Annual cycle of wrack supply to sandy beaches: effect of the physical environment

Abstract

Connectivity between ecosystems has been widely recognised as an important issue in ecological studies. Sandy beaches are very dynamic and open ecosystems, mainly supported by allochthonous subsidies of stranded organic matter (mostly macroalgae), also termed wrack supply. The magnitude and composition of algal wrack biomass throughout the annual cycle was assessed for 6 sandy beaches on the Galician coast, NW Spain. The effect of wave action and the topographical features of each beach in the wrack deposition process were investigated. Wrack species composition, biomass and coverage were measured monthly along 6 transects at each beach. Mean dry weight of wrack fluctuated from 14 ± 5.3 to 9189 ± 3594 g m -1 (along transects) between locations. Wrack was predominantly composed of brown algae, which accounted for 70% of the average biomass year round; the dominant species were Cystoseira sp. (30.3 ± 17.4%) and Sargassum muticum (14.2 ± 7.1%). A cyclical pattern in wrack composition, coupled with the life cycle of the predominant macroalgae, was observed. Wrack biomass and species composition were mostly explained by wave height and the ratio of beach length to beach area. Small, wave-sheltered beaches received the largest inputs of wrack, and had the lowest relative contribution of brown algae. These results provide evidence that variability in wrack supply on sandy beaches can be explained through interactions between wave exposure, coastal topography and seasonality.

Donor-Control of Scavenging Food Webs at the Land-Ocean Interface

“…Because beaches are depositional environments, clearly illustrated by the accumulations of wrack [16], we expect that the deposition of carrion on the strandline is not an infrequent event. Smaller carrion on beaches is, however, not widely reported in the literature.…”

“…On beaches, physical vectors that move marine matter onshore are primarily wind, currents, tides and waves [16]. These physical forces can deposit large amounts of stranded marine matter on the shore (i.e.…”

Reviews and syntheses: Hidden forests, the role of vegetated coastal habitats in the ocean carbon budget

“…Beach-cast deposits can reach phenomenal biomasses (Barreiro et al, 2011), such as up to 500 kg of dry wt m −1 of the shoreline of Posidonia oceanica litter washed on the shores of Tabarca, Spain (Mateo et al, 2003). Beachcast material supports high metabolic rates (Coupland et al, 2007) and represents a significant subsidy to terrestrial food webs (e.g.…”

Warming intensify CO2 flux and nutrient release from algal wrack subsidies on sandy beaches

“…3.5 m during spring tides. It harbours a diverse and variable macrophyte wrack supply, usually distributed in heterogeneous patches stranded along the drift line and in the upper beach, mainly composed of brown algaes Saccorhiza polyschides , Sargassum muticum and Cystoseira spp (Barreiro et al., ). Weather conditions correspond with a mild oceanic climate, with mean daily temperatures ranging between 7 and 24°C throughout the year (http://www.meteogalicia.es).…”