Invasive Green Crab Carcinus Maenas Research Articles

Predation of the invasive green crab Carcinus maenas on the edible snail Buccinastrum deforme, targeted as the most important nearshore marine gastropod fishery from Patagonia, Argentina

Biological invasions constitute one of the main problems for the conservation of marine environments and are among the major causes of biodiversity reduction. The green crabs, Carcinus maenas was first reported on the Patagonian Argentinean coast in 2003 and has rapidly spread northwards along the coast. In 2018, many empty shells of the edible gastropod Buccinastrum deforme were observed at the shoreline, showing scars compatible with those caused by crab-crushing predations. This study aimed to evaluate the effect of C. maenas on the edible gastropod B. deforme, a species of great fishing importance in Patagonia, Argentina. In order to characterize the green crab’s predatory marking patterns observed on the shell of B. deforme, aquarium experiments were conducted. At the same time, field sampling census of shells stranded in the intertidal zone were carried out in three different sites where high densities of B. deforme were previously recorded. Empty shells showing the characterized marking patterns were used as an indicator of predation and were randomly collected from the intertidal to quantify the frequency of each type of predatory mark. Additionally, the abundance of snails and crabs was estimated using baited traps in ten sampling sites. Our results are consistent with the fact that the non-native green crab C. maenas presents a highly aggressive behavior that affects native species' abundances once established in a new environment. The most frequent pattern of predation marks was the combined crush of the apex and lip, occurring simultaneously in the same individual. A decrease in B. deforme presence was inversely proportional to the increase in C. maenas populations. This is the first work that records the impact of predation of the invasive species C. maenas on Atlantic Patagonia's sandy bottoms, which negatively affects a fragile species such as the edible snail B. deforme. The dispersal capacity of the green crab, in addition to its predatory strength and voracity, could endanger the artisanal fishery of B. deforme and induce irreversible changes in the coastal ecosystems of Atlantic Patagonia.

Use of Invasive Green Crab Carcinus maenas for Production of a Fermented Condiment.

To control the population of an invasive species of green crab, we investigated the feasibility of producing a fermented crab condiment. Commercial fermented fish condiments were tested to assess variability in the marketplace and to identify targets for lab-fermented sauces. Finely chopped crab was combined with 100 mg g−1, 200 mg g−1, or 300 mg g−1 NaCl, and spontaneously fermented for up to 120 days. Chromatographic analysis revealed that histamine content was not a safety concern as all treatments were below the current U.S. legal threshold (50 mg 100 mL−1). The majority of microbial and physicochemical properties measured within salt level (proteolytic bacterial population, total volatile basic nitrogen (TVBN), amine nitrogen, water activity, moisture, and biogenic amines) were statistically unchanged between days 60 and 120 of fermentation, suggesting that most of the biochemical changes happened early in the fermentation. While the production of a fermented condiment was successful and could represent an opportunity for the valorization of this invasive species, additional work is needed to accelerate the process and further understand the dynamics of the early fermentation stages.

Comparative Field Trials to Examine the Efficacy of a Traditional Management Tool—Brushing—To Enhance Local Densities of 0-Y Class Recruits in the Soft Shell Clam Mya arenaria L. Fishery in Maine, USA

The intertidal soft-shell clam Mya arenaria fishery in Maine is comanaged under a cooperative agreement, or shellfish ordinance, between coastal communities and the state. The ordinance, among other things, defines conservation tools that encourage communities to engage in activities with a goal to enhance local densities of 0-y class individuals of this infaunal bivalve. One method used by communities for over 75 y is referred to as “brushing,” which involves forcing dozens of the recently cut white spruce Picea glauca boughs (approximately 70 cm in length) vertically into the soft sediments of a mudflat so that 40–45 cm protrudes into the water column. Typically, multiple rows of boughs are deployed on flats in the spring before clam spawning where they remain through the fall after annual settlement and recruitment have ended. Brushing purportedly results in slowing down tidal currents and creating eddies that allow recently settled clams that otherwise are susceptible to bedload transport away from the flat to establish themselves in the vicinity of the boughs. During spring–fall 2019, a comparative field experiment was conducted at three intertidal flats within a 160-km stretch of the Maine Coast to test, for the first time, the efficacy of this traditional management tool versus another approach used to enhance local densities of 0-y class clams—predator-exclusion netting. At each flat, neither treatment enhanced densities when compared with controls of recruits of Mya as well as recruits of another commercially important infaunal bivalve that occurred at a single site, the northern quahog Mercenaria mercenaria. That is, neither bivalve responded positively to experimental additions of spruce boughs to soft sediments at any study site. Passive bivalve collectors demonstrated that both species settled into plots, ruling out recruitment limitation. Comparison of recruit densities between collectors and core samples from both brushed and netted plots demonstrated losses greater than 97% for Mya and greater than 93% for Mercenaria. Collectors also provided data on densities of recruits of the invasive green crab Carcinus maenas, which ranged from 1.2 to 13.9 ind. m–2 across sites, and were 3–6× more abundant in collectors within plots with brush or netting versus adjacent control plots, suggesting that this predator selects heterogeneous versus homogeneous environments during its early life history. As green crab populations in Maine vary directly with seawater temperatures, and the Gulf of Maine is warming relatively rapidly, adding potential habitat for green crabs, such as brush, to intertidal flats should be discontinued in favor of more effective methods to enhance local densities of 0-y class individuals.

Lack of adult novel northern lineages of invasive green crab Carcinus maenas along much of the northern US Atlantic coast.

Introduced over 200 yr ago to the east coast of North America, Carcinus maenas now ranges from New York to Newfoundland. In the 1980s, a secondary invasion of European lineages, termed northern haplotypes, occurred in Nova Scotia. Young-of-the-year sampled in 2007 revealed that northern haplotypes were present in low frequencies at several northwestern Atlantic sites as far south as New York; a model predicted an increase in their range and frequency over time. We collected samples in 2013 and 2014 to determine the haplotypes of adult crabs from New York to Nova Scotia. Six haplotypes, encompassing previously identified northern and southern haplotypes, 1 novel southern haplotype, and 1 Scandinavian haplotype, were identified in 275 crabs sampled at 11 sites. Northern haplotypes were only found in Nova Scotia, Beals Island (Maine), and Mount Desert Island (Maine) at a frequency of 60, 8, and 24%, respectively; remaining sites were predominantly composed of a previously identified southern haplotype. Northern haplotypes are limited in adult crabs to Mount Desert Island and north, indicating that the southern haplotype is selectively favored at some point during their life history, recruitment of northern larvae is limited south of Mount Desert Island, or entire year-classes post-2007 were lost. Our results do not support the predictions of an increase in the range and frequency of northern haplotypes, at least among adults, and indicate that a more complete knowledge of factors affecting C. maenas life stages is necessary to understand the current distribution of haplotypes.

The effect of geographic origin on interactions between adult invasive green crabs carcinus maenas and juvenile American lobsters Homarus americanus in Atlantic Canada

The European green crab Carcinus maenas is an invasive species in the northwestern Atlantic that has the potential to compete and prey upon endemics such as juvenile American lobster Homarus americanus. Recent laboratory studies have reached opposite conclusions regarding the dominance relationship between these species, even documenting a reversal of roles as predator and prey. Interestingly, these contradicting results involved crab populations from different regions in Atlantic Canada (St. George's Bay in the Northumberland Strait and Passamaquoddy Bay in the Bay of Fundy), which are genetically different and presumed to be the result of different invasion events. In this study we housed juvenile lobsters and adult green crabs together in 3-m diameter flow-through tanks, and monitored their mortality, growth and behaviour from September through December 2009. The experiment involved five treatments, three experimental treatments with 2.5 lobsters/m2 housed with an equal density of green crabs from one of three regions (Passamaquoddy Bay, St. George's Bay or Chedabucto Bay on the Scotian Shelf) and two control treatments with lobsters alone stocked at either 2.5 or 5 individuals/m2. Chedabucto Bay was chosen as a third region as crabs there are genetically similar to conspecifics in St. George's Bay, but experience environmental conditions more similar to Passamaquoddy Bay. Green crabs had a significant and negative impact on lobster survival during the experiment, and the magnitude of this impact varied in relation to the green crabs' geographic origin, as mortality was significantly higher for lobsters paired with St. George's Bay and Chedabucto Bay crabs than Passamaquoddy Bay crabs. These differences in lobster mortality patterns lead to two important conclusions. First, the greater predatory impact of green crabs from St. George's Bay relative to Passamaquoddy Bay is consistent with the contrasting results recently reported in the literature, suggesting that these are of biological significance and not simply the result of procedural differences between studies. Second, the fact that the predatory impact of Chedabucto Bay green crabs was similar to that of conspecifics from St. Georges Bay, but greater than those from Passamaquoddy Bay, suggests that these differences in interspecific dominance patterns are correlated with genetic differences between green crab populations related to their invasion history in Atlantic Canada. The mechanisms underlying the effect of crab geographic origin on its interaction with juvenile lobster remain elusive, however, as no differences in crab behaviour or morphology were found that correlated with the pattern of lobster mortality.

Fatty acids tracers for native and invasive macroalgae in an experimental food web

We assessed the potential of fatty acid (FA) markers for tracing primary production from an invasive green alga (Codium fragile ssp. fragile) and a native kelp (Saccharina longicruris) through 2 trophic levels in an experimental food web: a primary consumer, the green sea urchin Strongylo- centrotus droebachiensis, and 2 secondary consumers, the native rock crab Cancer irroratus and invasive green crab Carcinus maenas. Sea urchins fed the 2 algal species had distinct gonadal FA compositions, and contained markers of each alga. Crabs of each species were then fed the gonads of sea urchins which had been fed either S. longicruris or C. fragile, and their hepatopancreases were analyzed. We were able to distinguish crabs of both species with C. fragile at the base of the food chain using the marker FAs 16:3n-3 and 18:3n-3. The overall FA composition of the hepatopancreas differed with diet in the green crab but not the rock crab. Our results suggest that 16:3n-3 may be a useful marker for tracing C. fragile production in grazers and some secondary consumers in rocky subtidal habitats in the Northwest Atlantic, but signal attenuation with each trophic transfer will limit the utility of this approach in higher consumers.