Small Mussels Research Articles

Blue mussel (Mytilus edulis) quality of preferred prey improves digestion in a molluscivore bird (Common Eider,Somateria mollissima)

Benthivorous predators like sea ducks rely on abundant but low-quality food. Because they ingest whole blue mussels (Mytilus edulis L., 1758), including shells, they have to consume large quantities of food to maintain energy balance. Digestive processes may therefore limit energy assimilation in these predators, although selecting mussel types that minimize shell ingestion may improve foraging profitability. To test this prediction, we first quantified mussel quality from different sizes and habitats by measuring energy content and various features of mussel morphology. Then, we conducted digestive experiments on captive Common Eiders (Somateria mollissima (L., 1758)) fed with various mussel types to determine their impact on Eiders’ digestion. Aquacultured and small mussels were of better quality, because of higher energy content and less resistant shells. These mussel characteristics allowed faster digestive processes for an equal digestibility compared with large intertidal mussels. Previous studies showed that aquacultured and small mussels were generally preferred by sea ducks. Hence, prey-selection behaviours and digestive processes seem closely connected in these highly digestive-constrained predators.

Size-dependent changes in toxicity of Perna viridis mussels exposed to natural populations of Pyrodinium bahamense var. compressum

The mussel Perna viridisis used in the Philippine saxitoxin monitoring program as an indicator organism for the presence of saxitoxin in shellfish in an effort to assess concentration beyond a level considered safe for public consumption. Saxitoxin bioaccumulates in mussels through ingestion of saxitoxin-producing algae Pyrodinium bahamense var. compressum(Pbc). This study focuses on the relationship between mussel length and mussel toxicity in mussels exposed to a natural bloom of Pbc. Mussel toxicity was assessed weekly in a 134-day sampling period using Receptor Binding Assay (RBA). Smaller mussels are more toxic than larger mussels at low Pbc cell density (≈102 cells/L) and the reverse is true at higher Pbc cell density (≈5×103 cells/L). These results can be useful in developing strategies for the collection of mussel samples in a toxic algal bloom monitoring program.

An enigmatic kilometer-scale concentration of small mytilids (Late Miocene, Guadalquivir Basin, S Spain)

Upper Miocene heterozoan carbonates crop out extensively in a NE–SW-trending belt (42 km long and 1.5–8 km wide) along the so-called El Alcor topographic high, from Carmona to Dos Hermanas (Seville, S Spain). These carbonates formed at the southern active margin of the Guadalquivir Basin, the foreland basin of the Betic Cordillera. They change to marls basinward (NE) and to sands landward (SE and SW). Therefore, carbonate production was constrained to a limited area in an otherwise siliciclastic shelf. The carbonates (up to 40 m thick) overlie a gradually coarsening-upward succession of marls followed by silts and sandstones. The carbonate sequence can be divided into three subunits corresponding, from bottom to top, to lowstand, transgressive, and highstand system tract deposits. The lower subunit, exhibiting extensive trough cross-bedding, is interpreted as a shallow-water bar deposit. The intermediate subunit onlaps underlying sediments and was deposited in deeper, low-turbulence conditions. The upper subunit deposits accumulated in a well-oxygenated outer platform based on benthic foraminiferal assemblages. The presence of hummocky and swaley cross-stratification in these latter deposits suggests that they were affected by storms. Pervasive fluid-escape structures are also observed throughout the carbonates. The three subunits consist of bioclastic packstones to rudstones made up of abundant fragments of small mytilids. Isotopic data from serpulid polychaete Ditrupa tubes show 13C-depleted values (up to − 16.1‰), whereas δ18O yields normal marine values. Additional isotopic data on shells of scallops, oysters, and small mussels, as well as bulk sediment, show diagenetic alterations. Based on actualistic examples of massive concentrations of mussels, the nearly monospecific composition of the El Alcor deposits, together with negative δ13C values of Ditrupa tubes, indicates that cold seeps presumably promoted carbonate formation. However, the absence of typical features of cold-seep deposits, such as authigenic carbonates mediated by anaerobic bacterial activity and the typical chemosynthetic shelly organisms, makes the large carbonate body of El Alcor an unusual cold-seep deposit.

Trematode infections reduce clearance rates and condition in blue mussels Mytilus edulis

Suspension feeders are important players in coastal food webs: by filtering particles suspended in the water column and depositing faeces and pseudofaeces in sediments, they mediate the coupling of pelagic primary and benthic secondary production. However, the potential interference of parasite infections on suspension feeding is not well investigated. We experimentally determined the effect of infections with metacercariae of the common trematode Renicola roscovita on clearance rates and condition of blue mussels Mytilus edulis. We also investigated whether there were differences in the effects of infections between different size classes of mussels. Using controlled infections under lab conditions, our experiment showed that infections significantly reduced the clearance rates of mussels. This effect was less pronounced in small (42% reduction) than in large mussels (71%). In addition, infections significantly reduced mussel body mass index in large (23% reduction) and small (17%) mussels compared to uninfected mussels. These reductions most likely resulted from a combined effect of an interference of the parasites with the mussel’s feeding apparatus (with the palps being the preferred infection site of the parasite) and of the energetic demands of the parasites (with metacercariae growing in size after initial infection). These negative effects on mussel filter feeding capacity indicate that parasites can alter a crucially important functional trait of marine suspension feeders.

A sad tale: has the small musselIdas argenteuslost its symbionts?

Idas argenteus (Bivalvia: Mytilidae) belongs to a genus of mussels that are often associated with sunken wood and vertebrate bones in the deep sea. By contrast to other species currently included within the genus Idas and other related genera, such as Bathymodiolus, I. argenteus was documented to lack chemosynthetic symbionts bacterial symbionts in its gills. In the present study, new specimens are assigned to I. argenteus based on shell and soft parts analysis. Molecular data confirm the absence or low abundance of symbionts. Phylogeny based on five genes indicates that the symbiont-bearing I. washingtonius is the closest relative of I. argenteus. Symbiosis loss or extreme reduction is thus inferred to have occurred subsequent to the speciation event, 11–13 Mya. This is the first report of a loss of symbiosis within the clade of deep-sea chemosynthetic mussels.

Mammal carcasses attract a swarm of mussels in the deep Atlantic: insights into colonization and biogeography of a chemosymbiotic species

AbstractFive mammal carcasses were experimentally deployed at 1000 m depth in the Setubal Canyon (NE Atlantic) in March 2011 and the remaining bones were collected after 18 and 28 months. High numbers (1.92–6.27 individuals·cm2) of small mussels were found among a diverse invertebrate assemblage colonizing surfaces, crevices and cavities in the trabecular matrix of bones. In this study we characterized the mussel population and their associated bacteria and investigated population structure and settlement patterns. The results of molecular analysis indicated that the mussels are conspecific with the widely distributed bathymodiolin species ‘Idas’ simpsoni and harbor sulfur‐oxidizing bacterial symbionts. Modal decomposition of length‐frequency distributions and estimated shell growth rate suggested that settlement of ‘I.’ simpsoni is continuous and that post‐settlement mortality affects the population structure. This study reports the highest densities and fastest growth rates within bathymodiolin mussels occurring on organic substrates yet recorded and provides evidence for effective mussel recruitment in organic falls in the NE Atlantic Ocean. These results highlight the importance of ephemeral habitats on the biogeographic distribution and dispersal of chemosymbiotic species in deep‐sea ecosystems.

Recruitment and population structure of the non-indigenous brackish-water mytilid Xenostrobus securis (Lamark, 1819) in the Kino River, Japan

The recruitment and population structure of the non-indigenous brackish water mytilid Xenostrobus securis (Lamark, 1819), native to Australasia, were studied in the lower reaches of the Kino River, central Japan. Post-larvae > 2 mm in shell length were found exclusively among barnacle stands of Fistulobalanus kondakovi (Tarasov and Zevina, 1957) and algal fronds of Gloiopeltis tenax (Turner) Decaisone, 1842 from January to May and from July to October. Density of the post-larvae was much greater in the latter period than in the former. Small mussels with shell lengths of 2–4 mm settled to the conspecific mussel beds in April and September. Primary and secondary settlements onto different substrates were observed in the early stages of the life cycle. Two or three cohorts were identified in conspecific mussel beds, and they grew at a rate of ca. 1 mm per month. Density in the beds fluctuated monthly and was greater in the lower than in the middle intertidal zone, suggesting greater spatial heterogeneity in density due to predation in the former.

Environmental factors affecting behavioural responses of an invasive bivalve to conspecific alarm cues

Antipredator defences of aquatic animals depend on various environmental parameters. We studied behavioural responses of a Ponto-Caspian invasive bivalve, the zebra mussel, Dreissena polymorpha, to conspecific alarm cues. We hypothesized that mussels would change their locomotion and aggregation in response to alarm signals. We also hypothesized that body size, light, substratum quality (suitable or unsuitable for attachment) and inclination would affect mussel defences. Changes in horizontal movement of mussels exposed to the alarm substance depended on light. In the presence of crushed conspecifics illuminated mussels (all sizes) moved longer distances than control individuals, whereas in darkness their reaction was the opposite. The response of small mussels was the strongest. Furthermore, the alarm substance reduced upward relocations of all size groups on an inclined surface but at the same time stimulated their downward movement. Large and medium mussels (but not small individuals) exposed to alarm signals formed aggregations more often than control individuals. This effect was only exhibited on sand, unsuitable for mussel attachment. Mussels were generally more clumped on sand than on hard substratum, suggesting that they did not prefer conspecific shells as attachment sites when alternative substrata were available. All responses of mussels to alarm cues tended to be stronger in light, which is an indirect indication of danger. Our study shows that the responses of the zebra mussel to conspecific alarm cues are not limited to activity reduction, as previously thought. They are adjusted to particular environmental conditions and may also involve increased locomotion when relocation to a safer site gives a better chance of survival.

Does differential predation explain the replacement of zebra by quagga mussels?

We examined the hypothesis that direct predation is part of the explanation for the displacement of zebra (Dreissena polymorpha) by quagga mussels (Dreissena rostriformis bugensis) in North America. We investigated selectivity and feeding rates by 3 predators (Round Goby, Pumpkinseed Sunfish, rusty crayfish) using 2 or 3 size classes of predators feeding on different size classes of both mussel species. Round Goby, the predator with a long evolutionary history with dreissenids, consumed a larger range of dreissenid sizes than the other 2 predators. Pumpkinseed Sunfish did not show a preference for either mussel species, but both rusty crayfish and gobies preferred quagga mussels over zebra mussels. The size of mussels vulnerable to these predators increased with predator size, but all predators preferred the smallest mussels (4–8 mm). Medium (105–125 mm) and large (135–155 mm) Round Gobies consumed the largest size class (16–20 mm) of quagga mussels, but only large Round Gobies were able to consume 16–20-mm zebra mussels. Crayfish consumed a higher number of quagga than zebra mussels in both the 8–12-mm and 12–16-mm size classes. Large Pumpkinseed Sunfish (170–185 mm) were able to consume the largest size class of quagga but not zebra mussels. Our results do not support direct predation as the cause for quagga mussels replacing zebra mussels. However, predation may affect mussel size structure because small mussels were more vulnerable to predation than larger mussels.

Tri- and tetra-nucleotide microsatellite DNA markers for the rayed bean freshwater mussel (Villosa fabalis)

Freshwater mussels are one of North America’s most imperiled species, and genetic characterization of these species is essential for recovery planning. The rayed bean (Villosa fabalis) is a small freshwater mussel found in the eastern United States currently listed as endangered. Fifteen microsatellite loci were identified and characterized in sixteen V. fabalis individuals. The number of alleles per locus observed ranged from 3 to 14 and averaged 7.9 alleles per locus. Average observed heterozygosity was 72.8 %. These markers should be useful for V. fabalis population analyses and restoration or recovery programs.

The origin and formation of hair on external valve surfaces of the tropical marine mussel Modiolus traillii (Reeve, 1857)

Direct observations using digital videography in an aquarium showed that hairs on the valve surfaces of Modiolus traillii are not periostracal in origin, as often assumed for similar features in other mussels, but are secreted and planted individually by the foot, so they are correctly termed ‘byssal hairs’. Deposition of byssal hair occurred most frequently just after dark, and the time taken to form a strand of serrated hair varied between slightly more than 1 min to almost 10 min, with a mean time of 4.4 min. We observed one individual deposit a total of 11 hairs in 3.5 h. The formation of some 25 hairs were successfully observed on video for six individuals, and about 3,000 individual hairs from 12 mussels were measured in relation to their position, size and density. While hairs varied considerably in length and width, they are consistently flattened, with one edge bearing serrations and the other edge being smooth. Long hair required more time to form compared with shorter hair, and longer hair was deposited farther away from the byssal gape towards the posterior end of the valves. However, a higher density of short hair was laid around the byssal gape. Smaller mussels tended to have an overall higher density of hair compared with larger individuals. There was no discernible pattern in the order in which long and short hairs were secreted on the periostracal surfaces of either valve. Byssal hair microstructure was generally consistent with the distal region of byssal threads, having a tough but thin outer cortex surrounding a ‘spongy’ honeycomb matrix.

Nutrient regeneration by mussel Mytilus edulis spat assemblages in a macrotidal system

Besides exercising grazing control over phytoplankton populations, suspension-feeding bivalves can also stimulate carrying capacity by regeneration of nutrients. This study provides new data on nutrient uptake and release dynamics, and potential implications for availability and stoichiometry of nutrients, for Mytilus edulis spat collectors in the Netherlands. Uptake and release rates were measured in situ on intact spat collector ropes in a eutrophic macrotidal system in relation to development of ropes in terms of mussel biomass and associated components (fauna, flora, and organic material).There was a good fit between uptake/release rates and mussel weight based on allometric scaling functions, despite the occurrence of a substantial biomass of associated fauna, flora and organic matter on ropes. On a unit biomass basis, nutrient release rates were much higher than reported in other studies, which we attribute to greater activity of small mussels. Accounting for greater weight-specific activity of small mussels, spat collectors released more P than reported for other systems. We show that spat collectors can affect relative availabilities of N, P and Si, and we show that SMCs (Seed Mussel Collectors) likely stimulated phytoplankton production through regeneration of N and of Si, which were at limiting concentrations at different points in time. In the case of Si, stimulation would be restricted to diatoms. We conclude that SMCs are able to stimulate phytoplankton production rates, and thereby carrying capacity, and are able to influence phytoplankton composition.

Shellfish Resources and Maritime Economy at Caylán, Coastal Ancash, Peru

ABSTRACT This article explores the relationships between mollusk exploitation and maritime economies in ancient coastal Peru. Data are drawn from the analysis of shell remains from the Early Horizon center of Caylán (800–1 cal BC), a large urban settlement interpreted as the primary center of a multi-tiered polity located in the Nepeña Valley, coastal Ancash. Excavations in 2009 and 2010 yielded a large amount of faunal remains including 220 kg of shell remains for more than 100,000 MNI. Taxonomic and quantitative analyses of the shell remains bring insights into patterns of exploitation, consumption, discard, and ritual use. Results indicate an emphasis on locally available mollusk species linked to the exploitation of different near-shore and coastal settings. The sample is dominated by small clams and mussels pertaining to the Donax spp., Perumytilus purpuratus, and Semimytilus algosus taxa. Intrasite distributions argue for social differences associated with the access to certain species used in maritime industries. Broader comparative perspectives from the Andean coast indicate variations in maritime subsistence strategies linked to the development of different forms of socioeconomic interactions and redistributive systems through time.

Effects of injured conspecifics and predators on byssogenesis, attachment strength and movement in the blue mussel, Mytilus edulis

Mussels respond to threats from predators by increasing anti-predator traits, which include a suite of inducible defenses. Blue mussels (Mytilus edulis) can modify the strength, number and attachment site of byssal threads in response to water borne cues from predators and injured conspecifics. We quantified byssal thread production, attachment strength and movement in blue mussels of two size classes in response to effluent from the American lobster Homarus americanus, the rock crab Cancer irroratus, the sea star Asterias rubens, and injured conspecific mussels. In a factorial laboratory experiment, effluent from the predatory crab, C. irroratus, resulted in higher numbers of functional byssal threads compared only to exposure to injured conspecific mussels, and not to any other treatment group. Large mussels produced stronger byssal attachments than small mussels. Over 24h, small mussels formed and released more byssus bundles than large mussels, an indication of increased movement. Small mussels started producing byssal threads sooner than large mussels. Mussels exposed to effluent from injured conspecific mussels began producing byssal threads earlier, compared to the control and not to any other treatment group. Our results show that byssogenesis was influenced by predator type and mussel size, whereas attachment strength and movement depended on mussel size. This study highlights the ability of two size classes of blue mussels to selectively alter byssal thread production and movement in the presence of injured conspecifics and potential predators.

Integrative Biology of Idas iwaotakii (Habe, 1958), a ‘Model Species’ Associated with Sunken Organic Substrates

The giant bathymodioline mussels from vents have been studied as models to understand the adaptation of organisms to deep-sea chemosynthetic environments. These mussels are closely related to minute mussels associated to organic remains decaying on the deep-sea floor. Whereas biological data accumulate for the giant mussels, the small mussels remain poorly studied. Despite this lack of data for species living on organic remains it has been hypothesized that during evolution, contrary to their relatives from vents or seeps, they did not acquire highly specialized biological features. We aim at testing this hypothesis by providing new biological data for species associated with organic falls. Within Bathymodiolinae a close phylogenetic relationship was revealed between the Bathymodiolus sensu stricto lineage (i.e. “thermophilus” lineage) which includes exclusively vent and seep species, and a diversified lineage of small mussels, attributed to the genus Idas, that includes mostly species from organic falls. We selected Idas iwaotakii (Habe, 1958) from this latter lineage to analyse population structure and to document biological features. Mitochondrial and nuclear markers reveal a north-south genetic structure at an oceanic scale in the Western Pacific but no structure was revealed at a regional scale or as correlated with the kind of substrate or depth. The morphology of larval shells suggests substantial dispersal abilities. Nutritional features were assessed by examining bacterial diversity coupled by a microscopic analysis of the digestive tract. Molecular data demonstrated the presence of sulphur-oxidizing bacteria resembling those identified in other Bathymodiolinae. In contrast with most Bathymodiolus s.s. species the digestive tract of I. iwaotakii is not reduced. Combining data from literature with the present data shows that most of the important biological features are shared between Bathymodiolus s.s. species and its sister-lineage. However Bathymodiolus s.s. species are ecologically more restricted and also display a lower species richness than Idas species.

Impacts of the invasive ascidian Didemnum vexillum on green-lipped mussel Perna canaliculus aquaculture in New Zealand

Biofouling can pose a significant threat to shellfish aquaculture, as fouling organisms are often strong spatial competitors that are able to reach high densities or biomass in relatively short time frames. This study investigated the potential impacts of the colonial ascidian Didem- num vexillum on cultured New Zealand green-lipped mussels Perna canaliculus at one farm in the Marlborough Sounds region. Three size classes of mussels were examined: small (20 to 40 mm shell length at deployment), medium (40 to 60 mm), and large (60 to 70 mm). Replicate 4 m mussel lines were assigned to 1 of 3 treatments: (1) ambient fouling, (2) fouling enhanced by D. vexillum fragment inoculation (in addition to ambient fouling), or (3) control lines that were kept free of D. vexillum. After 15 mo, subsections of lines (0.5 m length) were processed to determine the effects of fouling cover on mussel density within lines, as well as on individual mussel size and condition. A highly significant negative relationship was shown between D. vexillum biomass and mussel density for small mussels, and to a lesser extent for medium mussels. Values of mussel condition indices were similar across size classes and across fouling treatments within each size class. These results indicate that mussels may only be vulnerable to direct D. vexillum fouling impacts at early stages of production, and that impacts may be restricted to displacement of mussels as opposed to reduced size and condition. This information will assist in the implementation of management procedures through increased understanding of D. vexillum effects at different stages of mussel production.

Effect of oxygen concentration and temperature on the viability of small-sized mussels in hermetic packages

The objective of this study was to evaluate the behaviour of small-sized (∼19 g/unit) Mediterranean mussels packaged hermetically with different proportions of oxygen in the interior of the package and stored at 2 °C and 7 °C. The most favourable conservation conditions (83% O2 and 2 °C) were compared with larger mussels (∼24 g/unit). On day 3 of storage with 20 %O2 at 2 °C, the concentration of volatile fatty acids in the intervalval fluid was double that for the mussels packaged with 83% O2 and this difference increased during storage. Higher temperatures produced a larger and more rapid accumulation of ammonium nitrogen with concentrations of 49 mg N/L on day 6. Lower concentrations were observed at the end of storage at 2 °C (27 mg N/L on day 9). From day 7, the increase of N-TVB measured in the intervalval fluid of the small mussels at 2 °C was more pronounced than in the larger mussels. The organoleptic evaluation, percentage mortality and microbial counts collectively indicated that a high quality product was maintained on day 8–9 at 2 °C with mussels packaged with 83% O2. Inadequate temperatures have a stronger negative impact on shelf life than low oxygen concentrations.

Endemicity in the Gulf of Gabès: the small mussel drill Ocinebrina hispidula is a distinct species in the Ocinebrina edwardsii complex (Muricidae: Ocenebrinae)

The Gulf of Gabes (Tunisia) is a shallow gulf on the North African coast, in the Sicily Channel, characterized by weak currents, low-energy waves and high salinity (37.5–39.25‰) and temperature (13.2–26.58C) (Ktari-Chakroun & Azouz, 1971). It hosts very large meadows of Posidonia oceanica and is known as an important nursery area for demersal resources; nevertheless, studies on the benthic communities are scattered and more are needed (e.g. De Gaillande, 1970; KtariChakroun & Azouz, 1971). The Gabes populations of many animals show morphological features strikingly different from the norm in the rest of their ranges. This is particularly well known in gastropods, to the extent that many such populations have been given full specific rank and are considered to be endemic to the Gulf. In a recent review of the molluscan fauna of the Gulf of Gabes, 33 putative endemics were listed (7% of the total molluscan fauna; Cecalupo, Buzzurro & Mariani, 2008). This enormous number of presumed endemics in a restricted area has raised interest, because of the very young age of the Gulf of Gabes (Sabelli & Taviani, 1981, 2013). During the last glacial maximum (18,000 years before present), sea level reached a minimum of c. 2120 m, and the shallow-water areas of the Gulf of Gabes were completely exposed. It can reasonably be assumed that the Gabes ecosystem, as we know it today, is not older than 6–8 ka, when sea level rose sufficiently (see Morhange & Pirazzoli, 2005 and references therein). Therefore, some possible hypotheses should be tested for each distinct presumed endemic. Is it (1) a distinct species that has originated elsewhere and is now restricted in the Gulf; (2) a distinct species that has originated elsewhere, has colonized the Gulf and is also present elsewhere in the Mediterranean; (3) a distinct species that has originated in the Gulf very recently; or (4) is the Gabes population an ecophenotype characteristic of the extreme conditions in the Gulf? We examined the case of the small mussel drills of the genus Ocinebrina Jousseaume, 1880 (Muricidae: Ocenebrinae), which comprises c. 17–18 currently accepted species in European and West African waters (Houart, 2001; Bonomolo & Buzzuro, 2006; Cecalupo, Buzzurro & Mariani, 2008; Crocetta et al., 2012). (Note that Pacific species sometimes included in Ocinebrina are now ascribed to other genera, including Urosalpinx and Ocenebra). Their taxonomic status has been debated and the use of molecular data is required to stabilize the taxonomy of this group. Some of these taxa are known from single or restricted localities, and are often regarded as narrow-range endemics. Crocetta et al. (2012) recently described a new species in the O. aciculata group, based on subtle morphological features and clear genetic data (COI barcode sequences). Ocinebrina hispidula was originally described (Pallary, 1904: 232, pl. 7, fig. 18) as a variety of O. edwardsii from the Gulf of Gabes. Its status has long been debated, with some authors considering it as a distinct species and others as a mere variety of O. edwardsii. It is diagnosed from O. edwardsii by a narrower shell, a longer siphonal canal and more spiny sculpture with fewer primary spiral cords. It is currently (Houart, 2001) considered as a distinct species with a restricted distribution in the Gulf of Gabes, although shells with a similar morphology have been recorded from other Mediterranean localities (e.g. Cyprus: Houart, 2001; Sicily and Croatia: Giuseppe Bonomolo,

Distinctness, phylogenetic relations and biogeography of intertidal mussels (Brachidontes, Mytilidae) from the south-western Atlantic

Rocky shore intertidal communities along the cold- and warm-temperate coasts of the south-western Atlantic are dominated by small mussels of the genusBrachidontes s.l. (Mytilidae), yet the status of species occurring in the region remains unresolved. Taxonomic studies have been based on shell morphology, but high phenotypic variability has led to much confusion. Based on mitochondrial and nuclear genes (COI, 28S rDNA and ITS1) from nine localities in Uruguay and Argentina we confirmed the occurrence of three species in the south-western Atlantic:Brachidontes darwinianusandB. rodrigueziiin the warm-temperate andB. purpuratusin the cold-temperate sector. The latter two species coexist in the same beds along the transition zone (41–43°S). The phylogeny based on mitochondrial and nuclear genes, indicate an early divergence ofB. purpuratus. At the intra-specific level, low genetic differentiation and absence of fossil record forB. purpuratusfrom the earlier Quaternary marine terraces of Patagonia likely result from a relatively recent (post-LGM) colonization originated from populations in the south-eastern Pacific. In the case ofB. rodriguezii, by contrast, genetic intraspecific differentiation, a fossil record of phenotypically-related forms going back to the Late Miocene, and phylogenetic position in the COI-based phylogeny, prompts the hypothesis that this species is derived from a local stock with a long history of occurrence in the warm-temperate region of the south-western Atlantic. While intertidal mussel beds from the south-western Atlantic are ecologically similar in appearance, their assembly involves components clearly differentiated in terms of historical biogeography and phylogeny.

Impact of Engineered Zinc Oxide Nanoparticles on the Individual Performance of Mytilus galloprovincialis

The increased use of engineered nanoparticles (ENPs) in consumer products raises the concern of environmental release and subsequent impacts in natural communities. We tested for physiological and demographic impacts of ZnO, a prevalent metal oxide ENP, on the mussel Mytilus galloprovincialis. We exposed mussels of two size classes, <4.5 and ≥4.5 cm shell length, to 0.1–2 mg l−1 ZnO ENPs in seawater for 12 wk, and measured the effect on mussel respiration, accumulation of Zn, growth, and survival. After 12 wk of exposure to ZnO ENPs, respiration rates of mussels increased with ZnO concentration. Mussels had up to three fold more Zn in tissues than control groups after 12 wk of exposure, but patterns of Zn accumulation varied with mussel size and Zn concentrations. Small mussels accumulated Zn 10 times faster than large mussels at 0.5 mg l−1, while large mussels accumulated Zn four times faster than small mussels at 2 mg l−1. Mussels exposed to 2 mg l−1 ZnO grew 40% less than mussels in our control group for both size classes. Survival significantly decreased only in groups exposed to the highest ZnO concentration (2 mg l−1) and was lower for small mussels than large. Our results indicate that ZnO ENPs are toxic to mussels but at levels unlikely to be reached in natural marine waters.