Cost-effective monitoring of large micro- and meso-litter in tidal and flood accumulation zones at south-western Baltic Sea beaches.

Often, beach litter monitoring strategies focus only on macro-litter (>25 mm) and do not distinguish between litter left at beaches and litter washed up onshore. We tested inexpensive and user-friendly methods to examine meso-litter (5-25 mm) and large micro-litter (2-5 mm) washed up on German sandy beaches and evaluated our methods regarding the requirements of the Marine Strategy Framework Directive. With a sieve accumulation zone monitoring method, tested 41 times, we found 0.2-21.2 litter pieces/m2 (⌀ 5.3 pieces/m2 ± 8.9). With a bare eye accumulation zone monitoring method, tested 10 times, at other beaches, 9.1-65.6 litter pieces/m2 (⌀ 31.8 pieces/m2 ± 15.7) were found. Both methods are inexpensive, useful for volunteers, and can be carried out quickly, but are also limited, as they cannot be used regularly. A tested webcam and a modified Braun-Blanquet method turned out to be less suitable.