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The colonial tunicate Clavelina lepadiformis is a recent invader to the northwest Atlantic and has the potential to cause ecological and economic harm. This paper provides a review of the biological and ecological characteristics of C. lepadiformis, and hypothesizes the likely mechanisms of introduction, establishment and future expansion. The intent of this paper is to provide a consolidated source of information for marine ecosystem managers and provide a starting point for developing a management strategy, should one be desired. Although C. lepadiformis is not currently a management challenge because of the limited range of the invasion in North America; the similarities between C. lepadiformis and other tunicate invaders, and the proximity of incipient populations to boating, shipping, aquaculture, and energy infrastructure suggest future economic burden of this new invader. Other regions such as the west coast of North America and New Zealand may be at risk for invasion by C. lepadiformis.

The nematode Anguillicoloides crassus is one of the many threats hanging over anguillid eels, now known to infect six Anguilla species worldwide. It was first described in Japan, in 1974, and is commonly thought to natively stem from East Asia. Here our primary objective was to critically evaluate this long-held statement. We first retraced the factual history of this global invader, to later investigate the pros and cons for an East Asian origin. After exploring the alternative scenarios for the joint origin of the two anguillicolid parasites occurring in this area, we concluded that the geographic zone covering the natural range of the local eel A. japonica is still the most probable origin (in the absence of another identified candidate host and area). However, we cannot exclude that A. crassus may have been previously introduced along with exotic eel species, at some early stages of aquaculture in Japan. We call for caution when dealing with the native origin of this and other parasitic invaders in provenance of East Asia, a region to be regarded as a major crossroads for fish and parasites of the world. We finally identified the need for a possible resolution of the question, which includes a deeper sampling effort in the Indo-Pacific zone and the further development of molecular phylogeographic studies of all five anguillicolid species and their hosts.

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Multinucleate Sphere X (MSX) is an important pathogen of the eastern oyster (Crassostrea virginica) on the east coast of North America. This parasite is currently not present in Prince Edward Island (PEI), but there are concerns that it will spread from Cape Breton, Nova Scotia, where it was recently identified. Introduction of MSX to PEI would cause direct losses to the shellfish industry and it would have long-term implications for exports of oysters. The main goal of this study was to assess the risk of introduction and dissemination of MSX, as estimated by the number of movements of commercial oysters from three data sources. The in-degree (incoming) and out-degree (outgoing) of the contact network among bays, estuaries, and rivers were used to quantify the risks. For a single location on PEI, identification of up to 55 incoming and up to 26 outgoing movements to and from different locations within PEI were recorded. This suggests that if MSX was introduced it could be disseminated quickly. Movements of shellfish (oysters and mussels) from New Brunswick and Nova Scotia, which pose additional risks of pathogen introduction to PEI, were also identified. Two locations (New London Bay and the East-North-West River complex) were consistently ranked in the top quartile of incoming movements by the three data sources. In addition, two other locations (Bideford Area and Conway Narrows) were classified in the same quartile by only two of the data sources, suggesting that these four areas can be considered at high risk for pathogen introduction. Similarly, two locations were classified in the top quartile of outgoing movements (East-North-West River complex and Orwell Area) by the three data sources, whereas Bideford Area and Foxley River were only identified by two of the three data sources in the same quartile. These results indicate not only risk areas for pathogen introduction or dissemination, but also those areas having both high risk of introduction and high risk of dissemination (e.g., East-North-West River complex). Results of this study illustrate the potential consequences of MSX should Haplosporidium nelsoni reach PEI. Findings also highlight the need for the development of a system that captures all shellfish movements, which will be essential to mounting an effective response to pathogen introduction and mitigation of disease dissemination.