Mechanism of an epibiont burden: Crepidula fornicata increases byssus thread production by Mytilus edulis

Epibionts of mussels can have detrimental effects on their basibionts,such as reduced growth rates, lower fecundity, increased mortalityand an enhanced risk of dislodgement of the overgrown bivalvesdue to stronger hydrodynamic forces. In blue mussels Mytilusedulis, the epibiotic American slipper limpet Crepidula fornicatareduces growth and survival. In a field experiment we testedthe hypothesis that an enhanced byssus thread production withhigh energetic costs for the mussels due slipper limpet epibiontsis the underlying mechanism for the epibiont burden. Byssusthread production in overgrown mussels was twice as high asin unfouled M. edulis (11 ± 0.9 and 5.4 ± 0.6byssus threads/mussel/day, respectively). A control experimentrevealed intermediate byssus thread production (8.4 ±0.8 byssus threads/mussel/day) in mussels cleaned of C. fornicataat the beginning of the experiments, indicating that C. fornicatais responsible for the effects observed. We conclude that increasedbyssus production in fouled M. edulis is a functional responseto higher drag caused by epibionts and that it is associatedwith increased energy expenditure that reduces allocation ofresources for other processes such as growth, reproduction andsurvival. Such indirect effects of epibionts, mediated by anenhanced byssus production, may be widespread in byssus-producingbivalves, with important implications for their population dynamics. (Received 12 January 2006; accepted 21 November 2006)     

Byssus production rate of the White Sea blue mussel <Emphasis Type="Italic">Mytilus edulis</Emphasis> (Linnaeus, 1758) in the presence of metabolites of some hydrobionts

The byssus production of the blue mussel Mytilus edulis L. was studied in the laboratory in the presence of the metabolites of the following animals: a predator (a starfish Asterias rubens L.) and several species competing with the mussel in White Sea fouling communities (a bivalve Hiatella arctica L. and a solitary ascidian Styela rustica L.). The byssus threads and attachment plaques produced by each mussel per day were counted. The number of byssus threads and plaques was smallest in pure sea water and in the presence of metabolites produced by conspecific individuals.     

Novel Proteins Identified in the Insoluble Byssal Matrix of the Freshwater Zebra Mussel

The freshwater zebra mussel, Dreissena polymorpha, is an invasive, biofouling species that adheres to a variety of substrates underwater, using a proteinaceous anchor called the byssus. The byssus consists of a number of threads with adhesive plaques at the tips. It contains the unusual amino acid 3, 4-dihydroxyphenylalanine (DOPA), which is believed to play an important role in adhesion, in addition to providing structural integrity to the byssus through cross-linking. Extensive DOPA cross-linking, however, renders the zebra mussel byssus highly resistant to protein extraction, and therefore limits byssal protein identification. We report here on the identification of seven novel byssal proteins in the insoluble byssal matrix following protein extraction from induced, freshly secreted byssal threads with minimal cross-linking. These proteins were identified by LC-MS/MS analysis of tryptic digests of the matrix proteins by spectrum matching against a zebra mussel cDNA library of genes unique to the mussel foot, the organ that secretes the byssus. All seven proteins were present in both the plaque and thread. Comparisons of the protein sequences revealed common features of zebra mussel byssal proteins, and several recurring sequence motifs. Although their sequences are unique, many of the proteins display similarities to marine mussel byssal proteins, as well as to adhesive and structural proteins from other species. The large expansion of the byssal proteome reported here represents an important step towards understanding zebra mussel adhesion.     

The effect of food availability on byssogenesis by the zebra mussel (Dreissena polymorpha Pallas)

The effect of varying algal availability on byssal thread productionby re–attaching zebra mussels (Dreissena polymorpha) wasquantified. The byssal apparatus was severed and mussels allowedto re–attach to a hard substratum for a 21 day periodduring which they were fed at algal concentrations of 0.0, 0.1,0.5, 1.0 or 2.0 mg C l^-1. Byssal thread production was quantifiedby counting the number of new attachment plaques present eachday. Results showed that starved mussels continued to partition organiccarbon towards thread production but the resultant byssal masswas compromised, containing fewer threads than those producedby fed mussels. The daily average byssal thread production bymussels fed at 2.0 mg C l^-1 was greater than that of starved musselsand the final mean dry soft tissue weight higher. At algal Cconcentrations below maintenance requirements byssal threadproduction was elevated compared to starved mussels, but therewas no concurrent increase in soft tissue. This suggests thatbelow maintenance levels assimilated carbon was solely partitionedtowards byssus production and stored reserves may have beenutilized. The ratio of organic carbon contained in the byssusto that in the soft tissues remained relatively constant acrossall feeding levels. This suggests that the carbon content ofthe byssus is a constant function of that of the soft tissuemass. These results may explain seasonal variation in attachmentstrength of numerous byssate species and seasonal vertical migrationsby D. polymorpha. Present Address-Queen Mary & Westfield College, Dept of Biology,University of London, Mile End Road, London E1 4NS, UK (Received 16 March 1998; accepted 30 September 1998)     

Byssal proteins of the freshwater zebra mussel,Dreissena polymorpha

The freshwater zebra mussel (Dreissena polymorpha) is a notorious biofouling organism. It adheres to a variety of substrata underwater by means of a proteinaceous structure called the byssus, which consists of a number of threads with adhesive plaques at the tips. The byssal proteins are difficult to characterize due to extensive cross-linking of 3,4-dihydroxyphenylalanine (DOPA), which renders the mature structure largely resistant to protein extraction and immunolocalization. By inducing secretion of fresh threads and plaques in which cross-linking is minimized, three novel zebra mussel byssal proteins were identified following extraction and separation by gel electrophoresis. Peptide fragment fingerprinting was used to match tryptic digests of several gel bands against a cDNA library of genes expressed uniquely in the mussel foot, the organ which secretes the byssus. This allowed identification of a more complete sequence of Dpfp2 (D. polymorpha foot protein 2), a known DOPA-containing byssal protein, and a partial sequence of Dpfp5, a novel protein with several typical characteristics of mussel adhesive proteins.     

Zebra mussel adhesion: structure of the byssal adhesive apparatus in the freshwater mussel, Dreissena polymorpha

The freshwater zebra mussel (Dreissena polymorpha) owes a large part of its success as an invasive species to its ability to attach to a wide variety of substrates. As in marine mussels, this attachment is achieved by a proteinaceous byssus, a series of threads joined at a stem that connect the mussel to adhesive plaques secreted onto the substrate. Although the zebra mussel byssus is superficially similar to marine mussels, significant structural and compositional differences suggest that further investigation of the adhesion mechanisms in this freshwater species is warranted. Here we present an ultrastructural examination of the zebra mussel byssus, with emphasis on interfaces that are critical to its adhesive function. By examining the attached plaques, we show that adhesion is mediated by a uniform electron dense layer on the underside of the plaque. This layer is only 10-20 nm thick and makes direct and continuous contact with the substrate. The plaque itself is fibrous, and curiously can exhibit either a dense or porous morphology. In zebra mussels, a graded interface between the animal and the substrate mussels is achieved by interdigitation of uniform threads with the stem, in contrast to marine mussels, where the threads themselves are non-uniform. Our observations of several novel aspects of zebra mussel byssal ultrastructure may have important implications not only for preventing biofouling by the zebra mussel, but for the development of new bioadhesives as well.     

Morphology of the Bivalve Mollusks Crenomytilus grayanus and Mytilus coruscus in Relation to Their Spatial Distribution in the Upper Subtidal Zone

The morphology of the shell and byssus threads was studied in two closely related mussel species Crenomytilus grayanus and Mytilus coruscus. The two species differ significantly from each other in the shell shape and in the degrees of development and deformation of byssus threads. These differences, in turn, determine (either directly or indirectly) the differences in strength of the byssal attachment and are discussed in terms of their functional morphology with respect to the spatial distribution of the mussels in marine coastal zones.     

Effects of artificial epibionts on byssogenesis,attachment strength,and movement in two size classes of the blue mussel,Mytilus edulis

Blue mussels (Mytilus edulis) can alter the strength of byssal attachment and move between and within mussel aggregations on wave‐swept shores, but this movement ability may be limited by epibiont fouling. We quantified the effects of artificial epibiont fouling on the production of byssal threads, attachment strength, and movement in two size classes of blue mussels. In a factorial experiment, large epibiont‐covered mussels produced more functional byssal threads (i.e., those continuous from animal to substrate) after 24 h than large unfouled and small fouled mussels, but not more than small unfouled mussels. Small unfouled mussels formed and released more byssus bundles compared to any other treatment group, which indicates increased movement. Conversely, epibiont fouling resulted in decreased numbers of byssus bundles shed, and therefore reduced movement in small mussels. Epibiont‐covered mussels started producing byssal threads sooner than unfouled mussels, while small mussels began producing byssal threads earlier compared to large mussels. Mean attachment strength from both size classes increased by 9.5% when mussels were artificially fouled, and large mussels had a 34% stronger attachment compared to small mussels. On the other hand, a 2.3% decrease in attachment strength was found with increasing byssus bundles shed. Our results suggest that fouling by artificial epibionts influences byssal thread production and attachment strength in large mussels, whereas epibionts on small mussels impact their ability to move. Mussels are able to respond rapidly to fouling, which carries implications for the dynamics of mussel beds in their intertidal and subtidal habitats, especially in relation to movement of mussels within and among aggregations.     

PREDATION ON THE BIVALVE CHOROMYTILUS MERIDIONALIS (KR.) BY THE GASTROPOD NATICA (TECTONATICA) TECTA ANTON

The effects of a population of the boring gastropod Natica tectaon the bivalve Choromytilus meridionalis were investigated atBailey's Cottage, False Bay, South Africa. In July 1979 theN. tecta density on the mussel bed averaged 69 m^–2 andthe population consisted mainly of reproductively mature individualsbetween 20–33 mm shell width. Laboratory experiments on N. tecta showed that prey size selectionis an increasing function of predator size. The prey size rangetaken by large N. tecta is also greater than that taken by smallindividuals. The position of the borehole on the mussel shellis a function of the way in which the shell is held by the footduring the boring process. Consumption rates measured in thelaboratory showed an increase from approximately 1 kJ per weekin 18 mm N. tecta to 4.5 kJ per week in 28 mm individuals. Populationconsumption in the field was calculated as 663 kJ m^–2month^–1. It was estimated that at this rate the standingcrop of mussels in the pool would be eliminated within 10 months.Field measurements showed significant depletion after 6 months. New spat settlement of mussels occur every 4–6 years.The growth curve shows that after one year the population meansize exceeds 30 mm shell length, which is beyond the prey selectionsize range of small N. tecta. It was concluded that at the timeof a new mussel settlement a niche is provided for the simultaneoussettlement and growth of juvenile N. tecta in high densities.However, within one year the increase in prey size, togetherwith depletion due to over-exploitation, limits population growthand density in N. tecta. (Received 14 March 1980;     

SPATIAL VARIATION IN THE FAUNA ASSOCIATED WITH MYTILUS EDULIS ON A WAVE-EXPOSED ROCKY SHORE

The fauna associated with Mytilus edulis at a rocky wave-exposedlocality in North Wales is reported. A total of fifty-nine taxawith representatives from most of the main invertebrate phylawas recorded. In terms of species richness the community wasdominated by crustaceans (25 taxa), molluscs (10 taxa) and cheliceratearthropods (9 taxa), mainly mites. Fora-miniferans and crustaceanswere the most abundant taxa, representing 25% and 23% of thetotal associated fauna respectively. Nemerteans and nema-todeswere also well represented. The mussel bed was broadly stratifiedinto three distinct layers each dominated by a single species.Thus, the foramini-feran Ammonia batavus was restricted to thesediment in the bottom layer, the barnacle Semibalanus balanoidesoccurred only on the outer exposed surfaces of the mussel shells,whilst the tiny brooding bivalve, Lasaea rubra, nestled mainlyamongst the complex matrix of byssal threads and shell fragmentsin the middle layer of the bed. Species richness and diversitydecreased systematically with tidal elevation and both theseindices were also signifocantly depressed amongst mussel communitiesfrom high-shore tide pools. Inclination of the rock surfacehad little or no effect on the mussel populations or their associatedfauna. Small mussel patches generally supported fewer taxa perunit area and had a lower diversity than larger, more extensivepatches. These marked, small-scale spatial variations exhibitedby the fauna associated with M. edulis appear to be relatedlargely to the degree of aerial and tidal exposure, mussel density,the amount of accumulated sediment and mussel patch size. (Received 2 August 1993; accepted 8 November 1993)     

Location and analysis of byssal structural proteins of Mytilus edulis

The acellular attachment organ (byssus) of the marine mussel Mytilus edulis L. is composed of threads that emanate from the body of the mussel to adhesive discs that anchor the threads to rocks, sand and other mussels. Three proteins have been purified by immunohistological methods and located to specific regions of the byssus. A collagenous protein with subunit molecular weights of 53,000, 55,000 and 65,000 is found in the matrix of the elastic thread region. Its 73,000-MW precursor was extracted from foot glands in the area proximal to the animal body and was identified by immune cross-reactivity. A cystine-rich, acidic protein was found in all regions of the byssus associated with a third protein, the polyphenolic protein. The L-dopa-containing polyphenolic protein appears in the cortex of the entire thread and adhesive plaque and at the substrate-plaque interface. Antiserum to this protein stains spherical vesicles in the phenol gland of the foot. Using immuno-electrophoretic methods, the polyphenolic protein and the cystine-rich protein were shown to form high molecular weight aggregates with aging of the byssus.     

The byssus of the zebra mussel (Dreissena polymorpha): spatial variations in protein composition

The notorious biofouling organism Dreissena polymorpha (the zebra mussel) attaches to a variety of surfaces using a byssus, a series of protein threads that connect the animal to adhesive plaques secreted onto hard substrata. Here, the use of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to characterize the composition of different regions of the byssus is reported. All parts of the byssus show mass peaks corresponding to small proteins in the range of 3.7–7 kDa, with distinctive differences between different regions. Indeed, spectra from thread and plaques are almost completely non-overlapping. In addition, several peaks were identified that are unique to the interfacial region of the plaque, and therefore likely represent specialized adhesive proteins. These results indicate a high level of control over the distribution of proteins, presumably with different functions, in the byssus of this freshwater species.     

Mytilus edulis chilensis infested with Coccomyxa parasitica (Chlorococcales, Coccomyxaceae)

The association between the green alga Coccomyxa parasitica (Chlorococcales)and the mussel Mytilus edulis chilensis at Goose Green, Falkland Islandsis reported. C. parasitica occurred within the soft tissueswith an overall infestation rate of 16%. The highest levelsof infestation (23%) occurred in individuals from the middleof the main mussel bed, with considerably lower levels of infestation inthe upper and lower regions (<1% and 5% respectively). Noconsistent seasonal pattern in infestation rate was detectedbetween September 1993 and February 1996. C. parasitica wasmost commonly observed in tissues located in the posterior territoryof the host, in areas most directly exposed to light. Tissuesof infested mussels were rather watery and translucent and theadductor muscle appeared weak and stringy. During the summermonths when Falkland mussels are in peak reproductive condition,dry flesh weight of infested mussels was significantly lowerthan non–infected mussels of comparable size suggestingthat infestation by C. parasitica may reduce reproductive output.However it is uncertain whether poor condition of the host isdue to the presence of the parasitic alga or whether C. parasiticainfests only those mussels that are already in poor condition. ¹ Present address: 3, St Marys Walk, PO Box 530, Stanley, Falkland Islands (Received 10 June 1998; accepted 8 September 1998)     

Occurrence of dinoflagellate Alexandrium tamarense, a causative organism of paralytic shellfish poisoning in Chinhae Bay, Korea

A paralytic shellfish poisoning (PSP) incident caused by consumptionof the mussel Mytilus edulis occurred for the first time inKorea in April 1986. Weekly water samplings were carried Outduring the period from 7 March to 21 April 1989 in Chinhae Bay,Korea, in order to identify the causative organism. The temperaturecharacteristics of the water column indicated three differenthydrological regimes: well mixed (up to 7 March), weakly stratified(17–31 March) and stratified (7–21 April). Toxicityof the phytoplankton was detected during the weakly stratifiedperiod, but only in the 10–50 p.m phytoplankton size fraction.This study presents the occurrence of the toxigenic dinoflagellateAlexandrium tamarense, which is a causative organism of PSP,in Korean coastal waters. Its biomass varied at different depthsin the water column, ranging from 200 to 8000 cells 1^–1in the water column. The weekly fluctuation of A.tamarense toxicitywas similar to that of mussel toxicity. ¹ Present address: Department of Biology, College of NaturalSciences, Hanyang University, Seoul 133-791, Korea     

Spatial distribution of proteins in the quagga mussel adhesive apparatus

The invasive freshwater mollusc Dreissena bugensis (quagga mussel) sticks to underwater surfaces via a proteinacious ‘anchor’ (byssus), consisting of a series of threads linked to adhesive plaques. This adhesion results in the biofouling of crucial underwater industry infrastructure, yet little is known about the proteins responsible for the adhesion. Here the identification of byssal proteins extracted from freshly secreted byssal material is described. Several new byssal proteins were observed by gel electrophoresis. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to characterize proteins in different regions of the byssus, particularly those localized to the adhesive interface. Byssal plaques and threads contain in common a range of low molecular weight proteins, while several proteins with higher mass were observed only in the plaque. At the adhesive interface, a plaque-specific ~8.1 kDa protein had a relative increase in signal intensity compared to the bulk of the plaque, suggesting it may play a direct role in adhesion.     

Ultrastructural and cytochemical study on the enzyme gland of the foot of a mollusc

The enzyme gland of the foot of the mussel Mytilus has been so far considered a gland producing and exporting a phenol oxidase catalysing the general tanning processes of byssus threads. In contrast, the present study shows that this gland produces mainly secretory granules which form the cortical layers of byssus threads. Cytochemical methods at the ultrastructural level (phosphotungstic acid at low pH, silver methenamine, periodic acid-thiosemicarbazide-silver proteinate, silver methenamine for sulphur-rich proteins demonstration) and enzyme digestion tests (pepsin, trypsin, alpha-chymotrypsin) indicate that secretory granules contain glycoproteins rich in sulphydryl groups and in aromatic amino acids. The cytochemical demonstration of phenol oxidase shows that enzyme activity is present in Golgi complex, whereas it is absent in secretory granules. For this reason, phenol oxidase does not seem to be exported and utilized for tanning of byssus threads, but it might rather be involved in the elaboration and tanning of the content of the secretory granules in the enzyme gland itself.     

RECRUITMENT AND LIFE SPAN OF TWO NATURAL MUSSEL POPULATIONS PERNA PERNA(LINNAEUS) AND MYTILUS GALLOPROVINCIALIS (LAMARCK) FROM THE ALGERIAN COAST

Coexisting populations of the mussels, Perna perna and Mytilusgalloprovincialis, were monitored at two sites on the NorthAfrican coast, east of Algiers, over a five year period (1985–1989).While spatfalls were observed throughout the year, only themajor spring-summer recruitment, which occurred during favourableweather conditions, contributed to the renewal of both musselspecies at both sites. Very high densities (>10, 000 ind.m^–2) were observed at both sites, but the mussel bedswere composed principally of young and small specimens due toharvesting of the largest animals for use as bait and for humanconsumption. The maximal length observed was 75 mm in P. pernaand 49 mm in M. galloprovincialis. The life span of the specieswas low, 12–24 months in P. perna and 11–28 monthsin M. galloprovincialis. This survey showed that M. galloprovincialisbecame dominant in both mussel beds due to its resistance todisturbance by human activities. (Received 5 January 1995; accepted 18 April 1995)     

Clumping behavior and byssus production as strategies for substrate competition in Mytilus edulis

Laboratory experiments showed that the mussel Mytilus edulis aggregated more intensely around living organisms (the bivalve Hiatella arctica and the solitary ascidian Styela rustica, which commonly co‐occur with mussels in fouling communities) than around inanimate objects. When exposed to an inanimate object, mussels attached their byssal threads primarily to the substrate, close to the object, but when exposed to a living organism, they attached their byssal threads directly to the organism. The ascidian was more intensely covered with byssal threads than was the bivalve. Mussel attachment to the ascidians was apparently determined by the physical characteristics of the tunic and to a lesser extent by the excretion‐secretion products released by S. rustica. This study indicates that mussels can use byssus threads as a means of entrapment of potential competitors for space. It remains unclear why mussels preferentially attached to ascidians compared to the bivalve. This can be explained either by competitive interactions, or by attractiveness of the ascidian tunic as an attachment substratum.     

Preferences of the Ponto-Caspian amphipod Dikerogammarus haemobaphes for living zebra mussels

A Ponto-Caspian amphipod Dikerogammarus haemobaphes has recently invaded European waters. In the recipient area, it encountered Dreissena polymorpha , a habitat-forming bivalve, co-occurring with the gammarids in their native range. We assumed that interspecific interactions between these two species, which could develop during their long-term co-evolution, may affect the gammarid behaviour in novel areas. We examined the gammarid ability to select a habitat containing living mussels and searched for cues used in that selection. We hypothesized that they may respond to such traits of a living mussel as byssal threads, activity (e.g. valve movements, filtration) and/or shell surface properties. We conducted the pairwise habitat-choice experiments in which we offered various objects to single gammarids in the following combinations: (1) living mussels versus empty shells (the general effect of living Dreissena ); (2) living mussels versus shells with added byssal threads and shells with byssus versus shells without it (the effect of byssus); (3) living mussels versus shells, both coated with nail varnish to neutralize the shell surface (the effect of mussel activity); (4) varnished versus clean living mussels (the effect of shell surface); (5) varnished versus clean stones (the effect of varnish). We checked the gammarid positions in the experimental tanks after 24 h. The gammarids preferred clean living mussels over clean shells, regardless of the presence of byssal threads under the latter. They responded to the shell surface, exhibiting preferences for clean mussels over varnished individuals. They were neither affected by the presence of byssus nor by mussel activity. The ability to detect and actively select zebra mussel habitats may be beneficial for D. haemobaphes and help it establish stable populations in newly invaded areas.