Award: OCE-1850996

Invasive species are extremely good at spreading to new areas and surviving and thriving there. They often have extensive ecological and economic impacts, and a great deal of effort goes into predicting and preventing the spread of the most damaging invasive species. Part of this management depends on understanding how they spread, and how they might adapt to new conditions they encounter. Species invasions can also represent natural experiments to better understand the traits that allow many species to adapt to a changing world. One possibility is that they may carry genetic variation that allows them to evolve very quickly in response to new conditions. In this project, we explored the rapid and extensive spread of a damaging marine invasive species, the European green crab (Carcinus maenas), along the west coast of North America, to better understand how it has been so successful across a wide range of ocean conditions. During this project, green crabs expanded their range northward along the Pacific coast through Washington and British Columbia, and into Alaska. During the same period, green crabs became more abundant within coastal and inland waters of Washington, so much so that the Governor of Washington declared a State of Emergency in 2022. We tracked this expanding invasion closely using citizen science volunteer monitoring, oceanographic modeling, and genomics to better understand how crabs are spreading in Washington waters and how they are adapting as they spread. More broadly, this project tested the factors that allow marine species to thrive in a changing ocean. We found that temperature has played an important role in the spread of green crabs into the inland waters of the Salish Sea. This area was historically protected by a strong outflow of water in the summer, preventing crab larvae from entering and establishing there. A few warm years in 2017-2020 allowed larvae to survive in the earlier spring and later fall, when local oceanography experienced occasional current reversals bringing water from the outer coast into the Salish Sea. Our modeling suggested that this combination of warmer waters and specific current conditions allowed green crabs to invade the area; an idea that was supported by the genetic data. Further genetic tracking of the invasion showed that once crabs made it into the Salish Sea, they continued to arrive from multiple regions as they bred and spread. Genetic data showed that as crabs spread across a wide range of temperatures along the west coast, their genetic makeup changed predictably at a specific cluster of genes that influence temperature tolerance. This genetic variation evolved in the species native range and was introduced along with the first green crabs. Overall, our study highlights the adaptive importance of genetic diversity at specific parts of the genome, at least in marine species like green crabs that spread extensively via ocean currents. It also shows the importance of these currents, in conjunction with ocean conditions, in allowing species to spread: even areas that seem to be protected from invasion can lose that protection if conditions are right. In the course of this work, we have collaborated extensively with more than 30 resource managers and ecologists affiliated with US, Canadian, or tribal governments, as well as state and local agencies and institutions. In many cases, results from this research have been incorporated into their plans for managing this damaging invasive species. Through Washington Sea Grants Crab Team, we worked with 300 citizen science volunteers and partner staff whose regular monitoring provided us with an extraordinarily detailed view of crab spread into the Salish Sea and genetic samples from the very earliest stages of expansion. In total, we collected genetic data from 1,500 individuals from 2018-2023 across 20 sites spanning the species full Pacific coast range. We developed a more biologically realistic larval dispersal model that includes both larval temperature tolerances and behavior, and used it to understand the mechanism behind a major spread event. We also mentored one postdoctoral researcher and nine undergraduates on this project; for many of the undergraduates, this was their first research experience and two of them won awards for their work. Finally, the results of this research have been incorporated into the new US national plan for green crab management: the genetic and modeling data contributed to substantial new sections that have been added since the original plan was released in 2002. These data also inform the draft Washington State Management Plan for European Green Crab. So far, results from this project have been incorporated into two published papers, one national report, and one book chapter, with a second chapter currently in review. The genomic data either are or will soon be publicly available. We continue to analyze these data, and anticipate publishing at least three additional papers largely based on the genetic results in the next 2-3 years. Last Modified: 08/28/2024 Submitted by: CarolynKTepolt