Gregarious settlement in cypris larvae:the effects of cyprid age and assay duration

Gregarious behaviour of marine larvae is perhaps most clearly associated with finding a suitable habitat in a changeable or restricted environment, or with finding other conspecifics with which to mate. Prior work has shown that in settlement assays using cypris larvae of the barnacle Balanus amphitrite, gregarious interactions significantly affected the interpretation of experiments testing the activity of organic settlement promoters and inhibitors. Other studies have also shown effects of cyprid age and pheromone concentration on settlement behaviour. However, the effects of interactions between gregariousness and these two factors are not known. The aim of this study was to test the hypotheses that i) as cyprids age the effects of gregariousness become less apparent, and ii) as the duration of the experiment increases gregarious effects become more apparent, using cypris larvae of B. amphitrite and Balanus improvisus. Three age classes of cyprids were used at six densities in a fully factorial design. For B. improvisus cyprids significant gregarious effects occurred between 3 or more larvae, and although larval age and experiment duration had significant main effects, there were no interactions between these important factors and gregariousness. For B. amphitrite cyprids significant gregarious effects also occurred with 3 larvae per well, though this effect was strongly dependent upon experiment duration. B. amphitrite cyprid sensitivity to conspecific cues does not change with age, although increasing experiment duration and age interact to increase settlement. Differences between species may be due to different thresholds to conspecific larval cues, or B. improvisus cyprids release much more larval temporary adhesive during exploration.     

Combined effect of cyprid age and lipid content on larval attachment and metamorphosis of Balanus amphitrite darwin

Various algal diets of different lipid content and composition were used to rear batches of naupliar larvae of Balanus amphitrite. The cyprids in these larval batches differed in lipid content and were used to investigate the combined effect of cyprid lipid content and cyprid age on attachment and metamorphosis. For this purpose, cyprids were aged for 0,3 and 6 d at 8°C prior to utilization in laboratory attachment assays. The percentage attachment of cyprids with similar lipid content differed significantly among the three age categories. A strong and a weak positive relationship between cyprid lipid content and attachment were monitored in young and old cyprids, respectively. A significant interaction (two‐way ANOVA) between cyprid age and lipid content was observed, indicating that these factors jointly affect larval attachment and metamorphosis in B. amphitrite from the beginning of the cyprid stage.     

Proteomic analysis of larvae during development, attachment, and metamorphosis in the fouling barnacle, Balanus amphitrite

The barnacle, Balanus amphitrite, is one of the primary model organisms for rocky-shore ecology studies and biofouling research. This barnacle species has a complex life cycle during which the swimming nauplius molts six times and transforms into a cyprid stage. Cyprids must attach to a surface to metamorphose into a juvenile barnacle. To clarify the overall profile of protein expression during larval development and metamorphosis, 2-DE was used to compare the proteome of the nauplius, the swimming cyprid, the attached cyprid, and the metamorphosed cyprid. The proteome of the swimming cyprid was distinctly different from that of other life stages and had about 400 spots. The proteomes of the attached and metamorphosed cyprids were similar with respect to major proteins but had significantly lower numbers of spots compared to that of swimming larval stages. Obviously, synthesis of most proteins from swimming cyprids was switched off after attachment and metamorphosis. Our advanced MS analysis (MALDI-TOF/TOF MS/MS) allowed us to identify the proteins that were differentially and abundantly expressed in the swimming cyprid. These proteins included signal transduction proteins (adenylate cyclase and calmodulin) and juvenile hormone binding proteins. In summary, for the first time, we have analyzed the global protein expression pattern of fouling marine invertebrate larvae during metamorphosis. Our study provides new insights into the mechanisms of barnacle larval metamorphosis and also provides a foundation for exploring novel targets for antifouling treatments.     

Settlement behaviour of marine invertebrate larvae measured by EthoVision 3.0

Submerged marine surfaces are rapidly colonized by fouling organisms. Current research is aimed at finding new, non-toxic, or at least environmentally benign, solutions to this problem. Barnacles are a major target organism for such control as they constitute a key component of the hard fouling community. A range of standard settlement assays is available for screening test compounds against barnacle cypris larvae, but they generally provide little information on mechanism(s) of action. Towards this end, a quick and reliable video-tracking protocol has been developed to study the behaviour of the cypris larvae of the barnacle, Balanus amphitrite, at settlement. EthoVision 3.0 was used to track individual cyprids in 30-mm Petri dishes. Experiments were run to determine the optimal conditions vis-a-vis acclimation time, tracking duration, number of replicates, temperature and lighting. A protocol was arrived at involving a two Petri dish system with backlighting, and tracking over a 5-min period after first acclimating the cyprids to test conditions for 2 min. A minimum of twenty replicates was required to account for individual variability in cyprid behaviour from the same batch of larvae. This methodology should be widely applicable to both fundamental and applied studies of larval settlement and with further refinements, to that of smaller fouling organisms such as microalgae and bacteria.     

Lethal and sub-lethal impacts of pulsed laser irradiations on the larvae of the fouling barnacle Balanus amphitrite

Laboratory experiments were conducted to study the impact of laser irradiation on the larvae of the fouling barnacle Balanus amphitrite. Research pertaining to fouling invertebrate larvae-laser interaction is sparse and, hence, data on this aspect were thought significant in order to consider pulsed low power laser irradiations as a possible future antifouling tool. Lethal and sub-lethal impacts of four very low laser fluences, viz. 0.013, 0.025, 0.05 and 0.1 J cm-2 for three different durations, viz. 2, 10 and 30 s were investigated. Three growth stages of barnacle larvae, viz. nauplii stage II, nauplii stage IV and cyprids were exposed to the mentioned laser fluences for different durations. While lethal impact was assessed immediately after and 1 d after irradiation, sub-lethal impacts were studied by monitoring the success rate of the irradiated nauplii in reaching the cyprid stage. In addition, the swimming speed of VIth stage nauplii after irradiation was studied. In the case of cyprids, in addition to the mortality measurement immediately after and 1 d after irradiation, the settlement rate was investigated. In all the above experiments, non-irradiated larvae served as controls. The results showed an increase in mortality with increasing laser fluence and duration of irradiation. Irradiation for 2 s resulted in significant mortality in nauplii, while it was less in the case of cyprids. In IInd stage nauplii, the mortality immediately after irradiation for 2 s varied from 14.8 +/- 2.12 to 97.1 +/- 4.1% for laser fluences of 0.013 and 0.1 J cm-2, respectively. However, in cyprids, the mortality immediately after irradiation for 2 s varied from 12.2 +/- 3 to 13.4 +/- 1.2% for fluences of 0.013 and 0.1 J cm-2, respectively. The mortality in IVth stage nauplii was less than that for IInd stage nauplii but more than that for cyprids. There was a significant increase in mortality with time after irradiation. The formation of cyprids from the irradiated larvae was significantly less than that observed for non-irradiated larvae. Also, the irradiated larvae showed a significantly slower swimming speed compared to the control samples. The settlement rate in cyprids was reduced significantly by the laser irradiation. This was true even for the lowest fluence and shortest period of irradiation tested. Thus, the results of the experiment showed that even a low power pulsed laser irradiation of 0.013 J cm-2 for 2 s can cause significant damage to fouling barnacle larvae.     

Settlement Behaviour of Marine Invertebrate Larvae Measured by EthoVision 3.0

Submerged marine surfaces are rapidly colonized by fouling organisms. Current research is aimed at finding new, non-toxic, or at least environmentally benign, solutions to this problem. Barnacles are a major target organism for such control as they constitute a key component of the hard fouling community. A range of standard settlement assays is available for screening test compounds against barnacle cypris larvae, but they generally provide little information on mechanism(s) of action. Towards this end, a quick and reliable video-tracking protocol has been developed to study the behaviour of the cypris larvae of the barnacle, Balanus amphitrite, at settlement. EthoVision 3.0 was used to track individual cyprids in 30-mm Petri dishes. Experiments were run to determine the optimal conditions vis-à-vis acclimation time, tracking duration, number of replicates, temperature and lighting. A protocol was arrived at involving a two Petri dish system with backlighting, and tracking over a 5-min period after first acclimating the cyprids to test conditions for 2 min. A minimum of twenty replicates was required to account for individual variability in cyprid behaviour from the same batch of larvae. This methodology should be widely applicable to both fundamental and applied studies of larval settlement and with further refinements, to that of smaller fouling organisms such as microalgae and bacteria.     

Dispersal Patterns,Active Behaviour,and Flow Environment during Early Life History of Coastal Cold Water Fishes

During the pelagic larval phase, fish dispersal may be influenced passively by surface currents or actively determined by swimming behaviour. In situ observations of larval swimming are few given the constraints of field sampling. Active behaviour is therefore often inferred from spatial patterns in the field, laboratory studies, or hydrodynamic theory, but rarely are these approaches considered in concert. Ichthyoplankton survey data collected during 2004 and 2006 from coastal Newfoundland show that changes in spatial heterogeneity for multiple species do not conform to predictions based on passive transport. We evaluated the interaction of individual larvae with their environment by calculating Reynolds number as a function of ontogeny. Typically, larvae hatch into a viscous environment in which swimming is inefficient, and later grow into more efficient intermediate and inertial swimming environments. Swimming is therefore closely related to length, not only because of swimming capacity but also in how larvae experience viscosity. Six of eight species sampled demonstrated consistent changes in spatial patchiness and concomitant increases in spatial heterogeneity as they transitioned into more favourable hydrodynamic swimming environments, suggesting an active behavioural element to dispersal. We propose the tandem assessment of spatial heterogeneity and hydrodynamic environment as a potential approach to understand and predict the onset of ecologically significant swimming behaviour of larval fishes in the field.     

How whale and dolphin barnacles attach to their hosts and the paradox of remarkably versatile attachment structures in cypris larvae

How larvae of whale and dolphin epibionts settle on their fast-swimming and migrating hosts is a puzzling question in zoology. We successfully reared the larvae of the whale and dolphin barnacle Xenobalanus globicipitis to the cyprid stage. We studied the larval developmental ecology and antennular morphology in an attempt to assess whether an epibiotic lifestyle on this extreme substratum entails any unique larval specializations. Morphological parameters were compared with five other barnacle species that also inhabit extreme substrata. We found no larval specializations to a lifestyle associated with marine mammals. The external morphology of the antennules in Xenobalanus cyprids is morphologically similar to species from strikingly different substrata. We found variation only in the structures that are in physical contact with the substratum, i.e., the third segments carrying the villi-covered attachment disc. The third segments of the Xenobalanus cyprid antennules are not spear-shaped as in the stony coral barnacles, which are here used to penetrate the live tissue of their hosts. The presence of a cyprid cement gland implies that Xenobalanus uses cement protein when attaching to its cetacean host. Naupliar instars developed outside of the mantle cavity, indicating dispersal is planktonic. Our results militate against the idea that the cyprids settle during ocean migrations of their hosts. We suggest cyprids settle during coastal aggregations of the cetacean hosts. We conclude that the ecological success of barnacles has ultimately depended on a larva that with little structural alteration possesses the ability to settle on an amazingly wide array of substrata, including cetaceans.

     

Can bivalve veligers escape feeding currents of adult bivalves?

While the stock of introduced Pacific oysters (Crassostrea gigas) increased in the Oosterschelde estuary (SW Netherlands), so did the filtration pressure of all bivalve species together. In the same period, stocks of native bivalves declined slightly. The expansion of Pacific oysters in Dutch estuaries might be partially due to better abilities of their larvae to avoid or escape filtration, compared to larvae of native bivalves. In this context, escape and swimming abilities of Pacific oyster larvae and the larvae of the native blue mussel (Mytilus edulis) were compared.Swimming behaviour of C. gigas larvae and larvae of M. edulis was recorded in still water and in a suction current mimicking a bivalve feeding current, in a horizontal and in a vertical plane. Larval swimming behaviour in a suction flow field was reconstructed by subtracting local water movement vectors from the total movement of larvae, yielding movement paths due to larval swimming alone.Swimming speeds and the rate of displacement in vertical direction of C. gigas and M. edulis larvae were related to larval shell length, and to the pitch of up- or downward swimming.Larvae of both species did not show escape reactions in a suction flow field. With increasing shell length, larval swimming speeds of both species increased significantly. Swimming speeds of C. gigas larvae were significantly higher than swimming speeds of M. edulis larvae, resulting in a faster vertical displacement. The ability to migrate to more favourable water layers faster may offer C. gigas an advantage over native bivalves with slower swimming larvae.     

Schwimmverhalten und Schwimmgeschwindigkeit bei den Larven des HeringsClupea harengus

The present study is based on two year experiments; it analyses swimming behaviour and swimming speed at different developmental stages of the herring. Yolk sac larvae tend to sink rather rapidly during resting phases. At the end of the yolk sac stage the sinking rate is at its minimum; it increases again with increasing larva size. During the phase of yolk sac resorption, vertical movements become gradually transformed into horizontal ones. Generally, three types of swimming can be distinguished: (1) “Abrupt swimming” consisting of very short periods of fast swimming; normally each dart is connected with a change in swimming direction. (2) “Normal swimming” characterized by steady movements for several seconds; it results in a winding path. (3) “Slow meandering” representing search swimming, a slowly winding locomotion with a large amplitude of each winding but with very little net progression of the larva. Swimming speed varies considerably in all size groups. The 8 to 11 mm (total length) larvae reach a mean swimming velocity (undulation) of 1.0 to 1.2 cm per second. Swimming speed, measured as the straight line distance between start and end points of a single swimming phase, attains mean values of 7 to 8 mm/sec in 8 to 11 mm larvae, 10 to 11 mm/sec in 11 to 15 mm larvae, 21 to 25 mm/sec in 19 to 24 mm larvae, and 40 to 50 mm/sec in 32 to 40 mm larvae. Swimming activity changes during larval development and seems to be influenced by food supply. The total distance travelled in 5 minutes by the head of a yolk sac larva is 1 to 3 m. About 8 days after hatching, sinking rate is low and “search swimming” (slow meandering movements) prevails. The path covered by the head within 5 minutes is 0.8 to 1.5 m.     

Roles of larval supply and behavior in determining settlement of barnacles in a temperate mangrove forest

Recruitment is often a major influence on the spatial distribution of populations of benthic marine invertebrates, but the contributions of different components of recruitment are not well known, with the added complication that the relative importance of various life-history processes may be scale-dependent. Previously, we have shown that over a large scale across a mangrove (Avicennia marina) forest in southeastern Australia, settlement of the barnacle Elminius covertus explained its patterns of recruitment, which in turn explained the distribution of adults on mangrove pneumatophores. Post-settlement mortality had little influence on this pattern. In contrast, small-scale vertical distributions of adult barnacles along individual pneumatophores were determined by the pattern of recruitment, which differed from the pattern of settlement, so post-settlement mortality determined the vertical patterns of adults.

In this study, we tested whether larval supply and/or settlement behavior influence the observed settlement patterns of E. covertus across a forest (from seaward to landward zones). We also tested whether larval supply could explain the vertical settlement patterns along the pneumatophores. A pumping system was used to collect cypris larvae from seaward, mid and landward zones of a mangrove forest and an adjacent, unvegetated shore and from three heights above the sediment surface. We also used transplantation of wooden stakes bearing microbial films and barnacle recruits between horizontal zones of the forest to determine whether settlement was influenced by these films or recruits.

Both cyprid supply and cyprid behavior were important factors in determining the patterns of settlement of E. covertus across the forest. Cyprid supply was a result of three-fold differences in immersion times of different (landward, mid and seaward) zones across the forest and a decrease in density of cyprids in the water column from the seaward zone of the forest to the landward sections. In the absence of mangroves immediately adjacent to the forest, there was no temporally consistent difference in cyprid density across the shore and even the differences in immersion time did not produce consistent differences in cyprid supply across the shore. Wooden substrata that had been immersed at seaward sections of the forest attracted consistently more settlers than substrata immersed initially at other sections of the forest and settlement could be induced beyond the normal distribution of adults of E. covertus by stakes transplanted from the seaward zone.

The vertical settlement pattern could not be explained by the supply of cyprids, suggesting that larval behavior must determine the vertical settlement pattern.     

Cypris larvae of acrothoracican barnacles (Thecostraca: Cirripedia: Acrothoracica)

We used SEM to investigate the morphology of the cypris larvae from a range of species of the Cirripedia Acrothoracica, representing all three families and including the first detailed account of cyprids in the highly specialized Cryptophialidae. Special attention was given to the head shield (carapace), the lattice organs, the antennules, the thoracopods, the telson and the furcal rami. The cypris larvae of the Acrothoracica fall into two morphological groups; those of the Trypetesidae and Lithoglyptidae have a well-developed carapace (head shield) that can completely enclose the body and sports fronto-lateral pores, numerous short setae and lattice organs perforated by numerous small, rounded pores and a single, conspicuous terminal pore. The fourth antennular segment has the setae arranged in subterminal and terminal groups. There is a developed thorax with natatory thoracopods and a distinct abdomen and telson. In comparison, the cyprids of the Cryptophialidae exhibit apomorphies in the morphology of the carapace, the antennules and the thorax, mostly in the form of simplifications and reductions. They have a much smaller head shield, leaving parts of the body directly exposed. The shield is conspicuously ornamented by deep pits and hexagonally arranged ridges and bears a few, very long setae but lacks fronto-lateral pores. The lattice organs have numerous elongated pores, but no large, terminal pore. The fourth antennular segment has all the setae clustered in one terminal group. The thorax and thoracopods are rudimentary and not suitable for swimming. These reductions and simplifications in morphology correlate with cryptophialid cyprids being unable to swim. They can only disperse by antennular walking resulting in small, but highly gregarious populations of adults. The variations in antennular morphology and telson structure were traced for the genera of the families Lithoglyptidae and Trypetesidae. The traditional non-cladistic taxonomy in the suborders Pygophora (Cryptophialidae+Lithoglyptidae) and Apygophora (Trypetesidae) was based largely on symplesiomorphies in adult morphology and cannot be upheld. The Lithoglyptidae and Trypetesidae may form a monophylum, but evidence remains scarce. We expect that the use of larval (cyprid) characters will in the future play an important part in more detailed phylogenetic analyses of the Acrothoracica and also shed new light on their reproductive ecology.     

Effect of ultrasound on cyprids and juvenile barnacles

Settlement inhibition of barnacle (Amphibalanus amphitrite) cypris larvae resulting from exposure to ultrasound was measured at three frequencies (23, 63, and 102 kHz), applied at three acoustic pressure levels (9, 15, and 22 kPa) for exposure times of 30, 150, and 300?s. The lowest settlement was observed for 23?kHz, which also induced the highest cyprid mortality. Cyprid settlement following exposure to 23?kHz at 22?kPa for 30?s was reduced by a factor of two. Observing surface exploration by the cyprids revealed an altered behaviour following exposure to ultrasound: step length was increased, while step duration, walking pace, and the fraction of cyprids exploring the surface were significantly reduced with respect to control cyprids. The basal area of juvenile barnacles, metamorphosed from ultrasound-treated cyprids was initially smaller than unexposed individuals, but normalised over two weeks' growth. Thus, ultrasound exposure effectively reduced cyprid settlement, yet metamorphosed barnacles grew normally.     

Lethal and sub‐lethal impacts of pulsed laser irradiations on the larvae of the fouling barnacle Balanus amphitrite

Laboratory experiments were conducted to study the impact of laser irradiation on the larvae of the fouling barnacle Balanus amphitrite. Research pertaining to fouling invertebrate larvae‐laser interaction is sparse and, hence, data on this aspect were thought significant in order to consider pulsed low power laser irradiations as a possible future antifouling tool. Lethal and sub‐lethal impacts of four very low laser fluences, viz. 0.013, 0.025, 0.05 and 0.1 J cm^‐2 for three different durations, viz. 2, 10 and 30 s were investigated. Three growth stages of barnacle larvae, viz. nauplii stage II, nauplii stage IV and cyprids were exposed to the mentioned laser fluences for different durations. While lethal impact was assessed immediately after and 1 d after irradiation, sub‐lethal impacts were studied by monitoring the success rate of the irradiated nauplii in reaching the cyprid stage. In addition, the swimming speed of VI^th stage nauplii after irradiation was studied. In the case of cyprids, in addition to the mortality measurement immediately after and 1 d after irradiation, the settlement rate was investigated. In all the above experiments, non‐irradiated larvae served as controls. The results showed an increase in mortality with increasing laser fluence and duration of irradiation. Irradiation for 2 s resulted in significant mortality in nauplii, while it was less in the case of cyprids. In II^nd stage nauplii, the mortality immediately after irradiation for 2 s varied from 14.8±2.12 to 97.1±4.1% for laser fluences of 0.013 and 0.1 J cm^‐2, respectively. However, in cyprids, the mortality immediately after irradiation for 2 s varied from 12.2±3 to 13.4±1.2% for fluences of 0.013 and 0.1 J cm^‐2, respectively. The mortality in IV^th stage nauplii was less than that for II^nd stage nauplii but more than that for cyprids. There was a significant increase in mortality with time after irradiation. The formation of cyprids from the irradiated larvae was significantly less than that observed for non‐irradiated larvae. Also, the irradiated larvae showed a significantly slower swimming speed compared to the control samples. The settlement rate in cyprids was reduced significantly by the laser irradiation. This was true even for the lowest fluence and shortest period of irradiation tested. Thus, the results of the experiment showed that even a low power pulsed laser irradiation of 0.013 J cm^‐2 for 2 s can cause significant damage to fouling barnacle larvae.     

Spatial variation in larval concentrations as a cause of spatial variation in settlement for the barnacle,Balanus glandula

Summary Settlement rates of the high intertidal barnacle, Balanus glandula, were monitored at three sites in the rocky intertidal zone in Central California simultaneously with measurements of larval concentrations in the adjacent water column. In both 1983 and 1984, settlement rates onto vacant substrate differed among the sites by nearly two orders of magnitude. For all sampling dates, this spatial variation in settlement mirrored the spatial distribution of Balanus glandula cyprid concentration in the water column. A perfect rank correlation was found between cyprid concentrations near a site and subsequent settlement. A noteworthy observation was that the sites switched rank in their settlement rates from 1983 to 1984. This change in settlement rankings matched a switch in rankings for cyprid concentrations.Settlement itself appears to be an important cause of the spatial pattern of cyprid concentrations. Comparing the rates of settlement to estimates of the number of cyprids available at a site suggests that settlement causes a large drain on the cyprid population as a water mass passes over successive sites. No consistent spatial patterns were found in the distribution of other major plankton groups (calanoid copepods) that are similar in size to Balanus cyprids but do not settle.The large differences in settlement rates among these sites were previously shown to be a leading cause of large differences in the structure of benthic barnacle populations. The close correspondence shown here between these large differences in settlement and differences in larval concentrations suggests that nearshore oceanic processes affecting larval arrival contribute to the control of benthic community structure.     

Effect of ultrasound on cyprids and juvenile barnacles

Settlement inhibition of barnacle (Amphibalanus amphitrite) cypris larvae resulting from exposure to ultrasound was measured at three frequencies (23, 63, and 102 kHz), applied at three acoustic pressure levels (9, 15, and 22 kPa) for exposure times of 30, 150, and 300 s. The lowest settlement was observed for 23 kHz, which also induced the highest cyprid mortality. Cyprid settlement following exposure to 23 kHz at 22 kPa for 30 s was reduced by a factor of two. Observing surface exploration by the cyprids revealed an altered behaviour following exposure to ultrasound: step length was increased, while step duration, walking pace, and the fraction of cyprids exploring the surface were significantly reduced with respect to control cyprids. The basal area of juvenile barnacles, metamorphosed from ultrasound-treated cyprids was initially smaller than unexposed individuals, but normalised over two weeks' growth. Thus, ultrasound exposure effectively reduced cyprid settlement, yet metamorphosed barnacles grew normally.     

Relationship between swimming capacities and morphological traits of fish larvae at settlement stage: a study of several coastal Mediterranean species

Experimental measurements were made in the laboratory to determine the swimming capacities of settlement-stage fish larvae of several Mediterranean coastal species collected from the nearshore waters of Corsica, France. Critical swimming speed (U_crit, cm s⁻¹) was measured to provide a realistic laboratory estimate of in situ swimming speed. Morphometric traits were measured to assess potential predictors of a species’ swimming ability and, when possible, daily otolith increments were used to estimate age. Observed swimming speeds were consistent with other temperate species and demonstrated that the tested species are competent swimmers and not passive components of their environment. Morphological traits varied in their correlation with U_crit across groups and species. Direct measurements of morphological traits were better predictors than calculated ratios. Pelagic larval duration had little relationship with swimming speed among species for which daily otolith increments were counted. In addition to expanding the database on swimming capacities of settlement-stage fish larvae in the Mediterranean Sea, this study also developed methods that simplify the assessment of larval fish swimming ability. Swimming speed data are essential for improving larval dispersal models and for predicting recruitment rates in coastal fish populations.     

When similar beginnings lead to different ends: Constraints and diversity in cirripede larval development

Summary

Cirripedes are fascinating models for studying both functional constraints and diversity in larval development. Adult cirripedes display an amazing variation in morphology from sessile suspension feeders that still retain many crustacean characters to parasites that have lost virtually all arthropod traits. In contrast, cirripede larval development follows a common scheme with pelagic larvae comprising a series of nauplii followed by a cyprid. Variations are mostly concerned with whether or not the nauplii are feeding and the degree of abbreviation of development, culminating in species where the larvae hatch as cyprids. The cypris larvae are very similar among the ingroups of the Cirripedia, but interesting variations occur in structures used for substrate location and attachment. The cyprid is specialized to both swim through the water and actively explore the substratum by walking on the antennules and using an array of sensory organs in search for a suitable site to attach. This unique morphology and behavior of the cyprid have enabled the Cirripedia to colonize widely different habitats ranging from hard rock to soft animal tissue. Yet, the cyprid can metamorphose into juveniles as different as a setose feeding barnacle and the vermiform stages of the parasitic forms. This emphasizes the importance of the cyprid as one of the key features for the evolutionary success of the Cirripedia.     

Consistent spatial patterns of arrival of larvae of the honeycomb barnacle Chamaesipho tasmanica Foster and Anderson in New South Wales

The small honeycomb barnacle Chamaesipho tasmanica occurs in patches at high levels on exposed rocky shores, but often carpets the substratum at mid-shore levels of sheltered shores in south-eastern Australia. Studies of larval supply from 1990 to 1993 and concurrent monitoring of settlement from 1991 to 1993 revealed that larval arrival and settlement were typified by trickles of larvae from late July to December (although some were observed in January and February). Major pulses of arriving cyprids were also recorded once or twice each year. While local patterns of water-flow had no impact on numbers of larvae arriving, major peaks of larval arrival were always associated with strong southerly winds during new and full moons. There was a consistent spatial pattern of larval supply; more larvae were always caught in one area low on the shore. Numbers of larvae caught were, however, very sporadic within a given year and very variable from one year to the next. While the different numbers of cyprids in different places cannot be explained by cyprids arriving first on lower parts of the shore, longer periods of submersion nor aggregations of larvae in the plankton, recurrent patterns of arrival of larvae suggest that local site-specific characteristics have an influence on the demography of populations of this species. Variations in numbers of larvae arriving were responsible for the variations in distributions of juveniles on the substratum.     

Comparative swimming abilities of fed and starved larval largemouth bass (Micropterus salmoides)†

Sustained swimming abilities of fed and starved larval largemouth bass (Micropterus salmoides L.) were compared in the first week after swimming initiation. Fed larvae improved to a sustained velocity of 4·0 cm/sec while starved larvae attained a velocity of only 1·5 cm/sec. Swimming behaviour for fed and starved larvae was quantified for number of moves, average distance/move, and total distance for all moves in 1 min intervals. Fed larvae were always more active than starved larvae, although real differences did not appear until the 4th day after swimming initiation.