Gail V. Ashton

Mitochondrial DNA reveals multiple Northern Hemisphere introductions of Caprella mutica (Crustacea, Amphipoda)

Caprella mutica (Crustacea, Amphipoda) has been widely introduced to non‐native regions in the last 40 years. Its native habitat is sub‐boreal northeast Asia, but in the Northern Hemisphere, it is now found on both coasts of North America, and North Atlantic coastlines of Europe. Direct sequencing of mitochondrial DNA (cytochrome c oxidase subunit I gene) was used to compare genetic variation in native and non‐native populations of C. mutica. These data were used to investigate the invasion history of C. mutica and to test potential source populations in Japan. High diversity (31 haplotypes from 49 individuals), but no phylogeographical structure, was identified in four populations in the putative native range. In contrast, non‐native populations showed reduced genetic diversity (7 haplotypes from 249 individuals) and informative phylogeographical structure. Grouping of C. mutica populations into native, east Pacific, and Atlantic groups explained the most among‐region variation (59%). This indicates independent introduction pathways for C. mutica to the Pacific and Atlantic coasts of North America. Two dominant haplotypes were identified in eastern and western Atlantic coastal populations, indicating several dispersal routes within the Atlantic. The analysis indicated that several introductions from multiple sources were likely to be responsible for the observed global distribution of C. mutica, but the pathways were least well defined among the Atlantic populations. The four sampled populations of C. mutica in Japan could not be identified as the direct source of the non‐native populations examined in this study. The high diversity within the Japan populations indicates that the native range needs to be assessed at a far greater scale, both within and among populations, to accurately assess the source of the global spread of C. mutica.

Managing Multiple Vectors for Marine Invasions in an Increasingly Connected World

Invasive species remain a major environmental problem in the worlds oceans. Managing the vectors of introduction is the most effective means of mitigating this problem, but current risk assessments and management strategies are largely focused on species, not on vectors and certainly not on multiple simultaneous vectors. To highlight the issue that multiple vectors contribute to invasions, we analyzed the historical and contemporary contributions of eight maritime vectors to the establishment of nonindigenous species in California, where most species were associated with two to six vectors. Vessel biofouling looms larger than ballast water as a major vector and a management opportunity, but aquaculture risk appears reduced from historic levels. Standardized data on species abundances in each vector are lacking for a robust cross-vector assessment, which could be obtained in a proof-of-concept “vector blitz.” Management must shift away from one or two target vectors to coordination across multiple vectors.

Distribution of the introduced amphipod, Caprella mutica Schurin, 1935 (Amphipoda: Caprellida: Caprellidae) on the west coast of Scotland and a review of its global distribution

Caprella mutica Schurin, 1935 was first described from sub-boreal areas of north–east Asia. In less than 40 years C. mutica has spread throughout the northern hemisphere and the first recorded sighting in the southern hemisphere is reported here. Caprella mutica has been introduced to temperate oceanic coasts between latitudes of 25 and 70 °N. Outside its native range, C. mutica has only been found in areas of human activity, including ports, aquaculture facilities and an oilrig; the species has not yet been found in natural habitats. Shipping and aquaculture transfers are the most likely long distance vectors; recreational boating and drifting weed are the most likely short distance vectors. Temperature and salinity do not explain the small-scale distribution of C. mutica on the west coast of Scotland; globally its annual temperature range is 0–22°C. This suggests that the local scale distribution of C. mutica is potentially limited by the availability of suitable transportation vectors during the dispersal phase rather than by physical environmental factors following release.

Geographic variation in marine invasions among large estuaries: effects of ships and time

Coastal regions exhibit strong geographic patterns of nonnative species richness. Most invasions in marine ecosystems are known from bays and estuaries, where ship-mediated transfers (on hulls or in ballasted materials) have been a dominant vector of species introductions. Conspicuous spatial differences in nonnative species richness exist among bays, but the quantitative relationship between invasion magnitude and shipping activity across sites is largely unexplored. Using data on marine invasions (for invertebrates and algae) and commercial shipping across 16 large bays in the United States, we estimated (1) geographic variation in nonnative species richness attributed to ships, controlling for effects of salinity and other vectors, (2) changes through time in geographic variation of these ship-mediated invasions, and (3) effects of commercial ship traffic and ballast water discharge magnitude on nonnative species richness. For all nonnative species together (regardless of vector, salinity, or time period), species richness differed among U.S. coasts, being significantly greater for Pacific Coast bays than Atlantic or Gulf Coast bays. This difference also existed when considering only species attributed to shipping (or ballast water), controlling for time and salinity. Variation in nonnative species richness among Pacific Coast bays was strongly affected by these same criteria. San Francisco Bay, California, had over 200 documented nonnative species, more than twice that reported for other bays, but many species were associated with other (non-shipping) vectors or the extensive low-salinity habitats (unavailable in some bays). When considering only ship- or ballast-mediated introductions in high-salinity waters, the rate of newly detected invasions in San Francisco Bay has converged increasingly through time on that for other Pacific Coast bays, appearing no different since 1982. Considering all 16 bays together, there was no relationship between either (1) number of ship arrivals (from foreign ports) and number of introductions attributed to ships since 1982 or (2) volume of foreign ballast water discharge and number of species attributed to ballast water since 1982. These shipping measures are likely poor proxies for propagule supply, although they are sometimes used as such, highlighting a fundamental gap in data needed to evaluate invasion dynamics and management strategies.

Non-native Aquaculture Species Releases: Implications for Aquatic Ecosystems

* Corresponding author Abstract Aquaculture is undergoing a rapid worldwide expansion. Of significant concern is the increasing use of non-native species, with subsequent escapes of these species and their associated pathogens and parasites posing a serious threat to native biodiversity, economic value and ecosystem function, particularly in regions rich in endemic species. The contribution of non-native species to the growth of the global aquaculture industry and the economic benefits that it has brought to many developing countries cannot be underestimated. However, minimizing the escapes of non-native aquaculture species must be a high priority for resource managers, conservationists and the aquaculture industry. This paper reviews intentional and unintentional non-native aquaculture introductions and the environmental consequences that escapes can have on the aquatic environment and presents a potential system of risk evaluation, management and funding mechanisms to assist in the long term sustainable development of the aquaculture industry.

The Japanese Skeleton shrimp Caprella mutica (Crustacea, Amphipoda): a global invader of coastal waters.

Successful invasion must be viewed as the result of a unique sequence of events, with the established species overcoming a number of previously prohibitive obstacles, for example lack of dispersal vectors, habitat characteristics and environmental conditions of the new area, and the ability to persist in interspecific interactions in the new community. The Japanese skeleton shrimp, Caprella mutica, is proving to be a highly successful non-native crustacean in coastal waters outside its native range having overcome these obstacles. In the past 40 years, C. mutica has spread from its native sub-boreal waters of north-east Asia to numerous locations in both the northern and southern hemisphere, where it has successfully established self-sustaining and thriving populations. After its first European record from the Netherlands in 1995, C. mutica spread rapidly within the North Sea and later to the west coast of Scotland and to Ireland in less than 15 years. Caprella mutica is generally associated with man-made structures and can be found in abundance on boat hulls, floating pontoons and aquaculture infrastructure clinging to fouling organisms.

Seasonal population dynamics of the non-native Caprella mutica (Crustacea, Amphipoda) on the west coast of Scotland

Information on the life history and population dynamics of non-native species is essential to understand the process of invasion and impacts on invaded ecosystems. The non-native marine caprellid amphipod Caprella mutica has successfully established populations on coastlines throughout the temperate northern hemisphere and in New Zealand in the southern hemisphere. The introduction mechanism has been surpassed and it is now important to understand its ecology and biology in non-native habitats. The seasonal population dynamics of C. mutica were investigated over 18 months at four sites with different levels of anthropogenic disturbance on the west coast of Scotland. Abundance of C. mutica fluctuated seasonally at all sites, peaking during June to October. The highest abundance recorded on a single mesh collector was 319 000 individuals m-2 in August 2004 at one of the fish farms. Both seasonal and site-specific factors influenced the population dynamics of C. mutica. Both males and females were significantly larger and more abundant at the fish farm sites. Individuals displayed reproductive characteristics at a smaller size at the fish farm sites, indicating earlier maturity. The results suggest that anthropogenic disturbance and artificial resource enhancement contribute to the global establishment success of non-native C. mutica.

Geometric morphometric analysis discriminates native and non-native species of Caprellidae in western North America

Characteristics of the second gnathopod are traditionally used to distinguish between species of caprellid amphipods. However, these distinctions are often subjective and can be variable within a species. Geometric morphometrics were used to quantitatively assess shape variation of the second gnathopod propodus of three species of caprellids in North America, including the non-native Caprella mutica. Gnathopod shapes of C. mutica specimens from different latitudes revealed distinct morphologies; the factors responsible for the shape variations are unknown. Allometric change of propodus shape was observed in C. mutica. Larger individuals showed a wide array of possible propodus morphologies. Despite this variability, there were clear differences between large specimens of C. mutica and two species native to North America: C. alaskana and C. kennerlyi. The use of geometric morphometrics and the thin-plate spline method can serve to both complement descriptions using traditional keys and aid in identification of non-native species in novel geographical regions.

Response to van der Meer

In our recent Current Biology paper [1], we describe an ocean warming experiment in which we manipulated the temperature of panels set on the seafloor to provide a realistic and relevant indication of how benthic communities may change under future ocean warming. We describe increases in growth associated with warming by 1°C, with growth rates up to doubled in some species. The definition of Q10 is a measure of the temperature sensitivity of an enzymatic reaction rate or a physiological process due to an increase by 10°C; doubling of growth rates with a 1°C change gives Q10s around 1,000. In his correspondence, Jaap van der Meer [2] questions our methods and provides alternative analyses which lead him to conclude that our observed increases in growth rate were in fact much lower and in accordance with previous studies from temperate zones. We provide justification for our use of absolute growth rate, justification for not using instantaneous growth rate (or a measure of growth in proportion to previous growth) and encourage the on-going discussion of how to measure and compare growth rates.