Marine Invertebrate Larvae Research Articles

Low rates of predation on planktonic marine invertebrate larvae

We conducted in situ observations and experiments to evaluate predation on inverte- brate larvae in near-natural plankton assemblages captured in large-volume in situ corrals. In these captured assemblages, we placed known numbers of marked larvae and determined their fate after 24 h. Recovery of marked larvae averaged 99% (±0.25%, SE), enabling a thorough and direct deter- mination of predators and predation rates. The highest predation rate observed was on bivalve veligers by the heterotrophic dinoflagellate Noctiluca scintillans (7% lost in 24 h). Gastropod veligers experienced no predation and echinoplutei experienced only rare predation. While N. scintillans preyed on bivalve veligers in some runs, most runs yielded little or no predation. These observations suggest that larvae can encounter relatively safe assemblages. To investigate low predation, corral experiments were conducted which presented prey at near-natural and unnaturally high densities and in the presence or absence of natural background plankton. Predation observed at high prey densities decreased or disappeared at near-natural prey densities. This suggests that low encounter rates may explain some of the low predation. Predation rates also decreased in the presence of nat- ural background plankton. Background plankton may occupy the predator's time and decrease opportunities for encounters with larvae, obscure larvae from detection or capture, or serve as sub- stitute food. Since predation was usually low or absent in diverse corral assemblages, we recommend confirming natural relationships and predation rates for suspected predator-prey combinations before making assumptions about predator effects. It may frequently be the case that planktonic larvae suffer little or no predation by planktonic predators.

Effects of settler size and density on early post-settlement survival of Ciona intestinalis in the field

Effects of variation in larval quality on post-metamorphic performance in marine invertebrates are increasingly apparent. Recently, it has been shown that variation in offspring size can also strongly affect post-settlement survival, but variation in environmental conditions can mediate this effect. The quality of habitat into which marine invertebrate larvae settle can vary markedly, and 1 influence on quality is the number of conspecifics present. We tested the effects of settler size and settler density on early (1 wk after settlement) post-settlement survival in the field for the solitary ascidian Ciona intestinalis. Larger settlers survived better than smaller settlers, within and among groups of siblings. Increases in the density of settlers decreased survival, but the density-dependent effects were much stronger for smaller settlers. We suggest that larger settlers are better able to cope with intra-specific competition because they have greater energetic reserves or a greater capacity to feed than smaller settlers.

Variation in the dispersal potential of non-feeding invertebrate larvae: the desperate larva hypothesis and larval size

For many species of marine invertebrates, variability in larval settlement behaviour appears to be the rule rather than the exception. This variability has the potential to affect larval dispersal, because settlement behaviour will influence the length of time larvae are in the plankton. Despite the ubiquity and importance of this variability, relatively few sources of variation in larval settlement behaviour have been identified. One important factor that can affect larval settlement behaviour is the nutritional state of larvae. Non-feeding larvae often become less discriminating in their 'choice' of settlement substrate, i.e. more desperate to settle, when energetic reserves run low. We tested whether variation in larval size (and presumably in nutritional reserves) also affects the settlement behaviour of 3 species of colonial marine invertebrate larvae, the bryozoans Bugula ner- itina and Watersipora subtorquata and the ascidian Diplosoma listerianum. For all 3 species, larger larvae delayed settlement for longer in the absence of settlement cues, and settlement of Bugula ner- itina larvae was accelerated by the presence of settlement cues, independently of larval size. In the field, larger W. subtorquata larvae also took longer to settle than smaller larvae and were more dis- criminating towards settlement surfaces. These differences in settlement time are likely to result in differences in the distance that larvae disperse in the field. We suggest that species that produce non- feeding larvae can affect the dispersal potential of their offspring by manipulating larval size and thus larval desperation.

The kinematics of phototaxis in larvae of the ascidian Aplidium constellatum

Although phototaxis has an important influence on the vertical distribution and settlement of marine invertebrate larvae, few studies have explored the mechanisms of taxis in larvae at the organismal level. We examined how phototaxis changes over ontogeny in larvae of the ascidian Aplidium constellatum and experimentally tested hypotheses about the kinematics of oriented swimming. By video recording their swimming movements at regular intervals over their ontogeny, we found that larvae switched from positive to negative phototaxis. We tested hypotheses about the kinematics of phototaxis by recording the three-dimensional movement of larvae in response to a change in the direction of illumination and by tracking the tail motion of tethered larvae in response to sinusoidal changes in light intensity. Larvae swimming with negative phototaxis changed their rate of rotation about their antero-posterior and dorso-ventral axes in response to a change in the direction of illumination. These changes in the rates of rotation caused the axis of the helical trajectory to orient away from the light source. Tethered larvae oscillated their tails at a constant tail beat frequency and with a slow periodicity that was correlated with the stimulus frequency. These findings suggest that ascidian larvae orient by changing tail motion in proportion to perceived changes in light intensity. This method of orientation predicts that larvae achieve the switch from positive to negative phototaxis by changing the delay of their kinematic response to changes in perceived light intensity.

Chemical defense in ascidians of the didemnidae family.

Fluorescent analogues (DB1 and TA1) of the secondary metabolites didemnin B (DB) and tamandarin A (TA) were synthesized to investigate the potential chemical defense mechanisms of tunicates in the family Didemnidae. These compounds were found to alter predator-prey relations. Five species of freshwater fish and one marine fish, the damselfish Amphiprion ocellaris, were acclimated to a diet of mosquito larvae. Fish showed an immediate, negative reaction to mosquito larvae treated with >/=5 ng of DB1 or TA1, with consumption of larvae resulting in regurgitation. Both freshwater and marine fish learned to avoid tainted prey by associating species of larvae with "distaste". Distaste for a given organism also arose when depsipeptides DB1 or TA1 were transferred to the fish from the surrounding medium. Fluorescence microscopy in fish indicated that a similar processing and localization followed ingestion and absorption of DB1 or TA1. Fluorescent labeling of DB or TA provided an ideal tool to conduct short-term studies of predator-prey relationships between fish and marine invertebrate larvae.

Atlas of marine invertebrate larvae

Atlas of marine invertebrate larvae

Temperature responses in larvae of Macoma balthica from a northerly and southerly population of the European distribution range

Planktonic marine invertebrate embryos and larvae experience high mortality rates. Processes during these early vulnerable stages of development are an important determinant of the dynamics of marine invertebrate populations. In order to evaluate possible specific local adaptations of the bivalve Macoma balthica (L.), larvae from parents living in Norway (Balsfjord) and France (Gironde Estuary) were reared in the laboratory at 10, 15 and 20 °C. The rate of growth and the time it took to develop a foot were measured. Larvae grew faster and developed quicker at higher temperatures. This was true for both origins tested. Within temperature treatments, the French larvae always developed and grew fastest. Size at metamorphosis (defined as the appearance of the foot) was 250 μm (SD=12.7) in five out of the six cases; the only exception was Norwegian larvae kept at the highest temperature that metamorphosed at a smaller size (229 μm, SD=6.4). Size at metamorphosis thus appears to be largely independent of temperature. In both populations, instantaneous survival rates declined with temperature with no effect of origin. Instantaneous survival declined faster with temperature than development rates increased, resulting in lower net survival of larvae to metamorphosis at the higher temperatures. Although the French larvae had a shorter development time at the same temperature than the Norwegian larvae, the total survival of larvae from the two origins was not significantly different. The larvae of M. balthica of both populations prove to be tolerant to considerably higher rearing temperatures than they will ever experience in their natural habitat.

Tolerance to biodegraded crude oil in marine invertebrate embryos and larvae is associated with expression of a multixenobiotic resistance transporter

The toxicity of water-soluble fractions of biodegraded crude oil (BWSF) to embryos and larvae of two marine invertebrates, the white sea urchin ( Lytechinus anamesus) and the fat innkeeper ( Urechis caupo), was studied . Santa Barbara Channel crude oil was artificially weathered and subjected to biodegradation using a mixed microbe culture obtained from natural oil seep sites. The degradation culture inoculated with seep sediment microbes accumulated 43.7 μg/l water-soluble hydrocarbons. In contrast water-soluble fractions from the non-degraded cultures (NWSF) only accumulated 3.05 μg/l. BWSF proved deleterious to Lytechinus embryo development at low concentrations (EC50=0.33 mg/l) but was essentially non-toxic to Urechis embryos/larvae up to 3.0 mg/l. An established mechanism for handling of a wide array of xenobiotics in Urechis embryos is the multixenobiotoic resistance transporter multixenobiotic response (MXR, also known as multidrug resistance, MDR). This mechanism is primarily mediated by ATP-dependent, efflux pumps that extrude a wide array of xenobiotic compounds. In this study, we show that Lytechinus larvae do not appear to express MXR efflux protein nor MXR mediated dye efflux capacity. In contrast, BWSF acts as a competitive inhibitor of MXR transport-mediated dye efflux in Urechis larvae. These results suggest that MXR may be an important mechanism for extrusion of the by-products of crude oil degradation by microbes, and that the level of its expression may determine the susceptibility of organisms to degraded oil hydrocarbons.

Timing is everything: the effects of putative dopamine antagonists on metamorphosis vary with larval age and experimental duration in the prosobranch gastropod Crepidula fornicata.

The signal transduction pathway through which excess potassium ion stimulates the larvae of many marine invertebrates to metamorphose is incompletely understood. Recent evidence suggests that dopamine plays important roles in the metamorphic pathway of Crepidula fornicata. Therefore, we asked whether blocking dopamine receptors might prevent excess potassium ion from stimulating metamorphosis in this species. Surprisingly, the effects of the three putative dopamine antagonists tested (all at 10 microM) varied with exposure duration and the age of competent larvae. Chlorpromazine, a nonspecific dopamine antagonist known to have a number of other pharmacological effects, blocked the inductive action of excess potassium ion during the initial 5-8-h exposure periods in most assays, particularly for younger or smaller competent larvae. However, chlorpromazine in the absence of excess potassium ion also stimulated metamorphosis, particularly over the next 18 h, and worked faster on older competent larvae than on younger competent larvae. The specific D(1) antagonist R(+)-Sch-23309 had similar effects, blocking potassium-stimulated metamorphosis in short-term exposures and stimulating metamorphosis in longer exposures, particularly for older competent larvae. Although the specific D(2) antagonist spiperone (SPIP) blocked the inductive effects of excess potassium ion in only 1 of 6 assays during the first 6 h of exposure, it blocked metamorphosis in 2 of the assays during 24-h exposures. Our results indicate that dopamine receptors are involved in the pathway through which excess potassium ion stimulates metamorphosis in C. fornicata. In addition, the largely latent inductive effects of chlorpromazine, an inhibitor of nitric oxide synthase, suggest that endogenous nitric oxide may play a natural role in inhibiting metamorphosis in this species. Overall, our results would then suggest that exposing larvae of C. fornicata to excess K(+) leads to a shutdown of nitric oxide synthesis via a dopaminergic pathway, a pathway that can be blocked by some dopamine antagonists. Alternatively, chlorpromazine might eventually be stimulating metamorphosis by elevating endogenous cyclic nucleotide (e.g., cAMP) concentrations, again acting downstream from the steps acted on directly by excess K(+).

Induction of metamorphosis with KCl in three species of sea urchins and its implications in the production of juveniles

A common practice for inducing metamorphosis in larvae of marine invertebrates is the use of a wide variety of artificial inducers. Excess K+ and Cs+ in seawater have proved to be very effective for this purpose, but not universally effective to induce metamorphosis in different phyla of marine invertebrates. In the present study we tested the response of three species of sea urchins to excess K+ in seawater as an artificial inducer. Excess K+ in seawater was presented to the larvae as continuous (24 h) or pulse exposure in concentrations ranging from 0.01 to 100 mM. Results showed that excess K+ in the form of KCl added to seawater was an effective metamorphic inducer of the three species of sea urchins tested; the purple sea urchin Strongylocentrotus purpuratus, the red sea urchin S. franciscanus and the white sea urchin Lytechinus pictus. The response was dependent on concentration and time of exposure. Continuous exposure (24 h or more) to excess K+ (100 mM) resulted lethal to the larvae of the three species. Excess K+ (100 mM) for 15 min resulted the most effective pulse-period to induce metamorphosis in the three species. This method of induction allows us to produce synchronous metamorphosed postlarvae useful for aquaculture and studies of signal transduction mechanisms during metamorphosis of sea urchins.

Larval Settlement of Corals in Flowing Water using a Racetrack Flume

Although the larvae of marine invertebrates settle in currents, few studies have examined settlement under flow. We studied the settlement of two brooding coral larvae with different behavior in a flow using a small racetrack flume made of polycarbonate and acrylic (58 cm long). Flow was generated using a digitally controlled gear-motor-driven paddle wheel. The settlement rates of the larvae, Heliopora coerulea and Pocillopora damicornis, were observed at three flow speeds: 1.6, 4.4, and 9.8 cm/sec, which correspond to the currents at low, mean, and ebb or flood tides, respectively, at Shiraho Reef flat, Ishigaki Island, Japan. The settlement rate of H. coerulea larvae decreased with increasing flow speed (20% at 1.6 cm/sec, 2% at 9.8 cm/sec). In contrast, the settlement rate of P. damicornis larvae was high at all flow speeds (> 50% at all flow speeds). This difference in the larval settlement rates of the two species is in accordance with the current conditions in which the adult corals are distributed.

Identification and characterization of a putative transcriptional regulator controlling the expression of fouling inhibitors in Pseudoalteromonas tunicata.

The dark green pigmented marine bacterium Pseudoalteromonas tunicata colonizes living surfaces and produces a range of extracellular compounds that inhibit common fouling organisms, including marine invertebrate larvae, algae, bacteria, and fungi. We have observed a positive correlation between the antifouling activity of P. tunicata strain D2 and the expression of pigmentation. To address the hypothesis that pigmentation and antifouling may be jointly regulated in this organism and to begin to identify potential regulatory elements, we used transposon mutagenesis to generate a strain of P. tunicata deficient in antifouling activity. The data presented here describe the phenotypic and molecular characterization of a nonpigmented transposon mutant strain of P. tunicata (D2W2). Analyses of the antifouling capabilities of D2W2 demonstrate that this strain is deficient in the ability to inhibit each of the target fouling organisms. Genetic analysis of D2W2 identified a gene, designated wmpR (white mutant phenotype), with high sequence similarity to transcriptional regulators ToxR from Vibrio cholerae and CadC from Escherichia coli. Two-dimensional polyacrylamide gel electrophoresis analysis revealed that WmpR is essential for the expression of a significant subset of stationary-phase-induced proteins likely to be important for the synthesis of fouling inhibitors. The identification of a gene involved in the regulation of expression of antifouling phenotypes will contribute to the understanding of the interactions between bacteria and other surface-colonizing organisms in the marine environment.

Heat shock induces metamorphosis in the larvae of the prosobranch gastropod Crepidula fornicata

The mechanism through which external cues trigger the metamorphosis of marine invertebrate larvae is incompletely understood. Much of what we currently understand about signal transduction pathways in larval marine invertebrates is based on larval responses to neuroactive compounds, pharmacological agents, and elevated ion concentrations. This paper shows that the larvae of Crepidula fornicata can also be induced to metamorphose through brief exposure to thermal shock. Exposure of larvae to lower temperature regimens (e.g., a shift from 20 °C to 25 °C through 30 °C or from 25 °C to 28 °C or 30 °C) was not effective in inducing metamorphosis. By contrast, a 2-h exposure to 32 °C induced metamorphosis significantly above the control levels regardless of whether the larvae were reared at 20 °C or 25 °C. Thus, the absolute exposure temperature was more important than the magnitude of the temperature increase for inducing metamorphosis. Moreover, the larvae of C. fornicata became responsive to temperature shock several days after they became comparably responsive to a previously documented metamorphic trigger, elevated concentrations of potassium ions. Further exploration of the heat shock metamorphic response may improve our understanding of how the metamorphic pathway develops and works in this species.

Metamorphic Competence, a Major Adaptive Convergence in Marine Invertebrate Larvae

Larvae from diverse marine-invertebrate phyla are able to respond rapidly to environmental cues to settlement and to undergo very rapid metamorphic morphogenesis because they share the developmental trait of metamorphic competence. The competent state, characteristic of larvae as diverse as those of cnidarian planulae, molluscan veligers, and barnacle cyprids, is one in which nearly all requisite juvenile characters are present in the larva prior to settlement. Thus metamorphosis, in response to more or less specific environmental cues (inducers), is mainly restricted to loss of larva-specific structures and physiological processes. Competent larvae of two “model marine invertebrates” studied in the authors' laboratory, the serpulid polychaete Hydroides elegans and the nudibranch Phestilla sibogae, complete metamorphosis in about 12 and 20 hr, respectively. Furthermore, little or no de novo gene action appears to be required during the metamorphic induction process in these species. Contrasting greatly with the slow, hormonally regulated metamorphic transitions of vertebrates and insects, competence and consequent rapid metamorphosis in marine invertebrate larvae are conjectured to have arisen in diverse phylogenetic clades because they allow larvae to continue to swim and feed in the planktonic realm while simultaneously permitting extremely fast morphological transition from larval locomotory and feeding modes to a different set of such modes that are adaptive to life on the sea bottom.

Metamorphic Competence, a Major Adaptive Convergence in Marine Invertebrate Larvae1

Larvae from diverse marine-invertebrate phyla are able to respond rapidly to environmental cues to settlement and to undergo very rapid metamorphic morphogenesis because they share the developmental trait of metamorphic competence. The competent state, characteristic of larvae as diverse as those of cnidarian planulae, molluscan veligers, and barnacle cyprids, is one in which nearly all requisite juvenile characters are present in the larva prior to settlement. Thus metamorphosis, in response to more or less specific environmental cues (inducers), is mainly restricted to loss of larva-specific structures and physiological processes. Competent larvae of two “model marine invertebrates” studied in the authors' laboratory, the serpulid polychaete Hydroides elegans and the nudibranch Phestilla sibogae, complete metamorphosis in about 12 and 20 hr, respectively. Furthermore, little or no de novo gene action appears to be required during the metamorphic induction process in these species. Contrasting greatly with the slow, hormonally regulated metamorphic transitions of vertebrates and insects, competence and consequent rapid metamorphosis in marine invertebrate larvae are conjectured to have arisen in diverse phylogenetic clades because they allow larvae to continue to swim and feed in the planktonic realm while simultaneously permitting extremely fast morphological transition from larval locomotory and feeding modes to a different set of such modes that are adaptive to life on the sea bottom.

Tornaria of hemichordates and other dipleurula‐type larvae: a comparison*

The evolutionary origin of phylum Chordata is the subject of intensive discussion, with the most conflicting views prevalent. One popular theory advocates the separation of chordates from a dipleurula-like ancestor. Thus the dipleurula-type larvae (tornaria of enteropneusts, auricularia and bipinnaria of echinoderms) are considered to recapitulate the ancestral features and the direct evolutionary path from Echinodermata and Hemichordata to Chordata (i.e. Garstang 1894 Zool. Anzeiger 27, 122–125; Grobben 1908 Verh. Zool.-Bot. Ges. Wien 58, 491–511; Dillon 1965 Evolution 19, 436–446; Jollie 1973 Acta Zool. (Stockholm) 54, 81–100; Ivanova-Kazas and Ivanov 1987 Sov. J. Mar. Biol. 13, 67–80; Crowther and Whittaker 1992 J. Neurophysiol. 23, 280–292; Lacalli 1994 Am. Zool. 34, 533–541; Lacalli et al. 1999 Proc. R. Soc. Biol. Series B 266, 1461–1470; Nielsen 1999 Dev. Genes Evol. 209, 198–205). Comparison of the nervous system in enteropneust tornariae and echinoderm larvae has revealed however, striking differences in distribution of biogenic amines and cholinesterase activity. In tornariae, monoamine-containing cells concentrate in the aboral and oesophageal ganglia. In echinoderms, they are located along the ciliary bands throughout their length. The difference in distribution of cholinesterase activity in each group reasonably suggests that acetylcholine-dependent control of locomotion also differs. Our data do not support the homology of the dipleurula-type larvae. Therefore we believe in the course of adaptive evolution, larvae of certain marine invertebrates acquired a set of common morphological and behavioural characteristics, yet retained different physiological mechanisms of behavioural regulation. Thus, similarities in the dipleurula-type larvae (tornaria, auricularia or bipinnaria, and actinotrocha) may have originated from convergence rather then from a common dipleurula-type predecessor. In consequence we must call into question any attempt to trace the ancestors of Chordata to the dipleurula-type animal.

Evaluating whether velar lobe size indicates food limitation among larvae of the marine gastropod Crepidula fornicata.

Disproportionately large feeding structures have been used to infer food limitation in some marine invertebrate larvae, but few studies have investigated whether other factors alter larval morphology in similar ways. In this study, larvae of Crepidula fornicata were reared either at five different food concentrations of Isochrysis galbana (clone T-ISO) at a single temperature (22 degrees C) (Experiments I and II); or on three different phytoplankton species (Isochrysis galbana, Dunaliella tertiolecta, and Pavlova lutheri) at both high and low concentrations at a single temperature (22 degrees C) (Experiment III); or at high and low concentrations of Isochrysis galbana at four different temperatures between 16 and 25 degrees C (Experiment IV). Shell lengths and velar lobe dimensions were determined for individual larvae at intervals to monitor relative rates of velar and shell growth. In addition (Experiment V), fast growing and slow growing larvae in Experiment I were examined separately to determine whether velar lobes developed at similar rates (relative to shell growth) for fast and slow growing larvae within individual cultures. In general, velar lobes grew significantly larger, relative to shell length, when larvae were reared at low food concentrations (P<0.0001); for larvae of similar shell length, the velar lobes of those fed 1x10(4) cells ml(-1) were on average 17.7% larger than those of larvae fed 18x10(4) cells ml(-1) of T-ISO. In contrast, larvae fed different phytoplankton species at equivalently high food concentrations did not differ in relative velum size (P=0.2666), even though shell growth rates differed significantly for larvae raised on the different diets, indicating substantial variation in food quality. We also found that relative rates of velum and shell growth differed among fast and slow growing individuals within treatments. Temperature had no significant effect on relative rates of velar and shell growth within the 16-25 degrees C range tested (P=0.121), but may have altered the relationship between food concentration and relative velar growth. These results indicate that dramatically reduced food concentration induces disproportionate growth in the velar lobes of C. fornicata, but that interpretation of data from field-collected individuals of this species will be made difficult by the potentially confounding effects of temperature, food quality, and differences in individual growth potential. Assessments of food limitation using morphological measurements for field-collected larvae will need to be supplemented with other indicators before convincing conclusions about the extent of food limitation in C. fornicata can be drawn.

Optimal Egg Size in Marine Invertebrates: Theory and Phylogenetic Analysis of the Critical Relationship between Egg Size and Development Time in Echinoids.

Life-history models for marine invertebrate larvae generally predict a dichotomy in egg size in different species: eggs should be either minimal in size or large enough to support development fully without larval feeding. This prediction is contradicted, however, by the empirical observation of wide, continuous variation in egg size between these extremes. The prediction of dichotomy rests on the assumption of a negative linear relationship between egg size and development time. Here, I present a simple model in which development time is inversely proportional to egg size. Incorporating this relationship into an optimality model produces predictions of intermediate rather than extreme egg size. Modeled variations in mortality, food availability, fertilization rates, and temperature all produce continuous shifts in the value of the intermediate optimal size, in direct contrast to those produced by previous models, which predict shifts between two extreme optima. Empirical data on echinoid egg size and development time strongly support the model's assumption of an inverse proportional relationship between egg size and development time. A composite phylogeny is constructed of the 37 species for which egg size, development time, water temperature, and phylogenetic relatedness are known. Independent contrasts are made of the evolutionary changes in egg size and development time. This analysis indicates that evolutionary shifts in development time are correlated with the inversely proportional shifts in egg size assumed in the model. The assumption of a negative linear relationship used in previous models is rejected. This model provides a potential explanation for intraspecific variation in egg size along environmental gradients, sympatric differences in egg size among species, and biogeographic trends in egg size and development mode across taxa.

Development and application of elemental fingerprinting to track the dispersal of marine invertebrate larvae

The early life history of many marine benthic invertebrate and fish species involves a planktonic larval stage that allows exchange of individuals among separated adult populations. Here, we demonstrate how natural and anthropogenic trace elements can be used to determine larval origins and assess bay‐ocean exchange of invertebrate larvae. Trace elements can be effective site markers for estuaries because run‐off and pollutant loading often impart distinct elemental signatures to bay habitats relative to nearshore coastal environments. Crab larvae originating from San Diego Bay (SDB) were distinguished from those originating in neighboring embayments and exposed coastal habitats by comparing multiple trace‐element concentrations (“fingerprint”) in individuals. Discriminant function analysis (DFA) was used to characterize stage I zoeae of the striped shore crab, Pachygrapsus crassipes, of known origin (reference larvae) via trace‐elemental composition (i.e., Cu, Zn, Mn, Sr, Ca). Linear discriminant functions were used to identify the origin and characterize the exchange of stage I P. crassipes zoeae between SDB and the nearshore coastal environment during one spring tidal cycle. Elemental fingerprinting revealed that most (87%) of the stage I larvae collected at the bay entrance during the flood tide were larvae of SDB origin that were reentering the bay. Nearly one third of zoeae sampled (32%) at the entrance during ebb tide were coastal larvae leaving the bay and returning to open water. The observed bidirectional exchange contrasts with the unidirectional transport of zoeae out of the bay predicted from stage I vertical migratory behavior. Because P. crassipes zoeal survivorship is lower in SDB than in coastal waters, bay‐ocean exchange has significant implications for the dynamics of P. crassipes populations. Trace‐elemental fingerprinting of invertebrate larvae promises to facilitate investigations of many previously intractable questions about larval transport and dynamics.

Nature and perception of barnacle settlement pheromones

It is now almost 50 years since the gregarious settlement of barnacles and its chemical basis was first described. Although originally noted for Elminius modestus, mechanistic studies of gregariousness have focused on two species, Semibalanus balanoides and Balanus amphitrite. By virtue of its ease of study and its economic importance as a fouling organism, the latter species has assumed increasing importance in recent years. This paper will provide an overview of studies on settlement pheromones and their perception. An adult glycoprotein, arthropodin (now known as settlement‐inducing protein complex or SIPC), was once thought to be the sole pheromone involved in the induction of cypris larval settlement. At least two other pheromones are now known to be involved, a waterborne cue originating from the adult and the cypris temporary adhesive. The latter is related, immunologically, to SIPC. In keeping with many other examples of chemical communication, the available evidence suggests that barnacle settlement induction involves receptor‐ligand interactions and a signal transduction pathway(s) that translates into attachment and metamorphosis. Similar findings have been reported for some, but not all, marine invertebrate larvae examined thus far and the implications for antifoulant development are discussed.