Corals and sponges were collected on Red Sea reefs from 5-10 metre water depth and on an Atlantic reef from water depths of more than 100 metres. Despite the pronounced differences in the two locations, the experimental results were very similar. The researchers found that coral mucus, which is continuously released by corals in large quantities, is rapidly taken up by neighbouring sponges. This is remarkable because the majority of this coral mucus immediately dissolves in the water (in the form of sugars for example) and cannot be taken up by most reef inhabitants. Sponges, however, exhibit the unique ability to transform the energy and nutrients stored in dissolved coral mucus to other reef organisms, by transforming it to particulate pellets. In both shallow and deep-sea reefs, they transformed 20-40 % of the ingested mucus into particulate food. The pathway of transferring dissolved food to other reef organisms was discovered by De Goeij and colleagues in 2013 (published in Science) on the Caribbean reefs of Curaçao. Now, they provide evidence for the sponge loop pathway in the Red Sea and deep-sea.
Alonside Jasper de Goeij, the research was led by Prof. Christian Wild (Marine Ecology, University of Bremen), Dr Malik Naumann (Leibniz Center for Tropical Marine Ecology, ZMT) and Dr Dick van Oevelen (Royal Netherlands Institute for Sea Research, NIOZ). The findings have been published by lead author Dr Laura Rix, who obtained her PhD from University of Bremen, co-supervised by De Goeij.
Rix et al. Coral mucus fuels the sponge loop in warm- and cold-water coral reef ecosystems. Scientific Rep. 5, 18715; doi: 10.1038/srep18715 (2015)