Mussel Larvae Research Articles

Limnoperna fortunei (Dunker 1857) en el Sistema de Embalses del Rio Negro, Uruguay

Normal 0 21 false false false PT-BR X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;} LIMNOPERNA FORTUNEI (DUNKER 1857) IN THE RESERVOIR NEGRO RIVER SYSTEM, URUGUAY. Limnoperna fortunei is an invasive mollusk species reported in the Plata Basin since 1991, invading the major water systems in the region, affecting human infrastructure and causing ecological alterations. In Uruguay it is reported in five of the six major river basins, including the system of reservoirs in Río Negro since 1999. The development of population control strategies to mitigate the effects caused by this species requires basic studies of their life cycle. This contribution describes the annual cycle of pelagic stages and larval settlement of L. fortunei in the reservoir Palmar, Río Negro. Sampling was conducted during 2006-2008, using continuous sampling systems, static or stratified ones, by seasonal or monthly intervals. Environmental parameters were similar to previous studies in the system, the zooplankton community showed holo (Rotifera, Crustacea) and merozooplankton ( L. fortunei larvae), showing a seasonal behavior. The golden mussel larvae showed a seasonal pattern with peaks during austral spring and autumn and absence during winter, and did not differ between strata analyzed and the various stages did not show a clear temporal variation. The temperature did not show significant associations with larval abundances but was a set of environmental variables (temperature, Kd and residence time) which explained the variability of the zooplankton community and larvae of L. fortunei. The abundance L. fortunei individuals settled showed spatial and temporal variations, the minimum was found in February and March and the maximum in December. Significant differences were found between the abundance of organisms settled on substrates located at surface (0.5m) and bottom (10m). The observed maximum size of an individual settled was 22mm body large, showing differences in growth between surface and bottom. Recruitment patterns showed two peaks per year: January-February and September-October, coinciding with pelagic annual cycle, as evidenced by two annual cohorts, results similar to other studies in the region. The identification of larval behavior and settlement patterns of the golden mussel in the reservoir Palmar make possible the design of control strategies for the Río Negro reservoirs. Keywords: golden mussel; zooplankton; larvae; reservoir; Uruguay.

Has zooplankton 24 hour vertical distribution pattern in Lough Derg (Ireland) been changed over the period of ∼90 years?

Abstract The vertical distribution of zooplankton was examined in Lough Derg, Ireland. Zooplankton was collected at one location every 2 m from the surface to the bottom during 24 hours at four-hour intervals. Zooplankton was identified to the species level and its density was calculated for each taxon, depth and hour. We recorded 9 rotifer, 3 copepod, and 4 cladoceran species. The highest total zooplankton density (rotifers, copepods, cladocerans, mysids and zebra mussel larvae) was recorded at 3 a.m. Rotifers preferred mainly a depth from 0 to 8 m, while copepods and cladocerans were observed within the whole water column during a 24 hour observation. It was a different pattern of diurnal migration than that Southern and Gardiner (1932) received, though they didn’t study rotifers. Probably food concentration and/or predators, or other environmental factors could influence the diel vertical migration of zooplankton from Loug Derg.

Do gill parasites influence the foraging and antipredator behaviour of rainbow darters, Etheostoma caeruleum?

Parasites are known to affect an array of characteristics of their hosts, including morphology, physiology and behaviour. We examined the foraging and antipredator behaviour of rainbow darters, Etheostoma caeruleum, that were parasitized by glochidia larvae of freshwater mussels (Ptychobranchus occidentalis and Venustaconcha pleasii: Unionidae). Glochidia attach to the gills of the host and become encapsulated in host tissue. Over a period of days or weeks the larvae develop into free-living juveniles, which then leave the host. Parasitized darters increased ventilation rates (either early in the infestation or at the height of the infestation), were less active during foraging trials, lost more body size than nonparasitized darters and showed significantly weaker responses to predation risk (signalled by the presence of a chemical alarm cue). Therefore, even for a relatively short-term infection, parasitized darters may pay a cost in terms of decreased growth and decreased probability of survival.

Functional impacts of ocean acidification in an ecologically critical foundation species

Anthropogenic CO(2) is reducing the pH and altering the carbonate chemistry of seawater, with repercussions for marine organisms and ecosystems. Current research suggests that calcification will decrease in many species, but compelling evidence of impaired functional performance of calcium carbonate structures is sparse, particularly in key species. Here we demonstrate that ocean acidification markedly degrades the mechanical integrity of larval shells in the mussel Mytilus californianus, a critical community member on rocky shores throughout the northeastern Pacific. Larvae cultured in seawater containing CO(2) concentrations expected by the year 2100 (540 or 970 ppm) precipitated weaker, thinner and smaller shells than individuals raised under present-day seawater conditions (380 ppm), and also exhibited lower tissue mass. Under a scenario where mussel larvae exposed to different CO(2) levels develop at similar rates, these trends suggest a suite of potential consequences, including an exacerbated vulnerability of new settlers to crushing and drilling attacks by predators; poorer larval condition, causing increased energetic stress during metamorphosis; and greater risks from desiccation at low tide due to shifts in shell area to body mass ratios. Under an alternative scenario where responses derive exclusively from slowed development, with impacted individuals reaching identical milestones in shell strength and size by settlement, a lengthened larval phase could increase exposure to high planktonic mortality rates. In either case, because early life stages operate as population bottlenecks, driving general patterns of distribution and abundance, the ecological success of this vital species may be tied to how ocean acidification proceeds in coming decades.

Effect of neuroactive compounds on the settlement of mussel ( Perna canaliculus) larvae

Herein, we present the first laboratory study on the effects of pharmacologically active compounds on larval settlement of the green-lipped mussel, Perna canaliculus. Competent hatchery-reared larvae were exposed to seawater containing excess K + in the form of KCl and K 2SO 4 and the neurotransmitters γ-aminobutyric acid (GABA) and acetylcholine. Both KCl and K 2SO 4 were identified as active inducers of larval settlement with maximum inductions occurring after exposures to 10 and 7.5 mM, respectively. Peak settlement response to KCl was higher (> 64%) than that achieved with K 2SO 4 (> 41%). GABA did not induce larval settlement and displayed toxic and settlement inhibitive effects at 10 −4 and 10 −3 M. Acetylcholine induced larval settlement (> 49%) at 10 −4 M with minimal acute toxic effects (LC < 10%). To gain insight into the class of acetylcholine receptors involved, atropine was used to block the muscarinic-type receptors. Atropine treatment alone did not inhibit settlement compared to control assays, indicating that muscarinic-type receptors are not involved in settlement behavior. Furthermore, results showed that atropine did not significantly decrease acetylcholine induced settlement responses, which suggests an active role of the nicotinic-type receptors in the biochemical pathways of mussel settlement. Results of this study provide new insights on the mechanism of settlement behavior in P. canaliculus, which may have direct application to the growing New Zealand aquaculture industry.

Seasonal and species-specific patterns in abundance of freshwater mussel glochidia in stream drift

Abstract We examined seasonal patterns of abundance of mussel larvae (glochidia) in stream drift in a diverse, large-stream mussel assemblage in the Sipsey River, Alabama, across 1 y. We used recently developed techniques for glochidial identification combined with information about mussel fecundity and benthic assemblages to evaluate how well observed glochidial abundance corresponded to expected abundance based on glochidial production. Glochidia from short-term brooding species (Amblema plicata, Elliptio arca, Fusconaia cerina, Pleurobema decisum, Obliquaria reflexa, and Quadrula asperata) were abundant from May to August but did not occur in drift between November and the end of April. Long-term brooders (Lampsilis spp., Medionidus acutissimus, Obovaria unicolor, and Villosa spp.) occurred in several short peaks in spring, summer, and autumn, but generally were less abundant than short-term brooders. We estimated that the benthic assemblage at our study site produced >500,000 glochidia/m2 annually and...

A Method for Culturing Mussels Using In-River Cages

Abstract A variety of techniques have been used since the early 1900s to produce mussels for augmenting depleted populations, including the use of wire-covered crates to house fish bearing mussel larvae. Here we describe a modification of earlier techniques, which provides a viable, low-cost method for producing large numbers of mussels. Aluminum-framed cages covered with commercially available hardware cloth are used to confine glochidia-bearing fish. Juvenile mussels then excyst off the host fish, and fall to the substrate-covered cage bottom, which protects the mussels from predation until they mature into subadult mussels. To date, seven species of mussels totaling over 57,100 2- and 3-y-old mussels have been reared in these culture cages.

Marine protected areas export larvae of infauna, but not of bioengineering mussels to adjacent areas

Populations of organisms that create habitat can often be fragmented throughout landscapes by anthropogenic disturbances such as harvesting and loss or change to the identity of such bioengineers may lead to large changes in biodiversity. Using the fauna associated with a bioengineer, the intertidal mussel Perna perna, we tested hypotheses about the relative importance of larval export from protected populations in marine reserves. Harvesting led to the replacement of P. perna and the domination of shores outside reserves by turf-forming coralline algae, mostly Corallina spp. We determined whether the diverse fauna recruiting onto artificial units of habitat placed within mussel beds differed between reserves and non-reserve areas or whether shores outside reserves, and open to harvesting, received recruits through larval export from reserves. Furthermore, we determined whether this was affected by the distance away from reserves and whether colonisation was achieved by movement of adults from surrounding biogenic habitats or via the plankton. Overall, we found no effect of increasing distance away from a reserve on the cover of adult mussels or associated fauna. We found strong effects of the presence of marine reserves on abundances of molluscs and polychaetes but not crustaceans. There were greater densities of molluscs in sites with a reserve (i.e. inside reserves, and up to 5 km outside reserve boundaries), but more polychaetes in exploited sites. For molluscs, this pattern was driven by gastropods rather than bivalves. Furthermore, although reserves had greater cover of adult mussels than non-reserve areas, recruitment of mussels was not greater inside or near to reserves. Our study illustrates the effectiveness of these reserves in protecting stocks of adult mussels, and although there was no evidence that reserves provided export of the larvae of mussels (the target species), they did provide larval export of non-targeted associated species. By protecting a harvested bioengineer and through export of the larvae of its associated fauna, these reserves fulfil some, but not all the conservation aims of a marine protected area.

Fiordos de Chile: Potencial zona de crianza de Bathylagichthys parini (Pisces: Osmeriformes: Bathylagidae)

Eighteen juveniles of Bathylagichthys parini (Osmeriformes: Bathylagidae) were collected in fjords of southern Chile (ca. 48°S-74°W) in November 2008. Standard length and wet weight ranged from 22.6 to 37.7 mm, and between 0.049 and 0.243 g, respectively; density ranged between 3.56 and 41.77 juveniles x 10 m2. Stomach contents included calanoid copepods (mainly Acartia tonsa and Paracalanus parvus adults and copepodids), ostracods and mussel larvae. This finding suggests that juveniles feed near surface waters and aids evidence to the hypothesis the fjords are utilized as nursery zone for this rare oceanic species from South Pacific.

Mussel larval responses to turbulence are unaltered by larval age or light conditions

Lay AbstractWhen marine larvae change their behavior in response to small‐scale water motions, these responses potentially affect large‐scale patterns of larval dispersal and settlement. This study examined the behavior of mussel larvae (Mytilus edulis) in turbulence representative of nearshore currents. We video recorded the behavior of early‐ and late‐stage larvae in a tank with turbulence generated by two stirring grids at five turbulence levels under light and dark conditions. Water velocities and turbulence were measured using particle image velocimetry and acoustic Doppler velocimetry. We determined the vertical velocity distributions of sinking, hovering, and swimming larvae in still water and calculated the average behavioral velocity of larvae in turbulence. In still water, young larvae swam upward faster than old larvae, and both stages swam upward faster in light than in dark. In turbulence, the larval movements varied from upward swimming in weak turbulence to sinking in strong turbulence above a threshold level. At this threshold, the smallest eddy lengths were two to three times larger than the larval shell lengths, implying that turbulence is detectable even by larvae that are smaller than the smallest eddies. Responses to turbulence were unaffected by larval age or light conditions and contributed substantial behavioral variation. By sinking in strong turbulence, mussel larvae could contact the seabed more frequently in energetic coastal flows, particularly over rough materials like mussel beds. The response to turbulence by early‐stage larvae will also affect dispersal and may help larvae remain near coastal populations.

Influence of Cortisol on the Attachment and Metamorphosis of Larval Utterbackia imbecillis on Bluegill Sunfish (Lepomis macrochirus)

The larvae of unionid freshwater mussels (i.e., glochidia) undergo a parasitic stage requiring their attachment to the external epithelia of fish hosts, where they metamorphose into free-living juveniles. We describe the physiological effects in bluegill sunfish (Lepomis macrochirus) of infection with glochidia from the paper pondshell (Utterbackia imbecillis). Glochidia accumulation on bluegill increased dramatically at concentrations of 2000 glochidia liter(-1) and above, reaching a maximum attachment density of about 30 glochidia g(-1) fish at 4000 glochidia liter(-1). Plasma cortisol was the most sensitive indicator of biological effect to glochidial exposure, increasing significantly in hosts exposed to 2000 glochidia liter(-1) or greater. Glochidia were 31% more likely to undergo successful juvenile metamorphosis when attached to bluegill with elevated plasma cortisol, largely due to the enhanced survivorship of these larvae during the first 48 h after infection. We tested the hypothesis that glochidial attachment and juvenile metamorphosis were stimulated directly by plasma cortisol in fish hosts. Bluegill were given an intraperitoneal injection of cortisol, then infected with 1000 glochidia liter(-1) at 48 h after hormone supplementation. Cortisol-injected fish had a 42% increase in the number of attached glochidia g(-1) fish and a 28% increase in larval metamorphosis compared to sham-injected and control fish. We provide evidence that cortisol enhances glochidial metamorphosis on hosts by improving the retention of attached glochidia. This study gives insights into the influence of host physiology on glochidial attachment and juvenile mussel transformation.

Effects of Ocean Acidification on Early Life Stages of Shrimp (Pandalus borealis) and Mussel (Mytilus edulis)

Ocean acidification (OA) resulting from anthropogenic emissions of carbon dioxide (CO2) has already lowered and is predicted to further lower surface ocean pH. There is a particular need to study effects of OA on organisms living in cold-water environments due to the higher solubility of CO2 at lower temperatures. Mussel larvae (Mytilus edulis) and shrimp larvae (Pandalus borealis) were kept under an ocean acidification scenario predicted for the year 2100 (pH 7.6) and compared against identical batches of organisms held under the current oceanic pH of 8.1, which acted as a control. The temperature was held at a constant 10°C in the mussel experiment and at 5°C in the shrimp experiment. There was no marked effect on fertilization success, development time, or abnormality to the D-shell stage, or on feeding of mussel larvae in the low-pH (pH 7.6) treatment. Mytilus edulis larvae were still able to develop a shell in seawater undersaturated with respect to aragonite (a mineral form of CaCO3), but the size of low-pH larvae was significantly smaller than in the control. After 2 mo of exposure the mussels were 28% smaller in the pH 7.6 treatment than in the control. The experiment with Pandalus borealis larvae ran from 1 through 35 days post hatch. Survival of shrimp larvae was not reduced after 5 wk of exposure to pH 7.6, but a significant delay in zoeal progression (development time) was observed.

Dispersal limitation of unionid mussels and implications for their conservation

Summary 1. Freshwater unionid mussels are a highly imperilled group. Their dispersal abilities depend on the availability and the movement of host fish on which their parasitic mussel larvae develop. 2. We examined the relationship between the dispersal abilities of unionid mussels and their conservation status on a regional (SW Ontario) scale and their distribution and abundance on a catchment scale (Sydenham River, SW Ontario) by determining host specificity and estimating the dispersal abilities of mussels on fish from a review of the literature. 3. On the regional scale, we found that mussels with the most precarious conservation status relied on host fish with short movement distances, whereas vulnerable and more secure mussel species had host fish with 2–3 orders of magnitude larger movement distances. We were not able to detect a clear pattern on the catchment scale. 4. Our results suggest that limited dispersal by host fish affects the abundance and distribution of unionid mussels and ultimately their conservation status on a regional scale. Information on dispersal limitations because of differences in host fish communities should be included in conservation and management decisions to ensure connectivity and maintain functioning mussel metacommunities.

Recruit/algal interaction prevents recovery of overexploited mussel beds: Indirect evidence that post-settlement mortality structures mussel populations

The mechanisms maintaining community structure following an ecosystem shift are poorly understood and we propose that they must inherently be biological. Over-exploitation can provide a “natural experiment” with man as a predator driving a change in community structure, possibly an ecosystem shift. We examined a possible mechanism that maintains algal beds as an alternative state on the east coast of South Africa where the mussel Perna perna has been overexploited. Even on unexploited shores, about 50% of mussel larvae settle onto algae, but it is unclear whether they later recruit into adult beds. On such shores we used two indirect field approaches to understand the fate of recruits, testing whether inhibition of mussel recruitment by macroalgae could constitute a biological mechanism preventing reversion from the algal to the pre-disturbance mussel-dominated state. First, we examined possible ontogenetic migration of recruits from algae to adult mussels, testing the prediction that the ratio large:small recruits in adult beds is greater where algae are liberally interspersed with mussels. Second, we examined whether, like adults, recruits show spatial structure that is related to the distribution of topographic depressions, testing the hypothesis that large and small recruits show different co-variation with depressions, microhabitats where algae commonly occur. We found no evidence that recruits on algae actively move to nearby mussel beds as neither the ratio large:small recruits nor the abundances of small or large recruits showed any relationship with algal cover/variability. Small and large recruits showed different co-variation with topographic depressions on spatially structured transects. Like adults, large recruits commonly exhibited negative relationships with depressions. Thus, large recruits neither occur on algae nor migrate from algae to the primary substratum or onto adult beds. Consequently our results (a) highlight the importance of post-settlement mortality in structuring these mussel populations, and (b) suggest that the interception of larvae by algae forms a biological mechanism that can maintain macroalgal beds that develop following exploitative disturbance by man, thus preventing or at least drastically delaying the natural recovery of mussel beds.

Ingestion-rate method for measurement of clearance rates of the ctenophore Mnemiopsis leidyi

Clearance rates of small (about 12 mm oral-aboral length) Mnemiopsis leidyi were measured by means of the ingestion-rate method in order to compare with rates estimated from an equation (derived from Decker et al. 2004) used in previous studies. About 3 times higher clearance rates measured in the present study indicate that the estimated predation impact of small ctenophores may previously have been considerably underestimated. The prey-capture efficiency measured in M. leidyi depends on type and size of prey organism, and the study indicates that the clearance of slow swimming prey (e.g. mussel larvae) captured by auricular flow fields is higher than the clearance of fast swimming/jumping prey (copepods) captured by the lobes. The ingestion-rate method presented may open up not only more precise measurements of clearance rates, but also provide for digestion rates of M. leidyi offered different types of prey organisms.

Temperature effect on survival, growth, and triacylglycerol content during the early ontogeny of Mytilus edulis and M. trossulus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 417:183-191 (2010) - DOI: https://doi.org/10.3354/meps08774 Temperature effect on survival, growth, and triacylglycerol content during the early ontogeny of Mytilus edulis and M. trossulus Nathalie Rayssac1, Fabrice Pernet2,*, Olivia Lacasse1, Réjean Tremblay1 1Institut des Sciences de la Mer de Rimouski (ISMER), 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Ifremer, Laboratoire Environnement Ressources du Languedoc Roussillon, Bd. Jean Monnet, 34200 Sète, France *Corresponding author. Email: fabrice.pernet@ifremer.fr ABSTRACT: Temperature is a major factor contributing to the biogeography of intertidal poikilotherms. The population dynamics of intertidal invertebrates like mussels are strongly dependent on larval supply and larval mortality. Unlike adults, which are resistant to fluctuating environmental conditions, larvae are highly sensitive to the physicochemical conditions of the pelagic zone. The effects of rearing temperature on larval and post-larval performance of 2 coexisting mussels species, Mytilus edulis and M. trossulus, were examined in this study. In the first experiment, larvae of both species were reared separately at constant temperatures of 10, 17, and 24°C from D-larvae to the dissoconch stage. In the second experiment, pediveligers were reared under the same experimental conditions as the larvae for 2 wk. Survival, growth, and lipid composition (triacylglycerol [TAG] and sterol [ST] contents) were used to compare the performance of both species. The first experiment showed a species-specific thermal tolerance range, reflecting the biogeography of the species. M. trossulus larvae showed a preference for water at 10 and 17°C, corresponding to the more northerly distribution of this species, whereas M. edulis preferred temperatures of 17 and 24°C. Moreover, the TAG content in larvae of both species varied with temperature, supporting the hypothesis of a positive correlation between energy reserve content and the survival of mussel larvae. In contrast, the species-specific characteristics of thermal tolerance were not observed during post-larval development, suggesting that the selective effect of temperature on mussel species occurs during early ontogeny. KEY WORDS: Thermal adaptation · Bivalve mollusk · Selection · Biogeography · Lipid · Larval ecology Full text in pdf format PreviousNextCite this article as: Rayssac N, Pernet F, Lacasse O, Tremblay R (2010) Temperature effect on survival, growth, and triacylglycerol content during the early ontogeny of Mytilus edulis and M. trossulus. Mar Ecol Prog Ser 417:183-191. https://doi.org/10.3354/meps08774 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 417. Online publication date: November 04, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Transcriptional response of stress genes to metal exposure in zebra mussel larvae and adults

Development of stress markers for the invader freshwater zebra mussel (Dreissena polymorpha) is of great interest for both conservation and biomonitoring purposes. Gene expression profiles of several putative or already established gene expression stress markers (Metallothionein, Superoxide dismutase, Catalase, Glutathione S transferase, Glutathione peroxidase, Cytochrome c oxidase, the multixenobiotic resistance P-gp1, and heat shock proteins HSP70 and HSP90) were analyzed by quantitative Real-Time PCR in adults and pediveliger larvae after exposure to metals (Hg, Cu, Cd). A defined pattern of coordinated responses to metal exposure and, presumably, to oxidative stress was observed in gills and digestive gland from adults. A similar, albeit partial response was observed in larvae, indicating an early development of stress-related gene responses in zebra mussel. The tools developed in this study may be useful both for future control strategies and for the use of zebra mussel as sentinel species in water courses with stable populations.

Suitability of different salmonid strains as hosts for the endangered freshwater pearl mussel (Margaritifera margaritifera L.)

Abstract The complex life cycle of endangered European freshwater pearl mussel Margaritifera margaritifera L. involves an obligatory parasitic phase on a host fish. Knowledge on the host–parasite interaction and on the suitability of different host fish species and strains is required both for the management of wild fish and mussel populations as well as for improving the efficiency of captive breeding methods. In this study, the suitability of different salmonid strains for hosting glochidia was tested, including Danube salmon (Hucho hucho L.) and three brown trout (Salmo trutta L.) strains from inside and outside the freshwater pearl mussel distribution range. All brown trout strains as well as Danube salmon were successfully infected with freshwater pearl mussel glochidia and encystment of mussel larvae was detected. One brown trout strain originating from the natural pearl mussel distribution range was identified as the most suitable host, revealing the highest fish‐weight‐normalized infection rates and highest glochidial growth rates, whereas endemic Danube salmon was least suitable. Under natural conditions, the role of Danube salmon may be attributed to the long‐distance dispersal of glochidia in the Danube system, whereas sedentary brown trout appear to be the most important hosts at a local scale. Successful infection of suitable hosts and the maintenance of these host–parasite systems in calcareous water were demonstrated in this study. These results indicate that neither the infection process nor the encystment phase of freshwater pearl mussels is dependent on low lime concentrations. The results of this study suggest that careful selection and management of appropriate host fish strains is mandatory for sustainable conservation management of freshwater pearl mussel populations. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Effects of different dietary microalgae on survival, growth, settlement and fatty acid composition of blue mussel ( Mytilus galloprovincialis) larvae

The diatom Chaetoceros calcitrans is a major component of many bivalve hatcheries, yet it is expensive and notoriously difficult to culture on a commercial scale. In an attempt to reduce dependence on the diatom C. calcitrans, mussel larvae ( Mytilus galloprovincialis) were subjected to feeding experiments which altered levels of the diatom under controlled hatchery conditions. Growth, survival and settlement success of mussel larvae were determined in response to five mixed algal diets in which the relative contributions of C. calcitrans was varied over the experimental period (30 days). Fatty acid profiles of the larvae and algal diets were also assessed. The exclusion of C. calcitrans from the diet had no significant differences on larval growth and only minor differences in total fatty acid content were found between treatments. Fatty acid analysis revealed that larval survival was strongly influenced by the proportions of dietary docosahexaenoic acid (DHA), while settlement was positively correlated with higher ratios of the n-3 long-chained polyunsaturated fatty acid (n-3 LC-PUFA) (namely, DHA and eicosapentaenoic acid, EPA), to the n-6 LC-PUFA (arachidonic acid, ARA). Despite similar relative and absolute n-3 LC-PUFA levels in the larvae under different dietary treatments, the larvae receiving high levels of C. calcitrans performed significantly better in terms of survival and settlement success. These results indicate that the (DHA + EPA)/ARA ratio is a key factor in determining larval performance, rather than the total amount of these fatty acids.

Alteromonas macleodii 0444 and Neptunomonas sp. 0536, two novel probiotics for hatchery-reared Greenshell™ mussel larvae, Perna canaliculus

Antibiotic management of aquacultured animals, such as Greenshell™ mussel (GSM) larvae, Perna canaliculus, is undesirable because of health concerns and political pressures; hence, alternatives are needed. Herein, two novel probiotic bacteria were identified and trialled in a GSM larval rearing hatchery. Sequencing of the 16S rRNA gene and phylogenetic analysis identified the strains as Alteromonas macleodii 0444 and Neptunomonas sp. 0536. Both probiotics were evaluated separately at the Glenhaven Aquaculture Centre hatchery facility during routine larval rearing and when the larvae were challenged with both a high (10 7 and 10 6 CFU ml −1) and low (10 6 and 10 5 CFU ml −1) pathogenic dose of Vibrio sp. DO1 and V. splendidus respectively. In all experiments, probiotic application improved larval survival significantly when administered prior to pathogen exposure. Across all experiments, larvae that were exposed to the high and low dosages of pathogens averaged 14% and 36% survival respectively on the fourth day following pathogen exposure. The administration of probiotics prior to pathogen challenge resulted in larval survival of 50% and 66% respectively. Non-inoculated control larvae and larvae administered the probiotic alone demonstrated 67% and 79% survival respectively. Neptunomonas sp. 0536 appeared to suppress naturally occurring vibrios in the culture environment of healthy GSM larvae. This is the first report of A. macleodii and Neptunomonas sp. as probiotic bacteria in a large scale production facility.