Hide and seek: habitat-mediated interactions between European green crabs and native mud crabs in Atlantic Canada

Gehrels, Hannah; Knysh, Kyle M.; Boudreau, Monica; Thériault, Marie-Hélène; Courtenay, Simon C.; Cox, Ruth; Quijón, Pedro A.

doi:10.1007/s00227-016-2927-6

Cited by 30 publications

(47 citation statements)

References 58 publications

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“…From an ecosystem perspective, further studies should be conducted to assess the potential ramifications of the continued decline of oyster beds [20]. Of special concern are areas recently invaded [46] and those where invasions are deemed imminent.…”

Section: Discussionmentioning

confidence: 99%

“…They continue to spread and are now established in much of the Eastern and Southern shores of the island (Northumberland Strait) [45] where they currently co-exist with native species like the rock crab (Cancer irroratus) and the mud crab (Dypanopeus sayi) [46,47]. Relatively small oysters in these areas may be vulnerable to green crab predation [37,48,49].…”

Section: Introductionmentioning

confidence: 99%

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Exploring the decline of oyster beds in Atlantic Canada shorelines: potential effects of crab predation on American oysters (Crassostrea virginica)

et al. 2017

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Atlantic Canada's American oyster (Crassostrea virginica) beds, while economically and ecologically important, have been in decline over the past few decades. Predation by crabs, in particular by the European green crab (Carcinus maenas), has been proposed as one of the potential causes of such decline. Hence, this study examined oyster mortality levels in multiple beds across Prince Edward Island (PEI) and then experimentally assessed the contribution of green crab predation to oyster mortality. Results from surveys conducted in 10 estuaries across PEI in 2014 indicate that the probability of mortality for small oysters was significantly higher when green crabs were present then in areas without green crabs. This probability of mortality was significantly less when there was the presence of alternative prey like natural mussel beds (Mytilus edulis). The odds of oyster mortality were also higher when beds had rock crabs (Cancer irroratus) compared to beds with no rock crabs. Given the potential importance of green crab predation, its influence was assessed in 2015 using two field experiments with tethered oysters. Our results indicate that odds of small oyster mortality occurring were much higher in green crab inclusion cages than in the open environment and the exclusion cages. These results reaffirm that oysters up to ~40 mm SL are vulnerable to predation, and at least some of the mortality affecting these oysters can be causally attributed to green crab predation. Green crab predation rates upon small oysters are relevant given the economic benefits and ecosystem services provided by these bivalves. They highlight the need for the industry to consider mitigation measures and potentially adapt their oyster growing strategies.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exploring the decline of oyster beds in Atlantic Canada shorelines: potential effects of crab predation on American oysters (Crassostrea virginica)

et al. 2017

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“…In summer, water temperature increases with height in the water column, salinity is typically lower than near bottom, and other physicochemical parameters are more variable (Valiela, 1995). Predation risk is known to decrease with increasing habitat complexity (Russo, 1987; Gehrels et al, 2016) and may also decrease in hypoxic habitats that predators cannot tolerate (Nestlerode & Diaz, 1998). Floating mats are generally smaller and less dense than submerged mats but it is unknown if/how this affects predation risk (Marklund, Blindow & Hargeby, 2001).…”

Section: Discussionmentioning

confidence: 99%

Are floating algal mats a refuge from hypoxia for estuarine invertebrates?

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Knysh

Theriault

et al. 2017

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Eutrophic aquatic habitats are characterized by the proliferation of vegetation leading to a large standing biomass that upon decomposition may create hypoxic (low-oxygen) conditions. This is indeed the case in nutrient impacted estuaries of Prince Edward Island, Canada, where macroalgae, from the genus Ulva, form submerged ephemeral mats. Hydrological forces and gases released from photosynthesis and decomposition lead to these mats occasionally floating to the water’s surface, henceforth termed floating mats. Here, we explore the hypothesis that floating mats are refugia during periods of sustained hypoxia/anoxia and examine how the invertebrate community responds to it. Floating mats were not always present, so in the first year (2013) sampling was attempted monthly and limited to when both floating and submerged mats occurred. In the subsequent year sampling was weekly, but at only one estuary due to logistical constraints from increased sampling frequency, and was not limited to when both mat types occurred. Water temperature, salinity, and pH were monitored bi-weekly with dissolved oxygen concentration measured hourly. The floating and submerged assemblages shared many of the same taxa but were statistically distinct communities; submerged mats tended to have a greater proportion of benthic animals and floating mats had more mobile invertebrates and insects. In 2014, sampling happened to occur in the weeks before the onset of anoxia, during 113 consecutive hours of sustained anoxia, and for four weeks after normoxic conditions returned. The invertebrate community on floating mats appeared to be unaffected by anoxia, indicating that these mats may be refugia during times of oxygen stress. Conversely, there was a dramatic decrease in animal abundances that remained depressed on submerged mats for two weeks. Cluster analysis revealed that the submerged mat communities from before the onset of anoxia and four weeks after anoxia were highly similar to each other, indicating recovery. When mobile animals were considered alone, there was an exponential relationship between the percentage of animals on floating mats, relative to the total number on both mat types, and hypoxia. The occupation of floating mats by invertebrates at all times, and their dominance there during hypoxia/anoxia, provides support for the hypothesis that floating mats are refugia.

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“…Atlantic rock crabs (Cancer irroratus), mud crabs (Dyspanopeus sayi), and American lobsters (Homarus americanus), have all been suggested as species likely to interact with expanding green crab populations (e.g. Gehrels et al 2016). The evidence for interactions between rock crabs and green crabs is still inconclusive, with studies suggesting indirect, potentially negative relationships between them (Gregory and Quijón 2011;Gehrels et al 2016) and others showing little to no interaction (Bélair and Miron 2009).…”

Section: Implications For Rapid Range Expansion In Productive Communimentioning

confidence: 99%

“…The evidence for interactions between rock crabs and green crabs is still inconclusive, with studies suggesting indirect, potentially negative relationships between them (Gregory and Quijón 2011;Gehrels et al 2016) and others showing little to no interaction (Bélair and Miron 2009). In contrast, surveys and experimental data suggest more clear negative interactions (predation) between green crabs and the smaller mud crab (Gehrels et al 2016). Green crabs have been also shown to be detrimental to juvenile lobsters by altering some of their behavioural patterns (Williams et al 2009;Rossong et al 2011).…”

Section: Implications For Rapid Range Expansion In Productive Communimentioning

confidence: 99%

Revisiting recent history: records of occurrence and expansion of the European green crab across Prince Edward Island, Atlantic Canada

et al. 2017

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Background: Late in the 1990s, the non-indigenous European green crab (Carcinus maenas) colonized the shorelines of eastern Prince Edward Island, in Atlantic Canada. Due to concerns of further spread into productive shellfish habitats, an annual survey was conducted between 2000 and 2013 to detect a potential range expansion of this species. We compiled and analyzed that data and document green crab expansion using records of annual occurrence and relative density. Methods: Surveys were conducted during the fall season of each year by deploying baited traps at 29 sites along the island's two main shorelines (north and south shores). These sites were selected based on areas deemed more likely to be invaded by the green crab. Raw data per site and date was transformed to catch per unit effort (CPUE) to estimate relative abundances. Results: Populations of this species showed an uneven westward expansion along the north and south shores. Expansion rates changed among years but, overall, crab abundance was higher and changes in abundance were faster along the south shore than the north shore of the island. The westward expansion continues until this day. Conclusions: Based on the information compiled we hypothesize that the dissimilarity in range expansion rate was related to the availability of suitable habitat to sustain large green crab populations along the south shore. We also discuss implications of this expansion for commercial shellfish and native coastal communities.

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Hide and seek: habitat-mediated interactions between European green crabs and native mud crabs in Atlantic Canada

Cited by 30 publications

References 58 publications

Exploring the decline of oyster beds in Atlantic Canada shorelines: potential effects of crab predation on American oysters (Crassostrea virginica)

Exploring the decline of oyster beds in Atlantic Canada shorelines: potential effects of crab predation on American oysters (Crassostrea virginica)

Are floating algal mats a refuge from hypoxia for estuarine invertebrates?

Revisiting recent history: records of occurrence and expansion of the European green crab across Prince Edward Island, Atlantic Canada

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