ALBERT

Description: Invasions of freshwater habitats by marine and brackish species have become more frequent in recent years with many of those species originating from the Ponto-Caspian region. Populations of Ponto-Caspian species have successfully established in the North and Baltic Seas and their adjoining rivers, as well as in the Great Lakes-St. Lawrence River region. To determine if Ponto-Caspian taxa more readily acclimatize to and colonize diverse salinity habitats than taxa from other regions, we conducted laboratory experiments on 22 populations of eight gammarid species native to the Ponto-Caspian, Northern European and Great Lakes-St. Lawrence River regions. In addition, we conducted a literature search to survey salinity ranges of these species worldwide. Finally, to explore evolutionary relationships among examined species and their populations, we sequenced the mitochondrial cytochrome c oxidase subunit I gene (COI) from individuals used for our experiments. Our study revealed that all tested populations tolerate wide ranges of salinity, however, different patterns arose among species from different regions. Ponto-Caspian taxa showed lower mortality in fresh water, while Northern European taxa showed lower mortality in fully marine conditions. Genetic analyses showed evolutionary divergence among species from different regions. Due to the geological history of the two regions, as well as high tolerance of Ponto-Caspian species to fresh water whereas Northern European species are more tolerant of fully marine conditions, we suggest that species originating from the Ponto-Caspian and Northern European regions may be adapted to freshwater and marine environments, respectively. Consequently, the perception that Ponto-Caspian species are more successful colonizers might be biased by the fact that areas with highest introduction frequency of NIS (i.e., shipping ports) are environmentally variable habitats which often include freshwater conditions that cannot be tolerated by euryhaline taxa of marine origin.

Description: This paper examines the current status and future risks of biological invasions in the marine environments of the Arctic, within the context of climate change, natural resource development, and expanded Arctic shipping. The number of nonindigenous species introductions varied across the region with the greatest number of introductions recorded in the Iceland Shelf, followed by the Barents Sea and the Norwegian Sea. Most introductions were attributed to vessels, natural spread, and aquaculture activities. Vector management, horizon scanning, early detection, rapid response, and a pan‐Arctic biodiversity inventory are recommended to address future invasion risks. Abstract Climate change and increased anthropogenic activities are expected to elevate the potential of introducing nonindigenous species (NIS) into the Arctic. Yet, the knowledge base needed to identify gaps and priorities for NIS research and management is limited. Here, we reviewed primary introduction events to each ecoregion of the marine Arctic realm to identify temporal and spatial patterns, likely source regions of NIS, and the putative introduction pathways. We included 54 introduction events representing 34 unique NIS. The rate of NIS discovery ranged from zero to four species per year between 1960 and 2015. The Iceland Shelf had the greatest number of introduction events (n = 14), followed by the Barents Sea (n = 11), and the Norwegian Sea (n = 11). Sixteen of the 54 introduction records had no known origins. The majority of those with known source regions were attributed to the Northeast Atlantic and the Northwest Pacific, 19 and 14 records, respectively. Some introduction events were attributed to multiple possible pathways. For these introductions, vessels transferred the greatest number of aquatic NIS (39%) to the Arctic, followed by natural spread (30%) and aquaculture activities (25%). Similar trends were found for introductions attributed to a single pathway. The phyla Arthropoda and Ochrophyta had the highest number of recorded introduction events, with 19 and 12 records, respectively. Recommendations including vector management, horizon scanning, early detection, rapid response, and a pan‐Arctic biodiversity inventory are considered in this paper. Our study provides a comprehensive record of primary introductions of NIS for marine environments in the circumpolar Arctic and identifies knowledge gaps and opportunities for NIS research and management. Ecosystems worldwide will face dramatic changes in the coming decades due to global change. Our findings contribute to the knowledge base needed to address two aspects of global change—invasive species and climate change.

Description: Spread of alien species has increased with global trade and human movement, especially over the past century. Some alien species significantly alter the freshwater ecosystems they invade, thus there has been a growing tendency for governments to develop management programs to prevent invasions and their undesirable consequences. Two factors considered as null models when assessing the potential for biological invasions are colonization pressure ( i.e ., the number of species introduced) and propagule pressure [ i.e ., the number (propagule size), and frequency (propagule number), of individuals of each species introduced]. We translate the terminology of species abundance distributions to the invasion terminology of propagule size and colonization size (PS and CS, respectively). We conduct hypothesis testing to determine the underlying statistical species abundance distribution for zooplankton assemblages transported between freshwater ecosystems; and, on the basis of a lognormal statistical distribution, construct four hypothetical assemblages spanning assemblage structure, rank-abundance gradient ( e.g ., even vs uneven), total abundance (of all species combined), and relative contribution of PS vs CS. For a given CS, many combinations of PS and total abundance can occur when transported assemblages conform to a lognormal species abundance distribution; therefore, for a given transportation event, many combinations of CS and PS are possible with differing invasion outcomes. An assemblage exhibiting high PS but low CS (species poor, but highly abundant) easily overcomes demographic barriers to establishment, but with lower certainty of amenable environmental conditions in the recipient region; whereas, the opposite extreme, high CS and low PS (species rich, but low abundance per species) provides multiple opportunities for one of n arriving species to circumvent environmental barriers, albeit with lower potential to overcome demographic constraints. Species abundance distributions of transported assemblages and the corresponding influence of CS and PS are some of many factors ( e.g ., demographic and genetic stochasticity, environmental variability of recipient ecosystems) that will help refine our understanding of establishment risk following human-mediated movements of species assemblages between freshwater ecosystems.

Description: Invasions of freshwater habitats by marine and brackish species have become more frequent in recent years with many of those species originating from the Ponto-Caspian region. Populations of Ponto-Caspian species have successfully established in the North and Baltic Seas and their adjoining rivers, as well as in the Great Lakes-St. Lawrence River region. To determine if Ponto-Caspian taxa more readily acclimatize to and colonize diverse salinity habitats than taxa from other regions, we conducted laboratory experiments on 22 populations of eight gammarid species native to the Ponto-Caspian, Northern European and Great Lakes–St. Lawrence River regions. In addition, we conducted a literature search to survey salinity ranges of these species worldwide. Finally, to explore evolutionary relationships among examined species and their populations, we sequenced the mitochondrial cytochrome c oxidase subunit I gene (COI) from individuals used for our experiments. Our study revealed that all tested populations tolerate wide ranges of salinity, however, different patterns arose among species from different regions. Ponto-Caspian taxa showed lower mortality in fresh water, while Northern European taxa showed lower mortality in fully marine conditions. Genetic analyses showed evolutionary divergence among species from different regions. Due to the geological history of the two regions, as well as high tolerance of Ponto-Caspian species to fresh water whereas Northern European species are more tolerant of fully marine conditions, we suggest that species originating from the Ponto-Caspian and Northern European regions may be adapted to freshwater and marine environments, respectively. Consequently, the perception that Ponto-Caspian species are more successful colonizers might be biased by the fact that areas with highest introduction frequency of NIS (i.e., shipping ports) are environmentally variable habitats which often include freshwater conditions that cannot be tolerated by euryhaline taxa of marine origin. This article is protected by copyright. All rights reserved.

Description: Understanding the functional relationship between the sample size and the performance of species richness estimators is necessary to optimize limited sampling resources against estimation error. Nonparametric estimators such as Chao and Jackknife demonstrate strong performances, but consensus is lacking as to which estimator performs better under constrained sampling. We explore a method to improve the estimators under such scenario. The method we propose involves randomly splitting species-abundance data from a single sample into two equally sized samples, and using an appropriate incidence-based estimator to estimate richness. To test this method, we assume a lognormal species-abundance distribution (SAD) with varying coefficients of variation (CV), generate samples using MCMC simulations, and use the expected mean-squared error as the performance criterion of the estimators. We test this method for Chao, Jackknife, ICE, and ACE estimators. Between abundance-based estimators with the single sample, and incidence-based estimators with the split-in-two samples, Chao2 performed the best when CV 〈 0.65, and incidence-based Jackknife performed the best when CV 〉 0.65, given that the ratio of sample size to observed species richness is greater than a critical value given by a power function of CV with respect to abundance of the sampled population. The proposed method increases the performance of the estimators substantially and is more effective when more rare species are in an assemblage. We also show that the splitting method works qualitatively similarly well when the SADs are log series, geometric series, and negative binomial. We demonstrate an application of the proposed method by estimating richness of zooplankton communities in samples of ballast water. The proposed splitting method is an alternative to sampling a large number of individuals to increase the accuracy of richness estimations; therefore, it is appropriate for a wide range of resource-limited sampling scenarios in ecology. We propose a new methodology to randomly split species-abundance data from a single sample into two equally sized subsamples and use an appropriate incidence-based richness estimator to increase their performances. The proposed method is an alternative to having a large sample to increase estimation accuracy. This can be appropriate for a wide range of resource-limited sampling scenarios in ecology.

Description: Recent studies have recognized the importance of propagule pressure (number of individuals) and colonization pressure (number of species) for explaining establishment success of nonindigenous species. However, the International Ballast Water Management Convention, when ratified, will require ships to satisfy a numeric discharge standard that focuses only on cumulative propagule pressure of all individuals released. Because of practical constraints, the standard does not differentiate between discharges of single vs. multiple species. The assemblage-based approach, which uses rank-abundance gradients to quantify and manage introduction risk, may compensate for this limitation (e.g., even gradient [relatively consistent propagule pressures among n transported species] or uneven gradient [uneven propagule pressures among n transported species]). Here we explore species abundance distributions of zooplankton during transportation in ballast water to assess variability in the structure of assemblages, with implications for the potential development of an assemblage-based management model. Specifically, we explored species abundance distributions for voyages that lasted 〈 24 h, those from 24 to 48 h, and those from 48 to 72 h (i.e., three time scales). Species abundance distributions within and across transit time scales were highly variable. As transport time increased, we observed a shift from uneven to even rank-abundance gradients. Owing to variation in assemblage structure, the number of organisms necessary to quantify colonization pressure exhibited similarly strong variation within and across time scales. Our study indicates that assemblage-based approaches to estimate introduction risk are warranted, yet the variation inherent in transported assemblages will induce substantial uncertainty within management models.