Relationship between duration of cyprid attachment and drag forces associated with detachment ofBalanus amphitrite cyprids

Relationships between the duration of antennular attachment of cyprids ofBalanus amphitrite and forces associated with detachment were assessed in a small flume. For six of twelve sets of measurements obtained on separate dates between 27 January and 2 June 1989, drag forces associated with detachment were significantly and positively correlated with duration of attachment within the range 10⁰ to 10³ s. In general, the instantaneous drag force exerted on cyprids at detachment was more strongly correlated with duration of attachment than was either the maximum or mean force exerted prior to detachment. Our indirect method of estimating drag forces from shear velocities measured 0.5 cm from cyprids (i.e., 10 body lengths) probably underestimated the true association between detachment force and attachment time since the spatial coherence of shear velocities characterizing turbulent flows in the flume was not strong at these scales. The relationship between attachment time and drag force at detachment suggests that spatial and temporal variability in fluid forces in situ may contribute to stochastic variations in intensities of settlement ofB. amphitrite. Stresses sustained by the antennular adhesive of cyprids ofB. amphitrite were calculated to standardize forces to the area of antennular contact and permit comparisons with similar measurements made onSemibalanus balanoides by other investigators. Stresses sustained by the adhesive ofB. amphitrite were an order of magnitude lower than those reported for the adhesive of the larger cyprids ofS. balanoides. This difference may reflect differences in the stress sustainable by the adhesive secreted onto antennular pads when loaded purely in tension (measured previously) rather than in a combination of shear and tension (calculated here). Alternatively, there may be interspecific differences in the adhesive used for reversible attachment or in behavioral responses of exploring cyprids to strong flow.     

Attachment of the larva of the ascidian Diplosoma listerianum

Histological and ultrastructural studies of free-swimming and attached larvae of Diplosoma listerianum Milne Edwards indicate that initial attachment is by means of papillae, which secrete an adhesive substance. The source of the adhesive is the central mass cells of the papilla. These cells secrete large electron-dense granules, and also a mass of reticular material. The granules give rise to the adhesive seen in sections and scanning electron micrographs of attached larvae, although the reticular material may also contribute to the adhesive. Histochemical tests show that protein is present in the granules, together with a small amount of carbohydrate. The reticular material contains sulphated acid mucopolysaccharide.     

Importance of physical and biological settlement cues used at different spatial scales by the larvae of Semibalanus balanoides

The settling cues used by larvae of Semibalanus balanoides (L.) were examined at large (1 m), medium (1 mm), and small (<300 m) spatial scales, corresponding roughly to choices made during broad and close exploration and final inspection within the settling zone. The experiments were carried out at two locations in Canada in May and June 1984. Samples of substratum surfaces from above (n=87 sites unselected by cyprids) and below (n=84 sites selected by cyprids) the upper limit of the barnacle zone were characterized according to 13 quantitative and semi-quantitative variables (diatom cover, macroalgae, detritus) using scanning electron microscopy (SEM). The data were analysed using a stepwise logistic regression. At the large scale, the presence of an alga (Urospora wormskjoldii Mertens) in the upper uncolonized zone and a diatom (Achnantes parvula Kützing) within the settling zone are potential settlement cues. At the medium scale in the settling zone, larvae select clean sites, devoid of detritus and diatoms or on which detrital matter, when present, is of finer texture than on the unchosen sites within the settling zone. At the smallest scale (<300 m, equal to the average maximum width of the larvae), we tested the hypothesis that the larva seeks optimal microheterogeneity (presumably providing good adhesion). Microheterogeneity of the surface was measured immediately under the larva, around the settling organs, the antennules. Our results show that such surface microheterogeneity is significantly greater and the vertical center of gravity of the surface significantly lower on the sites selected by the cyprids than on the unselected contiguous sites. Fractal measurements carried out on selected and contiguous unselected surfaces indicate that larvae discriminate microheterogeneity levels below a step length of 35 m, a value approximately the size of the diameter of the antennular discs (40 m), which are used to explore the substratum and attach.Contribution to the programme of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

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.     

Marine bacterial fouling: A scanning electron microscope study

A range of substrates has been examined in order to determine the types of attachment mechanism employed by marine bacteria. Use of the scanning electron microscope (SEM) has also allowed an investigation of the initimate relationship between an antifouling paint matrix and its attached bacterial community. Plastic (Thermanox) and glass coverslips, together with Cu₂O-based and TPTF-based antifouling paints and their respective empty-matrix analogues have been used in this study. Observations over periods of up to 4 wk have shown that extensive bacterial communities can develop. A variety of bacteria have been found: cocci; various rods; stalked forms; and prosthecate types. These bacteria also exhibit a range of attachment mechanisms. Initial attachment is by simple stickiness of cell walls, flagella, pili (fimbriae) or stalks. This stickiness can be attributed to an actual adhesive, electrostatic forces, electrical double-layer phenomena or to London/van der Waals forces. Often, attachment is subsequently improved by the secretion of insoluble, high molecular weight, polysaccharidic material. This material is found in the form of strands, pads, sheets or capsules and acts to bridge the space between the cell wall and substrate or adjacent cells. Thus, stalked forms are found attached by basal pads of mucilage whilst cocci and rods are often found enmeshed in mucilage strands and sheets, but less often attached by pads and capsules. Initially, single bacterial cells attach and give rise to colonies by cell division. Continuing growth of adjacent colonies leads to the development of confluent films over the substrate surface. Further growth results in thickening until eventually the entire surface is coated with a dense community of mixed bacteria together with their adhesive mucilage. In the case of antifouling paints, the porous nature of the matrix allows invasion by bacteria and the possibility of pore blockage by adhesive polysaccharides. This problem is discussed with reference to the paint's loss of antifouling efficiency.     

Origin,composition, and function of secretions from pyriform organs and internal sacs of four settling cheilo-ctenostome bryozoan larvae

Settling larvae of the bryozoans Flustrellida hispida, Flustra foliacea, Alcyonidium polycum, and Bugula neritina exhibit a common behavioral pattern. A settlement site is selected after initial exploration, and temporary attachment is accomplished with a sticky acid mucopolysaccharide secretion exuded from the pyriform organ. Permanent attachment is accomplished by acid mucopolysaccharide and protein secretions of the everted internal sac.     

Apparent predation on ichthyoplankton by zooplankton and fishes in nearshore waters of southern California

Plankton collected at discrete depths in Santa Monica Bay, California, USA, during January 1982 were examined for fish eggs and larvae that had been attacked or consumed by zooplankton. The bongo net remained open for only 3 min and samples were preserved within 5 min of capture. Juvenile and adult fishes that had been captured by otter trawl and preserved within 20 min of capture were examined for ingested fish eggs and larvae. Three copepods (Corycaeus anglicus, Labidocera trispinosa, and Tortanus discaudatus), one euphausid larva (Nyctiphanes simplex), one amphipod (Monoculoides sp.), and an unidentified decapod larva were found attached to fish larvae in the preserved plankton samples (attachment to 23% of the fish larvae was observed in one sample). Overall, about 5% of the white croaker (Genyonemus lineatus) larvae and 2% of the northern anchovy (Engraulis mordax) larvae had attached zooplankton predators. Most fish larvae with attached zooplankton predators were small. We found no indication of zooplankton predation on fish eggs. Few fish eggs and larvae were found in the digestive tracts of juvenile or adult fishes, and the ingested fish larvae were relatively large. The discussion considers apparent preyspecificity of the zooplankton predators as well as potential biases that may be associated with preserved samples collected by nets.     

Reproduction,development and population biology of the Caribbean ophiuroidOphionereis olivacea,a protandric hermaphrodite that broods its young

Reproduction and development of the ophiuroidOphionereis olivacea H. L. Clark, a species that broods its young, were investigated in Florida from January through December 1985 and in Belize in June 1985 and April 1986.O. olivacea has a maximum disc diameter of 5.2 mm and is a protandric hermaphrodite. Sex reversal occurs at disc diameters ranging between 2.2 and 4.0 mm; it has 400 µm diameter oocytes and is ovoviviparous. As expected from an obligate out-crosser, this ophiuroid has a similar allocation to male and female reproduction, in terms of gonad volume. Reproduction of the Florida population was monitored for one year.O. olivacea is a sequential brooder and incubates its young during the coldest months of the year. The females produce a single clutch of juveniles each year. Spawning starts in November and peaks in January and February. The ova are spawned synchronously from all the ovaries of each female into the bursae and are retained there. Fertilization is accomplished by intake of sperm into the female bursae.O. olivacea develops through a ciliated embryonic stage that appears to be a modified vitellaria larva lacking ciliary bands. These modified larvae swim in seawater in the bursae. Direct development in this species has resulted from heterochrony in the loss of ophiopluteus features. The number of brooding females in the population increases in November and reaches a maximum in March. JuvenileO. olivacea emerge from the bursae at a disc diameter of 480 µm and each arm has three segments. Recruitment was first detected in April, and juveniles were particularly abundant in June. Small size inO. olivacea is associated with paedomorphic heterochrony with precocious maturation of the males at a disc diameter of 1.5 mm, ~2 mo after taking up their free existence. Brooding as a life history mode inO. olivacea is examined and the adaptations of this species to its warm-water habitats are discussed.     

X-ray diffraction study of calcification processes in embryos and larvae of the brooding oyster Ostrea edulis

X-ray powder diffraction was used to study shell calcifications of the oyster Ostrea edulis, sampled in the Limski Kanal, Istria (Adriatic Sea), in May 1992. All the developmental stages were followed, from the embryonic stage through the transition between the trochophore and veliger larva (prodissoconch I and II) and later, after swarming, the pelagic free-swimming larval stages, up to their settlement and attachment (from the D-shaped to the fully formed pediveliger larva), and finally during metamorphosis and juvenile stages (dissoconch). In the first gastrula stage, only an amorphous tissue is present (a periostracum and organic matrix). The beginning of shell formation (at the end of gastrulation) in early trochophores is manifested by the appearance of calcite (up to 1–7% of total volume) and then aragonite (about 1%). In the later stage of the veliger larva the fraction of calcite decreases as well as the amorphous fraction, while the fraction of aragonite rapidly increases. In the prodissoconch II stage and during the whole pelagic period aragonite is dominant, accompanied by a very small amorphous fraction and traces of calcite. The shell mineral composition does not change until metamorphosis, whereupon the fraction of calcite rapidly increases and the fraction of aragonite decreases. The postmetamorphic valves of the juvenile and adult oyster consist mainly of calcite, except the resilium and myostracum which remain aragonitic, possibly as a continuation of the inner layer of the larval shell. Received: 28 May 1997 / Accepted: 1 July 1997     

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.     

On the feeding and behaviour of the larva of Branchiostoma lanceolatum

Collections of Branchiostoma lanceolatum (Pallas) made in mid-May and mid-July at Helgoland before and after spawning have established that the larvae leave the amphioxus ground about June and therefore presumably become planktonic. Metamorphosing larvae and young adults can be collected on the ground in late August and early September and are either the same larvae returning, or others from a neighbouring ground within the same circulating current system. An examination of the gut contents of 67 larvae collected from the plankton at Helgoland in August showed that 30% of the animals had ingested calanoid copepods or other organic material of a size similar to that of the larval mouth. A few larvae had also taken small particles evidently by a ciliary mechanism. In 50% of the larvae the gut was empty. It has been found that, in addition to a muscular mouth and gill bars richly supplied with nerves, both the gut wall and the body wall are muscular and capable of passing, by peristalsis, large food masses that distend the body. The visceral muscles of the larva resemble the coelomyarian fibres of the Nematoda. The larva appears, therefore, to be both microphagous and macrophagous. Evidence from the swimming behaviour and from reports of the vertical distribution of larvae in the sea is discussed. It is suggested that the larvae normally swim upward with the mouth and gills closed and then sink passively in the horizontal position with the pharynx expanded and the open mouth directed downward. In the event of large organism such as a copepod or a mass of organic material coming into contact with the adhesive lower left surface of the larva, it could be captured by the mobile lower lip and engulfed. The straightening of the larval tail, the great increase in the number of eyecups and the growth of the metapleura at metamorphosis are suggested as factors leading to the settlement of the young adult. Attention is drawn to the possible significance of the structure of the larva in interpreting the relationships of the cephalochordates.     

Gametogenesis,embryogenesis, and larval features of the oviparous sponge <Emphasis Type="Italic">Petrosia ficiformis</Emphasis> (Haplosclerida,Demospongiae)

This study describes the reproductive cycle of Petrosia ficiformis and documents for the first time embryogenesis in an oviparous haplosclerid demosponge. Gonochoric adults, occurring in 2:1 female/male ratios, spawned in late autumn, after a 7-month long oogenesis and a 2.5-week-long spermatogenesis. Following a remarkable migration, the oocytes were released as 250 μm eggs bearing attached polar bodies and a thin mucous cover. Round-headed spermatozoa with three large mitochondria, and many proacrosomal vesicles fertilized the eggs externally. A fertilization membrane appeared around the zygotes. Nearly equal and total cleavage led to a stereoblastula that subsequently became an entirely ciliated larva. The larva alternated spherical and multilobate body shape and consisted of undifferentiated cells. It had poor abilities to swim and glide, probably experiencing passive dispersal and unselective attachment. Settlers developed choanocyte chambers after 1.5 months. Symbiotic microbes were absent from gametes and larvae, being necessarily acquired from the ambient at each sponge generation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Form and feeding mechanism of a living Planctosphaera pelagica (phylum Hemichordata)

We describe aspects of the anatomy and suspension-feeding mechanism of a single Planctosphaera pelagica captured from the plankton in June 1992 off Bermuda in the western Atlantic. We also describe several unusual features of the larva, including its occurrence in surface waters, unusually large size, and limited swimming ability. Our account of the form and feeding behavior of P. pelagica is the first based on observations of a specimen captured and observed alive. Our limited observations suggest that the planctosphaera may use a suspension-feeding mechanism much like that of the other feeding deuterostome larvae (the pluteus and bipinnaria larvae of echinoderms and the tornaria larva of enteropneust hemichordates) known to capture food particles using a single ciliated band. Although we could not observe cilia directly, the movement of dye streams and food particles and the structure of the ciliated band suggest that some particles may be captured at the ciliated band by the reversal of ciliary beat. The planctosphaera possesses many prominent mucous glands near the food grooves. This suggests an important role of mucus in the biology of the larva, but we were not able to observe directly any role of mucus in particle capture.     

Abundant ketone isolated from oily Plakortis sponge demonstrates antifouling properties

Marine sponges of the Genus Plakortis are typically unfouled; they can have a distinctive pleasant smell and an oily surface. A significant quantity of fragrant oil was obtained from a Jamaican Plakortis sp. by cryo-trap. The oil was determined to be exclusively 2-decanone. The antifouling character of the oil was evaluated by its effects on surface attachment of a gram negative bacterial model using confocal fluorescence microscopy as well as its effects on the attachment of Dreissena polymorpha (zebra mussel). The ketone dramatically inhibited attachment of the bacteria and zebra mussels. The results suggest that the oil impacts establishment of related epifauna on the Plakortis sponge in nature. Although the aliphatic ketone alone is not a potential commercial alternative for antifouling coatings, incorporating the functionality into coating design should be considered in future studies.     

Video recordings of prey capture behaviour and associated electric organ discharge of Torpedo marmorata (Chondrichthyes)

The results of an analysis of 16 laboratory records of Torpedo marmorata Risso attacks are presented: when a fish swims near a T. marmorata at rest, the latter jumps and simultaneously immobilizes the prey by its electric organ discharge (EOD). A water stream is used to direct the paralysed prey beneath its disc before swallowing. The attack is made if the prey swims at short distance ( 4 cm); height and direction of the jump are related to the position of the prey. The EOD, interrupted during the jump, reappears when the prey moves under the disc of T. marmorata, and ceases before swallowing. The strength of the EOD is sufficient to break the vertebral column of the prey. The possible receptor organs involved in this behaviour are presumed to be lateral line organs and touch detectors: the former to localize the prey before the jump, the latter to detect it under the disc. Evolutionary convergence of the prey capture behaviour of Torpedo, Malapterurus, and Electrophorus is also discussed.Supported by Research Grant No. 659440 from the Direction de Recherches et Moyens d'Essais (D.R.M.E.) to Dr. T. Szabo.Dr. Bauer's stay in France was sponsored by a N.A.T.O. and a D.F.G. research fellowship.     

Development of the echinothurid sea urchin Asthenosoma ijimai

Development of an echinothurid sea urchin is described for the first time; eggs of Asthenosoma ijimai (Yoshiwara) have been fertilized in the laboratory, and development has been followed light-microscopically up to the early juvenile stage. The eggs, which are orange and float, are 1.2 mm in diameter, by far the largest echinoid eggs on record. The embryos, larvae and early juveniles are lecithotrophic, and no exogenous food is needed for development. The embryonic stages include a remarkable biscuit-shaped late blastula, which has never been described for any echinoid before. The larva, with its para-arms unsupported by skeletal ossicles, is unlike the echinoid prism or pluteus and more resembles the early bipinnaria or early auricularia of asteroids and holothurians, respectively. All stages through late larvae float just beneath the surface until settlement occurs during the third and fourth weeks at 20°C. Metamorphosis from late larva to juvenile is gradual and no part of the larval body appears to be cast off.This paper is dedicated to Professor Juro Ishida on the occasion of his seventieth birthday.     

Studies on reef corals. I. Skeleton formation by newly settled planula larva of Pocillopora damicornis

Initiation of coral-skeleton formation was studied in the reef-coral Pocillopora damicornis Lamarck. Observations were made on sequential skeletal growth stages of newly settled planula larvae during the first 22 days following settling onto glass microscope slides. Techniques used include phase light microscopy, scanning and transmission electron microscopy, and powder X-ray and selected area electron micro-diffraction. Formation of the skeleton is initiated immediately on settling of the larva. The primary calcareous elements are of two types — flattened spherulitic platelets, and smaller rod-like granules. Rudimentary primary septa are clearly defined within 6 h after settling. Fusion of the primary calcareous elements results in the formation of the larval basal disc within 48 to 72 h. With transmission electron microscopy, this basal disc is found to differ from subsequent adult calcification in (1) considerably lesser degree of mineralization, (2) smaller crystal size, (3) more random orientation of the crystals, and (4) the presence of trace amounts of calcite in addition to aragonite. The basal disc with its septal rudiments constitutes a true larval skeleton, differing in morphology, micro-architecture, and crystal type from the fibrous growth characterizing the adult skeleton.Contribution 419, Hawaii Institute of Marine Biology, University of Hawaii.     

Localization of bioluminescence in the siphonophore Nanomia cara

The base of the tentacle of the developing physonect larva (Nanomia cara) has a bioluminescent region. The ability to produce light in the larva is transitory; this ability first appears at about two days of development and is disappearing by eight days, as the larva begins to feed. Subsequently paired bilaterally symmetrical bioluminescent organs are found on the nectophores and the bracts of the adult colony. In both the larva and the adult, bioluminescence is mediated by a calcium specific photoprotein. In all cases the photocytes lack a green fluorescent protein.     

Statolith implantation in the banana prawn Penaeus merguiensis

Specimens of Penaeus merguiensis de Man were captured between February and May 1981 from intertidal creeks and beaches of Cleveland Bay, Townsville, Australia, using a 15 m seine net. The statocyst of P. merguiensis resembles that of other macrurans in that it is a dorsal invagination of the basal antennular segment lined with groups of sensory hairs. The statolith is composed of sand grains implanted by the prawn from the substratum which must be done after every moult. Implantation begins within 90 min of ecdysis and has 3 phases: sifting; digging and finally eye withdrawal which pushes the sand grains into the statocyst chamber.