Ultrastructure of the gill of the hydrothermal-vent mytilid Bathymodiolus sp.

Specimens of Bathymodiolus sp. were collected at 2 620 m depth during the Biocyarise Cruise (12°5880N; 13°5660W) in March 1984, and samples of the gill were fixed for ultrastructural observations. The gill of this hydrothermal-vent mytilid constitutes the main organ in the nutritional processes. The lamellae display abundant ciliation, normally comprised of frontal cilia, compound latero-frontal cirri and lateral cilia. At the ventral margin of each demi-branch, a longitudinal, ciliated, feeding groove is present. the lamellae are composed of numerous homorhabdic filaments connected by tufts of cilia. Each filament is made of a thin wall overlying a central lumen containing amoebocytes. Ultrastructural observations revealed the filament wall to be composed of four types of cells: (1) The ciliated cells of the frontal, latero-frontal and lateral ciliation, characterized by an abundance of mitochondria. (2) Mucous cells present to some degree among the ciliated cells, but more abundant on the distal edge and containing dense droplets of mucus. (3) Cells colonized at their apical pole by numerous bacteria enclosed in membrane-delimited clear spaces and composing the major part of the filament wall. (4) Thin ciliated cells separating the bacterial cells and characterised by a dense fringe of microvilli at their apical pole. The lumen of the filament contains amoebocytes of different morphological aspects which seem to accumulate electron-dense granules, possibly related to detoxification processes.     

Elemental composition of the hydrothermal vent clam Calyptogena magnifica from the East Pacific Rise

Specimens of the hydrothermal vent clam Calyptogena magnifica were collected at a depth of 2 600 m from 21° N on the East Pacific Rise in spring, 1982. The elemental composition was determined for the total soft tissues, individual organs, and the shell. The soft parts contained high concentrations of a number of trace metals. Iron, copper, and zinc, at 760, 148 and 2 152 g g^-1 dry weight, respectively, were present at the highest concentrations. Silver and antimony exhibited the greatest enrichments when their concentrations in C. magnifica were compared with those measured in a shallow-water marine mussel, Mytilus edulis. In contrast to the soft parts, the shell was not a site of metal accumulation or deposition. Within the soft parts; gills, kidney, pericardium, and mantle were involved in the concentration of various metals; the degree of concentration varied depending on the particular metal under consideration. C. magnifica possesses metal body burdens which are ordinarily considered to be very high and potentially toxic in other species.     

Metabolic diversity in epibiotic microflora associated with the Pompeii wormsAlvinella pompejana andA. caudata (Polychaetae: Annelida) from deep-sea hydrothermal vents

Specimens of alvinellid polychaetes (Alvinella pompejana Desbruyères and Laubier, 1980 andA. caudata Desbruyères and Laubier, 1986) and their tubes were sampled from deep-sea hydrothermal vents at 13°N from the manned submersible Nautile during the Hydronaut cruise (October to November 1987) on the East Pacific Rise. Samples were subjected to bacterial analysis aboard the mother ship Nadir to detect bacteria involved in the nitrogen and sulphur cycles, in non-specific heterotrophic processes, and displaying resistance to selected heavy metals. Cultures were incubated at different temperatures under atmospheric and in situ (250 atm) pressures. Bacterial growth was observed in enrichment cultures for most metabolic types screened. Heavy-metal-resistant bacteria were also detected in many samples. No filamentous bacterial form was observed in the cultures. The results demonstrate a high metabolic diversity in episymbiotic flora, indicating that the worm (A. pompejana orA. caudata), its tube and its epiflora represent a complex micro-ecosystem.     

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>–ATPase activity and gill ultrastructure in the hyper-hypo-regulating crab<Emphasis Type="Italic"> Chasmagnathus granulatus</Emphasis> acclimated to dilute,normal, and concentrated seawater

We studied Na⁺/K⁺ –ATPase activity and ultrastructure in gills of the hyper-hypo-regulating crab Chasmagnathus granulatus Dana, 1851 acclimated to different salinities: 10, 30 and 45, known to be hypo-, iso-, and hyper-osmotic to the hemolymph, respectively. After centrifugation of homogenates at 11,000 g, Na⁺/K⁺–ATPase activity was almost entirely found in the pellets from the posterior (6–8) and anterior (3–5) gills, whereas very little was detected in the supernatant liquid. Specific activity of gill 6 was 41.3, 30.2, and 28.2 µmol Pi h^–1 mg prot^–1 for crabs acclimated to 10, 30, and 45, respectively, the result for 10 being significantly higher than those at 30 and 45. Although the concentration of sodium at which the reaction rate is half-maximal (K _M) was similar in the three acclimation salinities, only the enzyme from crabs acclimated to 10 was inhibited by high sodium concentration. Specific activity of gill 5 increased with the increment in external salinity (10.1, 15, and 18.1 µmol Pi h^–1 mg prot^–1 for 10, 30, and 45, respectively), the only significant difference being that between the extreme salinities. The epithelium thickness of the dorsal portion of gill 6 showed a variation among salinities: 21.7, 15.8 and 17.2 µm for 10, 30 and 45, respectively. There were significant differences in epithelium thickness between the 10 and the other salinities. In all three salinities, the ultrastructure of gill 6 epithelium showed a high density of mitochondria, estimated by their volume fraction (Vv _m=0.307–0.355). These mitochondria were packed between extensive basolateral membrane interdigitations in ionocytes and pillar cells. Gill 5 showed three cell types: pillars which possess mitochondria packed between membrane folds only in their interdigitations with neighbouring cells; type-I cells 8.0 µm thick with low density of mitochondria (Vv _m=0.088), and type-II cells, 9.9 µm thick and rich in mitochondria (Vv _m=0.423), but lacking basolateral interdigitations. Vv _m of type-I cells of gill 5 was significantly lower than those of type-II cells of the same gill and the ionocytes of gill 6. No significant difference in Vv _m was detected between the latter cell types.Communicated by P.W. Sammarco, Chauvin     

Sexual reproduction of the solitary sunset cup coral<Emphasis Type="Italic"> Leptopsammia pruvoti</Emphasis> (Scleractinia: Dendrophylliidae) in the Mediterranean. 1. Morphological aspects of gametogenesis and ontogenesis

Information on the reproduction in scleractinian solitary corals and in those living in temperate zones is notably scant. Leptopsammia pruvoti is a solitary coral living in the Mediterranean Sea and along Atlantic coasts from Portugal to southern England. This coral lives in shaded habitats, from the surface to 70 m in depth, reaching population densities of >17,000 individuals m^–2. In this paper, we discuss the morphological aspects of sexual reproduction in this species. In a separate paper, we report the quantitative data on the annual reproductive cycle and make an interspecific comparison of reproductive traits among Dendrophylliidae aimed at defining different reproductive strategies. The present study on L. pruvoti is the first in-depth investigation of the reproductive biology of a species of this genus. As expected for a member of the family Dendrophylliidae, L. pruvoti is a gonochoric and brooding coral. The gastrodermal tissue of the gametogenetic mesenteries we examined was swollen and granular, which led us to hypothesize that interstitial cells could have a trophic function favoring gametogenesis. Undifferentiated germ cells arose in the gastrodermis and subsequently migrated to the mesoglea, where they completed gametogenesis. During spermary development, spermary diameter increased from a minimum of 14 m during the immature stages to a maximum of 410 m during the mature stages. As oogenesis progressed, we observed a gradual reduction in the nucleus to cytoplasm ratio due to the steady synthesis of yolk. During the final stages of oogenesis, after having migrated to the extreme periphery of the oocyte and having firmly adhered to the oolemma, the nucleus became indented, assuming a sickle or dome shape. We can hypothesize that the nucleus migration and change of shape may have to do with facilitating fertilization and determining the future embryonic axis. During oogenesis, oocyte diameter increased from a minimum of 20 m during the immature stage to a maximum of 680 m when mature. Embryogenesis took place in the coelenteron. We did not see any evidence that even hinted at the formation of a blastocoel; embryonic development proceeded via stereoblastulae with superficial cleavage. Gastrulation took place by delamination. Early and late embryos had diameters of 204–724 m and 290–736 m, respectively. When released, the larvae had completed ontogenesis and swam by a ciliary movement with the aboral pole at the anterior, their shape varied from spherical to cylindrical (in the latter the oral–aboral axis measured 695–1,595 m and the transversal one measured 267–633 m).Communicated by R. Cattaneo-Vietti, Genova     

Changes of plasma osmolality,chloride concentration and gill Na−K-ATPase activity in tilapia Oreochromis mossambicus during seawater acclimation

Changes of plasma osmolality, chloride concentration and gill Na–K-ATPase activity in tilapia Oreochromis mossambicus (obtained from Tainan Fish Culture Station of Taiwan Fisheries Research Institute, 1987) during seawater acclimation were examined. Three experiments were performed. (1) Freshwater (FW) to 30 salinity seawater (SW): plasma osmolality and chloride rose violently immediately post-transfer. At 6 h, gill Na–K-ATPase activity began to increase but most fish died from excessive plasma osmolality and Cl. (2) FW to 20 salinity SW: plasma osmolality and chloride increased immediately post-transfer, but more slowly than in (1), and began to decrease at 24 h. However it was not until 12 h post-transfer that gill Na–K-ATPase activity rose slowly. (3) FW to 20 salinity SW for 24 h, then to 30 salinity SW: after transfer to 30 salinity, plasma osmolality and chloride showed only a small increase initially then declined, while gill Na–K-ATPase activity started to rise rapidly within 3 h. The present results coincided with our previous morphological data concerning the ultrastructural responses of gill chloride cells. These are discussed to elucidate the osmoregulation mechanisms in tilapia during seawater acclimation.     

Association between the mollusc bivalve Loripes lucinalis and a Chlamydia-like organism,with comments on its pathogenic impact,life cycle and possible mode of transmission

Loripes lucinalis is a littoral bivalve which has already been confirmed to harbour endo-cellular sulfur-oxidizing bacteria within its gills. Examination of the digestive gland of L. lucinalis collected from the Moulin Blanc Beach in the Bay of Brest (Brittany, France) revealed the existence of an additional association involving a Chlamydia-like organism. Three different forms of Chlamydia-like bacteria were observed: reticulate rod-shaped cells, electron-dense cells and enlarged cells. The reticulate rod-shaped cells and the electron-dense bodies are thought to represent the germinal initial body and infectious form of the bacteria, respectively. The enlarged cells were always associated with what are believed to be spherical or icosahedral phages. Initial infestation seems to occur by phagocytosis at the apical pole of the digestive cells of the tubule and duct epithelia. Within the host cell, the bacteria undergo binary fission and budding, forming an inclusion which gradually fills up the cell. Inclusions are generally between 15 and 30 m in size, and > 85% of all individuals examined possessed inclusion bodies. The level of infestation varied between individuals, some being heavily colonized, but did not seem to be related to season. Histological and ultrastructural observations suggest that, once developed, the colony has three possible fates: (1) the cells will degenerate due to phage infection; (2) colony overcrowding will occur, causing the development of electron-dense bodies that will be released into the lumen; (3) the entire membrane-bound inclusion will be released into the lumen and subsequently into the pallial cavity. Inclusions within the pallial cavity may be ingested by the host or may even be phagocytized by bacteriocyte cells of the gill. It is proposed that this association could be a form of symbiosis and that L. lucinalis may, therefore, be a rare example of an organism adapted to harbour two very different symbioses.     

Gill structure in Lucina pectinata (Bivalvia: Lucinidae) with reference to hemoglobin in bivalves with symbiotic sulphur-oxidizing bacteria

Lucina pectinata is a large tropical Lucinidae which is characterized by abundant tissue hemoglobin in its deep-red gills. In the present paper, hemoglobin is described as being located in cytoplasmic dark patches of the bacteriocytes together with a cystine-rich protein. Large microbodies contain a non-hemoglobin heme-compound which is identified with a previously described non-protein-bound hematin; however, it has not been established whether this heme is involved in a sulphur-oxidizing system or represents a catabolic by-product of hemoglobin. Electron-lucent vesicles are associated with the basal microbodies but their function is, so far, unknown. In addition, the bacteriocytes have been observed to have direct contact with sea water, modulated by large intercalary cells which overlap the bacteriocytes on their margin. Such relationships between bacteriocytes and intercalary cells, as well as their cytological features, are different from those observed in lucinid species inhabiting sea-grass beds, but very similar to those observed in Calyptogena magnifica. From the congruence between the shallow-water Lucinidae L. pectinata, inhabiting mangrove swamps, and the deep-sea Vesicomyidae C. magnifica, found at hydrothermal vents, we conclude that such features are likely to be adaptative to high-sulphide environments, notwithstanding the phylogenetic distance.     

Dance dialects and foraging range in three Asian honey bee species

Summary We measured the distance dialects in the dance languages of three honey bee species in Thailand (Apis florea, A. cerana, and A. dorsata), and used these dialects to examine the hypothesis that a colony's dialect is adaptively tuned to enhance efficiency of communication over the distances that its foragers typically fly. in contrast to previous interspecific comparisons in Sri Lanka (Lindauer 1956; Punchihewa et al. 1985), we found no striking dialect differences among the Asian bees in Thailand. The adaptive tuning hypothesis predicts that the foraging ranges of the three species should also be similar, but comparisons of colonial foraging range using the forage mapping technique (Visscher and Seeley 1982) actually revealed marked differences. This raises the possibility that the link between ecology and distance code is more subtle than previously supposed, if a link exists at all. Offprint requests to: F.C. Dyer     

Phenotypic variations in the gills of the symbiont-containing bivalve Lucinoma aequizonata

The marine bivalve Lucinoma aequizonata (Lucinidae) maintains a population of sulfide-oxidizing chemoautotrophic bacteria in its gill tissue. These are housed in large numbers intracellularly in specialized host cells, termed bacteriocytes. In a natural population of L. aequizonata, striking variations of the gill colors occur, ranging from yellow to grey, brown and black. The aim of the present study was to investigate how this phenomenon relates to the physiology and numbers of the symbiont population. Our results show that in aquarium-maintained animals, black gills contained fewer numbers of bacteria as well as lower concentrations of sulfur and total protein. Nitrate respiration was stimulated by sulfide (but not by thiosulfate) 33-fold in homogenates of black gills and threefold in yellow gill homogenates. The total rates of sulfide-stimulated nitrate respiration were the same. Oxygen respiration could be measured in animals with yellow gills but not in animals with black gills. The cumulative data suggest that black-gilled clams maintained in the aquarium represent a starvation state. When collected from their natural habitat black gills contain the same number of bacteria as yellow gills. Also, no significant difference in glycogen concentrations of the host tissues was observed. Therefore, starvation is unlikely the cause of black gill color in a natural population. Alternative sources of nutrition to sulfur-based metabolism are discussed. Denaturing gradient gel electrophoresis (DGGE) performed on the different gill tissues, as well as on isolated symbionts, resulted in a single gill symbiont amplification product, the sequence of which is identical to published data. These findings provide molecular evidence that one dominant phylotype is present in the morphologically different gill tissues. Nevertheless, the presence of other phylotypes cannot formally be excluded. The implications of this study are that the gill of L. aequizonata is a highly dynamic organ which lends itself to more detailed studies regarding the molecular and cellular processes underlying nutrient transfer, regulation of bacterial numbers and host–symbiont communication. Received: 1 September 1999 / Accepted: 1 February 2000     

Yolk utilization in the gastropod Crepidula fornicata

The increases in constituents per unit weight of eggs during embryonic development of the gastropod Crepidula fornicata amounted to 14.6% for ash, 1.0% for protein, and 0.3% for non-protein nitrogen. During the same stages, fat content decreased from 33.7 to 20.3%, carbohydrate from 10.2 to 7.7% and energy content from 6209 to 5298 cal/g dry organic substance. The cumulative efficiencies for yolk utilization were 83.8% for dry weight, 61.0% for energy, 85.1% for protein, 50.7% for fat, and 63.6% for carbohydrate. A single egg contained 0.0269 cal, a single veliger 0.0164 cal. Of the 0.0105 cal expended on metabolic processes of the embryo, oxidation of fat contributed as much as 65.3%, while that of protein and carbohydrate amounted only to 18.8 and 6.3%, respectively. On the basis of ecophysiological considerations, a new classification of eggs is proposed.This paper is based on a lecture presented during the first Convention of the Indian Association of Biological Sciences in Madras, December, 1968.     

Accumulation of metals by marine picoplankton

Pumping rates in undisturbed suspension-feeding bivalves were measured with a thermistor microflowmeter. Pumping rates are related to the dry weight of Clinocardium nuttallii, Macoma nasuta, Mytilus californianus and Chlamys hastata as the following equations: P=0.85 W^0.84, P=0.23 W^0.855, P=2.216 W^0.715, and P=2.419 W^0.943 respectively. Pumping rate and gill area increase at the same rate in C. nuttallii, M. californianus and C. hastata. The pumping rate per unit gill area is highest for C. nuttallii (approximately 0.14 cm³/s/cm²), with intermediate values for M. californianus (0.08 cm³/s/cm²) and C. hastata (0.11 cm³/s/cm²); the lowest rate was found in the deposit-feeder M. nasuta (0.0057 to 0.0089 cm³/s/cm²), which also has the smallest gill to body weight. C. nuttallii has the relatively smallest gill of the suspension feeders and the highest pumping rate per unit gill area. The absolute pumping rates, however, were highest for the filibranchs M. californianus and C. hastata. Indications are given that these differences are the results of different fluid-mechanical/ecological strategies to minimize the cost-benefit ratio.Contribution No. 132 of the Marine Science and Maritime Studies Center, Northeastern University     

Petroleum hydrocarbons in the marine bivalve Venus verrucosa: accumulation and cellular responses

Cellular and subcellular responses of the marine burrowing bivalve Venus verrucosa collected from the north-eastern coastline of Malta from January to June 1985, after exposure to petroleum hydrocarbons (PHC) were investigated. After long-term exposure to 100 gl^-1 of water-accomodated fractions (WAF) of crude oil, PHC were found to accumulate most rapidly in the digestive gland and then in the gills, with saturation levels being reached within 100 d of exposure in both cases. PHC accumulation, both in the mantle and muscle tissues, was more gradual and consistent throughout the whole exposure period. After 150 d of exposure, the digestive cells of the digestive gland were significantly reduced in height (atrophy) and exhibited reduced lysosomal membrane stability. After 144 h of exposure to higher concentration of PHC (820 and 420 gl^-1), several cytological effects were recorded, including an increase in cell volume and activity of gill mucocytes as well as in the number of haemocytes in gill blood sinuses. There was also evidence of damage to the epithelial lining of the foot, stomach and style sac and marked atrophy of the digestive cells of the digestive gland. The significance of such responses is discussed.     

Combined effects of temperature and salinity on fed and starved larvae of the mediterranean mussel Mytilus galloprovincialis and the Japanese oyster Crassostrea gigas

The combined effects of temperature, salinity and nutrition on survival and growth of larvae of the Mediterranean mussel Mytilus galloprovincialis and the Japanese oyster Crassostrea gigas were studied over a period of 7 d in the laboratory. Ripe adults, collected in spring and summer 1987 from natural populations in the Bay of Arcachon, France, were induced to spawn. Larvae of both species were cultured at four temperatures (15°, 20°, 25° and 30°C), four salinities (20, 25, 30 and 35S) per temperature, and two levels of nutrition (fed and unfed) per temperature/salinity combination. The fed larvae received a mixed algal diet of 50 cells each of Isochrysis galbana and Chaetoceros calcitrans forma pumilum per microlitre. In both bivalve species, larvae survived over a wide range of temperature and salinity, with the exception of mussel larvae, which died at 30°C. Statistical analysis indicated that nutrition had the greatest effect on larval development, explaining 64 to 75% of the variance in growth of M. galloprovincialis and 54 to 70% in growth of Crassostrea gigas. Unfed mussel larvae displayed little growth. Compared with temperature, the effect of salinity was very slight. M. galloprovincialis larvae exhibited best growth at 20°C and 35S and C. gigas at 30°C and 30S.     

Relationship between phytoplankton cell size and the rate of orthophosphate uptake: in situ observations of an estuarine population

Orthophosphate uptake by a natural estuarine phytoplankton population was estimated using two methods: (1) ³²P uptake experiments in which filters of different pore sizes were used to separate plankton size-fractions; (2) ³³P autoradiography of phytoplankton cells. Results of the first method showed that plankton cells larger than 5 m were responsible for 2% of the total orthophosphate uptake rate. 98% of the total uptake rate occurred in plankton composed mostly of bacteria, which passed the 5 m screen and were retained by the 0.45 m pore-size filter. There was no orthophosphate absorption by particulates in a biologically inhibited control containing iodoacetic acid. Orthophosphate uptake rates of individual phytoplankton species were obtained using ³³P autoradiography. The sum of these individual rates was very close to the estimated rate of uptake by particulates larger than 5 m in the ³²P labelling experiment. Generally, smaller cells were found to have a faster uptake rate per m³ biomass than larger cells. Although the nannoplankton constituted only about 21% of the total algal biomass, the rate of phosphate uptake by the nannoplankton was 75% of the total phytoplankton uptake rate. Results of the plankton autoradiography showed that the phosphate uptake rate per unit biomass is a power function of the surface: volume ratio of a cell; the relationship is expressed by the equation Y=2x10^-11 X ^1.7, where Y is gP m^-3 h^-1 and X is the surface: volume ratio. These results lend support to the hypothesis that smaller cells have a competitive advantage by having faster nutrient uptake rates.     

Biological production of nitrite in seawater

The relative importance of 3 different sources for biological production of nitrite in seawater was studied. Decomposition of fecal pellets of the copepod Calanus helgolandicus (at a concentration of approximately 12 g-at N/l), in seawater medium, released small amounts of ammonia over a 6 week period. It nitrifying bacteria were added to the fecal pellets nitrite was barely detectable over the same period. Decomposition of phytoplankton (present at a concentration of about 8 g-at particulate plant N/l) with added heterotrophic bacteria, released moderate amounts of ammonia over a 12 week period. If the ammonia-oxidizing bacterium Nitrosocystis oceanus was added to the decomposing algae, nitrite was produced at a rate of 0.2 g-at N/l/week. Heterotrophic nitrification was not observed when 7 open-ocean bacteria were tested for their ability to oxidize ammonia. The diatom Skeletonema costatum, either non-starved or starved of nitrogen, produced nitrite when growing with 150 or 50 g-at NO ₂ ^- -N/l at a light intensity of about 0.01 ly/min. When nitrate in the medium was exhausted, S. costatum assimilated nitrite. If starved of vitamin B₁₂, both non-N-starved and N-starved cells of S. costatum produced nitrite in the medium with 150 g-at NO ₃ ^- -N/l. Nitrate was not exhausted and cell densities reached 2x10⁵/ml due to vitamin B₁₂ deficiency. If light intensity was reduced to 0.003 ly/min under otherwise similar conditions, cells did not grow due to insufficient light, and nitrite was not produced. In the sea, it appears that, in certain micro-environments, decomposition of particulate matter releases ammonia with its subsequent oxidation to nitrite. The amounts of these nutrients and the rate at which they are produced are dependent upon the nature of the materials undergoing decomposition and the associated bacteria. In certain other areas of the sea, where phytoplankton standing stock is high and nitrate is non-limiting, excretion by these organisms is a major source of nitrite.     

Bacterial associations in the teredo Bankia australis (Lamellibranchia: Mollusca)

Electron microscope examination of the so-called Gland of Deshayes in the teredos Bankia australis and related species has revealed that this structure is not a glandular tissue, but represents associations of bacteria.     

Reproductive biology and population structure of the deep-sea hydrothermal vent worm Paralvinella grasslei (Polychaeta: Alvinellidae) at 13°N on the East Pacific Rise

Paralvinella grasslei is a polychaetous annelid living in the harsh, unstable and heterogeneous environmental conditions found at deep-sea hydrothermal vent sites in the eastern Pacific. The aim of this work was to examine the possible influence of the reproductive biology of P. grasslei on the structure of its populations. Maximum observed oocyte size inside the oviduct is 275 m, and fecundity is relatively low. Examination of gametes and young specimens suggested a direct benthic development for this species. The population structure of P. grasslei at 13°N/EPR (EPR=East Pacific Rise) revealed a discontinuous recruitment which seems to be synchronized within vent sites and fields. The data also suggested the occurrence of discrete breeding periods. P. grasslei probably reproduces several times a years, with an apparent periodicity. Tidal signals could be a possible cue for the coordination of the reproductive cycle. The life-history of P. grasslei is discussed in light of the reproductive biology of other terebellomorph polychaetes, and seems to be well adapted for colonizing the unstable environment of hot vents. Two main hypotheses can explain the dissemination processes of this species along axial oceanic ridges. The influence of nearbottom currents occurring along the central graben of the East Pacific Rise can be cosidered to account for part of the transport of larvae and juveniles, but the observations of polychaete erpochaetes on the test of hydrothermal bythograeid crabs and evidence that crab migrations occur between vents also support the possibility of zoochory for the dissemination of alvinellid polychaetes.     

Fluid motion and particle retention in the gill of Mytilus edulis: Video recordings and numerical modelling

Particle trajectories of 6.4m Latex spheres were recorded by video, both near an isolated blue mussel, Mytilus edulis, gill filament and, in place of an intact interfilamentary canal, in a model canal of width 200, 100 or 70m, formed by a transparent plate positioned next to a gill filament. Each arrangement was placed in a 2 x 10 x 10 cm test vessel filled with seawater. Serotonin (nerve-transmitter) stimulation was used to activate lateral cilia and to either lock latero-frontal cirri at the end of an active stroke (10^-5 M), or to activate them (10^-6 M), yielding lateral cilia beat frequencies of 19 and 16 Hz, respectively. With latero-frontal cirri locked, image analysis of particle tracks gave maximum velocities of ca. 2.9±0.2mm s^-1 close to the tips of lateral cilia, for both isolated filament and model canal cases. Experimental velocity profiles along the 200-m wide model canal were recorded and used as good approximations to the fluid velocity because of the low Reynolds number. A two-dimensional steady model was proposed for the gill pump, assumed to only comprise lateral cilia. This model was solved numerically for the experimental model, canal in the vessel and the results showed satisfactory agreement with experimental volocity profiles from particle tracks. The numerical approach was also applied to a model of a single interfilamentary canal in the vessel. The resulting mean velocity in the canal was 1.70 mm s^-1, but the resistance to flow in the model was less than that in an intact mussel gill. Video graphs of particle tracks indicated that active latero-frontal cirri play a role in the transfer of particles from through current to frontal current, probably by means of a strong interaction through the motion of intervening fluid rather than through a direct physical contact. M. edulis specimens used in the present study were collected in 1990 at Helsingør and in 1991 at Kerteminde, Denmark.