The temperate seagrass species Cymodocea nodosa and the associated bacteria co-response to sunscreen pollution

Abstract

Sunscreens are included among the contaminants of emerging concern (CECs) as their production and use have spread over years while damaging aquatic biota. Sunscreens can damage the photosynthetic systems and change the microbiome of seagrasses, triggering alterations in carbon metabolism –including primary production and dissolved organic carbon (DOC) fluxes– and ecological functions. Here, we conducted a 31-day mesocosm experiment exposing Cymodocea nodosa plants to a mixture of commercial sunscreens. Sunscreens produced a significant reduction on net production rates, switching the system from autotrophic to heterotrophic, which was ascribable to an increase in heterotrophic bacteria families (some known to degrade complex substrates) and, more importantly, to a significant reduction of photosynthetic pigments in plants. Moreover, a significant release of DOC at night attributed to exudation from disrupted roots was recorded, which accounted for the observed increase in bacteria abundance and family richness recorded in the phyllosphere. A higher accumulation of starch in rhizomes suggests a certain degree of resistance of this species. However, we observed a trend to reduce some protective bacteria taxa, whereas promoted the growth of other pathogenic ones for seagrasses, along with other taxa related with the consumption of plant-derived polysaccharides and lignin compounds. Therefore, our results indicated that this CEC may reduce the contribution of seagrasses to the blue carbon pool, among others ecosystem services, and suggest a possible prompt of seagrass diseases if stressing conditions are maintained over time.