Our warming global climate is already impacting marine ecosystems; in particular, the frequency of marine heatwaves. Rigorous data collection by citizen scientists, capable of covering geographic and temporal scales impossible for academic research teams alone, allows science to document and bound these events.
In this study, we analyse 29 years (1993-2021) of citizen science beached bird monitoring data across the northeast Pacific. This region has experienced at least five major marine bird mass mortality events from 2014 through 2021, collectively encompassing several million birds. Marine birds are highly visible, long-lived, and abundant predators who reflect shifts in trophic structure and stability; a sharp increase in marine bird mortality (easily visible to local coastal community members) is one signal of ecosystem impact. Our study utilizes observations of beached marine birds collected by four interoperable, effort-controlled, citizen science programs (~90,000 surveys); as well as anecdotal reports collected by coastal community members with local expertise. We examine: (1) whether marine heatwaves provoke seabird mortality events: (2) whether the duration of marine heatwave increases the likelihood of mortality event occurrence; and (3) the functional relationship between ocean warming and mortality event characteristics.
Mortality events were reported throughout the study period, and massive events (> 500 km in extent, > 10 carcasses km-1) occurred infrequently (N = 4), with an unprecedented sequence from 2014-2019. Mortality events occurred more frequently following marine heat waves, and a common sequence of mortality events (at 1-6 months and 10-16 months after heat wave onset) was observed in the California Current large marine ecosystem. Event characteristics, including magnitude, duration, and spatial extent were all positively associated with increased water temperatures, with a discontinuous uptick in event probability at a temperature anomalies above 1degree C. Collectively, this indicates events are becoming larger and longer-lasting, with higher carcass counts under warmer conditions. These data indicate that sudden, prolonged warming will result in an uptick in marine bird mortality, as the system continues to reset to a lower carrying capacity for these upper-trophic predators.
By engaging community members in scientific observation in places they know well, and analyzing their collective findings to reveal ecosystem-level impacts, we demonstrate the unique values of large-scale citizen science: ability to conduct highly rigorous, cost-efficient, ecological science at a grain and extent otherwise unrealizable; new scientific directions as a direct consequence of participant input and questions; and active engagement of a non-STEM public creating ecological and environmental literacy.
