Response on scallop culture to enhanced nutrient supply by experimental fertilisation of a landlocked bay

The effect of an enhanced nutrient supply to coastal waters of a landlocked bay, Hopavågen in Central Norway, on the phytoplankton production and biomass, and on growth of scallops (Pecten maximus) was studied in 1997–1999. Nitrogen, silicon and phosphorous (N:Si:P = 16:8:1, atomic) were added daily between May and October in 1998 at a level of 0.4 mg P m^–3 day^–1. The concentration of nutrient addition was doubled in 1999 during the same period. High addition of nutrients (1999) resulted in a significantly higher phytoplankton biomass in the summer period, expressed as chlorophyll a content, than without nutrient (1997) and low nutrient (1998). The respective mean chlorophyll a levels were 2.4 in 1999, 1.6 in 1998 and 1.2 g l^–1 in 1997. The mean primary production during the summers generally increased with the addition of nutrients from an average level of 320 mg carbon m^–2 day^–1 in 1997 to 1200 mg carbon m^–2 day^–1 in 1999. Scallops placed at 10 m depth in Hopavågen showed an increase in growth rate of the outer scallop shell in the period July–September from 0.16% day^–1 in 1997 to 0.53% day^–1 in 1998. Scallops grown in an unfertilised control station in the fjord outside Hopavågen had a significantly lower growth rate than those grown in the fertilised water of Hopavågen. The results showed decreased growth rate with increasing shell sizes. However, for all size groups studied a higher growth rate of the scallops was observed when nutrients were added to the bay. The tissue dry weight content of scallops grown in Hopavågen was 2–4 times higher than in the control scallops.     

Subtidal populations of the blue mussel <Emphasis Type="Italic">Mytilus edulis</Emphasis> as key determinants of waterfowl flocks in the southeastern Barents Sea

Ornithological surveys conducted over the Pechora Sea (the southeastern part of the Barents Sea) in the 1990 s revealed huge non-nesting flocks of marine ducks, the largest in the European North. Especially dense waterfowl aggregations are constantly observed at the shallows near Dolgij Island during molting period and migration to wintering places. All the marine ducks flocking there are specialized benthos feeders predominantly consuming mussels Mytilus edulis. At the same time, numerous previous benthic studies in the Pechora Sea did not reveal mussels near Dolgij Island where benthic biomass was somewhat lower than in the adjacent areas (Denisenko in Mar Ecol Prog Ser 258:109–123. 2003) which left the food source for these abundant bird flocks enigmatic. In the course of an expedition in summer 2007 we found subtidal populations of M. edulis in shallows to the southwest of Dolgij Island. These populations were confined to a coastal zone and were characterized by a highly disjunct distribution with the biomass reaching up to 4 kg m⁻². We describe these subtidal populations as well as an intertidal mussel population on the western shore of Dolgij Island.     

Littoral macrofauna (secondary) responses to experimental nutrient addition to rocky shore mesocosms and a coastal lagoon

Macrofauna secondary responses to controlled eutrophication within two MARICULT/MAST-III projects, EULIT and COMWEB, are compared. EULIT utilises a nutrient gradient established in eight hard bottom mesocosms, whereas the data from COMWEB originate from a whole-ecosystem study – the case of experimental nutrient addition to Hopavågen lagoon. In both systems, nutrient addition started in May 1998, after initial studies of the background macrofauna communities, thus allowing application of Before-After-Control-Impact-Pairs techniques (BACIP). The main objectives have been to investigate the macrofauna responses to eutrophication in littoral rocky shore ecosystems and to evaluate if similar responses could occur in mesocosm and `field' systems, despite their inherent differences. Apart from a distinct increase in numbers of Littorina littorea L. and some indications of increased abundance of the genus Jaera, no significant changes, caused by 2.5 years of nutrient addition, could be detected in the mesocosm fauna. It is interesting, however, that these two possibly stimulated animal groups have two things in common: (1) both belong to the rather few mobile taxa, which are not flushed out of the system through the mesocosm outlets, (2) both feed on microalgae and green algae in the upper littoral zone, i.e., algal groups that have shown the clearest response to the nutrient addition. In Hopavågen, 1.5 years of nutrient addition only caused modest plant and animal responses in the rocky shore ecosystem, although there was a markedly increased settlement of Mytilus edulis L. at one lagoon site. This increase was probably due to elevated levels of digestible particles (increased phytoplankton production) caused by the nutrient addition. There were also some indications of increased production of filamentous algae at this same lagoon site. All in all, both studies demonstrate only minor responses to increased nutrient levels within the littoral community (both plants and animals). One explanation to this may be that longer time-scales are needed in order for clear-cut changes to occur. Several observations also indicate that wave exposure (significant in both systems) may largely modulate the impact of increased nutrient load on the structure of littoral communities. Another explanation is the high degree of stability among littoral macroalgae-dominated communities with internal biological regulation factors (like grazing) possibly being able to counteract effects.     

Spatial patterns of abundance and growth of Mytilus edulis on boulders in the Northern Baltic Sea proper

Small scale spatial patterns of abundance, growth and condition of the mussel Mytilus edulis on sub-littoral boulders (approx. 1–2 m high) were investigated at the island of Askö in the northern Baltic proper. The effect of side (exposed/sheltered with respect to wave action and sunlight) of boulder and position (up/down) on boulder was investigated. A large spatial variability in abundance of M. edulis between boulders and between various sites within boulders were found. The highest numbers of mussels were found on the wave exposed side, near the top of boulders. Shell growth was favoured by a sheltered side and a down position. The body condition (meat weight/shell weight) of mussels was, on the other hand, affected only by position, the condition of mussels being better at the up position. Consequently, there seems to be temporal differences in the condition for growth within a spatial position. The body condition of the mussels was best near the top of boulders in the spring, but long-term shell growth was favoured by a sheltered side and a down position. This may reflect changes in the composition and availability of food during the year with phytoplankton as the major food source during the spring bloom and resuspension of benthic production and detritus as relatively more important during the rest of the year.     

Carbonic anhydrase activity and biomineralization process in embryos, larvae and adult blue mussels Mytilus edulis L.

To decide whether a physiological role can be attributed to enzymatic activity with respect to crystal formation and biomineralization of the first larval shell, carbonic anhydrase (CA) activity was measured in embryos and larvae of the blue mussels Mytilus edulis L. Also, CA activity was determined in the mantle edge and gonads of adult mussels with different shell length and condition index. The intention was to find a possible correlation between CA activity and adult shell calcification, i.e. gonadal maturation. The comparison of CA activity in different developmental stages of mussels and the results of an X-ray diffraction study of biomineralization processes in embryonic and larval shells indicate that CA activity is maximal at the end of several developmental stages. Consequently, the increase in CA activity precedes some physiological changes, i.e. the somatoblast 2d formation and the occurrence of the first calcite and quartz crystals in embryos, shell field formation in the gastrula stage, shell gland and periostracum production in trochophores, and rapid aragonite deposition in larval prodissoconch I and prodissoconch II shells. Furthermore, it was found that in adult mussels CA activity was quite variable and that in the mantle edge it was frequently inversely related to the activity in the gonad. Received: 28 November 1998 / Received in revised form: 30 August 1999 / Accepted: 31 August 1999     

The site of settlement indicates commensalism between bluemussel and its epibiont

Summary The site of settlement of barnacles (Balanus improvisus) attached on shells of bluemussels (Mytilus edulis) was mapped from a sample of mussels collected in the Baltic Sea. Most barnacles had settled near the siphonal apertures of the mussel. An experiment was made to measure the disadvantages and advantages that living in close association brings to barnacles and mussels. The barnacles on shells of living mussels were shown to grow significantly faster than those on empty mussel shells. Presence of barnacles had no effects on growth of mussels. The two-species association under study was demonstrated to be a case of commensalism.     

Benefit from an invader: American slipper limpet <Emphasis Type="Italic">Crepidula fornicata</Emphasis>reduces star fish predation on basibiont European mussels

Introduced species have recently become a major concern in ecological research and aquatic conservation. This is due to an increasing appearance of introduced species at a global scale and a multitude of negative impacts on native biota. However, impacts of introduced species are not necessarily only negative. The epizootic American slipper limpet Crepidula fornicata, native at North American Atlantic shores, was introduced to Europe in the 1870s and is now widespread along the Atlantic coast of Europe. Negative effects like trophic and spatial competition have been reported. In its major basibiont in the Wadden Sea, the blue mussel Mytilus edulis, attached limpets reduce survival and growth. However, a laboratory experiment also showed sea star (Asterias rubens) predation on mussels with limpet epigrowth to be three times lower than in unfouled mussels. Hence, although negatively affected by C. fornicatain one way, this epigrowth is beneficial for fouled mussels in another. This indicates that the actual impact of an introduced species is a complex interplay of positive and negative effects which may only be revealed experimentally.     

Settlement of bivalve spat on artificial collectors in Eyjafjordur, North Iceland

The seasonal pattern of bivalve spat settlement in Eyjafjordur, North Iceland, was investigated using artificial collectors of monofilament netting over 14 months (March 1998–January 2000) at 5, 10 and 15 m depth. SCUBA divers replaced the collectors at 4-weekly intervals. Twelve bivalve species settled on the collectors but only Mytilus edulis and Hiatella arctica were present throughout the year; they were the most abundant bivalve taxa. Of the remaining species, only Chlamys islandica, Heteranomia spp., Arctica islandica, Serripes groenlandicus and Mya spp. were sufficiently abundant to enable statistical analysis. All settled in late summer and autumn. Peak settlement of M. edulis, in September, consisted mainly of primary settlers (0.25–0.5 mm) although secondary settlers (>0.5 mm) were present in all samples. Mytilus edulis settled mostly at 5 m depth, especially larger individuals, possibly reflecting stronger currents at shallower depth and the proximity of mussel beds in the intertidal zone. Primary (<1 mm) and secondary H. arctica settlers (>1 mm) were present in most months, with the former being most numerous in September, 1999; settlement was equally abundant at 5 and 10 m depth. Primary settlement of C. islandica and S. groenlandicus occurred in autumn (mainly in September), and secondary settlers were very scarce and only seen in winter. Arctica islandica, Heteranomia spp. and Mya spp. settled mainly in September 1999 at 10 m depth, except for A. islandica, which was more numerous in August.     

Bioinvasion threatens the genetic integrity of native diversity and a natural hybrid zone: smooth‐shelled blue mussels (Mytilus spp.) in the Strait of Magellan

Smooth‐shelled blue mussels of the Mytilus edulis species complex are widely distributed bivalve molluscs whose introductions threaten native marine biodiversity (non‐indigenous species – NIS). The aim of the present study was to identify the species and hybrids of Mytilus present in the Magellan Region (southern Chile). Results indicate that three mussel species of the Mytilus edulis complex are found in the region – M. edulis, M. chilensis (or the Southern Hemisphere lineage of Mytilus galloprovincialis), and M. galloprovincialis of Northern Hemisphere origin. For the first time, alleles of the introduced M. trossulus are reported from the Southern Hemisphere. In the Strait of Magellan the native Pacific blue mussel, Mytilus chilensis and the native Atlantic blue mussel, Mytilus edulis, meet and mix at a natural hybrid zone (about 125 km in length). This is the first record of a natural Mytilus hybrid zone in the Southern Hemisphere and is also the first record of the co‐occurrence of genes from all four Mytilus species in any one region. These results contribute to the knowledge of the biodiversity and delimitation of mussel species in southern South America, and highlight how introduced species may threaten the genetic integrity of native species through hybridization and introgression.     

Genetic Divergence Detected by ISSR Markers and Characterization of Microsatellite Regions in Mytilus Mussels

The wide distribution of microsatellites in mussels of the Mytilus edulis complex (Mytilidae) enables the analysis of inter-simple-sequence repeat (ISSR) markers. The aim of this investigation was to assess genetic differentiation in six sampling localities distributed along the European Atlantic coast to expose the potential of these markers in genetic studies requiring the detection of low polymorphism and as a source of sequences for developing microsatellite markers. We detected low genetic structuring within each member of the Mytilus edulis complex. Nei and Li distances and AMOVA clustered the individuals studied into two groups. On the basis of these results two sampling localities coming from the M. edulis × M. galloprovincialis mosaic hybrid zone in Western Europe were assigned to one species. On the other hand, mussels of a sampling locality in the Baltic Sea were not significantly different from a pure M. edulis locality supporting an extensive introgression of M. edulis in these individuals. Finally, 148 microsatellites were found in the sequences of 51 ISSR markers, and two polymorphic microsatellite markers were developed.     

Secondary production of an intertidal mussel (Mytilus edulis L.) population in the Eastern Scheldt (S.W. Netherlands)

We monitored an intertidal mussel (Mytilus edulis L.) population between June 1981 and June 1982 in the Eastern Scheldt estuary (S.W. Netherlands). Density and biomass of the population remained relatively constant over the study period. The shell length growth was described by a Gompertz growth curve. The parameters of this equation were estimated from a log-log-modified Ford-Walford plot of the growth-ring data. The slope of the relationship between animal weight and shell length is season-dependent, mainly due to the spawning cycle in larger mussels.Secondary production is estimated with the growth rate method. In the calculated growth rates the change in slope of the length-weight relationship is incorporated, as well as differences in length growth rates between summer and winter. Secondary production amounts to 156 g AFDW m^–2a ^–1 (expressed per m² of mussel bank). P:B is 0.50 a^–1. The mussel productivity is probably a limiting factor for the density of overwintering Oystercatchers (Haematopus ostralegus).     

Temporal and spatial patterns of growth in mussels Mytilus edulis on an offshore platform: relationships to water temperature and food availability

Temporal and spatial (depth) patterns of shell growth were studied in the mussel Mytilus edulis in relation to water temperature and potential food availability, at an offshore oil platform, Holly (ARCO), in the Santa Barbara Channel, California. Length-specific growth rates were highest from late May to July and at a depth of 9 m. The time to achieve a length of 50 mm from recruitment was estimated at 6–8 months. Growth rates were not correlated with water temperature, using multiple regression and correlation analysis. Temporal variation in the growth of 20- and 35-mm mussels correlated with chlorophyll a concentration at time lags of 2 and 4 wk, respectively. Variation in growth of mussels with depth was more closely associated with the concentration of particulate organic carbon than with chlorophyll a. Our results indicate that water temperature can be disregarded as an important factor in regulating mussel growth in California waters, but that growth could vary in association with well-documented regional variation in phytoplankton biomass.     

Annual variation in condition,respiration and remineralisation ofMytilus edulis L. in the Sound,Denmark

By means of monthly in situ incubations, variations in oxygen uptake, nutrient release and C/N-ratio were monitored during a period of 14 months of a mussel population (Mytilus edulis L.) located on an exposed beach. A condition index calculated as weight/length³ showed that the condition of the mussels was highest in the spring. Specific oxygen uptake and nutrient release had separate maxima, with high oxygen uptake in the spring coinciding with a period of growth, and high nutrient release during summer when the temperature was highest. Oxygen uptake was significantly correlated with both the condition of the mussels and the temperature, while ammonium release was significantly correlated only with the temperature. Except in spring, the oxygen uptake, condition index and O/N-ratio were low, indicating a poor condition of the mussels. The mussels suffered from suboptimal conditions caused by inadequate food supply and failed to accumulate glycogen reserves essential for the development of mature gametes.     

Influence of genotype and geography on shell shape and morphometric trait variation among North Atlantic blue mussel (Mytilus spp.) populations

The influence of geography and genotype on shell shape (outline) and trait (morphometric) variation among North Atlantic blue mussels and their hybrids has been examined. Shape differences among reference taxa (Mytilus trossulus, Mytilus edulis and Mytilus galloprovincialis) were consistent with an association between taxon‐specific genes and shape genes. Newfoundland M. edulis × M. trossulus populations and northern Quebec M. trossulus populations exhibited an uncoupling of taxon‐specific genes from shape genes, whereas Nova Scotia M. trossulus populations and SW England M. edulis × M. galloprovincialis populations exhibited an association between taxon‐specific genes and shape genes. We found no evidence of a geographic effect (NE versus NW Atlantic) for shape variation, indicating that the genotype effect is stronger than any geographic effect at macrogeographic scales. Pronounced differences were observed in trait variability consistent with an association between taxon‐specific genes and trait genes in European populations, and trait divergence of New York M. edulis from all European mussels. Trait variability in mussels from Newfoundland, Nova Scotia and northern Quebec indicated an uncoupling of taxon genes from trait genes, whereas trait variability in SW England M. edulis × M. galloprovincialis populations was consistent with background genotype, indicating a strong association between taxon genes and trait genes. A pronounced macrogeographic split (NE versus NW Atlantic) regardless of taxonomy was observed, indicating that geography exerts a greater influence than genotype on trait variation at the macrogeographic scale. This is consistent with pronounced within‐taxon genetic divergence, indicative of different selection regimes or more likely of different evolutionary histories of mussels on either side of the North Atlantic. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96 , 875–897.     

Fouling community of the red king crab, <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> (Tilesius 1815), in a subarctic fjord of the Barents sea

We examined the species composition of red king crab (Paralithodes camtschaticus) fouling communities in Dolgaya Bay, a small fjord of the Barents Sea, in August 2005 and 2006. In total, there were 13 species observed on 301 crabs collected from water depths of 5–90 m. Barnacles (Balanus crenatus; prevalence 42.9%) and blue mussels (Mytilus edulis; 11.6%) were the most common epibionts, while amphipods (Ischyrocerus commensalis) were the most common symbionts (28.6%). Infestation rates in Dolgaya Bay were different from those in an “open” area of the Barents Sea (Dalnezelenetskaya Bay), probably due to differences in hydrodynamic conditions. Differences in infestation prevalence and intensity were detected neither between male and female crabs nor between crabs collected at 5–35 m versus 90 m depths. Prevalence of common fouling species increased with host size. Amphipods I. commensalis colonized the carapace and limbs in Dolgaya Bay less frequently than in Dalnezelenetskaya Bay, probably due to interspecific competition with barnacles occupying the dorsal parts of the host. Juvenile barnacles and mussels dominated the fouling communities on the crabs. The age of barnacles did not exceed 2–4 months. However, the presence of 4-year-old mussels suggests that these older mollusks have been directly transferred from mussel beds to the hosts. Our results indicate that colonization by epibionts and symbionts is generally not disadvantageous for the crab hosts, except for some possible negative impacts of amphipods occupying the gills.     

Phytoplankton composition of the Kandalaksha Gulf, Russian White Sea: Dinophysis and lipophilic toxins in the blue mussel (Mytilus edulis)

Dinophysis acuminata and D. norvegica were observed in plankton net samples during the summer of 2002 from the Kandalaksha Gulf in the White Sea (North European Russia). Prorocentrum lima was found as an epiphyte on subtidal macroalgae in August, but not observed in plankton net samples. Protein phosphatase 2A (PP2A) inhibition measured 127.8 ng OA-equivalent/g of mussel (Mytilus edulis) hepatopancreas from samples collected a few days after when Dinophysis was recorded at a density of 1550 cells L⁻¹. Liquid chromatography–mass spectrometry confirmed presence of several classes of lipophilic shellfish toxins associated with Dinophysis spp. in the mussels including okadaic acid, dinophysistoxin-1, pectenotoxins and yessotoxins. No azaspiracid was detected. This represents the first identification of phycotoxicity in the White Sea.     

Potential Impacts of a Western Pacific Grapsid Crab on Intertidal Communities of the Northwestern Atlantic Ocean

Population density and size distribution, salinity tolerance, and feeding activity were examined in a western Pacific grapsid crab, Hemigrapsus sanguineus, that was recently introduced to the mid-Atlantic coast of North America. Seasonal abundance on a boulder/cobble shore (Crane Neck Pt.) in central Long Island Sound, New York, USA, during 1997–1998, ranged from 7 to 10 crabs m⁻² averaged over the entire intertidal zone. Crabs occurred throughout the intertidal during summer and fall, but appeared to move from high to low elevations during winter. In laboratory experiments, H. sanguineus tolerated salinity down to 10 ppt for 7 d, but showed significant preference for 20 or 27 ppt over 10 ppt. The crabs readily consumed juvenile snails (Littorina littorea) and mussels (Mytilus edulis), as well as other common species of macroalgae and invertebrates occurring at Crane Neck Pt. High feeding rates and the ability to consume littorine snails up to 13 mm in height and mussels up to 20 mm in length suggest that this nonindigenous species has the potential to significantly affect the structure of rocky intertidal communities in the northwestern Atlantic Ocean; however, rigorous field studies are needed to accurately determine the impact of this recent introduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Linking genotype to phenotype in a changing ocean: inferring the genomic architecture of a blue mussel stress response with genome‐wide association

A key component to understanding the evolutionary response to a changing climate is linking underlying genetic variation to phenotypic variation in stress response. Here, we use a genome‐wide association approach (GWAS) to understand the genetic architecture of calcification rates under simulated climate stress. We take advantage of the genomic gradient across the blue mussel hybrid zone (Mytilus edulis and Mytilus trossulus) in the Gulf of Maine (GOM) to link genetic variation with variance in calcification rates in response to simulated climate change. Falling calcium carbonate saturation states are predicted to negatively impact many marine organisms that build calcium carbonate shells – like blue mussels. We sampled wild mussels and measured net calcification phenotypes after exposing mussels to a ‘climate change’ common garden, where we raised temperature by 3°C, decreased pH by 0.2 units and limited food supply by filtering out planktonic particles >5 μm, compared to ambient GOM conditions in the summer. This climate change exposure greatly increased phenotypic variation in net calcification rates compared to ambient conditions. We then used regression models to link the phenotypic variation with over 170 000 single nucleotide polymorphism loci (SNPs) generated by genotype by sequencing to identify genomic locations associated with calcification phenotype, and estimate heritability and architecture of the trait. We identified at least one of potentially 2–10 genomic regions responsible for 30% of the phenotypic variation in calcification rates that are potential targets of natural selection by climate change. Our simulations suggest a power of 13.7% with our study's average effective sample size of 118 individuals and rare alleles, but a power of >90% when effective sample size is 900.     

Assessing the potential benthic-pelagic coupling in episodic blue mussel (Mytilus edulis) settlement events within eelgrass (Zostera marina) communities

Coastal marine seagrass ecosystems are important nursery grounds for commercially and recreationally important species, and they serve as key settlement and recruitment sites for other species. We investigated several years (2001-2003) where episodic settlement events of blue mussels (Mytilus edulis) occurred in Barnegat Bay, NJ, USA. Population assessment indicated that blue mussels settled in eelgrass beds (Zostera marina) in late spring with peak densities exceeding 170,000 m⁻². Based on calculated filtration rates of M. edulis, we determined that for at least 53 days in 2001, the density and size distribution of M. edulis were sufficient to filter the water column volume in excess of twice a day, with maximum calculated filtration rates exceeding 8 m³ water m⁻² day⁻¹. While the settlement event in 2001 was very localized, in 2003, the settlement event was considerably more widespread throughout the bay, with maximum settling densities exceeding 175,000 individuals m⁻². Associated with these high densities, maximum calculated filtration rates exceeded 15 m³ water m⁻² day⁻¹. This filtration potential may have impeded the localized development of a brown-tide (Aureococcus anophagefferens) bloom in 2001, which occurred in other regions of the bay, but the widespread settlement event seen in 2003 may have impeded the development of any brown-tide blooms in Barnegat Bay during that summer. The decline in mussel densities throughout the summer may be a result of elevated water temperatures in this back bay, but at one site, the high settlement of M. edulis was followed by a substantial migration (>40 individuals m⁻²) of small sea stars (Asterias forbesii). In 2001, A. forbesii was a significant factor in reducing M. edulis density by the end of the summer at the Barnegat Inlet site and a community level assessment showed significant positive correlations between mussel aggregations and sea star densities (r=0.68-0.73, P<0.001). At this same site in 2003, the sea stars were again present in high densities (26 m⁻²) and were a potential mechanism for mussel decline. In other regions of the bay, sea star densities are very low, but numerous other predatory species exist, including blue crabs (Callinectes sapidus), green crabs (Carcinus maenus), spider crabs (Libinia spp.), and several Xanthid crabs. Given the high mussel densities seen in this study and the considerable predation by sea stars and other benthic predators, the benthic-pelagic coupling which these mussels provide in this system contributes to the high secondary production in these grass beds.