Ground truthing marine litter stranding hotspots for the Eastern Pacific Ocean coasts: A collaborative approach with school communities.

Oceanographic models predict relatively high rates of floating litter arrivals on shores influenced by onshore currents compared to regions with extensive offshore transport, such as Eastern Boundary Upwelling Systems. However, the lack of large-scale observations along continental coasts has prevented tests of this prediction. Volunteer participants (here, schoolchildren) sampled marine litter on continental beaches along 12,000 km of the East Pacific coast from 30°N to 45°S to assess the presence of biofouling organisms on objects with positive buoyancy. The presence of sessile biota indicates that litter items spent sufficient time in the water for these organisms to colonize, while positive buoyancy is necessary for litter to be transported by marine currents. In agreement with the predictions from Lagrangian particle simulations, higher proportions of floating litter with biofouling arrived along Central American beaches influenced by the Equatorial Current System than on the shores within Eastern Boundary Upwelling Systems. Our study highlights the considerable potential of participatory science to generate extensive, long-term, and reliable measures of floating litter and associated biota along coasts.