Three way symbiosis all at sea reported in ScienceNOW 14 June 2012 and Science vol. 336 pp.1432-1434 DOI: 10.1126/science.1219973. Seagrass meadows are important habitats for juvenile fish and grazing marine mammals. Seagrasses are not seaweed. They have leaves and roots like grasses that grow on land, but they grow at the bottom of shallow seas. They are believed to have evolved from land grasses 100 million years ago, but “their ecological success, however, remains a mystery because natural organic matter accumulation within sea beds should result in toxic sediment sulphide levels”.

Tjisse van der Heide of University of Groningen, Netherlands, and colleagues noticed large numbers of bivalves, (molluscs with two shells) living amongst seagrasses and wondered if the bivalves were helping to maintain the grasses, because bivalves have bacteria living in their gills that break down sulphides. They carried out of survey of 83 seagrass meadows around the world to discover if they also had such bivalves. They found bivalves living in 97 percent of the tropical seagrass meadows and 56 percent of temperate meadows. This fitted their theory that bivalves helped seagrasses thrive as sulphide levels are higher in tropic waters.

The researchers then grew seagrasses in the laboratory and compared the health of the grasses at different levels of sulphides, with and without bivalves. The seagrasses with bivalves living amongst them grew almost twice as much as those without bivalves. Furthermore, bivalves were healthier and more robust when they lived amongst seagrasses. The researchers measured the sulphides and oxygen levels of their simulated environments and concluded the bivalves with the sulphide digesting bacteria were helping the seagrasses thrive, and the seagrasses were producing oxygen which helped the bivalves thrive. Thus the bacteria, bivalves and grasses form a three-way symbiosis.

Marine biologist Emmett Duffy of the Virginia Institute of Marine Science in Gloucester Point claimed this could be a form of co-evolution that explains how seagrasses evolved from land grasses. He suggested bivalves could have enabled land-based grasses to invade shallow oceans without being poisoned by sulphides and commented: “The benefit of the bacteria to the bivalves and the bivalves to the seagrasses provides a very plausible explanation for how both the seagrasses and the bivalves radiated evolutionarily and increased in range over a short time”.

Editorial Comment: This is not the first three-way symbiotic relationship to be found, and we predict that it won’t be the last to be discovered. The more research we do into the way plants, animals and microbes live together we find that symbiosis and mutual support are the norm, not the exception. However, three way symbiosis is little understated. If you ask what conditions you need for such a system to function, it is so easy to miss the obvious. How about we add to the list: water, a planet with the right temperature, just the right gravity, etc., etc. Such effective three-way symbiosis between bacteria, bivalves and seagrass is exactly what you would expect to find given God created microbes, plants and animals in fully functioning ecosystems in real short time, i.e. a matter of days.

Also, note that such research does provide a very plausible explanation as to why seagrasses and bivalves grow well together, but it does not explain how they evolved from other kinds of living things. (Ref. marine biology, shellfish, ecology, prediction)

Evidence News 1 August 2012