Experimental Test of the Effects of a Non‐Native Invasive Species on a Wintering Shorebird

Abstract

The abundance of nearly one-quarter of the world's shorebird species is declining. At the same time, the number of non-native species in coastal ecosystems is increasing rapidly. In some cases, non-native species may affect negatively the abundance and diversity of shorebird prey species. We conducted an experimental study of the effects of the introduced European green crab (Carcinus maenas) on prey consumption by wintering Dunlin (Calidris alpina) in a central California estuary. We placed green crabs and Dunlin sequentially in field enclosures and measured changes in density of benthic invertebrate prey (e.g. polychaetes and small clams), Dunlin biomass, and gut contents of both Dunlin and crabs and observed foraging behavior of Dunlin. Green crabs significantly affected Dunlin foraging success through both direct and indirect multitrophic linkages. In enclosures with high densities of green crabs, crab foraging reduced the availability of polychaetes, and Dunlin consumed significantly fewer polychaetes compared with Dunlin in enclosures without crabs. High densities of green crabs were also associated with increased availability of small clams. Dunlin consumed significantly more small clams compared with Dunlin in enclosures without crabs. In our literature survey of studies of effects of non-native invasive species on shorebirds, we found three prior experiments that addressed the effect of non-native invasive species on shorebirds. Results of two of these studies showed positive direct effects of non-native invertebrates on shorebirds, 1 showed negative direct effects of a non-native plant on shorebirds through habitat conversion, and none showed indirect effects of non-native invertebrates. We suggest future management of shorebirds explicitly examine how non-native marine species, particularly invertebrates, directly and indirectly affect shorebirds.

Distribution and Habitat Use of the InvasiveCarcinus maenasL. (European Green Crab) and the NativeCancer irroratus(Say) (Rock Crab) in Intertidal Zones in the Upper Bay of Fundy, Canada

“…There is mixed evidence on the potential for adverse effects of a Green Crab invasion on other trophic levels. In an enclosure experiment, Estelle and Grosholz (2012) found that Green Crabs reduced polychaete consumption by Calidris alpina L. (Dunlin). Wong and Dowd (2014) modeled the effects of a Green Crab removal program on an intertidal sand flat and predicted that removal of 50% or 95% of Green Crabs from the food web would result in increased Pluvialis squatarola L. (Black-bellied Plover) biomass and increased removal of benthic prey by migrating shorebirds.…”

“…The Green Crab is an aggressive competitor, and may outcompete sympatric native crustaceans (Haarr and Rochette 2012, MacDonald et al 2007, McDonald et al 2001). It has a generalist diet, and has had negative effects on several invertebrate species, notably bivalves (DFO 2011, Klassen andLocke 2007), but also polychaetes (Estelle andGrosholz 2012, Gregory andQuijón 2011) and amphipods (Grosholz and Ruiz 1995). Green Crabs can destroy Zostera marina L. (Eelgrass) beds (DFO 2011, Garbary et al 2014, Neckles 2015, Matheson et al 2016, and their foraging behavior has the potential to affect shorebird prey consumption by altering the availability of benthic invertebrates (Estelle and Grosholz 2012).…”

“…Further, previous surveys at 5 mudflats in the Minas Basin in 2013, each comprising two 800-m transects perpendicular to shore and one 100-m transect parallel to shore at the high-tide line, reported a molted carapace density of 0.014m -2 (MacDonald 2014). Green Crabs have reduced amphipod and polychaete densities in enclosure experiments (Estelle and Grosholz 2012, Gregory and Quijón 2011, Grosholz and Ruiz 1995. These mudflat invertebrates provide important resources for native species; thus, the current status-early phase of establishment if Green Crab abundance is lower than Rock Crab, middle phase if abundances are similar, and late phase if Green Crabs are significantly more abundant than Rock Crabs (sensu O'Connor 2014)-of the Green Crab population in Chignecto Bay merits investigation.…”

An assessment of the extent and social-ecological impacts of salt marsh mosquito ditching

“…However, in the last 50 years, nearly thirty percent (~ 3 billion) of the birds that underpin these ecosystem functions and services have been lost across all biomes within the U.S. and Canada alone (Rosenberg et al 2019). Further losses are predicted as an additional 30% of all bird species are exhibiting population declines, particularly shorebirds and waterbirds (Butchart et al 2010, Estelle and Grosholz 2012, Ceballos et al 2017, Rosenberg et al 2019. While many of these declines can be partly attributed to shrinking habitat availability following land conversions for agriculture and housing (Newton 2004, Kirby et al 2008, Stanton et al 2018, Díaz and Malhi 2022, it is becoming increasingly clear that population declines can be exacerbated by manipulations of the remaining habitat area.…”