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BackgroundMolluscs are the most diverse marine phylum and this high diversity has resulted in considerable taxonomic problems. Because the number of species in Canadian oceans remains uncertain, there is a need to incorporate molecular methods into species identifications. A 648 base pair segment of the cytochrome c oxidase subunit I gene has proven useful for the identification and discovery of species in many animal lineages. While the utility of DNA barcoding in molluscs has been demonstrated in other studies, this is the first effort to construct a DNA barcode registry for marine molluscs across such a large geographic area.Methodology/Principal FindingsThis study examines patterns of DNA barcode variation in 227 species of Canadian marine molluscs. Intraspecific sequence divergences ranged from 0–26.4% and a barcode gap existed for most taxa. Eleven cases of relatively deep (>2%) intraspecific divergence were detected, suggesting the possible presence of overlooked species. Structural variation was detected in COI with indels found in 37 species, mostly bivalves. Some indels were present in divergent lineages, primarily in the region of the first external loop, suggesting certain areas are hotspots for change. Lastly, mean GC content varied substantially among orders (24.5%–46.5%), and showed a significant positive correlation with nearest neighbour distances.Conclusions/SignificanceDNA barcoding is an effective tool for the identification of Canadian marine molluscs and for revealing possible cases of overlooked species. Some species with deep intraspecific divergence showed a biogeographic partition between lineages on the Atlantic, Arctic and Pacific coasts, suggesting the role of Pleistocene glaciations in the subdivision of their populations. Indels were prevalent in the barcode region of the COI gene in bivalves and gastropods. This study highlights the efficacy of DNA barcoding for providing insights into sequence variation across a broad taxonomic group on a large geographic scale.

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Dreissenid mussels (including the zebra mussel Dreissena polymorpha and the quagga mussel D. rostriformis) are among the world's most notorious invasive species, with large and widespread ecological and economic effects. However, their long‐term population dynamics are poorly known, even though these dynamics are critical to determining impacts and effective management. We gathered and analyzed 67 long‐term (>10 yr) data sets on dreissenid populations from lakes and rivers across Europe and North America. We addressed five questions: (1) How do Dreissena populations change through time? (2) Specifically, do Dreissena populations decline substantially after an initial outbreak phase? (3) Do different measures of population performance (biomass or density of settled animals, veliger density, recruitment of young) follow the same patterns through time? (4) How do the numbers or biomass of zebra mussels or of both species combined change after the quagga mussel arrives? (5) How does body size change over time? We also considered whether current data on long‐term dynamics of Dreissena populations are adequate for science and management. Individual Dreissena populations showed a wide range of temporal dynamics, but we could detect only two general patterns that applied across many populations: (1) Populations of both species increased rapidly in the first 1–2 yr after appearance, and (2) quagga mussels appeared later than zebra mussels and usually quickly caused large declines in zebra mussel populations. We found little evidence that combined Dreissena populations declined over the long term. Different measures of population performance were not congruent; the temporal dynamics of one life stage or population attribute cannot generally be accurately inferred from the dynamics of another. We found no consistent patterns in the long‐term dynamics of body size. The long‐term dynamics of Dreissena populations probably are driven by the ecological characteristics (e.g., predation, nutrient inputs, water temperature) and their temporal changes at individual sites rather than following a generalized time course that applies across many sites. Existing long‐term data sets on dreissenid populations, although clearly valuable, are inadequate to meet research and management needs. Data sets could be improved by standardizing sampling designs and methods, routinely collecting more variables, and increasing support.

We examined the shell morphology of the bay mussel Mytilus trossulus (Gould) at six locations with various levels of wave exposure in Barkley Sound on the west coast of Vancouver Island, British Columbia, Canada. Young adult M. trossulus (29-35 mm shell length) collected from wave-exposed sites displayed striking differences in shell morphology from M. trossulus from sheltered sites. Mytilus trossulus from wave-exposed habitats had a lower shell height / shell width ratio and a thicker shell; they also had higher, more robust dysodont teeth, as well as a thicker hinge ligament. Examination of juveniles (12-14 mm shell length) collected from a wave-exposed shore and a sheltered shore separated by only a few hundred metres displayed similar differences in shell morphology and ligament thickness. These observations suggest that wave exposure is the cause of the observed differences in shell morphology and ligament thickness in M. trossulus. This is the first report of a correlation between wave exposure and morphology of the dysodont teeth and ligament in a bivalve. We discuss potential selective pressures that may favor characteristics of wave-exposed shells, including the probability of dislodgment and misalignment of valves in high wave energy areas.

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Martel, A. 1993. Dispersal and recruitment of zebra mussel (Dreissewa polymsrpha) in a nearshore area in westcentral Lake Erie: the significance of postmetamorphic drifting. Can. j. Fish. Aquat. Sci. 50: 3-12. Quantitative evidence that early postmetamorphic stages of zebra mussel (Dreissewa psbymsrpha) can disperse in the water column and colonize substrates has been obtained using off-bottom scouring pad collectors and plankton sampling in a nearshore, shallow-water area (2-7 rn) near Wkeatley, hake Erie, during August 1991.Collectors were deployed for 24-72 h, thus minimizing growth of recruits during deployments. Size criteria determined through an in situ growth experiment were used to discriminate between individuals arriving at a collector as (1) settling larvae or (2) postmetamorphic stages. During certain periods, 20-80% of individuals settling on collectors were psstmetamorphic stages. Plankton samples taken near csllectors also confirmed the presence of postmetamorphic stages in the water column. Most drifting juveniles ranged from about 300 Fm shell length to 800 gLm (some up to 1-2 mm). Although settlement by psstmetamorphie stages occurred during various periods, they drifted and settled on collectors in much higher numbers during periods of strong wave action generated during storms. Colonization of natural and man-made substrates by postmetamorphic stages may be significant in exposed or turbulent areas and may impact on population dynamics. Whether postmetamorphic drifting is adaptive and which mechanisms are involved are unknown.Bes resultats quantitatifs obtenus en aoOt 1991 ont demontr6 que les individus aux premiers stades post-rnetamorphiques de la moule zebree (Dreissena polymorpha) peuvent se disperser dans la colonne d'eau et coloniser des substrats. Ces resultats proviennent de I'kchantillsnnage du plancton et de I'utilisation de collecteurs constitues de tampons 2 recurer, dCptoyCs pr+s du fond, dans crn secteur d'eau peu profonde (2-7 m), places 2 proximite du rivage pr&s de Wheatley (Ontario), sur le lac Erie. Les collecteurs Ctaient submerges de 24 3 72 h, ne permettant ainsi qu'une croissanee limit& des recrues durant cette periode. Des crit6res de taille, determines lors d'une experience in situ sur la eroissance, ont wrvi A etablir une distinction entre les individus arrivant 3 un colleeteur soit 1) 2 l'etat larvaire (velig6re), soit 2 ) 3 l14tat.post-metamorph'sque (juvenile), Be 20 2 80 % des individus qui se fixaient aux csllecteurs 6taient des juveniles lors de certaines pkriodes, Les echantillons de zooplancton pre-lev& pr+s des collecteurs ont akessi confirme la presence de juveniles dans la colonne d'eau. La plupafl des juveniles 3 la derive avaient une coquille mesurant entre 300 et 800 pm (padois jusqulA 1-2 rnrn). Bien que des juveniles se soient fixes 2 diffkrentes periodes, ces derniers dkrivaient et se fixaient aux collecteurs en bien plus grand nsrnbre dkerant les periodes de fortes vagues produites lors des tempetes. La colonisation des substrats par les stades p...