Bioavailability and biological effects of microscopic plastic debris in the ocean, in the Gulf of Maine (2013) and the Western English Channel (2015) dataset https://portal.medin.org.uk/portal/start.php?tpc=006_0279d92cd4f857c7bef686afd94944f5 This project aims to provide an estimate of the extent to which microplastic concentrations are underestimated with traditional sampling. Sampling events focus on coastal waters, where microplastics are predicted to have the greatest influence on marine life, on both sides of the North Atlantic Ocean. Samples were collected in the Gulf of Maine (USA) in July 2013 and the western English Channel off the coast of Plymouth (UK) between July and September 2015. Microplastic debris was collected via surface trawls using 100, 333 and 500 micrometer nets. Data collection was funded by the Natural Environment Research Council (NERC Grant NE/L003988/1 and NE/L007010/1); University of Exeter and Plymouth Marine Laboratory collaboration fund; in-kind contributions from the ‘Rozalia Project’; March Limited of Bermuda philanthropic support. 20220218 20210519