Shift in the metabolic profile of sediment microbial communities during seagrass decline

Seagrass meadows are highly productive ecosystems that are considered hotspots for carbon sequestration and microbial activity. In seagrass sediments, microbial communities break down organic matter, facilitating the release and transformation of nutrients that support plant growth and primary production. The decline of seagrass meadows of various species has been documented worldwide, including that of Cymodocea nodosa (Ucria) Ascherson, a widespread seagrass in the Mediterranean Sea. To assess the influence of seagrass decline on the metabolic profile of sediment microbial communities, metaproteomes from two sites, one without vegetation and one with a declining Cymodocea nodosa meadow, were characterised at monthly intervals from July 2017 to October 2018.

Prior to seagrass decline, differences in the metabolic profiles between the vegetated and nonvegetated sediment were found, particularly in the deeper sediment layers. During the decline, these differences diminished as microbial communities in nonvegetated sediments exhibited increased protein richness and diversity, aligning more closely with those at the vegetated site. Notably, temporal variations in the structure of the metabolic profile were only observable in the nonvegetated sediment and were also more pronounced at greater sediment depths. Finally, the assessment of proteins involved in organic matter degradation such as ABC transporters, fermentation-mediating enzymes, and proteins involved in dissimilatory sulphate reduction mirrored these shifts.

Overall, the main results of this study suggest that the presence of seagrass meadows influences the metabolic profile of microbial communities in sediments, highlighting the distinctions between nonvegetated and seagrass-colonised sediments. In particular, the loss of seagrass leads to a shift in the metabolic profile of sediment communities in the surrounding area, while the metabolic profiles of previously colonised sediments appear to be more resilient to seagrass loss.