Andrea Locke

Spatial distribution of fishes and decapods in eelgrass (Zostera marina L.) and sandy habitats of a New Brunswick estuary, eastern Canada

We investigated spatial distribution of fishes and decapods in eelgrass (Zostera marina L.) and non-vegetated sandy habitats in Kouchibouguac Estuary, New Brunswick, Canada. During the ice-free season in 1999 and 2000, mobile fauna were sampled using fyke nets, minnow traps and an epibenthic sled. In general, fishes and decapods were more abundant and diverse (species richness) in eelgrass beds than in nearby sandy habitats, although the trend in abundance of decapods was not statistically significant. Abundance was greater at night than during daylight hours for most species. Atlantic tomcod (Microgadus tomcod), winter flounder (Pleuronectes americanus) and sand shrimp (Crangon septemspinosa) dominated night/crepuscular catches, whereas threespine stickleback (Gasterosteus aculeatus) and cunner (Tautogolabrus adspersus) predominated in diurnal periods. The nursery function of eelgrass habitat was most evident for juvenile white hake (Urophycis tenuis) and small cunners (<3xa0cm), which were found only in such habitat. This study is one of the few to have investigated the ecological importance of eelgrass habitats for mobile faunal communities in eastern Canada.

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.

User-friendly and evidence-based tool to evaluate probability of eradication of aquatic non-indigenous species.

Summary 1. The gap between practitioners and conservation or environmental management science is difficult to bridge. Managers sometimes use limited scientific information in their decisionmaking process, mainly because they have little time to review primary literature before making a decision. Making data readily available to managers is expected to improve the overall efficiency of management interventions. Here, we present an approach to develop userfriendly applications for evidence-based management and illustrate the concept by presenting a simple computer program designed to evaluate the probability of eradication of aquatic non-indigenous species. 2. We conducted a review of case studies that attempted to control aquatic non-indigenous species and used a statistical model to relate the outcome (eradication or non-eradication) to characteristics of the populations and interventions conducted. Based on a few key variables, the model returned accurate probabilities of eradication as evaluated with a receiver operating characteristic curve and jackknife and cross-validation procedures. 3. We packaged the statistical model in a user-friendly computer program that can be used by managers to (i) rapidly calculate the probability of success of a planned intervention with associated uncertainty, (ii) compare the success probabilities of different possible interventions and (iii) prioritize what information should be collected to increase the reliability of estimates. 4. Synthesis and applications. Our decision support tool is easy to implement, statistically flexible and could be used for any type of conservation or management intervention, given a sufficient number of case studies available in the literature. We recommend that scientists develop such tools whenever they conduct reviews of effectiveness of intervention. This is likely to result in greater use of data by practitioners, increased reliability of cost–benefit analyses and an overall increase in efficiency in conservation and environmental management.

Applications of the Menge‐Sutherland Model to Acid‐Stressed Lake Communities

The predictions of the Menge-Sutherland model with respect to the effects of environmental stress on species richness, food web complexity, food chain length, and the relative importance of predation, competition, and disturbance in structuring communities were examined using midsummer zooplankton communities of 46 lakes near Sudbury, Ontario with pHs of 3.8-7.2. The lakes were sampled in the 1970s and in 1990 yielding a total of 92 food webs. Species richness increased linearly with pH rather than peaking at intermediate levels of stress as predicted by the model. Food web complexity and food chain length increased with pH, as predicted. The importance of competition in food web structure was variable at low pH and consistently high at moderate pH, a result that does not support model predictions that disturbance, competition, and predation should sequentially predominate with increasing pH. High variability in the relative importance of competition in acidic lakes was explained by fish presence or absence; in lakes without fish, a larger proportion of links in the zooplankton food web was due to predation by invertebrates. Persistence of predators (fish) in some acidic lakes reduces the applicability of the Menge-Sutherland model.

Evidence‐based tool surpasses expert opinion in predicting probability of eradication of aquatic nonindigenous species

The main objective of evidence-based management is to promote use of scientific data in the decision-making process of managers, with data either complementing or replacing expert knowledge. It is expected that this will increase the efficiency of environmental interventions. However, the relative accuracy and precision of evidence-based tools and expert knowledge has seldom been evaluated. It is therefore essential to verify whether such tools provide better decision support before advocating their use. We conducted an elicitation survey in which experts were asked to (1) evaluate the influence of various factors on the success of eradication programs for aquatic nonindigenous species and (2) provide probabilities of success for real case studies for which we knew the outcome. The responses of experts were compared with the results and predictions of a newly developed evidence-based tool: a statistical model calibrated with a meta-analysis of case studies designed to evaluate probability of eradication. Experts and the model generally identified the same factors as influencing the probability of success. However, the model provided much more accurate estimates for the probability of eradication than expert opinion, strongly suggesting that an evidence-based approach is superior to expert knowledge in this case. Uncertainty surrounding the predictions of the evidence-based tool was similar to among-expert variability. Finally, a model based on >30 case studies returned more accurate predictions than expert opinion. We conclude that decision-making processes based on expert judgment would greatly benefit from incorporating evidence-based tools.

Will reduced summer UV-B levels affect zooplankton populations of temperate humic and clearwater lakes?*

We collected zooplankton samples from 4×4 m enclosures located in two acidified lakes (pH<5) in Nova Scotia from June to August 1996. One lake had mean dissolved organic carbon concentrations greater than 10 mg l−1 (brown water), while the other had values between 2 and 4 mg l−1. In each lake, three enclosures were open to ambient light, while three were covered by Mylar® sheets which removed UVB and UVC wavelengths. Weekly sampling was done at all sites in July and near the end of August. Individuals were identified and the total community weighed. Analysis of results using both t-test and canonical analysis revealed small differences in populations between open and UVB covered clearwater sites in early July, but not later. There was no response of midsummer zooplankton communities in the humic lake which had a 95% extinction depth of 3 cm. In the clearwater lake (95% UVB extinction at 50 cm), the effect of radiation exclusion was relatively weak compared to most other published studies, but nevertheless statistically significant.

Modelling the dynamics of invasion and control of competing green crab genotypes

Establishment of invasive species is a worldwide problem. In many jurisdictions, management strategies are being developed in an attempt to reduce the environmental and economic harm these species may cause in the receiving ecosystem. Scientific studies to improve understanding of the mechanisms behind invasive species population growth and spread are key components in the development of control methods. The work presented herein is motivated by the case of the European green crab (Carcinus maenas L.), a remarkably adaptable organism that has invaded marine coastal waters around the globe. Two genotypes of European green crab have independently invaded the Atlantic coast of Canada. One genotype invaded the mid-Atlantic coast of the USA by 1817, subsequently spreading northward through New England and reaching Atlantic Canada by 1951. A second genotype, originating from the northern limit of the green crabs European range, invaded the Atlantic coast of Nova Scotia in the 1980s and is spreading southward from the Canadian Maritime provinces. We developed an integrodifference equation model for green crab population growth, competition and spread, and demonstrate that it yields appropriate spread rates for the two genotypes, based on historical data. Analysis of our model indicates that while harvesting efforts have the benefit of reducing green crab density and slowing the spread rate of the two genotypes, elimination of the green crab is virtually impossible with harvesting alone. Accordingly, a green crab fishery would be sustainable. We also demonstrate that with harvesting and restocking, the competitive imbalance between the Northern and Southern green crab genotypes can be reversed. That is, a competitively inferior species can be used to control a competitively superior one.

Zooplankton communities of a dammed estuary in the Bay of Fundy, Canada

The upper estuary of the macrotidal Petitcodiac River, New Brunswick, Canada, was converted to a freshwater impoundment by construction of a causeway in 1968. Thirty years later, zooplankton community structure in the impoundment was characteristic of a disturbed ecosystem. The depauperate zooplankton consisted of a mixture of freshwater and marine/brackish taxa, but was not typical of regional estuaries or lakes. The causeway dam was an obstacle to fish migration, and several anadromous species that would formerly have been represented in the ichthyoplankton were absent. The invertebrate plankton community was dominated by rotifers, likely as a result of frequent water level fluctuations, and highly suspended sediment levels in the water column. Estuarine/marine calanoids (Eurytemora affinis, Temora longicornis, Centropages typicus, Tortanus discaudatus), the mysid Neomysis americana, and Cancer crab zoeae were collected in fresh water up to 14xa0km upstream of the causeway.

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.