The Green Wave: reviewing the environmental impacts of the invasive European green crab (Carcinus maenas) and potential management approaches

Abstract

The European green crab (Carcinus maenas), native to northwestern Europe and Africa, is among the top 100 most damaging invasive species globally. In some regions, including the Atlantic coast of North America, C. maenas has caused long-term degradation of eelgrass habitats and bivalve, crab, and finfish populations, while areas are near the beginning of the invasion cycle. Due to high persistence and reproductive potential of C. maenas populations, most local and regional mitigation efforts no longer strive for extirpation and instead focus on population control. Long-term monitoring and rapid response protocols can facilitate early detection of introductions that is critical to inform management decisions related to green crab control or extirpation. Once C. maenas are detected, local area managers will need to decide on management actions, including whether and what green crab control measures will be implemented, if local invasion might be prevented or extirpated, and if population reduction to achieve functional eradication is achievable. Due to the immense operational demands likely required to extirpate C. maenas populations, combined with limited resources for monitoring and removal, it is unlikely that any single government, conservation and/or academic organization would be positioned to adequately control or extirpate populations in local areas, highlighting the importance of collaborative efforts. Community-based monitoring, and emerging methods such as environmental DNA (eDNA), may help expand the spatial and temporal extent of monitoring, facilitating early detection and removal of C. maenas. While several C. maenas removal programs have succeeded in reducing their populations, to our knowledge, no program has yet successfully extirpated the invader; and the cost of any such program would likely be immense and unsustainable over the long-term. An alternative approach is functional eradication, whereby C. maenas populations are reduced below threshold levels such that ecosystem impacts are minimized. Less funding and effort would likely be required to achieve and maintain functional eradication compared to extirpation. In either case, continual control efforts will be required as C. maenas populations can quickly increase from low densities and larval re-introductions.

Extracellular vesicle signatures and protein citrullination are modified in shore crabs ( Carcinus maenas ) infected with Hematodinium sp

“…The common (green) shore crab Carcinas maenas is native to European coastal waters, yet represents one of the most damaging marine invasive species having extended its non-native range to the Americas, Australia, and Asia [ 1 , 2 ]. In part, ecosystem changes are brought about by C. maenas and their attendant pathogens and parasites.…”

Invasive investigation: uptake and transport of l-leucine in the gill epithelium of crustaceans

“…Predation and hunting practices of C. maenas are also particularly destructive to the native ecosystem. Canadian bivalve populations experience reduced recruitment and survival rates due to significant predation, with bivalve populations exhibiting 5- to 10-fold decrease in the presence of C. maenas ( Grosholz et al , 2000 ; Tan and Beal, 2015 ; Ens et al , 2022 ). While scavenging for bivalves, C. maenas also causes significant damage to Eelgrass ( Zostera spp.)…”

“…meadows that many estuarine organisms rely on for food and shelter. In Atlantic Canada, eelgrass meadows have experienced biomass declines between 50% and 100% when C. maenas invades their ecosystem ( Ens et al , 2022 ). In an attempt to preserve native species in the Canadian Pacific, researchers are often focused on slowing the growth of existing C. maenas populations to mitigate spread.…”

Molecular insights into the invasion dynamics of Carcinus crabs in South Africa

“…Yet, except for invasions in Japan and South Africa, these two species rarely co-invade (Geller et al 1997). Carcinus crabs are considered high-impact invaders across many of their invasive ranges (for reviews on C. maenas see Behrens Yamada 2001;Walton et al 2002;Chen et al 2004;Ens et al 2022). In regions such as Canada, multiple introductions of C. maenas have led to genetically diverse invasive populations (Roman 2006) while, in others, such as on the Pacific coast of North America, secondary introductions founded populations with limited genetic diversity (Darling et al 2008).…”

“…In recognition of the negative impacts of Carcinus crabs elsewhere in the world (e.g. Grosholz et al 2000, Matheson et al 2016, Ens et al 2022, and in support of authorities charged with managing biological invasions in South Africa, a management trial was implemented during 2014 and 2015 in Hout Bay harbour (Mabin et al 2020). The primary aim of that project was to assess the feasibility of eradicating Carcinus crabs from South Africa.…”