Spatial and Temporal Trends in Microplastic Ingestion by Pacific mole crabs (Emerita analoga) in San Diego, CA

Steven Searcy, University of San Diego, Environmental and Ocean Sciences, San Diego, CA, United States
Microplastics are commonly found in ocean water and sediments. Ingestion by marine organisms has been widely reported; however, little is known about how ingestion varies spatially and temporally. As part of an undergraduate/graduate class at the University of San Diego, we investigated microplastic ingestion by mole crabs (Emerita analoga) for three consecutive years (one date in September 2017, 2018, 2019) at 13 beaches throughout San Diego County. Mole crabs live in the swash zone of sandy beaches, burrow in the sand and filter feed on plankton and detritus making them highly vulnerable to the uptake of microplastics from the sand and the water around them. At each beach, a minimum of 30 mole crabs were collected along with three replicate seawater and sand samples. In the laboratory, sex of mole crabs was identified, they were measured for length and weight, and dissected to examine the number of microplastics ingested. Microplastics were found at every beach sampled; however, the number of microplastics varied among locations and by year. Understanding spatial and temporal trends in microplastic ingestion is a critical component to understanding dynamics of microplastic pollution in beach environments.