How did the marine heatwaves of 2014 - 2016 and 2019 affect Pacific Mole Crabs in central California?

Abstract:

The Careers in Science (CiS) intern program at the California Academy of Sciences is a science education and youth development program. Since early 2016, interns of the CiS program have monitored the Pacific mole crab (Emerita analoga) population Ocean Beach in San Francisco, California, as part of a partnership with the Long-term Monitoring Program and Experiential Training for Students (LiMPETS), an organization that conducts citizen science with Bay Area youth. Mole crabs are one of the largest filter-feeding herbivores on beaches and important seabird prey, thus they form a vital link in the nearshore food web. Mole crabs are also easy to monitor and provide a picture of the overall health of the sandy beach habitat. Data collected include sex, size, overall abundance, abundance of females with eggs, and parasite occurrence.

In the last few years, the California coast experienced two marine heat waves (MHW) - long periods of abnormally high temperatures: one from 2014 to 2016, and another in 2019. The first MHW in the Northeast Pacific, referred to as ‘The Blob’, had severe impacts on the coastal ecosystem, but the effects of the 2019 MHW are still under study. In this work, we investigate how MHWs have impacted mole crabs. In particular, we test the hypothesis that abundance and reproduction of crabs decreases during periods of warm temperatures.

To test our hypothesis we statistically compare mole crab abundance (and abundances of females with eggs) with sea surface temperature (SST) values at Ocean Beach and surrounding waters. We use the global, daily, 1 km, Amazon Web Services (AWS) Public Dataset Program NASA Multi-Scale Ultra High Resolution (MUR) SSTs to understand SST variability and how the environment changed during ‘The Blob’. All analyses are completed on the AWS cloud using Python and published in Jupyter notebooks using Pangeo-Binder, creating reproducible, open science.

Image Caption: Anomalously high sea surface temperatures in the Pacific Ocean in May 2015 as compared to the 2002–2012 average. This warm-water phenomenon is known as ‘The Blob’. Data shown are the JPL Multi-scale Ultra-high Resolution (MUR) and NASA Blue Marble. Image credit: Chelle Gentemann and JPL PO.DAAC: Charles Thompson and Jeffery R. Hall.