Cynthia H. McKenzie

‘Double trouble’: the expansion of the Suez Canal and marine bioinvasions in the Mediterranean Sea

‘‘Egypt to build new Suez canal... ‘This giant project will be the creation of a new Suez canal parallel to the current channel’ said Mohab Mamish, the chairman of the Suez Canal Authority, in a televised speech.’’ (http://www.theguardian.com/world/2014/aug/05/ egypt-build-new-suez-canal, viewed August 13, 2014). This is ominous news. Expected to double the capacity of the Suez Canal, the expansion is sure to have a diverse range of effects, at local and regional scales, on both the biological diversity and the ecosystem goods and services of the Mediterranean Sea. Of nearly 700 multicellular non-indigenous species (NIS) currently recognized from the Mediterranean Sea, fully half were introduced through the Suez Canal since 1869 (Galil et al. 2014). This is one of the most potent mechanisms and corridors for invasions by marine species known in the world. Further, molecular methods demonstrate high levels of gene flow between the Red Sea and the Mediterranean populations

Classification of Non-Indigenous Species Based on Their Impacts: Considerations for Application in Marine Management

Assessment of the ecological and economic/societal impacts of the introduction of non-indigenous species (NIS) is one of the primary focus areas of bioinvasion science in terrestrial and aquatic environments, and is considered essential to management. A classification system of NIS, based on the magnitude of their environmental impacts, was recently proposed to assist management. Here, we consider the potential application of this classification scheme to the marine environment, and offer a complementary framework focussing on value sets in order to explicitly address marine management concerns. Since existing data on marine NIS impacts are scarce and successful marine removals are rare, we propose that management of marine NIS adopt a precautionary approach, which not only would emphasise preventing new incursions through pre-border and at-border controls but also should influence the categorisation of impacts. The study of marine invasion impacts requires urgent attention and significant investment, since we lack the luxury of waiting for the knowledge base to be acquired before the window of opportunity closes for feasible management.

Regional differences in foraging behaviour of invasive green crab (Carcinus maenas) populations in Atlantic Canada

Invasive green crab populations initially established in Canada within the Bay of Fundy, New Brunswick in the 1950s and were present in all five Atlantic provinces by 2007. Genetic evidence suggests that the Atlantic Canadian populations originated from two separate introductions with differences in time of establishment among regions and possible population-level behavioural differences. In this study, we examine intraspecific foraging behaviour among crabs from different populations, and interspecific foraging behaviour between genetically similar crabs and juvenile lobsters. Both sets of foraging experiments involved competition for a limited food source over a 1-h period. In intraspecific match-ups, recent invaders from Newfoundland (NL) were significantly superior foragers than long-established invaders from Nova Scotia (NS) and New Brunswick (NB) populations; however, we found no differences between NL and Prince Edward Island (PE) invaders. Crabs from PE were better competitors than those from NS and NB, but these differences were not significant. Interspecific competition experiments indicated that the feeding behaviour of recent invaders (NL) and genetically similar, but long-established invaders (NS), differed in the presence of juvenile lobsters. Our study documents striking behavioural differences among populations of green crab from a small geographic region, which may reflect a combination of both genetic differences and time since establishment. These differences may result in varying impacts on newly invaded habitats.

RAD sequencing reveals genomewide divergence between independent invasions of the European green crab (Carcinus maenas) in the Northwest Atlantic

Abstract Genomic studies of invasive species can reveal both invasive pathways and functional differences underpinning patterns of colonization success. The European green crab (Carcinus maenas) was initially introduced to eastern North America nearly 200 years ago where it expanded northwards to eastern Nova Scotia. A subsequent invasion to Nova Scotia from a northern European source allowed further range expansion, providing a unique opportunity to study the invasion genomics of a species with multiple invasions. Here, we use restriction‐site‐associated DNA sequencing‐derived SNPs to explore fine‐scale genomewide differentiation between these two invasions. We identified 9137 loci from green crab sampled from 11 locations along eastern North America and compared spatial variation to mitochondrial COI sequence variation used previously to characterize these invasions. Overall spatial divergence among invasions was high (pairwise FST ~0.001 to 0.15) and spread across many loci, with a mean FST ~0.052 and 52% of loci examined characterized by FST values >0.05. The majority of the most divergent loci (i.e., outliers, ~1.2%) displayed latitudinal clines in allele frequency highlighting extensive genomic divergence among the invasions. Discriminant analysis of principal components (both neutral and outlier loci) clearly resolved the two invasions spatially and was highly correlated with mitochondrial divergence. Our results reveal extensive cryptic intraspecific genomic diversity associated with differing patterns of colonization success and demonstrates clear utility for genomic approaches to delineating the distribution and colonization success of aquatic invasive species.

Genomewide evidence of environmentally mediated secondary contact of European green crab (Carcinus maenas) lineages in eastern North America

Genetic‐environment associations are increasingly revealed through population genomic data and can occur through a number of processes, including secondary contact, divergent natural selection, or isolation by distance. Here, we investigate the influence of the environment, including seasonal temperature and salinity, on the population structure of the invasive European green crab (Carcinus maenas) in eastern North America. Green crab populations in eastern North America are associated with two independent invasions, previously shown to consist of distinct northern and southern ecotypes, with a contact zone in southern Nova Scotia, Canada. Using a RAD‐seq panel of 9,137 genomewide SNPs, we detected 41 SNPs (0.49%) whose allele frequencies were highly correlated with environmental data. A principal components analysis of 25 environmental variables differentiated populations into northern, southern, and admixed sites in concordance with the observed genomic spatial structure. Furthermore, a spatial principal components analysis conducted on genomic and geographic data revealed a high degree of global structure (p < .0001) partitioning a northern and southern ecotype. Redundancy and partial redundancy analyses revealed that among the environmental variables tested, winter sea surface temperature had the strongest association with spatial structuring, suggesting that it is an important factor defining range and expansion limits of each ecotype. Understanding environmental thresholds associated with intraspecific diversity will facilitate the ability to manage current and predict future distributions of this aquatic invasive species.

PREDATION OF SEA SCALLOPS AND OTHER INDIGENOUS BIVALVES BY INVASIVE GREEN CRAB, CARCINUS MAENAS, FROM NEWFOUNDLAND, CANADA

ABSTRACT Populations of green crab (Carcinus maenas) have expanded within Newfoundland, and this has raised concern from fish harvesters and scientists regarding bivalve predation in coastal areas on species such as juvenile sea scallops (Placopecten magellanicus). We used 2 microcosm experiments to determine (1) the effects of water temperature (5°C and 12°C) on scallop predation; (2) scallop size selection in small and large green crabs and a large indigenous predator, the rock crab (Cancer irroratus); and (3) bivalve prey selection in large green crabs between softshell clams (Mya arenaria), blue mussels (Mytilus edulis), and sea scallops. Overall, green and rock crabs captured 4 times more scallops in warm water (12°C) than cold (5°C). Large green (60–70 mm) and rock (75–90 mm) crabs captured similar numbers of scallops, selected medium-size (30–40 mm) scallops, and avoided small (10–20 mm) scallops. Small green crabs (40–50 mm) captured only small scallops. Large green crabs selected softshell clams and blue mussels over scallops. Overall, our research demonstrated that both green and rock crabs can prey on similar sizes of scallops, and suggests that green crabs may be a new predation threat to the shallow coastal scallop populations in Newfoundland.

Evaluation of a new screening-level risk assessment tool applied to non-indigenous marine invertebrates in Canadian coastal waters

Screening-level risk assessment tools for non-indigenous species are useful to inform management and policy decisions. While a number of tools have been developed to evaluate the risk of introductions in terrestrial and freshwater environments, only one tool is available for marine invertebrates [Marine Invertebrate Invasiveness Scoring Kit (MI-ISK)] and it has not been calibrated or evaluated previously. This paper introduces the Canadian Marine Invasive Screening Tool (CMIST), a tool based on a series of questions related to the sequence of events in the invasion process. We assessed the performance of both CMIST and MI-ISK using 60 species/ecosystem combinations of non-indigenous marine invertebrate species known to have been introduced to three Canadian marine ecoregions. Assessment scores were compared to the results of an expert opinion survey about the level of ecological risk posed by these species in these ecoregions. In addition, a simple way to quantify uncertainty and compute confidence limits surrounding expert evaluations and CMIST scores is presented; the technique could be incorporated into other existing tools. The risk scores returned by the two tools generally were similar, had comparable levels of inter-assessor variability, and correlated well with the results of the expert opinion survey for two of the three ecoregions. In the third ecoregion, we believe the lack of highly problematic species and greater uncertainty (linked to less reliable information) contributed to the weaker correlation. For all ecoregions, CMIST scores were more strongly correlated with expert opinion scores when compared to MI-ISK scores. Finally, we demonstrate how CMIST can be used for new incursions; for each ecoregion we scored 15 additional species not yet introduced and compared these scores with those of species already present. Overall CMIST is a promising screening-level tool; it distinguishes between elements of invasion risk (likelihood and impact), has fewer questions to score than similar tools, and could easily be adapted for other taxa.

Temporal dynamics of genetic clines of invasive European green crab (Carcinus maenas) in eastern North America

Two genetically distinct lineages of European green crabs (Carcinus maenas) were independently introduced to eastern North America, the first in the early 19th century and the second in the late 20th century. These lineages first came into secondary contact in southeastern Nova Scotia, Canada (NS), where they hybridized, producing latitudinal genetic clines. Previous studies have documented a persistent southward shift in the clines of different marker types, consistent with existing dispersal and recruitment pathways. We evaluated current clinal structure by quantifying the distribution of lineages and fine‐scale hybridization patterns across the eastern North American range (25 locations, ~39 to 49°N) using informative single nucleotide polymorphisms (SNPs; n = 96). In addition, temporal changes in the genetic clines were evaluated using mitochondrial DNA and microsatellite loci (n = 9–11) over a 15‐year period (2000–2015). Clinal structure was consistent with prior work demonstrating the existence of both northern and southern lineages with a hybrid zone occurring between southern New Brunswick (NB) and southern NS. Extensive later generation hybrids were detected in this region and in southeastern Newfoundland. Temporal genetic analysis confirmed the southward progression of clines over time; however, the rate of this progression was slower than predicted by forecasting models, and current clines for all marker types deviated significantly from these predictions. Our results suggest that neutral and selective processes contribute to cline dynamics, and ultimately, highlight how selection, hybridization, and dispersal can collectively influence invasion success.