Microarchitecture and function of the lophophore in the bryozoan Cryptosula pallasiana

The architecture and function of the lophophore of the marine bryozoan Cryptosula pallasiana (Moll) are described, including some new features not previously discovered in bryozoans. The nature of fluid movements within the lophophoral coelom during feeding activities is postulated on the basis of the arrangements of epithelia and muscles. Epithelial cells at the tentacle bases are blastemic in nature, and there is a ciliated pit of unknown function in the angle between every pair of tentacles. There are 6 nerves in each tentacle, including a pair of single-axon subperitoneal nerves. Neurosecretory-like vesicles and glycogen occur in some neurons of the ganglion. The basal lamina collagen has a diameter smaller than that previously recorded for an invertebrate. Filament dimensions are given for several different muscles. Tentacle muscles and lophophore retractor muscles are smooth. Thick paramyosin-like filaments up to 75 nm diameter occur in two muscle types. A new set of muscles is described: the basal transverse muscles of the tentacles.     

Methods of ciliary filter feeding in adult Phoronis muelleri (phylum Phoronida) and in its free-swimming actinotroch larva

Microscope-video recordings were used to describe basic characteristics of particle capture in adult Phoronis muelleri and in its actinotroch larva. The larva captures food particles by means of close interplay between the tentacles and the oral hood. Suspended particles in the incoming water flow set up by the lateral "pump" cilia on the tentacles approach the tentacles with a velocity of about 1.5 mm s^-1. Near the tentacles, the particles are stopped by the stiff sensory laterofrontal cilia acting as a mechanical sieve. Simultaneous with stoppage of a particle, the oral hood is rapidly lifted so that water from the surrounding area flows in to occupy the volume created under the hood. Due to the proximity of the tentacle with the arrested particle, this suction will draw the particle away from the laterofrontal cilia into the increased space under the oral hood with a velocity of about 0.6 mm s^-1 before it is subsequently carried to the mouth. If a particle is stopped near the tip of a tentacle this may trigger a tentacle flick, with a tip velocity of about 5-7 mm s^-1, which brings the particle down toward the lifting edge of the hood. A stopped particle may cause a local disruption of the metachronism of the lateral cilia for about 0.14 s. Likewise in the adult, when an incoming particle with a velocity of about 1.6 mm s^-1 is stopped near the tip of a tentacle this triggers a flick, which brings the particle down towards the mouth. The duration of the active flick phase is about one-tenth of the flick cycle. Only when a particle is stopped on the outer part of a tentacle is a flick triggered. Otherwise the particle is either transported down along the frontal surface of the tentacle by means of the frontal cilia, or transferred into the downward current created by the lophophore. The metachronal wave velocity is about 0.25 mm s^-1, the wavelength about 12 µm, and hence the ciliary beat frequency about 21 Hz (at ~16°C). Essential features of the filter-feeding process in both actinotroch larvae and adult P. muelleri reported here resemble the ciliary-sieving process described for bryozoans in recent years. It should be pointed out that the stiff, mechanosensory laterofrontal cilia may be a decisive factor for understanding ciliary upstream collecting, also in pterobranchs and brachiopods in which sensory laterofrontal cilia are present.     

Sexual dimorphism and male mating success in the tentacled blenny, <Emphasis Type="Italic">Parablennius tentacularis</Emphasis> (Teleostei: Blenniidae)

Although external sexually dimorphic traits are commonly found in males of combtooth blenny species, little is known about the benefit they can convey to male mating success. Indeed, while female preferences for large males have been demonstrated in some species, the possible role played by dimorphic ornaments has been neglected. We now report on the tentacled blenny, Parablennius tentacularis, a species where males are characterized by bulb glands on the anal fin and both sexes exhibit a dark spot on the dorsal fin and orbital tentacles. Males are territorial, make nests in empty bivalve shells, and provide solitary parental care for the eggs. Using morphometric analysis and field collected data on male and female external features, nest characteristics and number of eggs in the nests, we have assessed the development of dimorphic traits in both sexes and male mating success. The results reveal that orbital tentacles of males are more developed and more variable in size than those of females. Larger males exhibit longer orbital tentacles and larger anal glands but do not necessarily occupy larger nests. Male mating success is significantly correlated with the inner nest surface area and with orbital tentacle size but not with body size. These results provide support for a primary role of male ornaments in enhancing blenny male mating success and are discussed in the context of mate choice for direct and indirect benefits.     

Hydrodynamic study of the functional morphology of the benthic suspension feeder Phoronopsis viridis (Phoronida)

Ambient water currents were altered by the morphology of an active suspension feeder, Phoronopsis viridis Hilton (phylum Phoronida), to produce a flow around its ciliated crown of feeding tentacles (lophophore). To test the effects of specific morphological characteristics on patterns of water movement, the morphology of model phoronids was varied and the resultant paths of water movement were compared to those around living phoronids. Living individuals were collected from the intertidal sandflats at Bodega Bay, California/USA, in the springs of 1984 and 1985. Although P. viridis actively produce a feeding current, use of various models demonstrated that the gross pattern of flow around a living phoronid was created by the physical interaction of its morphology with ambient currents. The important aspects of that morphology were the presence of a wide, porous crown of tentacles atop a cylindrically-shaped body. A hydrodynamic consequence of this morphology was that dye eroded off the substratum from a circular area around the base of the body and entrained upwards into the lophophore. In addition, rates of water movement were slowed at the lophophore and near the substratum adjacent to a phoronid, particles were slowed and diverted from horizontal paths immediately downstream of the lophophore, and the number of visible suspended particles within the wake per unit time increased with ambient velocity. Paths of water movement around a phoronid were also influenced by its angle and height relative to the substratum, indicating that P. viridis could behaviorally modify their local flow environment.     

Trophic ecology and the related functional morphology of the deepwater medusa <Emphasis Type="Italic">Periphylla periphylla</Emphasis> (Scyphozoa,Coronata)

Remotely operated vehicle (ROV)-based field studies on the distribution and behaviour of Periphylla periphylla Péron and Lesueur (Ann Mus Hist Nat Marseille 14:316–366, 1809), from three Norwegian fjords have been combined with on-board experiments and morphological and histological studies in order to understand the trophic ecology of this species. Field studies from one of the fjords showed that the zooplankton biomass was negatively related with P. periphylla abundance, indicating a predatory effect. The majority of zooplankton biomass tended to be distributed above the aggregation of P. periphylla, which in turn showed highest abundance at 100–200 m depth. Observation on the orientation of medusae passing the ROV when descending down in the water column at dawn and dusk, showed no consistency with the theory of diel vertical migration. Estimated metabolic demand of P. periphylla indicated a daily predation impact on the prey assemblage of 13% as an average for the fjord. In situ behavioural observations showed that the dominant tentacle posture of large medusae was straight upward, with tentacles extended to the oral–aboral body axis. The hunting mode alternates between ambush and ramming, whereby tentacle posture minimises the water turbulence that may otherwise alarm the prey. The musculature of the tentacles is well developed, with an especially strong longitudinal muscle on the oral side, facilitating fast movement of the tentacle towards the mouth. In addition, ring-, radial-, and diagonal musculatures are also present. The diagonal is probably most important for the corkscrew retraction of the tentacle, used at the moment of prey capture. Results from laboratory experiments show that different body-parts of P. periphylla vary in sensitivity for chemical and mechanical stimuli, including hydrodynamic disturbance and vibration in the surrounding water. Feeding success is facilitated by combining the vibration-sense on the tentacle tips and the marginal lappets, the touch-sense on the tentacle bases and marginal lappets, and a taste control of the captured prey at the mouthlips.     

Influence des courants sur l'éthologie alimentaire des phoronidiens. Etude par séries de photographies cycliques

Subjected to water currents, phoronideans orientate their lophophores as follows: the mouth is turned into the current at the bottom of a funnel formed by the tentacles; the anus, behind the lophophore, is under the current. If the current direction changes, the position of the lophophore moves in the same direction. Our results confirm Bullivant's (1968) classification of Phoronidea as “impingement feeders”. The technics of a new automatic shutter release are described.     

Diversity of swimming behavior in hydromedusae as related to feeding and utilization of space

Feeding behaviors of the following 4 species of hydromedusae are described from field and laboratory observations: Probosidactyla flavicirrata, Stomotoca atra, Phialidium gregarium and Polyorchis penicillatus. Feeding efficiency of medusae has previously been considered equivalent to fishing with a given amount (combined tentacle length) of adhesive fishing line; however, detailed observation shows that behavior of medusae greatly modifies the fishing capacity of each species. It is hypothesized that in addition to (1) tentacle number and length, the following factors strongly influence feeding efficiency: (2) tentacle posture, (3) velocity of tentacles moving through water (4) swimming pattern of medusa, (5) streamlining effects of medusa bell on water flow, (6) diameter of prey, (7) swimming pattern and velocity of prey. Each species of hydromedusa utilizes the above factors in different combinations.Mailing address     

Effects of food particle concentration on feeding current velocity in sex species of marine Bryozoa

Experiments were carried out using established methods to measure feeding current velocity in six species of marine Bryozoa collected in 1982 and 1983 around low-tide mark at Port St. Mary, Isle of Man (Flustrellidra hispida, Alcyonidium gelatinosum, A. hirsutum, Electra pilosa, Membranipora membranacea and Bowerbankia gracilis feeding on Tetraselmis suecica). It was found that there was a positive correlation between feeding current velocity and the concentration of food (phytoplankton) in the environment. It was also found that, at a fixed particle concentration, feeding current velocity was strongly correlated with lophophore height and (less strongly) with tentacle number. The competitive and evolutionary implications of these relationships are considered. It is tentatively suggested that interspecific competition for food may be of some significance in marine Bryozoa and that the removal of food supplies to competing colonies may play a role in colony overgrowth and competition for space.     

Effects of artificial eutrophication on the metabolism of the Japanese oyster Crassostrea gigas

The morphology of the primary tube feet in 15 species of comatulid (unstalked) crinoids from coral reefs in the Palau Islands and Lizard Island, Great Barrier Reef, was investigated using close-up underwater photographs of the tube feet taken in the natural habitat. Measurements of length of the tube feet and their spacing along the pinnule were taken from these photographs. Tube feet of species of the family Comasteridae have a mean length of 0.75 mm and a mean spacing of 6 tube feet mm^-1. Tube feet of non-comasterid species occurring in the same environments have a mean length of 0.55 mm and a mean spacing of about 8 tube feet mm^-1. The relationship between spacing and length of the tube feet is highty significant for both the Palau and Lizard Island samples (P<0.01). Species having longer and more widely spaced tube feet live partly concealed within the infrastructure of the reef and hold the arms and pinnules in a multidirectional posture. Species having shorter and more closely spaced tube feet perch on top of reef pinnacles or alcyonarians and form planar filtration fans normal to unidirectional currents or wave oscillations. Longer and more widely spaced tube feet in species dwelling within the reef infrastructure provide more efficient filtration in the slow, meandering flow prevailing there. Closer spacing of the tube feet in species exposed to near-mainstream flow provides a more efficient filtration mechanism at higher flow velocities. Reduced length of the tube feet in these species may be a consequence of closer spacing of the pinnules. Differentiation of these co-occurring species in spacing and length of the tube feet implies differentiation in food particles captured. This may in some cases constitute resource partitioning. Most species which overlap in living habits are significantly different in spacing and length of the tube feet.     

Growth of the kelp Ecklonia radiata near the northern limit of its range in Western Australia

The length, growth and survivorship of mature sporophytes of Ecklonia radiata (C.Ag.) J. Agardh were measured on two patch reefs within the lagoon of a high-latitude, coralreef atoll (Easter Group, Houtman Abrolhos; 28° to 29° S; 113°35 to 114°03E) for 1 yr (1982–1983). The sites differed in their proximity to the perimeter reef, but had similar regimes of temperature, light, nutrient concentration and water movement. Kelp length, growth rate and survivorship differed significantly between sites, although plant density was similar (less than l m^-2). At the site near the lagoon perimeter, the central lamina averaged 381 mm in length, grew at an annual mean rate of 1.28 mm d^-1, and 56% of tagged individuals had died after one year. The corresponding values for the site near the centre of the lagoon were: 257 mm, 0.75 mm d^-1 and 92%. Three other sites on the coastal limestone reefs near Perth (400 km to the south) were studied for various intervals over a 5 yr period (April 1979 to August 1984). The kelp from the low-latitude sites were smaller, grew more slowly, and suffered similar or greater mortality than their southern counterparts. Latitudinal comparisons were confounded by differences in kelp density between sites, but there is no evidence for density-dependent effects on the measured parameters across the range of natural densities observed. Growth rates at all sites were negatively correlated with ambient sea temperatures when these were above 20°C. There was no evidence of adaptation to the higher sea temperatures experienced at the Abrolhos, and temperature cannot be dismissed as a factor controlling the growth of the species near the northern limit of its distribution on the Western Australian coast. Other factors however must be involved in determining the latitudinal position of that limit.     

Functional morphology of the larval tentacles of Phragmatopoma californica (Polychaeta: Sabellariidae): composite larval and adult organs of multifunctional significance

Larvae of the sabellariid polychaete Phragmatopoma californica (Fewkes), which were collected in San Diego, California and were competent to metamorphose after 18 to 30 d of development were observed in vivo by videoequipped light microscopy, and the fine structure of the larval tentacles was examined by transmission and scanning electron microscopy. Each tentacle has tufts of at least two types of immotile cilia arranged in dorsolateral and ventrolateral rows, and a ventral groove covered by two types of motile cilia that beat independently of each other. The epidermis is regionalized into glandular, sensory, locomotory, and support cell types and contains four longitudinal bundles of basiepithelial nerve fibers. A layer of connective tissue separates the epidermis and the nerve tracts from obliquely striated muscles that occur within the peritoneum that lines the central coelomic cavities. The peritoneum forms an intact coelomic epithelium that overlies and interdigitates with the muscle cells, with no intervening basal lamina. The muscle cells are considered to be intraperitoneal because they are located above the basal lamina and they lack intercellular junctions with the peritoneal cells. Specialized peritoneal cells form a striated myoepithelial blood vessel that partitions the coelom into medial and lateral cavities. No neuromuscular junctions were found, but both muscular and ciliary movement seem to be under neuronal control. The basiepithelial nerve terminals appear to synapse into the connective tissue layer toward the intraperitoneal muscle. Several similarities in tissue organization are noted between the larval tentacles of P. californica and the tube feet of echinoderms. Observations on the ontogeny, morphology, and behavior of the tentacles suggest that they are multifunctional organs involved in feeding, construction of the juvenile sand tube, locomotion, attachment, and sensory perception during larval and adult lives.     

Halistaura bruuni sp. nov. (Leptomedusae,Mitrocomidae) with notes on its distribution and ecology

A new hydromedusa collected in 1963 in the Bay of Bengal during the International Indian Ocean Expedition by the RV Anton Bruun is here described as Halistaura bruuni sp. nov. Some environmental data are given. The new species is characterized by a number of open marginal vesicles approximately equal to that of the tentacles, oval gonads on the distal half of the radial canals, and by the presence of nematocyst depots in the tentacle bulbs.Publ. No. 273 of the Instituto Oceanográfico da U. S. P.     

Feeding behaviour of the sea cucumber <Emphasis Type="Italic">Cucumaria frondosa</Emphasis> (Echinodermata: Holothuroidea) in the laboratory and the field: relationships between tentacle insertion rate,flow speed,and ingestion

The sea cucumber, Cucumaria frondosa, is a benthic suspension feeder that captures food particles on its tentacles and then inserts them into its mouth one at a time. Previous studies have suggested that tentacle insertion rate (TIR) could be a useful indicator of food intake. The present study determined whether flow velocity affects TIR and whether TIR is a good indicator of ingestion. Video observations of sea cucumbers in Passamaquoddy Bay (45°01.70N, 66°55.74W) in August 1995 showed that TIRs increased with velocities up to 55 cm s⁻¹ and decreased steadily at flows above that up to 130 cm s⁻¹. In October 2006, laboratory flume studies were carried out on specimens collected from the same site in the previous August. Temperature and salinity (12°C and 32) in the flume were the same as in the field at the time of collection. There was high individual variation in feeding behavior at free-stream velocities of 4–40 cm s⁻¹ and TIR was independent of flow. As the number of tentacle insertions increased in the flume experiments, the amount of chloropigments in the digestive tracts of the sea cucumbers also increased. This suggests that TIR, which can be measured non-intrusively using remote video techniques, could be a good indicator of feeding behavior and ingestion in C. frondosa.     

Macrobenthic species assemblages in Ellis Fjord,Vestfold Hills,Antarctica

A study was made of the sub-littoral benthic environment of Ellis Fjord, a 10 km-long fjord located near Davis Station, in the Vestfold Hills, Antarctica, over a 15 mo period (November 1984 to February 1986). Data were collected by SCUBA diving and underwater photography and were inhitially analysed by ordination techniques (non-metric multidimensional scaling). Ordinations showed substratum type to be the factor most strongly associated with changes in the distribution and abundance of macrobenthic species within the fjord. Other factors shown to be associated with changes in macrobenthic species assemblages were depth, distance from the fjord mouth, bottom slope, shoreline characteristics, current speed, and the presence of low-salinity water at shallow depths during the summer melt. The four major substratum types in Ellis Fjord were sand, rock, Serpula narconensis colonies and Phyllophora antarctica thalli. S. narconensis colonies supported the most species and sand substrate supported the least. P. antarctica is the only macrophyte species which occurred in the fjord. S. narconensis colonies in Ellis Fjord from one of the largest known tubeworm reefs in the world. The assemblages of benthic species in Ellis Fjord were different from those seen at other sub-littoral benthic sites off the Vestfold Hills, and at other Antarctic sites. There was a far greater proportion of filter-feeding species in the fjord than at other sub-littoral benthic sites off the Vestfold Hills. Factors which are thought to have caused these differences are the high level of organic but low level of inorganic input into the benthic system of the fjord, and the absence of anchor ice from the fjord.     

Seagrass and algal beds as nursery habitats for tiger prawns (Penaeus semisulcatus and P. esculentus) in a tropical Australian estuary

We evaluated the importance of seagrass and algae to two species of tiger prawns (Penaeus semisulcatus and P. esculentus) by detailed sampling at four sites (two seagrass, two algae) in the Embley River estuary, and through sampling 26 sites in 7 adjacent estuaries at one time of year. Samples of tiger prawns were collected in the Embley River estuary with a small beam trawl at night every 2 wk from September to May for 2 yr (1990 to 1992). The two seagrass sites, which were 11 and 13 km from the river mouth, showed less seasonal variation in salinity than the two algal sites, which were 15 and 20 km from the river mouth. The algal beds at the two upstream sites almost disappeared during the wet season, but the biomass of seagrass did not change significantly between the wet and dry seasons. The grooved tiger prawn (P. semisulcatus), the main species at all sites, comprised 88% of the total tiger prawn catch over the two years. They were found at all sites during the pre-wet season, but after the onset of the wet season, they disappeared along with the algae, from the upstream sites. The brown tiger prawn (P. esculentus) was found almost exclusively (97% of the total catch) on the seagrass sites downstream. In the study of several estuaries, juvenile P. semisulcatus were caught at all 26 sites, and P. esculentus were caught in much smaller numbers, at 16 sites. Approximately equal numbers of P. semisulcatus were caught in seagrass and algal beds in the pre-wet season. Very few individuals >10 mm carapace length of either species, were caught. The results from this study highlight the importance of algal beds during the pre-wet season as nursery areas for one species of tiger prawn (P. semisulcatus).     

Activity patterns in the terebellid polychaete <Emphasis Type="Italic">Eupolymnia nebulosa</Emphasis> assessed using a new image analysis system

The activity and surface sediment displacement by the terebellid polychaete Eupolymnia nebulosa were monitored, using new image acquisition and image analysis procedures. We used a video sensor mounted on a motorized table, to acquire adjacent images of the whole studied aquarium within about 2 s. These images were then grouped within a composite image acquired every 15 s. Consecutive composite images were compared to infer activity and surface sediment displacement. This procedure proved efficient for E. nebulosa as indicated by (1) the continuity of the tentacles within composite images, and (2) the direct comparison of images and detected activities. There were important temporal changes in the relative importance of the three main types of activity: feeding, tube-building and (both partial and total) emergence from the tube, accounting, respectively, for 75, 15 and 10% of the entire experiment duration. Activity intensity (cm² min^-1) was assessed through the surface of pixels with grey levels differing by more than 20 (on a 0–255 scale) between two consecutive images. Feeding was associated with low activity intensity, whereas tube-building and emergence from the tubes were associated with high activity intensities. Surface sediment displacement mostly resulted from tentacle activity both during feeding and tube-building and was almost zero when worms emerged from their tube. We used our experimental set up to assess spatial changes in activity intensity and particle displacements along the tentacles. Most of the activity occurred within the first 4–6 cm from the tube aperture. Particle loss during their transfer along the tentacles preferentially affected larger particles as postulated by the model of particle selection and transport in tentaculate deposit-feeders. Moreover, the speed of the particles along the tentacles correlated negatively with their size. This contributed to increase in the residence time of larger particles on the tentacles and thus, to further enhance their probability of being lost. The size distributions of particles during feeding and tube-building did not differ significantly although visual observations confirmed the preferential use of larger particles for tube-building. This suggests the existence of a sorting step occurring elsewhere than on the tentacles as already demonstrated for spionid polychaetes.     

Appraisal of visual assessments of habitat complexity and benthic composition on coral reefs

Visual assessments of topographic habitat structure and benthos on coral reefs were appraised using quantitative data collected from 16 replicate surveys within each of 21 sites on Seychelles reefs. Results from visual assessments of reef benthos were similar to those obtained using techniques frequently used to assess benthic complexity and composition. Visual estimates of habitat topography were correlated with rugosity, reef height and holes of 10–70 cm diameter, whilst visual estimates of benthic composition were very similar to those obtained from line intercept transects. Visual estimates of topography correlated strongly with species richness of fish communities and explained 42% of the variation in these data. The relationship between visual estimates of topography and species richness is strongest with fish 10–30 cm total length (TL), abundance of fish within this size category also correlating positively with topographic visual assessments. Visual techniques are prone to observer bias, however with regular training they can be used to quickly provide a reliable and effective means of assessing habitat complexity and benthos on coral reefs.     

Effects of particle concentration on clearance rate and feeding current velocity in the marine bryozoan Flustrellidra hispida

Colonies of the marine bryozoan Flustrellidra hispida (Fabricius) were collected intertidally from Port St Mary, Isle of Man (UK) during the autumn and winter 1981/1982. Suspension feeding in F. hispida was examined in some detail, using as food the alge Tetraselmis suecica. Previous studies had not examined variation in the speed of suspended food particles travelling through the lophophore. It is clear that feeding rate, as measured by particle velocity, varies over periods of time, even when all external factors are kept constant. Moreover, particle speed within the lophophore can be shown to be positively correlated with the concentration of suspended food particles in the surrounding environment. It is also apparent that feeding current velocity varies at different positions within the lophophore. In addition observations are made on the involvement of the tentacles in particle capture.     

Comparative species richness,composition, and abundance of invertebrates in Caribbean seagrass (Thalassia testudinum) meadows (Panamá)

The results of a year-long study in which epibenthic invertebrates were collected monthly from seagrass (Thalassia testudinum) meadows along the Caribbean coast of Panamá and the Panamá Canal Zone are described in this paper. Differences in species composition and abundance among sites were primarily due to the proximity of surrounding habitats, especially coral reefs, which contain a number of species that utilize the seagrass meadows. In contrast to many previous characterizations of tropical marine habitats, important seasonal fluctuations in both species number and abundance took place at each of the sites. Data on breeding activity among several species of decapod crustaceans indicate year-round reproduction, although considerable seasonal differences occur in the percentage of ovigerous females. These interspecific differences in observed reproductive output may be explained by differences in life-cycle length, a factor not often considered in discussions of seasonal breeding patterns in tropical marine invertebrates. Overall species composition was qualitatively similar to that reported in comparable studies of tropical and subtropical seagrass meadows elsewhere, although caridean shrimp and xanthid orab species were reduced in number and total abundance were much lower than in previous studies.     

Reproductive patterns in the Antarctic brachiopod Liothyrella uva

The reproductive cycle of the Antarctic articulate brachiopod Liothyrella uva (Broderip, 1833) is described from monthly samples collected between September 1985 and July 1987 from a population at Signy Island, Antarctica. Spermatogenesis and oogenesis are described for the first time in this species. Surface dried-tissue masses for a standard individual (41 mm shell length) were calculated for the digestive diverticula, gut, lophophore and gonad from monthly dissections of 15 brachiopods. Seasonal patterns, with summer peaks, were observed in the digestive diverticula and gut. The lophophore and gonad masses did not exhibit seasonal trends. Females showed a sharp decrease in proportion of large oocytes between October and November in 1986, suggesting spawning during this period. There was no similar decrease during the same period in 1985. Mean percent spermatozoa measurements revealed a large increase in November 1985 and a rapid decline in December 1985. This suggested a large spawning event for males in 1985 which was not repeated the following year. These data indicate large inter-annual differences in reproductive activity as well as differences between males and females. They also suggest the possibility of sperm storage by females. Brood characteristics were also highly variable. The smallest brooding female was 31.5 mm in length. Some females brooded more than one developmental stage simultaneously, and variation in brood size (numbers of embryos or larvae held in the lophophore) and brood composition between individuals was high. All samples collected throughout the 2 yr period contained some females with broods. The data suggest that the reproductive strategy of L. uva is highly plastic, and that there may be three reproductive periodicities on seasonal, annual and inter-annual time scales. Received: 16 May 1997 / Accepted: 2 March 1998