Seagrass meadows are crucial for maintaining healthy coastal environments, yet they are declining globally at an alarming rate. Traditional conservation efforts focus on reducing environmental stressors, but their limited success highlights the need for innovative approaches that do not look at the plants as single entities but acknowledge the role of key symbiotic interactions. One example is the symbiosis between seagrass, lucinid clams and their sulphur-oxidizing bacteria (SOB), which has been shown to enhance seagrass health by mitigating sulphide stress and increasing nutrient availability through nitrogen fixation. However, this symbiosis is absent in seas above 53°N, like Wadden and Baltic Seas. Cable bacteria (CB) are centimetre-long, filamentous bacteria, capable of long-distance electron transfer, coupling sulphide oxidation in anoxic sediments with oxygen reduction. These bacteria have recently been found in the seagrass rhizosphere, suggesting they could serve as an alternative symbiotic system, protecting seagrasses in northern regions. Despite reports linking CB presence with reduced sulphide levels, little is known about the mechanisms and potential benefits of this interaction for the plant. 

• The Symbio-CB-Seagrass project aims to investigate the CB-seagrass interaction across spatial and temporal micro- and macro-scales.
• Through a series of laboratory experiments, I will test whether CB positively impact seagrass fitness by reducing sulphide stress and by enhancing nutrient availability through nitrogen fixation. Field surveys and publicly available data will be used to assess the geographical distribution of these symbiotic systems and whether CB can serve as beneficial symbionts for seagrasses in northern European waters, analogous to the lucinid clams in southern European seas.
• This study will deepen our understanding of the beneficial seagrass microbiome and stimulate the development of innovative solutions in seagrass protection and restoration.