Temporal variability of microparticles under the Seattle Aquarium, WA: Documenting the global Covid‐19 pandemic

Anthropogenic debris including microparticles (MP; <5mm) are
ubiquitous in marine environments. The Salish Sea experiences seasonal
fluctuations in precipitation, river discharge, sewage overflow events,
and tourism– all variables previously thought to have an impact on MP
transport and concentrations. Our goals are two-fold: 1) Describe
long-term MP contamination data including concentration, type, and size
and 2) Determine if seasonal MP concentrations are dependent on
environmental or tourism variables in Elliott Bay, Salish Sea. We sampled
100 L of seawater at depth (~9 m) at the Seattle Aquarium approximately
every two weeks 2019 – 2020 and used an oil extraction protocol to
separate MP. We found MP concentrations ranged from 0 – 0.64 particles L⁻¹
and fibers were the most common type observed. Microparticle concentration
exhibited a breakpoint on April 10, 2020, where estimated slope and
associated MP concentration significantly declined. Further, when
considering both environmental as well as tourism variables, temporal MP
concentration was best described by a mixed-effects model with tourism as
the fixed effect and the person counting MP as the random effect. While
monitoring efforts presented here set out to identify effects of
seasonality and interannual differences in MP concentrations, it instead
captured an effect of decreased tourism due to the global Covid-19
pandemic. Long-term monitoring is critical to establish temporal MP
concentrations and to help researchers understand if there are certain
events, both seasonal and sporadic (e.g. rain events, tourism, or global
pandemics), when the marine environment is more at risk from anthropogenic
pollution.