Aeolian transport of seagrass (Posidonia oceanica) beach-cast to terrestrial systems

Abstract

The annual export of the Mediterranean seagrass (Posidonia oceanica) litter to adjacent beaches and coastal dunes was quantified by examining the fortnight evolution of seagrass beach-cast volume on two beaches in the NW Mediterranean (Son Real and Es Trenc, Mallorca Island, Spain) for two years and analyzing the wind speed and direction obtained from the closest Meteorological Spanish Agency surface weather stations. The decomposition stage of the deposits was examined by analyzing the total hydrolysable amino acids, its percentage distribution and derived degradation indexes. Prevalent winds exceeding 6 m s-1 , the coastline morphology and type of terrestrial vegetation determine the annual dynamics of the seagrass beach-cast. In the most protected beach (Son Real) the seagrass beach-cast remained nearly stationary during the two studied years while it exhibited wide annual fluctuations in the less protected one (Es Trenc). The amounts of P. oceanica wrack washed on Son Real and Es Trenc beaches, respectively, were estimated at 309 kg DW m coastline-1 yr-1 and 1359 kg DW m coastline-1 yr-1. They supplied between 20 kg CaCO 3 m coastline-1 yr-1 and 47 kg CaCO 3 m coastline-1 yr-1. Between 54% (Son Real) and 70 % (Es Trenc) of seagrass beach-cast, respectively accounting for 1.5 kg N m coastline-1 yr-1 and 8.6 kg N m coastline-1 yr-1 , were annually exported from the beaches to adjacent dune systems. Our results reveal that Mediterranean seagrass meadows might be an important source of materials, including sand and nutrients, for adjacent terrestrial systems, able to support their functioning. KEY WORDS: wrack, detritus, beach-cast, wind rose, weather conditions, Mediterranean Sea, Balearic Islands, coastal systems, dune dynamics, land-sea interface HIGHLIGHTS (3 to 5 bullet points with 85 characters) * The annual evolution of the seagrass beach-cast depends on the beach exposure. * Changes of the seagrass beach-cast are linked to strong wind events. * Winds are the responsible of the mass transport of nutrients to the dunes. * Beach-cast deposits might be an important source of carbonates and nutrients to the coastal dune system.

Seagrasses provide a novel ecosystem service by trapping marine plastics

“…The occurrence of an extraordinary convective rainfall event in Mallorca Island in autumn 2017 44 may had loaded coastal waters with an extra amount of PP pellets (Supplementary Table 2). Drifting floating plastic items were flushed ashore during autumn storms, alongside with seagrass remains from natural massive seasonal leaf loss 45 . Interestingly, plastic debris in wracks along the shoreline undergo photo-oxidative degradation and gradual fragmentation 46 , and may be eventually backwashed to the coastal sea and transported seaward by swash waves 47 .…”

Sea wrack delivery and accumulation on islands: factors that mediate marine nutrient permeability

“…Factors such as winds and swell, and the interactions among these conditions and the tides, can detach macroalgae and macrophytes from their anchorages (Witman 1987, Seymour et al 1989, Krumhansl & Scheibling 2011, creating areas or times with predictable wrack depositions (Oldham et al 2010, López et al 2019, especially where there are consistent winds. For instance, increased seagrass deposits in the northwest Mediterranean are attributed to strong wind events (Jiménez et al 2017), higher than normal tides have increased wrack accumulation along Estonian shorelines (Suursaar et al 2014), and on the Pacific coastline of the USA, wave events caused by swell in creased wrack ac cu mu lations (Reimer 2014). Additionally, storms can facilitate sporadic long-distance kelp dispersal events, disrupting patterns of connectivity across ecosystem boundaries (Waters et al 2018).…”

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

“…Southerly winds and high water temperatures favor the accumulation of CDOM in Es Caragol Beach. Given the position and orientation of this beach, in the southern tip of Mallorca Island, it is expected that southerly winds favor the accumulation of leaf litter in the beach shoreline [77] and higher temperatures favor leaching [44,78,79].…”