Habitat alteration by invasive European green crab (Carcinus maenas) causes eelgrass loss in British Columbia, Canada
Dominant, habitat-forming plant species, such as seagrasses, are key components of coastal ecosystems worldwide. Multiple stressors, including invasive species that directly alter, remove, or replace the foundation plant species, threaten these ecosystems. On the Atlantic coast of North America, ecosystem engineering by invasive European green crab (Carcinus maenas) has been linked to the loss of some eelgrass (Zostera marina) beds. However, the interaction of the same co-occurring species on the Pacific coast has not been investigated. We conducted an enclosure experiment in Barkley Sound, British Columbia, to determine if the engineering impacts of green crabs on Pacific eelgrass ecosystems mirror those previously identified on the Atlantic coast. Eelgrass shoot density declined rapidly over 4 weeks, with a 73–81% greater loss in enclosures with high crab density compared to the low-density and control treatments. The low ratio of eelgrass blades to rhizomes in the high-density treatment suggests that blade shredding, rather than bioturbation of whole plants, was the main mechanism of eelgrass loss. Eelgrass was detected in green crab stomach contents, consistent with observations from the Atlantic coast. Crab density did not have a detectable effect on the biomass or community composition of benthic fauna associated with eelgrass over the duration of the experiment. The eelgrass loss we observed was consistent with losses observed on the Atlantic coast, which raises management concerns on the Pacific coast, particularly in areas where green crabs co-occur with other coastal stressors and with ecologically and economically important species such as salmon.
KeywordsHabitat alteration Aquatic conservation Disturbance Ecosystem engineering Enclosure Zostera marina
We thank Dickson Wong, Sarah Calbick, Kyla Jeffrey, Emma Atkinson, Andrew Bateman, Helen Yan, and Elizabeth Oishi for their help, and the Bamfield Marine Sciences Centre for logistical support.
The study was funded by the Second Canadian Aquatic Invasive Species Network (CAISN II) (BRH, IMC, TWT), a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant (IMC), an NSERC - Canada Graduate Scholarships-Doctoral award (FTF), and the Fisheries and Oceans Canada’s Aquatic Invasive Species program (TWT).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Archambault P, Snelgrove PVR, Fisher JAD, Gagnon JM, Garbary DJ, Harvey M, Kenchington EL, Lesage V, Levesque M, Lovejoy C, Mackas DL, McKindsey CW, Nelson JR, Pepin P, Piché L, Poulin M (2010) From sea to sea: Canada’s three oceans of biodiversity. PLoS ONE. https://doi.org/10.1371/journal.pone.0012182 Google Scholar
- Behrens Yamada S (2001) Global invader: the European green crab. Oregon State University, CorvallisGoogle Scholar
- British Columbia Marine Conservation Analysis (2011) Marine atlas of Pacific Canada. British Columbia marine conservation analysis, Vancouver, BCGoogle Scholar
- Fei S, Phillips J, Shouse M (2014) Biogeomorphic impacts of invasive species. Annu Rev Ecol Evol Syst 45:69–87. https://doi.org/10.1146/annurev-ecolsys-120213-091928 CrossRefGoogle Scholar
- Gillespie GE, Phillips AC, Paltzat DL, Therriault TW (2007) Status of the European green crab, Carcinus maenas, in British Columbia - 2006. Can Tech Rep Fish Aquat Sci 2700:vii-39Google Scholar
- Guy-Haim T, Lyons DA, Kotta J, Ojaveer H, Queirós AM, Chatzinikolaou E, Arvanitidis C, Como S, Magni P, Blight AJ, Orav-Kotta H, Somerfield PJ, Crowe TP, Rilov G (2018) Diverse effects of invasive ecosystem engineers on marine biodiversity and ecosystem functions: a global review and meta-analysis. Glob Change Biol. https://doi.org/10.1111/gcb.14007 Google Scholar
- Kelly JR, Proctor H, Volpe JP (2008) Intertidal community structure differs significantly between substrates dominated by native eelgrass (Zostera marina L.) and adjacent to the introduced oyster Crassostrea gigas (Thunberg) in British Columbia, Canada. Hydrobiologia 596:57–66. https://doi.org/10.1007/s10750-007-9057-6 CrossRefGoogle Scholar
- Moore KA, Short FT (2006) Zostera: biology, ecology, and management. In: Larkum AWD, Orth RJ, Duarte C (eds) Seagrasses: biology, ecology and conservation. Springer, Dordrecht, pp 361–386Google Scholar
- Oksanen et al (2012) Vegan: community ecology package. R package version 2.5–3. http://CRAN.R-project.org/package=vegan/
- Parker IM, Simberloff D, Lonsdale WM, Goodell K, Wonham M, Kareiva PM, Williamson MH, Von Holle B, Moyle PB, Byers JE, Goldwasser L (1999) Impact: toward a framework for understanding the ecological effects of invaders. Biol Invasions 1:3–19. https://doi.org/10.1023/A:1010034312781 CrossRefGoogle Scholar
- Pikitch EK, Rountos KJ, Essington TE, Santora C, Pauly D, Watson R, Sumaila UR, Boersma PD, Boyd IL, Conover DO, Cury P, Heppell SS, Houde ED, Mangel M, Plagányi É, Sainsbury K, Steneck RS, Geers TM, Gownaris N, Munch SB (2014) The global contribution of forage fish to marine fisheries and ecosystems. Fish Fish 15:43–64. https://doi.org/10.1111/faf.12004 CrossRefGoogle Scholar
- R Development Core Team (2008) R: a language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar
- Ruesink JL, Hong JS, Wisehart L, Hacker SD, Dumbauld BR, Hessing-Lewis M, Trimble AC (2010) Congener comparison of native (Zostera marina) and introduced (Z. japonica) eelgrass at multiple scales within a Pacific Northwest estuary. Biol Invasions 12:1773–1789. https://doi.org/10.1007/s10530-009-9588-z CrossRefGoogle Scholar
- Thompson WJ (2007) Population-level effects of the European green crab (Carcinus maenas, L.) in an eelgrass community of the southern Gulf of St. Lawrence. Dissertation. University of New BrunswickGoogle Scholar
- Zwerschke N, Hollyman PR, Wild R et al (2018) Limited impact of an invasive oyster on intertidal assemblage structure and biodiversity: the importance of environmental context and functional equivalency with native species. Mar Biol 165:1–13. https://doi.org/10.1007/s00227-018-3338-7 CrossRefGoogle Scholar