Marine Invertebrate Larvae Research Articles

Effect of Benthic Microhabitat Cues on the Metamorphosis of Pueruli of the Spiny Lobster Panulirus Argus

To determine whether settlement microhabitat induces metamorphosis in the puerulus stage of the Caribbean spiny lobster (Panulirus argus) and to identify the specific features of the habitat that might elicit the response, we monitored the metamorphic progress of more than 200 pueruli exposed to 6 different settlement substrates: sea water alone (no substrate), red algae, sea grass, artificial algae, algae-treated sea water, and artificial algae plus algae-treated sea water. Initial pigmentation followed settlement by approximately 1 day and began 3-6 days (mean = 5 days) after the swimming pueruli were intercepted entering the Florida Bay nursery. Presence of red algae, Laurencia spp., a preferred settlement substrate, accelerated the rate of pigmentation, but by < 1 day. Metamorphosis to the first benthic juvenile stage occurred 7-9 days (mean = 8 days) after pueruli entered the bay and was unaffected by any of the substrates tested. Rates of both pigmentation and metamorphosis varied by as much as 2 days among replicate experiments conducted during the summers of 1986-1988. These results suggest that metamorphosis of pueruli of P. argus is essentially determinant; thus, physiological constraints may limit the distance that pueruli can disperse into the nursery and may force many pueruli to settle in inappropriate habitats where survival is improbable. Settlement and metamorphosis of planktonic larvae of many marine invertebrates can be induced by physical or chemical cues associated with settlement habitat (see Chia and Rice, 1978; Burke, 1983, for reviews). Specific environmental cues are thought to stimulate neural or hormonal processes that trigger larval settlement and metamorphosis in habitats that offer greater survival for subsequent life stages (Burke, 1983). Larvae that can retard development until favorable conditions are encountered are capable of increased dispersal, which is a function of both transport processes and length of larval life (Sulkin and Van Heukelem, 1986). Such physiological plasticity in the onset of metamorphosis may be a desirable trait for widely dispersing larvae or larvae with ecological requirements that differ from adults, because the probability of encountering suitable settlement habitat within a specific locality or period of time may be low. Alternatively, marine animals living in regions where currents are seasonally predictable and can reliably transport larvae to appropriate nursery grounds may evolve more canalized larval development with physiologically constrained metamorphic rates (Lipcius et al., 1990). For-sessile or sedentary invertebrates (e.g., hydroids, ascidians, echinoids, molluscs, barnacles), on which most research on this topic has focused, selection of a settlement site ultimately reflects the habitat requirements of the adult stage (Meadows and Campbell, 1972; Highsmith, 1982; Morse et al., 1988; and many ot ers). But for invertebrates such as decapod crustaceans, with more complex life cycles and mobile adult s ages, habitat choice by larvae or postlarvae should be influenced by factors that affect juvenile survival, factors that may be unrelated to adult habitat requirements. Despite their widespread abundance and distribution in the marine environment, little information is available concerning metam rphic induction in decapod crustaceans (Felder et al., 1985). Induction or inhibition of metamorphosis from the larval or puerulus stage to he first benthic stage in resp nse to the presence/absence of natural substrates has been recorded for a brachyuran crab (Castro, 1978), a homarid lobster (Botero and Atema, 1982), and a palinurid lobster (Serfling and Ford, 1975). The absence of metamorphic induction for a pagurid crab was reported by Roberts (1971). In contrast to observations made by Serfling and Ford (1975), who reported that the pueruli of the California spiny lobster Panulirus interruptus apparently required surf

Characteristic bacteria associated with surfaces of coralline algae: a hypothesis for bacterial induction of marine invertebrate larvae

Crustose coralline algae (CCA) induce high rates of settlement and metamorphosis in a diversity of marine invertebrate larvae. It is often assumed that inducers associated with CCA are algal in origin, but an alternative hypothesis is that they originate from bacteria on the algal surface. Because many species manifest specificity in settling on CCA, a necessary condition of the hypothesis of bacterial origin is that bacterial assemblages on CCA are distinctive. Bacteria isolated from surfaces of 2 South African species of CCA (Sporolithon sp. and Clathromorphum sp.), 2 seawater samples collected adjacent to the CCA, and ground-glass slides incubated next to the corallines were examined for 34 morphological and physiological characters. Bacteria from the 2 CCA were distinct from those from other microhabitats and from each other, whereas isolates from the 2 seawater samples were similar, and those from glass slides were more similar to seawater populations than to coralline-associated bacteria. Bacteria from corallines were distinguished by narrower temperature ranges for growth, and in general, inability to (1) utilize glucose, (2) hydrolyse complex carbohydrates and urea, (3) utilize simple amino acids, and (4) reduce nitrate. These characteristics and the distributions of bacteria on crust surfaces suggest that epiphytic bacteria may utilise compounds from the algae for growth. Bacteria on Sporolithon sp. grew mostly from within recently damaged cells, whereas on Clathromorphum sp. they proliferated on a mucus-like matrix on its surface For some strains the association of bacteria with host alga may be specialised. These results are consistent with the hypothesis of bacterial origin of inducers associated with CCA, but they do not provide a critical test and thus do not resolve the question of algal or bacterial origin of inducers. In examining both hypotheses, we suggest methods to critically discern among these 2 alternatives. There was no trace of free GABA (y-aminobutyric acid) or L-DOPA (L-beta-3,4- dihydroxyphenylalanine) in cell-free extracts of either species of South African coralline algae or in bacteria isolated from the corallines and the other microhabitats. This finding supports other work suggesting that these compounds have no ecological relevance as inducers.

Characteristic bacteria associated with surfaces of coralline algae: a hypothesis for bacterial induction of marine invertebrate larvae

Characteristic bacteria associated with surfaces of coralline algae: a hypothesis for bacterial induction of marine invertebrate larvae

Induction of Metamorphosis of Larvae of the Green Sea Urchin, Strongylocentrotus droebachiensis, by Coralline Red Algae.

The coralline red algae, Lithothamnion glaciale, Phymatolithon laevigatum, P. rugulosum, and Corallina officinalis, induced >85% of laboratory-reared larvae of Strongylocentrotus droebachiensis to metamorphose. Larvae must contact live L. glaciale or its spores for metamorphosis to occur; the inducer is not sensed in the water column. However, aqueous extracts of L. glaciale can induce metamorphosis, suggesting that the inducing factor is chemical. Neither ashed nor boiled L. glaciale induces metamorphosis, indicating that the factor is heat-labile and that thigmotaxis, per se, is not important in the response. The amino-acid, γ-aminobutyric acid (GABA), which induces settlement of other marine invertebrate larvae, also induces significant rates of metamorphosis of S. droebachiensis at concentrations ≥ 10-4 M. A reduction (with antibiotics) in the number of live bacteria on the surface of L. glaciale does not affect the rate of metamorphosis of larvae.

Delayed metamorphosis by larvae of benthic marine invertebrates: Does it occur? Is there a price to pay?

Abstract In the laboratory, the swimming larvae of benthic marine invertebrates are generally capable of prolonging their larval period beyond the time that they first become physiologically competent to metamorphose. Larvae seem to differ markedly in their ability to postpone metamorphosis, both interspecifically and intraspecifically. The proportion of this variability that is genetically controlled has not yet been determined; if under genetic control, both pre-competent and competent periods would be subject to selection, although the selective pressures and the physiological or developmental mechanisms through which such pressures might operate remain purely speculative. Limited data strongly suggest that at least a few species delay metamorphosis in the field. The frequency with which they do so, and under what conditions they do so, and for how long, are unexplored questions. Some of these issues can now be explored, with the finding that various inorganic and organic substances can trigger the met...

Natural mortality of marine invertebrate larvae

Abstract Planktonic marine invertebrate embryos and larvae lead transitory lives of great risk and grave uncertainty. Estimation of the magnitude of risk and mortality, however presents a formidable challenge. Three methods are currently in use to estimate levels of mortality among populations of marine invertebrate larvae: 1) theoretical models where rates of instantaneous mortality are correlated with other life history parameters, 2) estimation of mortality based on laboratory observations of predator-prey interactions and 3) analysis of relationships among gamete production, larval populations, and densities of post-larvae in the field. Theoretical exercises indicate that rates of larval mortality are correlated with duration of the planktonic period, and that differences in mortality rates may be offset by differences in egg size and fecundity. Results from laboratory investigations suggest that mortality rates change with larval size or age. Attempts to monitor cohorts of larvae in the plankton offe...

Larval orientation mechanisms: The power of controlled experiments

Abstract Recent reports of field-based experimental research on ecology of marine invertebrate larvae has renewed debate on the applicability of laboratory-based research. This paper addresses the context in which the laboratory approach to larval ecology is appropriate, using research on larval orientation mechanisms as examples. The basic premise is that application of laboratory-derived results requires acceptance ofthe principal underlying assumptions; namely, that application of naturally-occurring conditions provides a rigorous description of species-specific traits that are the results of adaptation and that contribute to larval success. Larval orientation contributes to vertical distribution by regulating direction of locomotion, thus compensating for, or complementing, the effects of gravity. Special care must be taken in designing orientation experiments that determine taxis response by use of larval movement and of groups of organisms. Such approaches can confound responses related to activity level of experimental subjects for an orientation response, particularly when activity level varies among individuals, through time, or as a function of the stimulus. Laboratory investigation of behavioral adaptations requires a careful assessment of the response components and an experimental design that permits unequivocal interpretation, an approach that many may consider to be very reductionist.

A brief review and critique of zooplankton sampling methods: Copepodology for the larval ecologist

Abstract A brief review and critique of zooplankton sampling methods is presented. Both conventional and nonconventional methods are discussed with special emphasis on their potential application to ecological studies of marine invertebrate larvae.

A review of methods for labeling and tracking marine invertebrate larvae

Abstract Methods for marking invertebrate larvae for use in dispersal studies include staining, tagging with calcium replacements, radiotracers and rare elements, and use of genetic, morphological, and parasite markers. The mark, release and recapture method provides a valuable approach to the study of larval movements but has been attempted only rarely, in part because of difficulties with larval recovery. Methodological and instrumentational advances may improve the feasibility of release and recovery efforts. Additional approaches to tracking larvae include visual tracking, use of isolated or point sources, Lagrangian and Eulerian methods, energetic calculations, hydro-graphic modeling and simulations. Recent emphases on physical transport mechanisms, and on the interrelationship of behavior and passive transport can be considered in the context of tracking methods. Newly-developed and recently-conceived techniques offer promise of considerable advance in our understanding of larval dispersal phenomena.

Stochastic models of gregarious larval settlement

Abstract Many marine invertebrate larvae exhibit gregarious settlement behavior. Gregariousness may interact with larval preferences for different substrata in producing settlement patterns. Consequently, the results of laboratory studies of substrate selection that use more than one larva per replicate may be confounded by gregariousness. I present results of computer simulations of larval settlement that illustrate the joint effects of larval selectivity and gregariousness. Each consecutive larva is offered two surfaces for settlement. Individuals settle randomly, and the probability of settlement is determined by both the underlying preference for that surface (selectivity) and the distribution of individuals that have already settled (gregariousness). Gregariousness leads to a consistent over-estimate of preference at intermediate or high values of selectivity. At low values of selectivity, gregarious settlement increases the chances of spuriously rejecting the null hypothesis and of misclassifying the direction of the larval response. These effects may be enhanced or diminished by small sample sizes, depending on whether larvae respond qualitatively or quantitatively to the distribution of settled individuals. These computer simulations suggest that gregariousness cannot simply be ignored or “averaged out” of settlement experiments. Laboratory settlement experiments should explicitly incorporate gregariousness as an additional factor to reveal whether substrate choices are modified by the presence of previously settled individuals. Such experiments should provide additional insight into patterns of recruitment in the field.

Attachment behavior in the barnacle Balanus amphitrite amphitrite (Darwin): genetic and environmental effects

The occurrence of “fatal errors” in settlement (Strathmann et al., (1981)) suggests the possibility of natural selection for habitat choice by settling larvae of sessile marine invertebrates. The effectiveness of this selection depends upon the amount of additive genetic variation present for habitat choice. A sib analysis was used to assess genetic and environmental variation in the response of Balanus amphitrite cyprids to two surface treatments, a glass “control” surface and glass modified by adsorption of a settlement-inducing pheromone. The pheromone treatment caused a significant increase in the percentage of B. amphitrite cyprids attaching to the surface of assay tubes. Attachment to glass and pheromone-treated surfaces was significantly positively correlated. The sib analysis of cyprid response to the two surface treatments revealed no effect due to male parent, and therefore little or no additive genetic variation in cyprid attachment behavior, but a highly significant effect due to the female parent. Further analysis indicated that part of the female effect could be explained by temporal variation in larval culture conditions (glass and pheromone surfaces) and part by maternal and/or nonadditive genetic effects (glass surfaces only). These results suggest that barnacle settlement behavior may be quite plastic in nature and that planktonic factors, already implicated in larval survival and dispersal, may also affect habitat choice at settlement.

Roles of hydrodynamics and larval behaviour in determining spatial aggregation in the tunicate Ciona intestinalis

Much attention has been paid in the literature to the importance of gregariousness of marine invertebrate larvae and its potential role in the formation of aggregated assemblages in the field. In the waters of the Swedish west coast Ciona intestinalis L. can be highly aggregated. Laboratory experiments showed that lanrae of C. intestinalis were not stimulated to settle and metamorphose in aqueous extracts of adult tunic, nor were settlement patterns on uniform, plane substrata aggregated. Field experiments with adult C. intestinalis and adult C. intestinalis mimics indicated that recruitment was dependent on the number of adults or mimics present (higher numbers yielded higher settlement). However, recruitment density around a given number of C. intestinalis was not significantly different from that around the same number of mimics. These results indicate that formation of aggregations of C. intestinalis in the field are probably the result of hydrodynamic processes rather than gregarious larval settlement. This result is in contrast to those obtained from similar investigations of other ascidian species.

Chemical factors that influence the settlement and metamorphosis of marine invertebrate larvae: Pawlik, J.R. and M.G. Hadfield, 1990. [Symposium, Annual meeting, American Society of Zoologists, San Francisco, December, 1988.] Bull. mar. Sci., 46(2):450–554; 6 papers

Chemical factors that influence the settlement and metamorphosis of marine invertebrate larvae: Pawlik, J.R. and M.G. Hadfield, 1990. [Symposium, Annual meeting, American Society of Zoologists, San Francisco, December, 1988.] Bull. mar. Sci., 46(2):450–554; 6 papers

Food Limitation of Planktotrophic Marine Invertebrate Larvae: Does it Control Recruitment Success?

Article de synthese sur l'etude de l'influence des insuffisances dans la quantite de nourriture larvaire sur un jeune alimentaire et la vraisemblance que cela puisse constituer un facteur primordial dans la regulation du succes de recrutement des larves du zoobenthos marin

Ontogenic Changes in the Rates of Amino Acid Transport from Seawater by Marine Invertebrate Larvae (Echinodermata, Echiura, Mollusca)

Transport rates of amino acids were determined for larvae of different ages of the echiuran worm Urechis caupo, the gastropod Haliotis rufescens, the bivalve Crassostrea gigas, and the sea urchin Strongylocentrotus purpuratus. All larval forms showed an increase in the transport rate of amino acids during development. Trochophores of U. caupo increased their rate of net flux for each of 5 amino acids (100 nM each) by a factor of 1.6 and 2.2 during 1-3 days and 4-8 days, respectively, for two independent cultures. In H. rufescens, the maximum transport capacity (Jmax) for alanine increased 3-fold during the 24 h required for the trochophore to develop into a veliger. In C. gigas veligers, there was a 9-fold increase in the maximum transport capacity for alanine during larval development from an 80 µm to a 300 µm larva. In sea urchins, the prism-stage larvae (2-day-old) had an alanine transport system with a Kt of 1.9 µM and a Jmax of 8.1 pmol larva-1h-1. The kinetics of alanine transport in the pluteus-stage (4-day-old) were best described by two systems (System I: Kt = 1.0 µM with a Jmax of 5.6 pmol larva-1h-1; System II: Kt = 132.0 µM with a Jmax of 8.4 pmol larva-1h-1). In larvae of C. gigas, the relationship between the rate of alanine transport and body size was described by the equation, log Jmax (pg larva-1h-1) = 1.6894(X) + (-0.5937), where X is the shell length in µm. It is illustrated that the allometric increase in respiration rates, during the growth of bivalve larvae, is matched by an ontogenic increase in amino acid transport capacity.

Influence of Delayed Metamorphosis on the Growth and Metabolism of YoungCrepidula fornicata(Gastropoda) Juveniles

Larvae of most marine invertebrates delay metamorphosis ifthey fail to contact an appropriate en vironmental stimulus. We conducted seven experiments with the slipper shell snail, Crepidulafornicata, to deter mine if delaying metamorphosis decreases juvenile fit ness. Larvae were reared in the laboratory at 25°C on the unicellular alga Isochrysis sp. (clone T-ISO, 18 X iO@ cells m1'), and were induced to metamorphose after long, medium, or short periods ofdelayed metamorpho sis. Long delay larvae were reared until they metamor phosed spontaneously in acid-cleaned glassware. Me dium and short delay larvae were induced to metamor phose with adult-conditioned seawater or 20 mM elevations ofKCl. Juveniles were subsequently reared for about one to two weeks at 25°C in the laboratory on a diet ofT-ISO. Delaying metamorphosis generally did not lower juvenile weight-specific feeding rates, increase ju venile weight-specific respiration rates, or lower juvenile shell or tissue growth rates, any of which effects would suggest that delaying metamorphosis reduces juvenile fitness. Moreover, there was no indication that delaying metamorphosis reduced juvenile tolerance of tempera ture-salinity stress. Delaying metamorphosis of C.forni cata does not appear detrimental, at least for the first few weeks ofjuvenile life.

Extracellular matrix of sea urchin and other marine invertebrate embryos.

The extracellular matrix surrounding the sea urchin embryo (outer ECM) contains fibers and granules of various sizes which are organized in recognizable patterns as shown by ultrastructural studies, particularly stereoimaging techniques. The use of the ruthenium red method for retaining and staining the ECM, with modifications of the Luft (Anatomical Record 171:347-368, 1971) method for invertebrate embryos, allows for the clarification of certain structures, particularly fiber compaction in the interzonal region, and microvillus-associated bodies. The inner ECM in the sea urchin embryo includes the basal lamina and blastocoel matrix. Stereoimages show that the fibers which are loosely distributed in the blastocoel matrix become compacted around the periphery of the blastocoel to form the basal lamina. The ruthenium red method was also used on a number of marine invertebrate embryos and larvae, representing different phyla, to facilitate comparisons between their surface coats. The similarities observed in the specimens shown suggest that ECMs are widely found on marine invertebrate eggs, embryos, and larvae, and that they resemble vertebrate ECMs and may, therefore, have similar functions.

Inhibition of attachment of larval barnacles, Balanus amphitrite, by bacterial surface films

Films of bacteria on solid substrata can positively or negatively influence the attachment of marine invertebrate larvae. Effects of marine bacteria on the attachment of cypris larvae of the barnacle Balanus amphitrite Darwin were examined in the laboratory. Bacteria, grown to mid-exponential phase and allowed to adsorb irreversibly to polystyrene petri dishes, attached in densities of 107 cells cm-2. Assays (22h) were used to compare the effects of adsorbed cells of 18 different bacterial species on larval barnacle attachment. Most of the adsorbed bacteria either inhibited or had no effect on larval attachment compared to clean surfaces. Experiments testing the effect of larval age on barnacle attachment were conducted with six species of bacteria and showed that older larvae attached in higher percentages to clean surfaces and that bacterial films generally inhibited larval attaschment. Both the species of bacteria and the in situ age of the adsorbed bacteria affected barnacle attachment response: older films of Deleya (Pseudomonas) marina were more inhibitory. Bacterial extracellular materials may be involved in the inhibitory process.

Availability of chemosensory receptors is down-regulated by habituation of larvae to a morphogenetic signal.

Larvae of the gastropod mollusc Haliotis rufescens are induced to settle from the plankton and metamorphose in response to exogenous gamma-aminobutyric acid (GABA) and a number of GABA-mimetic compounds, including a GABA-mimetic inducer uniquely associated with the surfaces of the naturally recruiting algae. Previous evidence has shown that recognition of these inducers is mediated by specialized chemosensory receptors on the larval epithelium and that transduction of the morphogenetic signal then is mediated by cAMP and excitatory depolarization. We demonstrate here the specific and saturable labeling of a population of larval receptors with the GABA analog beta-(p-chlorophenyl)-[3H]GABA ([3H]baclofen); identification of these labeled receptors with those controlling metamorphosis is suggested by four independent criteria: the effectiveness of GABA and its close structural analogs to induce metamorphosis is closely correlated with the effectiveness of these compounds to compete for binding to this receptor; the natural inducer purified from the recruiting algae competes for binding to this receptor; (-)-[3H]baclofen specifically bound to the receptors is shed from the larvae after approximately 20 hr, at the time corresponding to the metamorphic abscission and shedding of sensory cilia and other structures from the larvae; and the availability of the receptors for labeling and the ability of the larvae to respond to GABA and GABA analogs can be down-regulated in parallel by habituation of the larvae early in their development. These down-regulated larvae are fully capable of settlement and metamorphosis in response to agents that elevate intracellular cAMP or depolarize the chemosensory membrane, confirming that down-regulation is confined to the receptors, with no effect on the postreceptor pathway. The results reported here thus suggest that the sensitivity of marine invertebrate larvae to morphogenetic stimuli from the environment can be down-regulated by reduction in the number of chemosensory receptors available for interaction with the molecules that induce settlement and metamorphosis. In this respect, chemosensory receptors for environmental and morphogenetic signals are demonstrated biochemically to respond to habituation in a similar manner to neuronal and hormonal receptors.

Field evidence for delayed metamorphosis of larval gastropods: Crepidula plana Say, C. fornicata (L.), and Bittium alternatum (Say)

The ability of marine invertebrate larvae to delay metamorphosis to adult form and habitat is known mostly from laboratory studies. However, larvae of Bittium altematum (Say), Crepidula fornicata (L.), and C. plana Say that are delaying metamorphosis in the plankton should be recognizable since the larvae of these species continue to increase their length and biomass after becoming competent to metamorphose and, in the two Crepidula species, also show altered shell morphology. Delaying larvae of C. fornicata and C. plana made up ≈ 5–20% of the Crepidula spp. larvae captured in the plankton in June, 1974. Larvae of Bittium alternatum that could be induced to metamorphose within 8–10 h of their collection from the plankton were ≈25–50 % heavier than individuals induced to metamorphose upon first becoming competent to do so, suggesting that the larvae of this species also delay metamorphosis in the field under at least some circumstances.