Posidonia oceanica as a Source of Chromophoric Dissolved Organic Matter for the Oligotrophic NW Mediterranean Coast

Abstract

Posidonia oceanica is a well-recognized source of dissolved organic matter (DOM) derived from exudation and leaching of seagrass leaves, but little is known about its impact on the chromophoric fraction of DOM (CDOM). In this study, we monitored for two years the optical properties of CDOM in two contrasting sites in the Mallorca Coast (Balearic Islands). One site was a rocky shore free of seagrass meadows, and the second site was characterized by the accumulation of non-living seagrass material in the form of banquettes. On average, the integrated color over the 250–600 nm range was almost 6-fold higher in the beach compared with the rocky shore. Furthermore, the shapes of the CDOM spectra in the two sites were also different. A short incubation experiment suggested that the spectral differences were due to leaching from P. oceanica leaf decomposition. Furthermore, occasionally the spectra of P. oceanica was distorted by a marked absorption increase at wavelength < 265 nm, presumably related to the release of hydrogen sulfide (HS−) associated with the anaerobic decomposition of seagrass leaves within the banquettes. Our results provide the first evidence that P. oceanica is a source of CDOM to the surrounding waters.

Towards Sustainable Management of Beach-Cast Seagrass in Mediterranean Coastal Areas

“…Importantly, in sensitive areas (e.g., protection zones for fish, sea turtles, or other biological resources, and areas subjected to coastal erosion), the seagrass banquettes should not be removed and their possible uses within the beach system (temporary displacement, creating beach walkways, dune consolidation) can be favored after considering the benefits derived for the beach-dune ecosystem. On the other hand, the uses for beach cast outside the beach system (agricultural and farm solutions [35,36], compost, and bedding [37]) should be considered as possible alternative solutions for a circular economy [38][39][40][41][42], especially in cases of consistent biomass deposits along the shores.…”