Ecosystem Effects

Unlike the bee, parasite and virus, some symbiotic relationships can form positive feedback loops that can fortify the basis of an ecosystem instead of destroying it. A good example of this is the positive feedback loop between seagrass, bivalves and their sulphur oxidizing bacteria. In 2012, de Fouw et al. demonstrated that Lucinidae bivalves play an important role in the health and abundance of seagrass meadows. Seagrasses are an important costal marine ecosystem that provide habitat, food and shelter for a vast array of marine and coastal animals and are natural carbon sinks (Ugarelli et al. 2017).

A turtle eating seagrass (Lindgren 2013)

Seagrasses evolved from terrestrial angiosperms approx. 100 million years ago and mostly rely on the nitrogen fixing bacteria in their rhizosphere to neutralize toxic sulfur buildup from degrading biomass (Ugarelli et al. 2017). However studies have shown that the sulfur oxidizing activity of Lucinidae bivalve symbionts further reduce sulfur build up complimenting seagrass growth and preventing die offs (Ugarelli et al. 2017; Derksen-Hooijberg et al. 2017; Heide et al. 2012). Bi-valves in the family Lucinidae share and obligatory symbiotic mutualism with bacteria in their gills that use sulfur from broken down biomass and oxygen to produce energy for the mollusc and itself (Heide et al. 2012). By living together, the mollusc holobiont receives oxygen and biomass from the seagrass while the bivalve reduces toxic sulfur build up for the seagrass (Heide et al. 2012).

Lucinidae bivalves break down sulfur in exchange for oxygen. This mutualism can be disrupted in certain environments (de Fowe et al. 2016)

Studies have shown that supplementing struggling seagrass ecosystems with Lucinidae bivalves may help improve ecosystem resilience and may be a useful conservation tool (de Fouw et al. 2018; Derksen-Hooijberg et al. 2017). Heide et al. (2012) ran experiments with the seagrass Zostera noltii and the bivalve Loripes lacteus while Derksen-Hooijberg et al. (2017) conducted a similar experiment with a marshland mutualism between cordgrass Spartina alertniflora and the mussel Geukensia demissa. Both studies found that the plants grew better with their facultative mutualists then they did alone and that sulfur levels were reduced. However, De Fowe et al. (2016) found that climate change may break down the mutualism between seagrass and bivalves. It is thought that the importance of sulfur oxidising bacteria in marine ecosystems and nutrient cycles may be an overlooked factor that may help us to conserve marine ecosystems (Burdoff et al. 2017).

For more information on seagrass meadows go here: http://www.oceanhealthindex.org/methodology/components/seagrass-area

Thank you for reading! 😊 Check back next week for more.