Invasive species alter ecosystems and harm economies. Improved understanding of past invasions can inform and improve current and future management efforts. We investigated the global and North American distribution of nonindigenous species (NIS) prior to their establishment in the Laurentian Great Lakes (GL). For the subset of NIS first recorded in North America in the GL, we also investigated the likelihood of these species to spread beyond the basin. With respect to biological invasions, we assessed if the GL basin is a beachhead (i.e., most NIS in the basin originating from outside North America) or a gathering place (i.e., most NIS arriving in GL already in North America). We found that the GL are both a beachhead and a gathering place, depending on the vector of introduction to the basin. Ballast water release introduces most beachhead NIS (43 of 65, 66%), whereas canals, authorized release, and unauthorized release primarly introduce gathering place NIS (67 of 101, 66%). Overall, gathering place NIS currently outnumber beachhead NIS in the GL (101 vs. 65). Regarding spread of beachhead NIS beyond the GL, we found that time elapsed since discovery in the GL predicts secondary spread with 87% accuracy. Our classification model suggests that beachhead NIS established populations outside the GL basin within 77 years of discovery there, suggesting that numerous NIS may be poised to spread beyond the GL basin in the near future. Given the established policy goal of both Canada and the United States to reduce harm from invasions, several recommendations arise from our analysis: (1) maintain, strengthen, and monitor the efficacy of ballast water regulations to prevent the introduction of additional beachhead NIS, (2) conduct risk assessments of NIS that are already in North America but not yet in the GL to prioritize management actions, and (3) seek regional coordination of regulations of vectors of gathering place NIS to shore up weak policy links.

Prince Edward Island (PEI), Canada, has seen the introduction and the establishment of many exotic tunicate species since the late 1990’s. Exploratory research in the Orwell Bay identified turbidity as a potential factor in this failure of tunicates, and in particular Ciona intestinalis, to establish despite multiple unintentional introductions. Laboratory experiments showed significant negative effect of increased suspended inorganic matter on the fertilization success, larval settlement, and the survival of juvenile tunicates. Although the levels of turbidity tested (up to 22 and 32 NTU) reduced all of these processes it did not completely eliminate them. High levels of turbidity have the potential to prevent establishment of non-native tunicates in some locations where establishment would otherwise be expected.

Zebra mussels were first observed in Texas in 2009 in a reservoir (Lake Texoma) on the Texas-Oklahoma border. In 2012, an established population was found in a near-by reservoir, Ray Roberts Lake, and in June 2013, settled mussels were detected in a third north Texas reservoir, Lake Lewisville. An established population was detected in Belton Lake in September 2013. With the exception of Louisiana, these occurrences in Texas mark the current southern extent of the range of this species in the United States. Previous studies indicate that zebra mussel populations could be affected by environmental conditions, especially increased temperatures and extreme droughts, which are characteristic of surface waters of the southern and southwestern United States. Data collected during the first three years (2010–12) of a long-term monitoring program were analyzed to determine if spatio-temporal zebra mussel spawning and larval dynamics were related to physicochemical water properties in Lake Texoma. Reproductive output of the local population was significantly related to water temperature and lake elevation. Estimated mean date of first spawn in Lake Texoma was approximately 1.5 months earlier and peak veliger densities were observed two months earlier than in Lake Erie. Annual maximum veliger density declined significantly during the study period (p < 0.0001). A population crash occurred as a result of thermal stress and variability of lake elevation. In summer 2011, water temperatures peaked at 34.3°C and lake elevation declined to the lowest level recorded during the previous 18 years, which resulted in desiccation of substantial numbers of settled mussels in littoral zones. Veliger spatial distributions were associated with physicochemical stratification characteristics. Veligers were observed in the deepest oxygenated water after lake stratification, which occurred in late spring. Results of this study indicate environmental conditions can influence variability of population sizes and spatial distributions of zebra mussels along the current southern frontier of their geographic range. Although the future population size trajectory and geographic range are uncertain, increased temperatures and intermittent, extreme droughts likely will affect spatio-temporal dynamics of established populations if zebra mussels spread farther into the southern and southwestern United States.

Samples of three hard clam Meretrix spp. (M. lusoria, M. petechialis, and Taiwanese Meretrix) were collected from 12 localities in Japan, China, Korea, and Taiwan between 2004 and 2013. PCR-RFLP analysis and nucleotide sequence analysis for the mtDNA COI region was performed on these samples. HincII and AseI restriction assay discriminated M. lusoria, M. petechialis, and Taiwanese Meretrix, corresponding to the relatively large nucleotide substitution (6.35–8.20 %). In Taiwan, M. lusoria was introduced from Japan in the 1920s; however, our results suggest that Taiwanese Meretrix is genetically differentiated from M. lusoria. As well, the exotic Taiwanese Meretrix was found from Nishinagisa on the north coast of Tokyo Bay, demonstrating the Taiwanese Meretrix now occurs with M. lusoria in its native habitat. Meretrix seedlings (Kumamoto origin) from a Taiwanese aquaculture facility has been released into Nishinagisa since 2008 suggesting the Taiwanese Meretrix is inadvertently mixed with the M. lusoria produced in the aquaculture facility. In contrast, all samples from Kisarazu, on the east coast of Tokyo Bay, were identified as M. lusoria despite there being mass releases of M. lusoria (Kumamoto origin) cultured in Taiwan since 2007. Quality control procedures are needed for future Meretrix spp. releases to prevent further spread of the Taiwanese Meretrix.

Melanoides tuberculata, an exotic thiarid snail that originated in the Middle East, eastern Africa, and Southeast Asia, has invaded subtropical and tropical areas worldwide. This study provided a detailed picture of the characteristics of a population in central Florida. We collected 40 specimens of Melanoides tuberculata from a cool spring and cultured them and 54 of their offspring in the laboratory for 7 and 10 months, respectively. For both the adults and their F1 offspring, weekly or bimonthly measurements of individuals and counts of offspring produced estimates of growth, age at first reproduction, offspring production, and survival. From these measurements, we produced estimates of birth and death rates and a growth curve using a monomolecular model. We estimated predation rates on the snails with a three-day incubation of small (1–4 mm) M. tuberculata with crayfish in the laboratory. Finally, we produced a static life table from measurements of ~2,200 specimens of M. tuberculata collected from the spring. Growth and reproduction measurements from the laboratory indicated that the snails grew rapidly and were prolific. Only initial size significantly explained any variation in the growth of individuals and only first clutch size explained any variation in fecundity. Nonpredatory mortality in the laboratory was low, but crayfish-induced mortality was high. The life table analysis suggested that the spring population was stable and that mortality was extremely high on the smallest individuals, such as those used in the crayfish predation rate measurements, and on the largest individuals. Therefore, the potential of M. tuberculata to invade new habitats and quickly establish populations may be the result of its high population growth rate, but its population growth may be checked by local predators, such as crayfish and perhaps snail-eating turtles and raccoons.

The spotted sea hare Aplysia dactylomela Rang, 1828 is a large and conspicuous opisthobranch sea slug that since 2002 has rapidly colonized the eastern Mediterranean, establishing populations in numerous localities. The source of the Mediterranean populations has been the subject of debate, with two main hypotheses considered (Atlantic and Red Sea origin). A recent study on the taxonomy of A. dactylomela has shown that the spotted sea hare is a complex of at least two genetically distinct species (A. dactylomela in the Atlantic and A. argus in the Indo-Pacific), facilitating the correct identification of Mediterranean specimens by molecular means. We used sequence data from the mitochondrial cytochrome oxidase I gene to identify the Mediterranean individuals for the first time and to infer their origin. Our results confirmed that all the specimens collected in the Mediterranean belong to A. dactylomela and therefore have an Atlantic origin. The limited sample size does not allow identification of the dispersal pathway of A. dactylomela into the Mediterranean, but the colonization sequence is consistent with a “natural” dispersal event. This hypothesis is evaluated in light of local surface circulation patterns. Possible causes for the recent and rapid invasion of the eastern Mediterranean by A. dactylomela are discussed.

The veined whelk Rapana venosa (Valenciennes, 1846) is an active, Asian, invasive mollusk predator that has been present along the coastal zone of Maldonado, Uruguay since 2004. The feeding rate of R. venosa on native mussels was estimated in a laboratory experiment. A flume with a constant water flow was used, in which the mean (± SD) temperature was 25.4 ± 1.8 °C, the mean (± SD) salinity was 18.5 ± 1.6, and a 15:9 light-dark schedule was followed. Each experimental trial lasted 9 days and a constant prey supply was maintained. Three size classes of predators and three size classes of prey (Brachidontes rodriguezii and Mytella charruana), were used. For all sizes of predator combined, the average (± SD) absolute consumption rate was 0.88 ± 0.3 g day-1, and the relative consumption rate was 0.057 ± 0.034 g g-1 day-1. No significant differences were found between the number of prey and total grams consumed among the three size categories of snails. However, for the relative consumption rate, small snails consumed significantly greater (0.10 g g-1 day-1) amounts than intermediate and large snails (0.04 and 0.02 g g-1 day-1 respectively). All sizes of snails consumed significantly more intermediate- than small-sized mussels. This study provides important knowledge for future research to assess the impact of this invasive species on native bivalve resources.

The Peruvian jingle shell, Anomia peruviana d’Orbigny, 1846 is native to the Eastern Pacific including Panama. During recent surveys of Panama’s marine fauna using settlement plates, we discovered A. peruviana in Limon Bay, near the Atlantic entrance of the Panama Canal. We confirmed our initial morphological identifications using partial sequences of the COI barcode locus. All Anomia individuals collected on the settlement plates from Atlantic and Pacific Panama were confirmed to be A. peruviana, which is genetically distinct from the native Atlantic A. simplex. We suspect A. peruviana was transported through the Canal from the Pacific to the Atlantic attached as hull fouling on vessels or recreational boats. Salinity tolerance experiments in the laboratory showed that all individuals in the seawater control survived while 25% survived a 12-hour exposure to freshwater from Gatun Lake, confirming that some A. peruviana individuals can survive even the estimated maximum transit of up to 12 hours through the Panama Canal.