Metamorphosis Of Larvae Research Articles

G protein‐linked receptors and induction of metamorphosis in Bugula stolonifera (Bryozoa)

Abstract. Induction of metamorphosis in larvae of the marine bryozoan Bugula stolonifera was examined for potential roles of G protein‐linked cell‐surface receptors. Two compounds that modulate components of the G protein system were tested in a bath‐applied experimental design over concentrations of 10−8 to 10−3 M, plus a seawater control, and 2 controls to assess metamorphic competence (10 mM excess KCl and a biofilmed surface). The G protein activator Gpp[NH]p and the G protein inhibitor GDP‐β‐s did not affect rates of metamorphosis, under the conditions tested. We found no evidence that G protein‐linked cell‐surface receptors are the receptors of the metamorphic cue in this species. This negative finding parallels reports on a gastropod and a polychaete; by contrast, G proteins are involved in metamorphic induction in several cnidarians, a nematode, and barnacles. Thus, as no single model can account for induction across phyla, our results may serve to focus attention on identifying possible roles of the other 2 major classes of cell‐surface receptors in triggering metamorphosis in B. stolonifera and other invertebrates.

Testing various substances that have been bound to plastic plates with agar to induce larval settlement and metamorphosis of abalone Haliotis discus discus (Reeve)

An experimental culture system was developed as an alternative to diatom biofilms for settling larval abalone and on-growing the resulting post-larvae. The system is designed to allow artificial micro-particulate food to be sprayed (continuously until abalone are capable of feeding on seaweed) onto hard corrugate plastic plates, using agar as a fixative. Two trials were conducted to test substances that could be utilized to improve the settlement and metamorphosis rate of larval Haliotis discus discus when using the above experimental system. In trial 1, plates were sprayed with a mixture containing 1% agar and one of the following: natural diatom powder, Spirulina powder, Chlorella powder and two different concentrations of γ-aminobutyric acid (GABA), each with and without antibiotics. The negative control was a clean plastic plate without any additives and the positive control was plastic plates covered with a living natural diatom biofilm. There was no significant difference in the final metamorphosis rate of larvae induced to settle on the three micro-algal powders and the positive control (25.8–35.8%). However, these treatments had a significantly higher larval metamorphosis rate when compared to the negative control and the GABA treatments (1.7–7.5%). GABA did not induce metamorphosis of larvae at a significantly higher rate than the negative control, regardless of whether antibiotics were used or not. In trial 2, the effect of using both algal powders and mucus was tested to determine settlement and metamorphosis rates of larval abalone. Combining the effects of mucus and micro-algal powders or the positive control and mucus resulted in a final larval settlement rate of 80.8–89.2% and metamorphosis rate of 73.3–87.5%. This was significantly higher than the treatments that only incorporated micro-algal powder or the positive control, having an attachment rate of 20.8–41.7% and a total metamorphosis rate of only 3.3–28.3%. There is potential to use micro-algal powder as a substitute to living diatoms, to act as a settlement cue for larval H. discus discus. Abalone mucus should also be used in addition to micro-algal powders to increase the settlement rate of larvae and also ensure a high rate of metamorphosis.

Interaction between noradrenaline or adrenaline and the β 1-adrenergic receptor in the nervous system triggers early metamorphosis of larvae in the ascidian, Ciona savignyi

Molecular mechanisms underlying the metamorphosis of larvae, e.g., ligand and receptor interaction, have to be determined and roles for the nervous system in marine invertebrates are not well understood. We report here that treatment of swimming larvae of the ascidian Ciona savignyi with noradrenaline or adrenaline promoted morphological changes in early metamorphosis, e.g., tail resorption. Antagonists of the β-adrenergic receptor, propranolol, and the β 1-adrenergic receptor, metoprolol, inhibited the noradrenaline-induced tail resorption, while an antagonist of the α-adrenergic receptor, phentolamine, and of the β 2- adrenergic receptor, butoxamine, had no inhibitory effects. In addition, a selective agonist of the β-adrenergic receptor, isoproterenol, the concentration of which was lower than the effective concentration of the neurotransmitters, facilitated tail resorption. Immunohistochemical studies, using an anti-dopamine-hydroxylase antibody, showed that neurotransmitters such as noradrenaline and adrenaline localized around the brain vesicle of the larvae during metamorphosis. The β 1-adrenergic receptor stained with antibodies was localized on the nervous system. Temporal expression of the β 1-adrenergic receptor was intense in the nervous system in the larvae competent for metamorphosis. We propose that interactions between noradrenaline or adrenaline and the β 1-adrenergic receptor in the nervous system mediate the process of metamorphosis of Ciona larvae.

Ethyl 4-[2-(6-Methyl-3-pyridyloxy)butyloxy]benzoate, a novel anti-juvenile hormone agent.

Ethyl 4-[2-(6-methyl-3-pyridyloxy)butyloxy]benzoate (2) was prepared as a novel anti-juvenile hormone (anti-JH) agent. Compound 2 induced precocious metamorphosis in larvae of the silkworm and black pigmentation of the larval cuticle, which are clearly recognized as JH-deficiency symptoms. The 4-ethoxycarbonyl group on the benzene ring was indispensable for activity. The activity of compound 2 could be fully counteracted by methoprene, a JH agonist, but not by the dietary administration of 20-hydroxyecdysone.

Composition and density of bacterial biofilms determine larval settlement of the polychaete Hydroides elegans

Larvae of the polychaete worm Hydroides elegans settle and metamorphose in response to marine biofilms. Phylogenetic relationships among 4 marine-biofilm bacterial species identified by 16S rDNA sequences were not predictive of their inductive capacity. Two bacterial species separated by a genetic distance of 30% shared the greatest capacity for inducing metamorphosis in H. elegans. Two bacterial strains with only a 3% divergence in 16S rRNA gene sequences were very different; one strain induced metamorphosis strongly while the other one did not. The percent of larvae that metamorphosed correlated positively with bacterial density in either natural biofilms or biofilms com- posed of a single bacterial species. When results of tests across 4 bacterial species were compared, the most inductive bacterial species was effective in much lower biofilm densities than weakly or non-inductive bacteria. Evidence presented here indicates that the cue that triggers settlement and metamorphosis in larvae of H. elegans is not unique to a single bacterial taxon and is likely to be an insoluble, surface-bound material.

Different iodine and thyroid hormone levels between Atlantic halibut larvae fed wild zooplankton or Artemia from first exogenous feeding until post metamorphosis

The iodine concentration in wild zooplankton was 700 times higher than in Artemia and threefold higher in Atlantic halibut Hippoglossus hippoglossus larvae fed wild zooplankton than in those fed Artemia. In larvae fed wild zooplankton thyroxine (T4) and triiodothyronine (T3) concentrations were significantly higher than in those fed Artemia at the commencement of metamorphosis, 68–77 days post hatching. There was no difference in the amino acids phenylalanine and tyrosine levels in larvae fed Artemia in comparison with those fed wild zooplankton. The selenium level was significantly higher in larvae fed Artemia than in those fed wild zooplankton, but concentrations in the prey were not different. The results indicate sufficient amounts of phenylalanine, tyrosine and selenium in Artemia, but indicated a lower thyroid status due to an insufficient iodine supply at commencement of metamorphosis in larvae fed Artemia. This may partly explain the higher frequency of juveniles with complete eye migration and asymmetric pigmentation in the group fed wild zooplankton.

Aspects of the larval biology of the sea anemones Anthopleura elegantissima and A. artemisia

Abstract. We investigated several aspects of the larval biology of the anemone Anthopleura elegantissima, which harbors algal symbionts from two different taxa, and the non‐symbiotic A. artemisia. From a 7‐year study, we report variable spawning and fertilization success of A. elegantissima in the laboratory. We examined the dynamics of symbiosis onset in larvae of A. elegantissima. Zoochlorellae, freshly isolated from an adult host, were taken up and retained during the larval feeding process, as has been described previously for zooxanthellae. In addition, larvae infected with zooxanthellae remained more highly infected in high‐light conditions, compared to larvae with zoochlorellae, which remained more highly infected in low‐light conditions. These results parallel the differential distribution of the algal types observed in adult anemones in the field and their differential tolerances to light and temperature. We report on numerous failed attempts to induce settlement and metamorphosis of larvae of A. elegantissima, using a variety of substrates and chemical inducers. We also describe a novel change in morphology of some older planulae, in which large bulges, resembling tentacles, develop around the mouth. Finally, we provide the first description of planulae of A. artemisia and report on attempts to infect this non‐symbiotic species with zooxanthellae and zoochlorellae.

Abnormal forms in the brittle-star Amphipholis squamata: a field study

Deviation from pentamerism is a rare phenomenon in 5-armed echinoderm species. Qualitative and quantitative data from field observations of 14 populations around the world were used for a biogeographical study of this phenomenon. Four abnormal forms presenting deviation from the classical pentamerism of echinoderms were observed within the brittle-star species Amphipholis squamata (Echinodermata: Ophiuroidea). Although these forms were rare in global populations (0·29%), they can reach important frequencies in some locations. Our results suggest that habitat structure has an influence on the occurence of abnormal forms. Moreover, deviations from pentamerism are not a heritable character but are a consequence of environmental perturbations on the metamorphosis of larvae and/or abnormal regeneration of arms.

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.

Nest-site selection in a terrestrially breeding frog with protracted development

Metamorphosis of larvae of the Australian moss frog (Bryobatrachus nimbus) occurs in a terrestrial nest approximately one year after oviposition. Neither parent attends the eggs, thus selection of an appropriate nest site is critical to egg viability. This study examined the dynamics of nest-site utilisation over six years and the characteristics of nests chosen as oviposition sites. Nest cavities were located at ground level amongst heath within one of 10 species of bryophyte, lichen and lycopod. On average, 2.6% of nests contained a male B. nimbus during daytime monitoring during the breeding season, and 7.3% of nests contained an egg mass. Despite an abundance of potentially suitable nests from previous years, males constructed a small proportion (<10%) of new nests each year and new nests were more likely to be used as oviposition sites than older nests. Discriminant function analysis showed that moss nests used as oviposition sites were distinguishable from empty nests by their greater horizontal dimensions. Eggs deposited in wider nests are restricted to fewer layers, and a preference for wider nests may be adaptive because embryonic oxygenation is enhanced under such conditions. However, rather than demonstrating nest-site selection, the use of relatively large nests as oviposition sites may be an artifact of their occupancy by a breeding pair.

Influence of food quality and quantity on the growth and development of Crassostrea gigas larvae: a modeling approach

A biochemically based model was developed to simulate the growth, development and metamorphosis of larvae of the Pacific oyster, Crassostrea gigas. The model is unique in that it (1) defines larvae in terms of their protein, neutral lipid, polar lipid, carbohydrate and ash content; (2) tracks weight separately from length to follow larval condition index and (3) includes genetic variation in growth efficiency and egg quality to better simulate cohort population dynamics. The model includes parameterizations for larval filtration, ingestion and respiration that determine growth rate and processes controlling larval mortality and metamorphosis. Changes in tissue composition occur as the larva grows and in response to the biochemical composition of the food. The simulations show that genetically determined variations in growth efficiency produce significant changes in larval survival and success at metamorphosis. Larvae with low growth efficiency are successful under a much narrower range of culture conditions than larvae with high growth efficiency. The impact of low growth efficiency is primarily controlled by the ability of larvae to store lipid for metamorphosis. Culture conditions that provide increased dietary lipid counterweigh low growth efficiency. Changes in food quantity and quality had little effect on size at metamorphosis. On the other hand, larval life span and success rate at metamorphosis varied over a wide range depending upon the conditions of the simulation. Food quality and food availability both influence larval life span and, hence, larval survival. As ingestion rate decreases, larval life span increases and cohort survival declines. Increased lipid or decreased protein in the diet improves cohort survival. Changes in carbohydrate content are less influential. If cohort success is significantly affected by mortality during larval life rather than success at metamorphosis, the influence of food quality becomes more complex. The range of food compositions yielding high survival is restricted by a balance between improved success at metamorphosis obtained by increased lipid storage and the shortening of larval life span as a result of more rapid growth, a function of protein availability. These simulations illustrate the strength and utility of numerical models for evaluating and designing hatchery protocols for optimizing yield of C. gigas larvae.

CHEMICAL MEDIATION OF INTERACTIONS AT SEAWEED SURFACES

Steinberg, P. D.School of Biological Science and Centre for Marine Biofouling and Bio‐innovation, University of New South Wales, Sydney 2052, AustraliaChemical mediation of surface colonization of seaweeds by epibiota is much less well understood than analogous seaweed/herbivore interactions. Fundamental to studies of colonization is the localization and quantification of metabolites on or near seaweed surfaces. Halogenated furanones from the Australian alga Delisea pulchra are present at the surface of the alga in concentrations which strongly inhibit settlement of epibiota, and are examples of “natural antifoulants”. However, many other chemically rich seaweeds do not appear to use natural products as antifoulants, either because the compounds are not present at the thallus surface, or because they do not persist there in high enough concentrations. We suggest that natural antifoulants in seaweeds will most commonly be non‐polar metabolites, and restricted to species with morphologies that allow for their release. In contrast, primary (and often water soluble) metabolites appear to be more common as inducers of settlement. Several examples of inducers will be briefly presented, including our own research on the floridoside ‐ isethionic acid complex from red algae which induces metamorphosis of larvae of the echinoid Holopneustes purpurascens. The leaky nature of such metabolites in seaweeds suggests that delivery systems for positive cues will be less important. These and other suggested generalities regarding the production of deterrents vs. inducers of colonization will be considered.

Application of bacterins and yeast Acremonium dyosporiito protect the larvae ofMacrobrachium rosenbergiifrom vibriosis

The fresh water prawn, Macrobrachium rosenbergii, has proven potential for use as an aquaculture species (Hanson & Goodwin, 1997; Kurup, 1984). In India alone, culture of this species of prawn in low saline areas requires about 200 million seed per year (Kurup, 1984). In hatcheries poor survival rate has been associated with vibriosis at different stages of the larval cycle. Members of the family Vibrionaceae associated with the larvae of M. rosenbergii were shown to be pathogenic under laboratory conditions (Bhat et al., 2000, in press). Vibrios have been associated with mortality of penaeid prawns by several workers (Aquacop, 1977; Hameed, 1993; Karunasagar et al., 1994). Two methods have been suggested to protect both the larvae and juveniles from vibriosis; one is the administration of bacterins prepared from pathogenic strains (Itami et al., 1989, 1991; Adams, 1991; Song & Sung, 1990; Sung et al., 1991) and the other is the utilization of yeast f 1-3 and 1-6 glucans as immunostimulants for enhancing the non-specific defense system (Sung et al., 1994; Song et al., 1997). In the light of these observations it was hypothesised that bacterins and yeast glucans may also be effective in protecting the larvae of M. rosenbergii from vibriosis as has been achieved in the case of penaeids. To examine this hypothesis, the ability of bacterins and an extracellular glue an-producing yeast to increase the overall survival and metamorphosis of larvae in a hatchery, as well as to protect against an experimental challenge under laboratory conditions, was evaluated. A strain each of Vibrio (ANM 708) and Photobacterium (AAC 727) isolated from diseased larvae of M. rosenbergii and found to be affiliated to V. fisheri, V. logei or V. marinus and P. angustrum, respectively, at G+C ratio level (determined from Tm values), but phenotypically dissimilar to the type strains and proven to be pathogenic to the larvae under laboratory conditions (Bhat et al., 2000, in press) were used for the preparation of bacterins. The bacteria were cultured in nutrient agar (Peptone 0.5%, Beef extract 0.5%) (HI Media Laboratories, Bombay, India), aged sea water (15 ppt), pH 7.5 at 28' C for 48 h and harvested in phosphate buffered saline (PBS) composed of NaH2PO4 6.42 g; Na2HPO4 34316 g; NaCl 10 g (SRL, Bombay, India), distilled water 1000 ml. The cultures were diluted in PBS to obtain 0.5 OD (Abs600) and were exposed to a final concentration of 0.2% (v/v) formalin for 24 h at room temperature and subsequently stored at 4' C for 14 days. To confirm inactivation an aliquot of 1 ml

Neural inhibition of the corpus allatum in the last larval instar differs from that in adults in the blood-feeding insect,Rhodnius prolixus

An active corpus allatum (CA) in the blood feeding insect, Rhodnius prolixus, releases a substance that inhibits metamorphosis in larvae, and activates egg production in adults. In adults, transecting the nervus corporis cardiacum II's (NCCII), which are attached posteriorly to each protocerebral lobe, greatly increases egg production indicating that the adult CA is activated and receives neural inhibition from cells associated with the NCCII [Chiang, Arch. Insect. Biochem. Physiol. 39:126-131 (1998)]. In the present study, the NCCII's in fifth instar larvae were transected immediately before or after feeding to determine if these nerves normally inhibit CA activity in the last larval instar. Approximately 20 to 25 days following ingestion of a blood meal, L5's with transected NCCII's emerged as fully-formed adults with no larval characteristics. Examination of the brain in these recently emerged adults revealed that the NCCII's were absent. Since fifth instar larvae with transected NCCII's emerged with no juvenile characteristics, cutting the NCCII's did not activate the CA, indicating that the mechanism for inhibition of the CA differs in the last larval instar and adult animals.

The apical sensory organ of a gastropod veliger is a receptor for settlement cues.

On the basis of anatomy and larval behavior, the apical sensory organ (ASO) of gastropod veliger larvae has been implicated as the site of perception of cues for settlement and metamorphosis. Until now, there have been no experimental data to support this hypothesis. In this study, cells in the ASO of veliger larvae of the tropical nudibranch Phestilla sibogae were stained with the styryl vital dye DASPEI and then irradiated with a narrow excitatory light beam on a fluorescence microscope. When its ASO cells were bleached by irradiation for 20 min or longer, an otherwise healthy larva was no longer able to respond to the usual metamorphic cue, a soluble metabolite from a coral prey of the adult nudibranch. The irradiated cells absorbed the dye acridine orange, suggesting that they were dying. When larvae not stained with DASPEI were similarly irradiated, or when stained larvae were irradiated with the light beam focused on other parts of the body, there was no loss of ability to metamorphose. Together these data provide strong support for the hypothesis. Potassium and cesium ions, known to induce metamorphosis in larvae of many marine-invertebrate phyla, continue to induce metamorphosis in larvae that have lost the ability to respond to the coral inducer due to staining and irradiation. These results demonstrate that (1) the ASO-ablated larvae have not lost the ability to metamorphose and (2) the ions do not act only on the metamorphic-signal receptor cells, but at other sites downstream in the metamorphic signal transduction pathway.

Multiple cues for induction of metamorphosis in larvae of the common mud crab Panopeus herbstii

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 195:221-229 (2000) - doi:10.3354/meps195221 Multiple cues for induction of metamorphosis in larvae of the common mud crab Panopeus herbstii Raymond A. Rodriguez, Charles E. Epifanio* University of Delaware, College of Marine Studies, Hugh R. Sharp Campus, 700 Pilottown Rd., Lewes, Delaware 19958, USA *Corresponding author. E-mail: epi@udel.edu ABSTRACT: Cues associated with biofilms from the adult habitat previously have been found to accelerate metamorphosis in the megalopae of the common mud crab Panopeus herbstii (Milne-Edwards). In this study, we investigated several properties of this biofilm and further investigated the response of megalopae to exudates from adult P. herbstii. Results showed the cue to be water-soluble and suggest that it is associated with the bacterial component of the film. Biofilms from a rocky intertidal area produced a response, while films from an intertidal sand flat did not. When biofilm was allowed to form on clean glass slides in adult habitat, megalopae showed a stronger response to 10-d-old biofilms than to 2-d-old biofilms. Exudates from adult P. herbstii produced a strong response while exudates from prey species Crassostrea virginica and a closely related mud crab Dyspanopeus sayi produced a weaker, but significant response. Exudates from fiddler crabs Uca pugnax did not elicit a response. Results from these experiments suggest that there are multiple water-soluble cues that induce metamorphosis of mud crab megalopae. KEY WORDS: Mud crab · Megalopae · Metamorphosis · Biofilm · Exudate Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 195. Publication date: March 31, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Variation in attachment of the barnacle Balanus amphitrite: sensation or something else?

Settlement, attachment, and metamorphosis of larvae of marine invertebrates is extremely variable in the laboratory and in nature. The relative contributions of genetic, ontogenetic and environmental effects to this variation are not well understood. We tested for genetic, maternal and ontogenetic effects on permanent attachment of cyprids of the barnacle Balanus amphitrite (Darwin). Larvae were assayed for attachment in response to a control treatment and 3 artificial inducers: 20-hydroxyecdysone (20-HE), 3-isobutyl-1-methylxanthine (IBMX), and phorbol 12,13- dibutyrate (PDB). We observed strong family effects on attachment in the control, 20-HE, and IBMX treatments, suggesting that attachment in response to these treatments is influenced by genetic or maternal factors. In addition, attachment responses were correlated, indicating that the same genetic or maternal factors may affect attachment in each treatment. Family effects on attachment in the control treatments decreased with cypris age, suggesting the loss of genetically- or maternally- influenced discriminatory behavior in older larvae. The mechanisms underlying genetic or maternal effects on attachment may act via the external receptors and signal-transduction pathways regulat- ing larval responses. Alternatively, there may be variation in larval 'vigor' or the rate at which cyprids attain metamorphic competence.

An analysis of sea urchin metamorphosis

Metamorphosis of sea urchin larvae is initiated by one or more cues from the environment. The cues can be from bacterial films (Cameron & Hinegardner, 1974), algae (Kitamura et al., 1993) or sand and seawater from adult habitats (Highsmith, 1982). The substances from sand are peptides (Burke, 1984), and those from red algae are free fatty acids (Kitamura et al., 1993) and dibromomethane (Taniguchi et al., 1994). Burke (1983a) suggested that chemical and physical stimuli were received by sensory receptors, probably podia of the adult rudiment, and transmitted to effectors of metamorphosis such as larval and adult tissues. Morpho-genetic, histolytic and histogenic processes progress during metamorphosis to create a juvenile, though direct evidence for the mechanism of induction has not been shown.Glutamine (Gin) induces metamorphosis in larvae of many sea urchin species (Strongylocentrotus intermedius: Naidenko, 1991; Pseudocentrotus depressus: Yazaki & Harashima, 1994; Hemicentrotus pulcherrimus: Yazaki, 1995). We have analysed the metamorphosis of sea urchin larvae using Gln, neurotransmitters and a natural cue (green algae).

Loss of test cells leads to the formation of new tunic surface cells and abnormal metamorphosis in larvae of Ciona intestinalis (Chordata, ascidiacea).

The larvae of the ascidian Ciona intestinalis from which the chorion with the test cells and follicle cells were removed developed normally without the test cells until the early tailbud stage. A number of round-shaped cells morphologically similar to the test cells but with different lectin affinities and autofluorescence, then appeared on the neck region of the demembranated embryos. The new cells had three different types: round, particulate, and granular, and these cells increased in number after the late tailbud stage. The morphology of the adhesive papillae, tunic layers and epidermis of the demembranated larvae was similar to that of control larvae; however, the affinity to lectins was different in the swimming period. Control larvae attached to the substratum after the swimming period, resorbed the tail completely and underwent rotation of the visceral organs. Conversely, rotation occurred before completion of tail resorption in the demembranated larvae. Furthermore, the metamorphic events progressed more slowly in the demembranated larvae. These results suggest that the test cells play important roles in normal development and morphogenesis of ascidian larvae.

Relative importance of parental and larval nutrition on larval development and metamorphosis of the sea urchin Strongylocentrotus droebachiensis

We examined the relative importance of parental nutritional condition and larval food ration on the rates of development, growth and metamorphosis of larvae of Strongylocentrotus droebachiensis (Müller) in a laboratory experiment. Parents were reared for 22 months on either a high ration of kelp ( Laminaria spp., 6 days week −1 ) supplemented with mussel flesh ( Mytilus spp., 1 day week −1 ) (KM), or a low ration of kelp (1 day week −1 ) (KL). Larvae were fed either a high ration (5000 cells ml −1 ) or a low ration (500 cells ml −1 ) of microalgae ( Dunaliella tertiolecta ). Larval food ration had a strong effect on the rates of development, growth, and metamorphosis, which were all significantly greater in larvae fed the high ration. Test diameter of settlers also was significantly greater in the high than the low ration. Parental nutritional condition had little or no effect on the rates of development and growth, and no effect on settler size. The rate of metamorphosis was significantly higher in larvae from the KM than the KL treatment in the high but not the low ration (where rates of metamorphosis were similar). Although parental condition generally had a small effect on larval development , our results suggest that when planktonic food is abundant, larvae of adults from nutritionally rich habitats (such as kelp beds) may metamorphose sooner than those of adults from nutritionally poor habitats (such as barrens).