From the Dutch Caribbean Nature Alliance (DCNA) on Wednesday 20 November 2013:
Coral reefs around the world are naturally surrounded by nutrient depleted waters. One might suspect a lack of nutrients would prohibit their growth; however, coral reefs are amongst the most biodiversity-rich marine ecosystems in the world. Charles Darwin observed this during his voyage on the Beagle in the 19th century, but only now has that phenomenon, aptly called ‘Darwin’s Paradox’, been explained.
A team of researchers has recently looked into the role of sponges on the coral reefs around Curaçao and found some surprising results. By recycling vast amounts of organic matter, it is the sponges that keep the reef alive. Bacteria have the reputation to be ‘nature’s recyclers’, but on coral reefs they are not abundant enough to serve as the recyclers of the whole reef community. Sponges were found to be bigger recyclers than bacteria and to produce nearly as many nutrients as all the primary producers, corals and algae, in a tropical reef combined.
By feeding the sponges isotope-labelled sugars, and by tracing these molecules on their journey, they found that the sugars were quickly shed to the seabed in dead cells (detritus). Within two days, the same molecules were present in snails and other lower organisms that feed on the sediment containing dead sponge cells. These organisms are in turn eaten by larger animals, and so the cycle continues.
Apart from the speed, it was the sheer volume of food turnover which took the researchers by surprise; nearly tenfold the amount that is recycled by bacteria. To illustrate this, the sponge Halisarca caerulea takes up two-thirds of its body weight in dissolved organic matter every day, but barely grows in size because old cells are continuously shed to the seabed.
Recognising this newly discovered role of sponges for these threatened and fragile ecosystems will hopefully aid coral reef conservation efforts worldwide.
Read the entire article in BioNews.
Three shipwrecks were removed from coral reefs in the Pacific. How long will it take the reefs to recover? Here.
- Sponges solve coral reef mystery (bbc.co.uk)
- Nutrient Recycling by Sponges Is Key Element in Sustaining Reefs, Study Says (e360.yale.edu)
- Conserving potential coral reef refuges at high latitudes (news-oceanacidification-icc.org)
- Exploring Individual- to Population-Level Impacts of Disease on Coral Reef Sponges: Using Spatial Analysis to Assess the Fate, Dynamics, and Transmission of Aplysina Red Band Syndrome (ARBS) (plosone.org)
- Saving Curaçao coral reefs (plunderfortheplanet.wordpress.com)
- Can corals adapt to climate change? (earthsky.org)
- Ecology of Caribbean Sponges: Are Top-Down or Bottom-Up Processes More Important? (plosone.org)