Adaptive host choice and avoidance of superparasitism in the spawning decisions of bitterling (Rhodeus sericeus)

Choice of a site for oviposition can have fitness consequences. We investigated the consequences of female oviposition decisions for offspring survival using the bitterling, Rhodeus sericeus, a freshwater fish that spawns inside living unionid mussels. A field survey of nine bitterling populations in the Czech Republic revealed a significantly lower rate of release of juvenile bitterling from Anodonta cygnea compared to three other mussel species. A field experiment demonstrated that female bitterling show highly significant preferences for spawning in A. anatina, Unio pictorum, and U. tumidus. Within a species, female bitterling avoided mussels containing high numbers of bitterling embryos. Mortality rates of bitterling embryos in mussels were strongly density dependent and the strength of density dependence varied significantly among mussel species. Female preferences for mussels matched survival rates of embryos within mussels and females distributed their eggs among mussels such that embryo mortalities conformed to the predictions of an ideal free distribution model. Thus, female oviposition choice is adaptive and minimizes individual embryo mortality. Received: 6 October 1999 / Received in revised form: 7 January 2000 / Accepted: 13 March 2000     

Response of mussel Brachidontes variabilis to chlorination

Brachidontes variabilis is a common fouling mussel species in cooling water systems of tropical coastal power stations. However, there are hardly any data available on the response of B. variabilis to chlorine, a commonly used antifouling biocide. Therefore, lethal and sublethal responses of this mussel to chlorine are of considerable interest to the industry. The response of mussels in terms of mortality pattern (LT₅₀ and LT₁₀₀) and physiological activities (oxygen consumption, filtration rate, foot activity and byssus thread production) in different size groups (with shell lengths of 7–24 mm) of B. variabilis was studied in the laboratory under different chlorine concentrations (0.25, 0.50, 0.75 and 1.00 mg l^?1 for sublethal responses and 1, 2, 3 and 5 mg l^?1 for mortality). The results showed that the exposure time for 100% mortality of mussels decreased significantly with increasing chlorine concentration. However, mussel size was not a determinant of its chlorine tolerance: all size groups tested (with shell lengths of 7–24 mm) took comparable exposure times to reach 100% mortality at a given chlorine concentration (1–5 mg l^?1). All size groups of B. variabilis showed a progressive reduction in physiological activities such as oxygen consumption, filtration rate, foot activity and byssus thread production, when chlorine residuals were increased from 0 to 1 mg l^?1. The data generated in the present work are compared with similar data available for other tropical fouling mussel species to see how far relative chlorine toxicity could have influenced the relative distribution of the mussels inside the seawater intake tunnel of a power station at Kalpakkam in India. It is shown that in this insufficiently chlorinated system, the relative distribution of Brachidontes striatulus, B. variabilis and Modiolus philippinarum reflects the relative tolerance of the species to chlorine.     

Distribution of a marginal population of <Emphasis Type="Italic">Mytilus edulis</Emphasis>: responses to biotic and abiotic processes at different spatial scales

Physical and biological processes interact to produce pattern in nature. Pattern is scale dependent as processes generating pattern are heterogeneous in time and space. We tested some causes of variation in abundance and distribution of three marginal populations of sublittoral blue mussels, Mytilus edulis, in the non-tidal northeastern Baltic Sea. We studied the role of substrate inclination, perennial algae and siltation along local wave exposure gradients on mussel distribution over a regional salinity gradient. We found marked differences on regional scales (p < 0.001) with lower densities and biomasses of mussels with declining salinity. Along local gradients, mussel densities increased with increasing exposure (p < 0.001) and declining slope and sedimentation (p < 0.01). Site specifically, densities of blue mussels and the perennial red algae, Furcellaria lumbricalis, were positively related, results supported by a colonisation experiment. Also, young post-recruits showed significant relations to adult biomass, wave exposure, algal biomass, bottom slope and sediment cover. Findings showed that the relative importance of the determinants affecting blue mussels at the edge of their range vary with scale and are affected by the density and size structure of mussel populations. The study provides an indication of the types of factors that may be invoked as causes of spatial variation in marginal blue mussel populations and reinforces the need to consider multiple aspects when distributional patterns are assessed.     

Mud crab predation on ribbed mussels in salt marshes

Mud crab (Panopeus herbstii H. Milne Edwards) predation on Atlantic ribbed mussels (Geukensia demissa Dillwyn) was studied by a series of laboratory and field experiments at two sites at Morehead City, North Carolina, USA from 1987 to 1989. Tidal elevation had no effect on predation intensity, although mud crabs were active only when they were submerged. Horizontal distance from the water-marsh edge significantly affected mussel mortality in one of two winter experiments, despite the occurrence of virtually all the crabs at the marsh edge. Of the juvenile mussels attached to adult mussels, those totally buried in the sediment suffered mortality from mud crab predation at a rate not detectably different from those exposed above the surface. Juveniles attached to adult conspecifics, however, experienced significantly less mortality than those attached to oysters. Interestingly, the two groups of mussels (those attached to conspecifics and those attached to oysters) display shell morphological dimorphism. The more oblate shells of the mussels attached to oysters as compared to those attached to conspecifics might be induced by the higher predation rate. Alternatively, slimmer shells from individuals attached to conspecifics may be the result of living within physically compact mussel clumps.Please address all correspondence and requests for reprints to Dr Lin at his present address: Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, Maryland 21037, USA     

Implications of movement behavior on mussel dislodgement: exogenous selection in a<Emphasis Type="Italic"> Mytilus</Emphasis> spp. hybrid zone

Rocky intertidal habitats often exhibit high levels of environmental heterogeneity, and the ability of organisms to move between microhabitats is likely to have a profound influence on their rates of mortality and overall fitness. Mussels within the Mytilus edulis complex are morphologically very similar, yet at sites where these species hybridize in southwest England, populations repeatedly show evidence of selection against individuals with alleles specific to M. edulis Linnaeus, in favor of those with alleles specific to M. galloprovincialis Lamarck. Differential movement rates of these two species were examined within simulated mussel beds (gravel substrate) in the winter (February) and summer (July) of 2001. M. edulis-like mussels moved more frequently and more quickly to the exterior of gravel beds than did M. galloprovincialis-like mussels. Coupled with measurements of attachment strength in the field conducted in July 2001, we used a wave force model to examine the probability of dislodgement for each species under a range of water velocities. Results suggest that by preferentially moving to the exterior of beds, M. edulis experiences higher dislodgement rates due to exposure to large hydrodynamic forces than do M. galloprovincialis. As a consequence of lower attachment strengths, M. edulis is also predicted to have higher mortality rates than M. galloprovincialis in interior portions of the bed. Thus, differential movement behavior may contribute to the differential genotype-specific mortality rates observed in the Mytilus spp. hybrid zone in southwest England, and is an example of behavior potentially modifying rates of exogenous selection in an intertidal hybrid zone.Communicated by J.P. Grassle, New Brunswick     

Detrimental effects of the isopod, <Emphasis Type="Italic">Edotia doellojuradoi,</Emphasis> on gill morphology and host condition of the mussel, <Emphasis Type="Italic">Mytilus edulis platensis</Emphasis>

There are many reported associations between mussels and other invertebrates, such as pea crabs, polychaetes, turbellarians and copepods, which live in their mantle cavities. The boundary between commensalism and parasitism is often indistinguishable because of insufficient knowledge or because the interaction is variable. Preliminary evidence led to a closer examination of the relationship between the mussel, Mytilus edulis platensis, and an isopod, Edotia doellojuradoi, previously described as commensalism. Monthly intertidal samples of mussels were taken from September 2004 to August 2005 at Caleta Cordova Norte (45°43′S, 67°22′W) in southern Argentina and assessed for the prevalence and abundance levels of isopods. Mussels with and without isopods were measured, examined for evidence of gill damage and their condition (soft tissue dry weight) was determined. The overall isopod prevalence in mussels was 57.9% and infestation varied with mussel length, with maximum occurence at 30.2 mm (medium-sized mussels). Experimental evidence indicated that the position of the isopod inside the mussel depended on the feeding activity of the mussel. Female isopods were observed grasping the ventral food groove of the gill demibranchs and feeding on the mucous food strand produced by the mussel. Juveniles and males were observed clustered together on the dorsal side of the single female in each occupied mussel, suggesting extended maternal care. Gill damage was observed in 58.2% of mussels at the Argentine site and was significantly associated with isopod occurrence. Categorical regression analysis showed that the most important factor associated with the degree of gill lesions was the number of male and juvenile isopods per mussel, followed by the length of female isopods and the developmental stage of juveniles. Conversely, the degree of gill damage decreased with increasing mussel length. Overall, E. doellojuradoi had a significant effect on mussel condition throughout the year, with low flesh weight in mussels with isopods, except during the austral summer and early autumn. In contrast to previous studies, which concluded that the isopod was a commensal, the present study clearly demonstrates that E. doellojuradoi is a parasite of M. edulis platensis. Other symbiotic interactions formerly classified as commensal might not be innocuous on further investigation, especially if samples are taken at multiple sites and at different times of the year.     

Sensitivity of veliger larvae of Mytilus edulis and mussel of various sizes to chlorination

The blue mussel Mytilus edulis is one of the dominant fouling organisms in cooling water systems. In this work, how veliger larvae and different size groups of the mussels responded against chlorine dosage was examined. Veliger larvae mortality was studied at different residual chlorine concentrations (0.05–0.5 mg L^?1), and it was found that a chlorine dose of 0.5 mg L^?1 is 4 times as effective as 0.05 mg L^?1 and twice as effective as 0.1 mg L^?1. Mortality of 100% for three size groups (1.4, 14, and 25 mm) and relative physiological activities of two size groups (14 and 25 mm) were observed. The exposure duration for 100% mortality of mussels decreased with the increasing residual chlorine concentration (0.1–4.0 mg L^?1). Mussel size was also found to be an important factor, considering that the continuation times for mussel mortality were 28 h for the 1.4 mm and 410 h for the 25 mm size groups. All size groups showed progressive reduction in physiological activities, such as oxygen consumption, foot activity, and byssus thread production with increasing chlorine dose (0.05–1.0 mg L^?1); the two data-sets were strongly correlated with each other. The results of this study should be of significance for optimizing the chlorine content, and minimize the environmental threat to industries where mussels are the dominant fouling organisms.     

Effects of substrate type on growth and mortality of blue mussels (<Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">edulis</Emphasis>) exposed to the predator <Emphasis Type="Italic">Carcinus</Emphasis><Emphasis Type="Italic">maenas</Emphasis>

Structure and complexity of the substrate are important habitat characteristics for benthic epifauna. The specific growth and mortality rates and inducible defence characters on medium-sized blue mussels (Mytilus edulis L.) exposed to shore crabs (Carcinus maenas L.) were examined on three different substrate types in combined field and laboratory experiments. The experiments showed that complexity of the substrate increased blue mussel survival significantly, through a decrease in predation pressure. However, increased intraspecific competition for food on the complex substrate resulted in significantly lower growth rates of the mussels. Inducible defence characters were also influenced by substrate type. Blue mussels were more affected by predators on the structurally simple substrate, where they developed thicker shells and a larger posterior adductor muscle.     

Combining heat-transfer and energy budget models to predict thermal stress in Mediterranean intertidal mussels

Recent studies have emphasised that organisms can experience physiological stress well within their geographic range limits. Developing methods for mechanistically predicting the presence, absence and physiological performance of organisms is therefore important because of the ongoing effects of climate change. In this study, we merged a biophysical–ecological (BE) model that estimates the aquatic (high tide) and aerial (low tide) body temperatures of Mytilus galloprovincialis with a Dynamic Energy Budget (DEB) model to predict growth, reproduction and mortality of this Mediterranean mussel in both intertidal and subtidal environments. Using weather and chlorophyll-a data from three Mediterranean sites along the Italian coasts, we show that predictions of sublethal and lethal (acute) stress can potentially explain the observed distribution (both presence and absence) of mussels in the intertidal and subtidal zones, and the maximum size of animals in the subtidal zones. Importantly, our results suggest that different mechanisms limit the intertidal distribution of mussels, and that these mechanisms do not follow a simple latitudinal gradient. At the northernmost site (Palermo), M. galloprovincialis appears to be excluded from the intertidal zone due to persistent exposure to lethal aerial temperatures, whereas at the southernmost sites (Porto Empedocle and Lampedusa) sublethal stress is the most important driver of mussel intertidal distribution. Our predictions provide a set of hypotheses for future work on the role of climate change in limiting intertidal distribution of mussels in the Mediterranean.     

Effects of an Odh null allele and a GPI low-activity allozyme on shell length in laboratory-reared Mytilus edulis

Mytilus edulis L. heterozygotes with a null allele at the octopine dehydrogenase (Odh) locus or an allele coding for low activity at the glucose phosphate isomerase (Gpi) locus were found to grow significantly faster (p(0.05) than other juvenile mussels in the same laboratory cultures. Odh null homozygotes were not significantly different in growth from mussels with active Odh alleles. No additive effects were seen in individuals which had both the Odh null allele and the allele coding for low GPI activity. These results do not support the contention that null alleles are a significant cause of the observed correlation between multiple-locus heterozygosity and fitness in mussels. The apparent deficiencies of heterozygotes against Hardy-Weinberg expectations observed at the Odh locus in two Netherlands M. edulis populations can be more than accounted for by the null-allele frequency calculated, assuming Hardy-Weinberg equilibrium, from the observed frequency of null homozygotes in these populations.     

Roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>) as an important predator on blue mussel (<Emphasis Type="Italic">Mytilus edulis</Emphasis>) populations in a brackish water environment,the northern Baltic Sea

Suspension-feeding bivalves are organisms of major functional importance in several aquatic environments around the world. They are also important food items for many fish and benthivorous seabirds. It has commonly been thought that predation pressure on blue mussel (Mytilus edulis) populations is negligible in the Baltic Sea, owing to the scarcity of major invertebrate predators such as starfish and crabs. It has recently been shown, however, that the blue mussel is the main food item for roach (Rutilus rutilus) in the archipelago areas of the western Gulf of Finland, where this freshwater fish species has become increasingly abundant, mainly due to increased eutrophication. To quantify the influence of roach predation on blue mussel populations we measured the standing biomass and size structure of the local blue mussel population and used a bioenergetic model to estimate mussel consumption by individual roach during two consecutive summers, 1997 and 1998. The results of the model were combined with existing data on roach abundance, giving annual consumption estimates of 75–105 kg blue mussel dry weight ha^–1 in the study area, approximately two-thirds of these consumed mussels being >10 mm. This corresponds to approximately one-third of the standing population of mussels >10 mm in the area. Our results suggest that the predation effects of vertebrates on Baltic blue mussel populations are not insignificant, as previously believed. Predation by roach and other predators may have an important structuring effect on unstable blue mussel communities within the Gulf of Finland, where the species lives at the edge of its range.Communicated by M. Kühl, Helsingør     

Population dynamics of the endangered fan mussel <Emphasis Type="Italic">Pinna nobilis</Emphasis> in a marine lake: a metapopulation matrix modeling approach

A metapopulation, time-invariant, stage-classified matrix model was developed to assess the dynamics of an important Pinna nobilis population in the marine Lake Vouliagmeni (Korinthiakos Gulf, Greece). The main aim of the study was to provide insight on the life cycle of the fan mussel and reveal influential factors for its population dynamics, with a special focus on the effect of poaching. The size of the fan mussel shell was selected as a state variable, and the model consisted of five size classes. The lake was divided in two regions, a shallow region of high (illegal) fishing mortality and high recruitment (region 1) and a deeper region of low mortality and low recruitment (region 2). The estimation of the transition matrix (stage-specific growth and mortality probabilities) was based on a tagging survey between 2005 and 2006, while independent annual surveys for abundance estimation using distance sampling techniques were utilized for the estimation of recruitment and stage-specific fertilities. The population was found to be increasing with an intrinsic rate of increase r = 0.038; however, r was not statistically different from zero. The life expectancy and expected lifetime offspring production of individuals in region 1 was markedly lower than that of individuals in region 2. Due to poaching, the life expectancy of a yearling fan mussel was less than 2.5 years in region 1, while it was almost 12 years in region 2. The highest expected annual natural mortality of fan mussels occurred on their first year of life after settlement (~43%) and greatly declined at greater sizes. Perturbation analysis revealed that the population growth rate was most sensitive to the vital rates of the larger size classes in region 2 and to fertilities corresponding to offspring that settled in the same region. The spatial distribution and abundance of the species was greatly dependent on the extent of poaching, which caused a size segregation of individuals, with small and young individuals being abundant in region 1, and larger and older individuals being restricted in region 2. If poaching ceased, the fan mussel population would be increasing with a significantly higher intrinsic rate of increase (r = 0.186), while if region 2 was also illegally exploited at the same intensity as region 1, the fan mussel population would be decreasing with r = −0.364 and would eventually collapse. The existence of refuge areas, where fan mussels may grow and reproduce, providing adjacent areas with offspring, seems crucial for the viability of local populations. Transplantation of fan mussels from high mortality areas to low mortality refuges might prove to be an effective measure to protect local populations of the species.     

Very long-chain aliphatic hydrocarbons in lipids of mussels (Mytilus edulis) suspended in the water column near petroleum operations off Sable Island,Nova Scotia,Canada

Mussels (Mytilus edulis) suspended in the water column in 1994 and 1995 for the monitoring of oil drilling operations off Sable Island, Nova Scotia were examined for hydrocarbon profiles, particularly aliphatic hydrocarbons. A spring bloom of phytoplankton occurred during the 90-d suspension period in 1995. Hydrocarbons isolated from the 1995 suspended mussels showed very high concentrations of both biogenic hydrocarbons and very long-chain n-alkanes from C₂₀ to C₃₂, initially thought to be petrogenic. Both types of hydrocarbons were either not detected or were only present in trace amounts in the mussels suspended in 1994 at similar sites. The biogenic hydrocarbons in the 1995 mussels were apparently of planktonic origin, from the spring bloom, and were dominated by heneicosahexaene (21:6), followed by pristance, heptadecane, and varions monounsaturated and polyunsaturated phytenes, heptadecenes, nonadecenes and heneicosenes. They could be readily hydrogenated to yield the basic alkanes. The 1995 mussels suspended within 1 km from the oil well platform were probably slightly tainted by petrogenic hydrocarbons, as evidenced by the detection of phytane and high concentrations of total aliphatic hydrocarbons, whereas the mussels suspended 10 km from the platform showed only high concentrations of biogenic hydrocarbons and the novel long-chain n-alkanes. The occurrence of an unusual phytoplankton bloom during the suspension period severely interfered with the petroleum monitoring role of mussels by altering the mussel hydrocrbon profiles through the accumulation into and probably selective depuration of xenobiotic hydrocarbons from the mussel, tissues.J. Parsons (deceased)     

Interactive effects of wave exposure and tidal height on population structure of the mussel Perna perna

The influence of wave exposure and of tidal height on mussel (Perna perna Linnaeus) population structure (size, density, biomass and adult/juvenile correlations) was examined at 18 sites along the south coast of South Africa. Sites were classified as exposed or sheltered prior to sampling, without reference to the biota, on the basis of aspect, topography and wave regime. A single set of samples was collected from each site during three spring tide cycles. Adult mussels on these shores almost always attach directly to the rocks, and layering of mussels is virtually absent. Shore height always had a strong influence on population structure, but exposure had significant effects only lower on the shore, and almost exclusively on mussel sizes. Principal component analysis (PCA), based on size distribution data for each population, revealed a general upshore decrease in the modal size of the adult cohort. The effects of exposure on size distribution, however, varied with tidal height. PCA separated exposed zones, with larger mussels, from sheltered zones on the low-shore. Farther upshore the two shore types were increasingly confounded. The maximum size of mussels showed a similar pattern, with significant differences (ANOVA, p < 0.05) between exposed and sheltered sites only on the low- and mid-shores. Density was calculated from randomly placed quadrats (i.e. not necessarily from areas of 100% cover) and showed a different pattern. Adult (>15 mm) densities decreased up the shore, with low-, mid- and high-shore zones being significantly different from one another (ANOVA, p < 0.0001; followed by multiple range tests). However, exposure had no significant effect on density, nor was there a significant interaction with zone. Recruit (<15 mm) densities were positively correlated with adult (>15 mm) densities in all zones and for both exposure regimes ( p < 0.05 in all cases), but there was considerable variability and extremely low predictability in these relationships (r ² generally <0.2). Predictability tended to be greater towards the high-shore, where adults were more clumped. As with density, biomass was not affected by exposure, but decreased upshore as mean size and density decreased. A reduction in the influence of exposure farther upshore may be caused by greater emersion overriding the effects of exposure. The presence of free space within mussel beds and significant correlations between recruit and adult densities suggest that these mussel populations are recruit limited. Received: 7 January 2000 / Accepted: 6 July 2000     

Positive effects of the introduced green alga, Codium fragile ssp. tomentosoides, on recruitment and survival of mussels

The green macroalga, Codium fragile ssp. tomentosoides, is an important component of sheltered low-shore assemblages on breakwaters along sandy shores in the northern Adriatic Sea. Macroscopic thalli of C. fragile are not perennial, but develop from propagules and/or undifferentiated forms in early spring, when the dominant native space-occupier, the mussel Mytilus galloprovincialis, recruits. By mid-summer, rapid growth of C. fragile leads to the formation of a dense canopy. We investigated the effects of juvenile and adult thalli of C. fragile on recruitment, survival and growth of mussels. Two experiments tested the hypotheses: (1) that recruitment of mussels is greater within patches of juvenile thalli (primordia) of C. fragile than on adjacent bare surfaces; (2) that the presence of a canopy of C. fragile affects the survival and growth of mussel recruits. The number of recruits of mussels was significantly larger within clumps of primordia of C. fragile than on bare surfaces. The removal of the canopy of C. fragile affected negatively the density of mussels after 2 months from the start of the experiment, but there were no effects on the mean size of individuals, nor on the size–frequency distribution. The same trend persisted after 4 months from the start of the experiment. These results show that re-colonisation of space by mussels is enhanced by C. fragile. Given that mussels, in turn, have the potential to reduce recruitment rates of C. fragile, quick recovery of mussel beds after disturbances could be crucial for controlling the abundance of this alga on breakwaters. Results also suggest that the effects of introduced species on native assemblages can be explained only through studies encompassing different life-stages of interacting organisms.     

High intertidal community organization on a rocky headland in Maine,USA

A mosaic patchwork of the barnacle Balanus balanoides L., the mussel Mytilus edulis L., and the alga Fucus vesiculosus L. was found in the transitional region between the mid and high intertidal zones on a rocky headland on Mount Desert Island, Maine, USA. The development of the mosaic was observed by following recruitment and survival of B. balanoides in denuded patches located at the same tidal level along a 60 m stretch of shore. Barnacle recruitment was least under canopies of F. vesiculosus and greatest in open areas kept moist at low tide by surf. Barnacle survival after settlement was least under the F. vesiculosus canopy due to the whiplash effect of the algal fronds in the surf and greatest in open areas free from competition from mussels. In open areas, early mortality was correlated with settlement density. In areas of dense settlement (60 spat cm^-2) up to 90% mortality resulted within 5 months from crowding associated with growth. In older individuals crowding produced hummocks of elongated, weakly attached barnacles which were more prone to removal by surf than uncrowded barnacles. Mussels exerted competitive dominance over barnacles for space and the presence of mussel beds prevented further barnacle recruitment. Mussels suffered extensive mortality during winter storms when surf removed dense mats of weakly attached mussels. The patchy distribution of mussels and barnacles results from irregular rock substrata producing numerous environmental patches with respect to wave exposure and drainage at low tide, and from densitydependent mortality of both mussels and barnacles which creates patches of new colonizable space within each environmental patch.     

Hydrocarbon uptake and loss by the mussel Mytilus edulis

The dynamics of accumulation and elimination of hydrocarbons by the blue mussel Mytilus edulis were studied in a continuous-flow system. Mussels were exposed for as long as 41 days to 200 – 400 g/l of diesel fuel adsorbed on kaolin particles. Hydrocarbons were accumulated in the tissues in excess of 1000 times the exposure levels. Upon termination of dosing, the mussels exhibited a rather rapid loss of hydrocarbons for the first 15 to 20 days (biological half-life=2.7 to 3.5 days). Subsequently, however, elimination was reduced to a minimum and a considerable fraction of the hydrocarbons could be recovered from the tissues after as long as 32 days of depuration. The mussels exhibited definite signs of physiological stress due to chronic exposure to diesel fuel, although recovery was rapid upon termination of dosing. It is concluded that mussels could be utilized as a test organism for monitoring long-term hydrocarbon pollution in marine waters. The implications for the mussel culture industry are discussed.     

Population dynamics of Mytilicola intestinalis in Mytilus edulis in south west England

The population dynamics of Mytilicola intestinalis Steuer in mussels (Mytilus edulis L.) from the River Lynher, Cornwall, England, have been studied over 3 years. By transplanting uninfested mussels from the River Erme, South Devon, into the Lynher mussel bed, the study was extended to the growth and development of new infestations under natural conditions. Female Mytilicola intestinalis are shown to breed twice, and two generations of parasites coexist for most of the year, with recruitment taking place in summer and autumn. One generation contributes its first brood to the autumn recruits before overwintering and contributing its second brood to the following summer's recruits. The other generation overwinters as juvenile and immature stages to contribute its two broods successively to the summer and autumn recruits. Environmental temperatures are believed to control the rates of development at all stages rather than acting as triggers in the onset or cessation of breeding at specific times. There is no evidence to support the contention that heavily infested mussels are killed, and parasite mortality is shown to be density-independent.     

Prevalence, patterns, and effects of shell damage on Geukensia demissa in South Carolina estuarine habitats

Shelled molluscs frequently exhibit a record of damage on exterior surfaces that can evidence past predation attempts and may affect survival and growth. In South Carolina populations of the ribbed marsh mussel, Geukensia demissa, >90% of the individuals and up to 60% of the total shell area are damaged. A trend toward greater amounts of damage occurred on mid-marsh compared to oyster reef mussels from the barrier beach side of inlets. Shell damage effects on survivorship and shell and tissue growth were assessed seasonally during multi- and single-season field experiments. Mussels from a common mid-marsh site were divided into size classes (~50 or 70 mm), treated to create two damage levels (undamaged and damaged), and replaced within mid-marsh exclusion cages to minimize additional shell damage. In both multi- and single-season experiments increased shell damage resulted in significantly greater mortality. Linear shell growth was unaffected by increased damage, but 50 mm mussels grew twice as fast. Shell mass increased 16–50% in the multi-season and single-season winter period, but decreased 7–12% during the single-season summer period. Tissue mass significantly decreased 31–43% in 50 mm damaged mussels, but increased by 33% for 70 mm mussels in both multi-season and the single-season winter period experiments. Shell damage did reduce tissue mass 43% in 70 mm single-season summer mussels. Experimental results indicate shell damage from a simulated increase in predation can affect negatively both survival and growth of marsh mussels. Seasonal timing of shell damage and initial mussel size also influenced the effects of sublethal predation on shell and tissue growth. The previously unrecognized importance of sublethal predation and the resultant significant negative effects of shell damage on survival and growth will affect the distribution and population dynamics of G. demissa in coastal marshes and will influence the overall contribution of ribbed mussels to estuarine ecosystems.     

Hydrodynamic stress and habitat partitioning between indigenous (Perna perna) and invasive (Mytilus galloprovincialis) mussels: constraints of an evolutionary strategy

The ability of a mussel to withstand wave-generated hydrodynamic stress depends mainly on its byssal attachment strength. This study investigated causes and consequences of different attachment strengths of the two dominant mussels species on the South African south coast, the invasive Mytilus galloprovincialis and the indigenous Perna perna, which dominate the upper and the lower areas of the lower balanoid zone, respectively and co-exist in the middle area. Attachment strength of P. perna was significantly higher than that of M. galloprovincialis. Likewise solitary mussels were more strongly attached than mussels living within mussel beds (bed mussels), and in both cases this can be explained by more and thicker byssal threads. Having a wider shell, M. galloprovincialis is also subjected to higher hydrodynamic loads than P. perna. Attachment strength of both species increased from higher to lower shore, in response to a gradient of stronger wave action. The morphological features of the invasive species and its higher mortality rates during winter storms help to explain the exclusion of M. galloprovincialis from the low shore. The results are discussed in the context of the evolutionary strategy of the alien mussel, which directs most of its energy to fast growth and high reproductive output, apparently at the cost of reduced attachment strength. This raises the prediction that its invasive impact will be more pronounced at sites subject to strong but not extreme wave action.