Little clams play big part in keeping seagrass ecosystems healthy, new study finds

 A recent study in the journal Science suggests it’s the small things that matter – in this case, clams. The study found that clams living within sea grass beds consume toxic sulphides that accumulate in the silt, thus helping to maintaining a healthy environment.  The study, a collaboration between a University of Florida researcher and a team of Netherland scientists, appears in the June 15 edition of the journal Science. “Seagrass meadows are buffers against pollution and erosion that can damage the coast,” said Brian Silliman, the UF associate professor of biology who co-authored the study. “They also serve as nurseries for a variety of important fishery species and support healthy coral reef communities by absorbing nutrients and reducing turbidity.” Seagrass beds are a vastly undervalued habitat.  They buffer the coasts from wave action, provide spawning and nursery sites for myriads of fish species and provide grazing for many species that are highly adapted to live within these ecosystems.  They also trap debris which decomposes producing marine humus.  Sulphides ought to build up in these layers, but in most they don’t and this has set researchers wondering if clams are responsible. Silliman and his team suspected that clams belonging to the Lucinidae lineage might be playing a role. Lucinid clams are known to host bacteria in their gills that oxidize sulphides in the water and convert it to energy that sustains the mollusc. The team tested their theory in laboratories at the University of Groningen in the Netherlands. They grew containers of seagrass in aquariums and monitored the rise in sulphide levels as leaves of grass died and accumulated in the tank. The researchers then introduced clams into half of the containers and noted that sulphide levels began to drop relative to tanks without clams. Satisfied with the results of their experiment, the team began to look for hard evidence that what they saw in the lab was representative of what happens in nature. They analyzed data from 84 studies describing fauna of seagrass beds in 83 sites around the world and found Lucinid clams in 97 percent of the tropical systems. “Finding the clams in 97 percent of the tropical sites shows that this is a globally important interaction that supports the foundation of seagrasses,” Silliman said. The researchers calculated that at least 40 percent of the variation in grass growth across expansive meadows of seagrasses could be directly attributed to the abundance of Lucinid clams. The study is an important one because it clearly shows that preserving natural interactions between species is vital to success when seagrass beds or other habitats are being restored, said Tjisse van der Heide, the study’s lead author from the University of Groningen in the Netherlands. Making sure the little clams are present when new seagrass is planted could give a new meadow a big advantage, he said.