Induction of anti-predator responses in the green-lipped mussel Perna viridis under hypoxia

Hypoxia due to the over enrichment of waters by nutrients is becoming a global problem. In mussels, enhanced byssus thread production is an important adaptation to the presence of crustacean predators and to energetic hydrodynamic regimes. Thread production is an energy-consuming process, so this study used the green mussel Perna viridis (L.) to examine the response to predator exposure combined with hypoxia. Hypoxia is common in sheltered bays in Hong Kong, and the mussels were collected in one such bay, Lok Wo Sha (latitude/longitude: 22o18′ N/114o10′ E) in January, 2009. The predator used in the experiments was the swimming crab Thalamita danae. Oxygen concentrations used in the 48-h experiments ranged from hypoxic to normoxic (1.5 ± 0.3 mg l⁻¹, 3.0 ± 0.3 mg l⁻¹ and 6.0 ± 0.3 mg l⁻¹). Fewer byssus threads which were also shorter and thinner were produced at reduced oxygen levels, no matter if the predator was present or not; the frequency the mussels shed stalks was also lower. Mussels exposed to the predator, however, have enhanced byssus thread production at all oxygen levels when compared with the control. This has highlighted the significance of anti-predator responses for the survival of individuals even under a stressful environment in which energy supply is limited by aerobic metabolism. Interactive effects between oxygen level and predator exposure were observed for the byssus thread production (frequency of shed stalks, mean byssus thread length, cumulative byssus thread volume), with values obtained at 1.5 and 3.0 mg O₂ l⁻¹ being statistically indistinguishable for the control group without predator but not for the predator group. The lack of differences in the byssus thread production at lower oxygen levels in the absence of predator may indicate the minimum amount of byssus that is required for settlement on a substrate.     

Observations on the function of the glands of the foot of the pediveliger of Ostrea edulis during settlement

The use during settlement of secretions of the 9 different types of gland in the foot of the pediveliger of Ostrea edulis L. was examined experimentally. During settlement, there is a progressive decrease in the crawling speed of the larva and a strengthening of its bond with the substratum. Both changes are related to (a) a change from ciliary to muscular pedal locomotion; (b) the increasing acidity and viscosity of the mucoid secretions used; (c) the secretion of a byssus thread by the glands of the byssus duet; (d) changes in the form and composition of this byssus. At the termination of settlement, the entire contents of 2 types of gland are discharged. Their secretions give rise to the cement which permanently fixes the larva to the substratum. The 9 types of gland are utilised sequentially in a manner closely related to the 6 phases recognised in settlement behaviour.     

Cementation vs mobility: development of a cemented byssus and flexible mobility in Anomia chinensis

The mobility of Anomia chinensis Philippi was studied in relation to its byssal development stage. This species shows high mobility even after it begins cementation in its post-larval stage. Juveniles develop a calcified byssus in the post-larval stage and cement to substrata. However, juveniles up to about 10 mm in shell length can relocate by repeating a sequence of formation of the calcified byssus, abandonment of it, locomotion by crawling, reattachment, and recementation. Juvenile anomiids up to 25 mm in shell length also can move, without breaking their byssal attachments, by shifting the center of byssal calcification dorsally. Even an adult can change its orientation by forming a twisted byssus. These possible methods of movement are closely related to five stages of byssal development. Anomiids can use this mobility to seek a preferable position for attachment after initial cementation, or to adjust their orientation, and thus promote higher survivorship. Received: 18 August 1997 / Accepted: 19 July 1998     

On the functional morphology of Hiatella solida (Hiatellidae: Bivalvia)

Hiatella solida (Sowerby, 1834) is the only species of the genus Hiatella represented in Southern Brazilian waters. It occurs on the coast of São Paulo and Rio Grande do Sul. The bivalves were found nestling or attached by byssus threads to specimens of the sea squirt Polyandrocarpa zorritensis or between the tubes of the polychaete Phragmatopoma lapidosa in the intertidal zone. The structure, adaptation and functional morphology were studied in detail, including the functioning of the stomach. H. solida were found with mature ova in August.     

Interactions of 233Pa with tissues of Mytilus galloprovincialis and Carcinus mediterraneus

Uptake of ²³³Pa from sea water by mussels Mytilus galloprovincialis L. and shore crabs Carcinus mediterraneus Csrn. was studied. Results indicate a high contamination factor in digestive tract, gills and skeleton of both investigated species and an increment of the contamination factor in mussel byssus. In spite of this, reproductive system, muscle and hemolymph were only negligibly contaminated. The presence of complexone EDTA in sea water has no effect on uptake of ²³³Pa in the animal tissues tested.     

Observations on the behaviour of the pediveliger of Ostrea edulis during attachment and cementing

The behaviour of pediveligers of Ostrea edulis L. during attachment can be divided into 5 clearly defined phases. These behavioural phases are generally successive, and may be a hierarchy of fixed motor patterns which terminates in the consummatory act of cementing. During attachment, the larva utilises two different mechanisms of movement: the first, a fast, smooth, gliding action is probably due to cilia only; the second, a jerky, muscular method which becomes progressively slower as cementing is approached, is related to the burrowing movements of adult lamellibranchs. The byssus thread, which is discharged during the period of muscular locomotion, was the only secretion seen, but the site of its discharge could not be determined by direct observation.     

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.     

Fungi in corals: black bands and density-banding of Porites lutea and P. lobata skeleton

 Dark coloration of coral skeleton forming black bands is commonly observed in fractured, massive-coral colonies (Porites lutea and P. lobata) collected from May- otte Island in the Mozambique Channel and Moorea Island in French Polynesia. Black-banding was similar in corals from the two areas and was associated with an assemblage of microbial endoliths: Ostreobium queketti, a common siphonal chlorophyte, and a type of Aspergillus-like fungus. Fungi of coral skeletons are capable of euendolithic growth entirely within the skeleton, and of cryptoendolithic growth whereby they spread from the skeleton into the skeletal pores. The morphology and size of fungal hyphae differs significantly between euendolithic, cryptoendolithic and reproductive phases. Reproductive phases involve formation of conidiophores. Insoluble residues in black bands involve a dark pigment and a dark membranous veil. When attacked by fungi, the algae are usually destroyed. They darken and are threaded by dense, dark-brown, fibrous excrescences. The fungi excrete a dark pigment that stains the surrounding skeletal carbonate black. The pigment is organic, and its presence correlates with higher concentrations of polysaccharides. Black bands match high-density bands of the coral skeleton. Both black bands and high-density bands form at the end of the rainy season in Mayotte. Thus, black-banding in the corals studied is caused by a series of events, beginning with an increase in the abundance of endolithic algae followed by an increase in skeletal density. The algae are then attacked by fungi, which produce more cryptoendolithic hyphae and conidia that are associated with production of the dark pigment. Received: 29 January 1999 / Accepted: 29 September 1999     

Experimental analysis of byssus thread production by Mytilus edulis and Modiolus modiolus in sediments

Laboratory experiments have been conducted on byssus thread production by two species of mussel, Mytilus edulis L. and Modiolus modiolus (L.), representing the epibyssate and endobyssate species of the Mytilidae, respectively. Mussels were placed in seven particle sizes of sediment ranging from 50 m to 16 mm for 12 d. The number of byssus threads per mussel, length of threads, number of threads per particle and size of pads were then recorded. Modiolus modiolus (endobyssate) produced more threads than Mytilus edulis (epibyssate). M. edulis produced most threads in the size range 2 to 16 mm and Modiolus modiolus in the size range 500 to 1000 m. M. modiolus produced longer threads than Mytilus edulis. Both species produced longer threads in particle sizes finer than 2 mm. M. edulis produced smaller pads than Modiolus modiolus. Both species produced larger pads in sediments coarser than 1 000 m. Results were also analysed in terms of attachment units (a thread attached to one or more particles, or a particle to which more than one thread is attached). The thread:particle ratio of the attachment units ranged from ca. 1:10 in the finest sediments to ca. 10:1 in the coarsest sediments. Mytilus edulis attached more threads to single particles (72% of attachment units) than Modiolus modiolus (37% of attachment units). M. modiolus had a wider spread of ratios in the finer particle sizes than Mytilus edulis. The significance of our results are discussed in relation to the ecology and palaeoecology of epibyssate and endobysste species.     

Energy expended on growth and gonad output in the ribbed musselAulacomya ater

Length/weight relationships have been computed for shell, flesh and byssus ofAulacomya ater (Molina) and energy values used to convert the weights to energy equivalents. Shell accounts for some 26% of total body energy, while the contribution of the byssus declines from 15 to 8% during growth. Observations of juvenile growth rates have been used to generate a Gompertz growth equation which predicts attainment of maximum length (90 mm) after 11 years. Reproductive condition has been assessed by monitoring seasonal fluctuations in the flesh weight of standard-sized individuals, calculated from monthly length/weight regressions. There appear to be three spawnings, of variable date and intensity, each year. From the above data, annual energy expenditure on growth and gonad output has been calculated for individuals of various sizes. The ratio of total production to biomass is a declining clining function of shell length, dropping from 29.5 at 5 mm to 0.8 at 85 mm. The proportion of total production expended on gamete output increases steadily from 25% at attainment of maturity (15 mm) to 81% at 85 mm length. The considerable effects of changing size composition on the amount and type of production in natural populations are discussed.     

Salinity-temperature relationships in the queen scallop Chalamys opercularis

The effects of reduced salinities on different size-ranges of Chlamys opercularis (L.) were studied at various temperatures using 3 methods of analysis: median lethal mortality over 24 h (LD₅₀, 24 h); surface-response analysis; time-mortality relationships. Reduced salinities ranging from 16 to 28 were lethal after a 24 h exposure, depending on the temperature and size of the scallop. Mortality increased at extremes of temperature, and spat appeared to have a slightly greater tolerance than larger individuals. Observations were also made on behavioural responses and byssus attachment at reduced salinities.     

Vanadium transfer in the mussel Mytilus galloprovincialis

Radiotracers were used to study processes controlling the accumulation and elimination of vanadium in the Mediterranean mussel Mytilus galloprovincialis. Vanadium uptake rates varied inversely with both salinity and vanadium concentration in water, but were independent of temperature. After a 3 wk exposure to ⁴⁸V, the highest concentration factors were found in the byssus (1900) with much lower values computed for shell ( 70) and soft tissues (5). More than 90% of the total ⁴⁸V accumulated was fixed to shell, suggesting that uptake is primarily a result of surface sorption processes. Much of the vanadium in shell was firmly bound to the periostracum and was not easily removed by acid leaching. Food-chain experiments indicated that the assimilation coefficient for ingested vanadium is low (7%) and that the assimilated fraction is rapidly excreted from the mussel. These findings coupled with knowledge of in situ and experimentally-derived vanadium concentration-factors have allowed a preliminary assessment of the relative importance of the food and water pathways in the contamination of mussels under conditions of acute and chronic exposure. Contaminated mussels transferred to clean sea water lost ⁴⁸V at rates that depended upon temperature but were largely unaffected by either salinity or by vanadium levels in mussel tissues. Total vanadium depuration was slow and was governed by loss from a slowly-exchanging compartment with a characteristic half-time of about 100 d. Individual mussel tissues were analyzed for stable vanadium and the possibility of using these tissues, particularly the byssus, as bioindicators of ambient vanadium levels in the marine environment is also discussed.     

A method for rearing Pecten maximus larvae in the laboratory

Development of the scallop Pecten maximus (L.) from egg to metamorphosis takes 33 to 38 days at 16°C. The shelled veliger first appears 2 days after fertilisation, and crawling pediveligers at around 2 days before metamorphosis. The pediveliger can attach temporarily to filamentous objects by means of a byssus thread and, even after metamorphosis, periods of attachment alternate with periods of crawling. The larvae are reared in polythene bins containing 30 l of full salinity sea water (pre-filtered through 0.2 filters), which is changed every 2 days. Mixtures of algal foods (Isochrysis galbana, Chaetoceros calcitrans, Pyramimonas obovata and Tetraselmis suecica), concentrated by centrifugation, are added at each change from the third day onwards to give a concentration of 50 cells/l. Larval density is maintained below 10/ml. Antibiotics are added at each change, but very careful sterilisation of all equipment is necessary to guard against the introduction of diseases.     

Expression of multiple forms of an adhesive plaque protein in an individual mussel, Mytilus edulis

Individual blue mussels, Mytilus edulis L., can express at least 20 variants of a small protein known as M. edulis foot protein 3 or Mefp3. Mefp3 has been shown to be a component of the adhesive plaque of the byssus, the structure securing mussels to solid substrata. The cDNAs and deduced fp3 protein sequences display more variation at the carboxy-terminus than at the N-terminus, although there is some variation present throughout the protein. This indicates that there most likely are multiple copies of the gene encoding this protein. Each protein sequence contains a signal peptide, 24 to 25 residues in length, and a mature protein sequence of 44 to 54 residues. Gly is the most common amino acid in the mature protein at 20 to 25 mol%. Tyr and Arg follow closely at 20 to 23 and 16 to 21 mol%, respectively. Both of these amino acids were previously shown to be post-translationally modified to 3,4-dihydroxyphenylalanine (Dopa) and 4-hydroxyarginine, respectively, in this protein. MALDI-TOF (matrix-assisted laser desorption ionization with time-of-flight) mass spectrometric analysis of the underside of adhesive plaques reveals the presence of Mefp3-like proteins. Curiously, only four or five out of 20 possible fp3 variants are detectable in plaques deposited on glass or plastic. This would suggest that selection of protein variants for deposition onto surfaces is determined at the level of translation. Received: 11 August 1998 / Accepted: 15 April 1999     

Effects of the toxic dinoflagellate <Emphasis Type="Italic">Gymnodinium catenatum</Emphasis> on uptake and fate of paralytic shellfish poisons in the Pacific giant lions-paw scallop <Emphasis Type="Italic">Nodipecten subnodosus</Emphasis>

Juvenile Pacific giant lions-paw scallops Nodipecten subnodosus were fed the toxic dinoflagellate Gymnodinium catenatum, a producer of paralytic shellfish poison (PSP), supplied with Isochrysis galbana (a nontoxic microalgae). Short-term (<24 h) experiments were performed to determine clearance and ingestion rates of G. catenatum. Kinetics of PSP was examined in longer-term experiments (>2 days). At high food concentrations, juvenile scallops showed production of pseudofeces, partial shell valve closure, and reduction in feeding. According to HPLC analysis, the only toxins present in the dinoflagellate G. catenatum and in the scallops were the gonyautoxins (GTXs), except in the labial palps and digestive gland, where trace amounts of saxitoxin (STX) were present in scallops. These tissues could play an important role in toxin biotransformation. The ranking of toxin concentration in tissues was: digestive gland > labial palps > intestine > gills > mantle > adductor muscle, where the total contribution of viscera was more than 80% of the total toxin body burden. Juvenile scallops exhibited no apparent detrimental physiological responses during the long-term feeding experiment. The dinoflagellate may contribute nutrients to the scallop, in addition to the microalgae I. galbana. The dinoflagellate may enhance cell uptake and byssus production. Once PSP accumulated during the first 12 days, it was slowly eliminated. The limited capacity for accumulating toxins in the adductor muscle favors domestic marketing of scallops.     

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.     

Byssus drifting and the drifting threads of the young post-larval mussel Mytilus edulis

The long, drifting threads secreted by young post-larval mussels (Mytilus edulis L.) are simple monofilaments, distinct in form and function from the attachment byssus threads. The diameters of both thread types are in the micron or sub-micron range but, whereas the attachment threads are of restricted length and terminate in an attachment plaque, drifting threads exceed the post-larva in length by more than two orders in magnitude and are without plaques or any other structures. Transmission electron micrographs of drifting threads show no evidence of internal sub-structure. In contrast, attachment threads appear to be made up of filaments. These studies confirm that the drifting threads are highly effective in enhancing the dispersal of young mussels. The terminal sinking velocity of young drifters is typically ca. 1 mm s^-1. At this velocity the suspension range above the sea bed, assuming given values of vertical diffusivity, is estimated to be 0.5 to 5 m. Calculations of the fluid drag experienced by post-larvae in the water column show that the theoretical viscous drag force on the thread is sufficient to account for the reduced sinking rate of drifters. The calculated contribution of the thread to the total drag is approximately one order of magnitude greater than that of the post-larval body. A rapid thread-deployment strategy, shown by post-larvae which are brought into suspension, may prolong each drifting excursion and thus further enhance dispersal in turbulent marine environments.     

Développement larvaire de deux Tellinacea,Scrobicularia plana (Semelidae) et Donax vittatus (Donacidae)

Scrobicularia plana Da Costa and Donax vittatus L. were reared in the laboratory through settlement. Fertilizable eggs were obtained by perfusing the ovary with 5% 0.1 M ammonium hydroxyde in sea water. S. plana eggs have a thick chorion, inside which the early larval stages develop; they hatch as straight-hinge larvae more than 60 h after fertilization. This brood protection is considered to be an adaptation to osmotic pressure changes and pollution in the environment. D. vittatus eggs have a very thin chorion and are unprotected. Further development is planktotrophic and very similar for the two species. Under laboratory conditions, the pediveliger stage is attained 3 weeks after fertilization and settlement occurs 1 week thereafter. S. plana spat stop growing until a suitable substratum is available. Meanwhile they undergo a byssus drifting important for postlarval dispersion. Post larvae resume growth as soon as a small quantity of fine sand is added to the rearing jar. The exhalant siphon is developed first, when the post larvae reach a length of 600 m; the inhalant siphon is formed later, at a length of approximately 900 m. Evolution from the larval hinge to the juvenile hinge stage occurs sooner in S. plana than in D. vittatus. Comparison of laboratory larval development with field development indicates that spawning occurs in June and August for S. plana in North Wales (UK).     

A study of the morphology,ultrastructure, and histochemistry of the food of the pediveliger of Ostrea edulis

During the settlement of Ostrea edulis L., the foot of the pediveliger implements temporary attachment and cementing. The morphology of the foot has been re-examined to try to clarify its role during this period. The foot has a highly developed nervous system and musculature, but mainly consists of sub-epidermal gland cells of 9 different types. Cells of the first gland contain acid mucopolysaccharide, and open over the ventral surface of the foot. The second type of gland contains a neutral glycoprotein, and opens at the tip of the foot. The third gland opens mid-ventrally half way down the foot, and largely contains an aromatic protein. The fourth type of gland contains mainly proteoglycan, and the cells open mid-ventrally behind the third gland. The fifth gland contains acid mucopolysaccharide, and the cells open onto the heel of the foot. The sixth, seventh, eighth and ninth glands contain a variety of acid mucopolysaccharides, proteoglycans and possibly a neutral glycoprotein; their cells open into the byssus duct, which discharges at the base of the heel. The grouping of the glands, position of the openings of the cells, and histochemical properties of the secretions suggest that they may be involved in localised and general adhesion of the foot during temporary attachment, as well as in cementing of the larva.