Spatio-Temporal Variability of Anthropogenic and Natural Wrack Accumulations along the Driftline: Marine Litter Overcomes Wrack in the Northern Sandy Beaches of Portugal

Abstract

Marine litter can end up deposited on sandy beaches and become entangled in the natural wrack, threatening its roles in ecosystems. However, it is currently unknown whether the storage of both artificial and natural accumulations on sandy beaches is correlated. Here, we quantified and compared, by first time, the litter and natural wrack on five sandy beaches in the north of Portugal. Results showed that the amount of marine litter and natural wrack were not correlated. Most of the sandy beaches had more litter than wrack and both artificial and natural accumulations disclosed high spatio-temporal variability. In summer, annual and opportunistic macroalgae dominated the wrack, while the litter was mainly formed by cigarette butts and leftover food. In winter, perennial taxa were more abundant in the wrack and plastics from mussel farming and cotton bud sticks dominated the litter. The macroalga Fucus spp., plastic pieces and materials from fishing were frequent in both periods. This study confirms that, currently, more litter than natural wrack reaches the Northern Portuguese sandy beaches, evidencing the need to take urgent measures against this contamination. Future management measures should consider this spatio-temporal variability to quantify both depositions.