Rates of energy consumption and acquisition by lecithotrophic larvae of Bugula neritina (Bryozoa: Cheilostomata)

Lecithotrophic larvae of the cheilostome bryozoan, Bugula neritina (L.), lose metamorphic competence 12 to 24 h after release from the maternal zooid. The high respiration rate of newly released larvae (mean=306.3 pmol O₂ larva^-1 h^-1, range=149.3 to 466.6, n=18 trials, 22.5°C) from adults collected at Link Port, Fort Pierce, Florida during the winter/spring of 1990–1991 reflects their active swimming behavior. The average energy content per larva was 15.24 mJ (range: 13.35 to 20.17 mJ ind^-1, n=5 groups). If all cells have an identical energy content and metabolic rate, then 2 and 20% of the total energy content would be consumed by the onset (2 h post-release) and the loss (24 h post-release) of metamorphic competence. Larvae of B. neritina are a composite of both larval and juvenile tissues and the loss of metamorphic competence may be due to regional depletion of labile energy stores in transitory larval cells, particularly the ciliated cells that comprise the locomotory organ, the corona. Although nonfeeding, B. neritina larvae can acquire nutrients from the environment in the form of dissolved organic materials (DOM) in seawater. Both the amino acid alanine and the fatty acid palmitic acid can be transported from seawater ([S]=1 M, 22.5°C). The rates of alanine influx (appearance of label in tissue) averaged 0.366 pmol larva^-1 h^-1 and, based on comparisons between rates of solute transport and metabolism, would contribute little (<1% of required energy) to offset the metabolic demand. The average rate of palmitic acid influx was 4.668 pmol larva^-1 h^-1 and assuming that the measured influx equals the net solute flux, could account for 21 to 72% of energy requirements. These data suggest that the duration of planktonic life of B. neritina larvae is principally regulated by the amount of endogenous energy stores, but may be modulated by available DOM in seawater.     

Role of protein in larval swimming and metamorphosis of Bugula neritina (Bryozoa: Cheilostomatida)

Larvae of the marine cheilostomatid bryozoan Bugula neritina (L.) were prevented from settling for 1, 4 and 8 h by mechanical agitation, following which settlement and metamorphosis success were examined. Settlement rates were significantly affected by swimming time, which decreased from 100% after 2 h to 93.7 ± 4.3% after 8 h. Similarly, metamorphosis to the feeding ancestrula was significantly impaired following a swimming time of 8 h, declining from 93.7 ± 4.3% after 1 h to 65.9 ± 7.0% after 8 h. The resultant colonies grew well for the first 3 wk, following which time, growth patterns became erratic. Growth rate was in all cases highly variable, and did not correlate with enforced swimming times. Larval protein composition was examined after 1, 4 and 8 h swimming time, and post-larval composition 1, 2, 5, 24 and 48 h after settlement using sodium-dodecyl-sulphate polyacrylamide-gel electrophoresis (SDS-PAGE). Individual protein content was measured using a densitometer. Larvae did not consume protein during swimming, however a protein measuring 170 kdaltons was consumed during metamorphosis. These results are discussed in the context of larval settlement and energetics. Received: 19 July 1998 / Accepted: 3 December 1998     

Dissolved histamine: a potential habitat marker promoting settlement and metamorphosis in sea urchin larvae

Many species of marine invertebrate larvae settle and metamorphose in response to chemicals produced by organisms associated with the adult habitat, and histamine is a cue for larvae of the sea urchin Holopneustes purpurascens. This study investigated the effect of histamine on larval metamorphosis of six sea urchin species. Histamine induced metamorphosis in larvae of three lecithotrophic species (H. purpurascens, Holopneustes inflatus and Heliocidaris erythrogramma) and in one planktotrophic species (Centrostephanus rodgersii). Direct comparisons of metamorphic rates of lecithotrophic and planktotrophic larvae in assays cannot be made due to different proportions of larvae being competent. Histamine (10 μM) induced metamorphosis in 95% of larvae of H. purpurascens and H. inflatus after 1 h, while the coralline alga Amphiroa anceps induced metamorphosis in 40–50% of these larvae. Histamine (10 μM) and A. anceps induced 40 and 80% metamorphosis, respectively, in the larvae of H. erythrogramma after 24 h. Histamine (10 μM) and the coralline alga Corallina sp. induced 30 and 70% metamorphosis, respectively, in the larvae of C. rodgersii after 24 h. No metamorphosis of any larval species occurred in seawater controls. Larvae of two planktotrophic species (Tripneustes gratilla and Heliocidaris tuberculata) did not metamorphose in response to histamine. Seagrasses, the host plants of H. inflatus, induced rapid metamorphosis in larvae of the two Holopneustes species, and several algae induced metamorphosis in C. rodgersii larvae. Histamine leaching from algae and seagrasses may act as a habitat marker and metamorphic cue for larvae of several ecologically important sea urchin species.     

Growth and differentiation during delayed metamorphosis of feeding gastropod larvae: signatures of ancestry and innovation

Extent of larval growth among marine invertebrates has potentially profound implications for performance by benthic recruits because body size influences many biological processes. Among gastropods, feeding larvae often attain larger size at metamorphic competence than non-feeding larvae of basal gastropod clades. Delay of metamorphosis can further influence size at recruitment if larvae continue to grow during the delay. Some caenogastopod larvae grow during delayed metamorphosis, but opisthobranch larvae do not. Data on larval growth of neritimorph gastropods are needed to help determine which of these growth patterns for planktotrophic gastropod larvae is more derived. We cultured planktotrophic larvae from all three major gastropod clades with feeding larvae through delays of metamorphosis of 3–10 weeks. Larvae of the caenogastropod Euspira lewisii and the euthyneurans Haminoea vesicula (Opisthobranchia) and Siphonaria denticulata (Pulmonata) conformed to previously described growth patterns for their respective major clades. Furthermore, the caenogastropod continued to lengthen the prototroch (ciliary band for swimming and feeding) and to differentiate prospective post-metamorphic structures (gill filaments and radular teeth) during delayed metamorphosis. Larvae of the neritimorph Nerita atramentosa arrested shell growth during delayed metamorphosis but the radula continued to elongate, a pattern most similar to that of non-feeding larvae of Haliotis, a vetigastropod genus. Character mapping on a phylogenetic hypothesis suggests that large larval size and capacity for continued growth during delayed metamorphosis, as exhibited by some caenogastropods, is a derived innovation among feeding gastropod larvae. This novelty may have facilitated post-metamorphic evolution of predatory feeding using a long proboscis.     

Evidence for a water-borne cue inducing metamorphosis in the dorid nudibranch mollusc Adalaria proxima (Gastropoda: Nudibranchia)

The dorid nudibranch Adalaria proxima (Alder & Hancock) is a specialist predator of the cheilostome bryozoan Electra pilosa (L.). Natural induction of metamorphosis of the pelagic lecithotrophic larva of A. proxima was assessed in response to solutions from sonicated prey tissue and (live) E. pilosa-conditioned seawater (Electra-CSW). We exploited the tendency of larvae to become entrapped (rafted) at the air-water interface in cultures to examine whether larvae require direct contact with the live prey for metamorphosis to proceed. Larvae metamorphosed when rafted above colonies of live E. pilosa, above plankton mesh bags isolating live E. pilosa, and in choline chloride controls; there was no metamorphosis of larvae that were rafted in filtered seawater controls. Entrapped veliger shells remained rafted throughout the experimental period in all cases. No metamorphosis occurred in treatments containing either the supernatants or pelleted particulates obtained from sonicated colonies of E. pilosa. Both one-colony and three-colony Electra-CSW induced metamorphosis of larvae. These data are at variance with previous results in showing that direct contact with the live prey is not necessary for metamorphosis to proceed. Furthermore, the fact that competent larvae metamorphosed in response to Electra-CSW in the absence of any other cue strongly suggests that the inductive cue is water-borne.     

Active salinity choice and enhanced swimming endurance in 0 to 8-d-old larvae of diadromous gobies,including Sicydium punctatum (Pisces), in Dominica,West Indies

We studied the early life history of diadromous gobies in Dominica, West Indies, from May 1989 to May 1991, emphasising Sicydium punctatum Perugia. The transition of newly hatched larvae from upriver nest sites to the sea was studied in laboratory experiments. Newly hatched larvae are negatively buoyant but avoid settling to the bottom by active swimming during drift to the sea. Laboratory experiments evaluated salinity preferences and effects on swimming endurance. Larvae in haloclines actively selected low to intermediate salinities. Initially (0 to 5-d post-hatch), larvae minimized exposure to salinities >10 ppt, but later (5 to 8-d) occupied increasingly saline water. Larvae in no-choice freshwater or seawater treatments ceased activity at 4 to 5 d, but in haloclines larvae remained active up to 8 d post-hatch. Salinities <10 ppt are important for early survival of sicydiine gobies. Implications for larval survival and transport are discussed.     

Biofilm cue for larval settlement in Hydroides elegans (Polychaeta): is contact necessary?

Larvae of many sessile marine invertebrates settle in response to surface microbial communities (biofilms), but the effects of soluble compounds from biofilms in affecting larval behavior prior to settlement, attachment, and metamorphosis have been little studied. This question was addressed by videotaping the behavior of competent larvae of the serpulid, Hydroides elegans, above settlement-inducing biofilms. Adult worms were collected in Pearl Harbor, Hawaii, USA in November 2012 and spawned almost immediately. Six-day old larvae were placed in five replicated treatments in small cups: (1) with a natural biofilm; (2) with a natural biofilm on an 8-µm screen, 1 mm above the bottom of a clean cup; (3) with a natural biofilm beneath a clean screen; (4) in a clean cup; and (5) in a clean cup with a clean screen. Using the videotapes, larval swimming speeds and trajectories were quantified within 5 min of the larvae being placed in a treatment. Only larvae that touched a biofilm, i.e., in treatments (1) and (2), slowed their swimming speed and increased the amount of time spent crawling rather than swimming. This shows that under these conditions, any soluble cues emanating from a biofilm do not affect settlement behavior. Furthermore, after 24 h close to 100 % of larva in the two accessible biofilm treatments had metamorphosed and <15 % in treatments that included a biofilm under a clean screen and no biofilm at all, strongly suggesting that soluble cues for settlement were not produced by the biofilms over the longer time period.     

Requirement of exogenous inducers for metamorphosis of axenic larvae and buds of Cassiopea andromeda (Cnidaria: Scyphozoa)

Planula larvae and asexually-produced buds of the rhizostome scyphozoan Cassiopea andromeda (collected throughout the year in Eilat, Israel) have the ability, under axenic conditions, to attach to a substrate and undergo morphogenetic development to form a polyp (=scyphistoma) in: (1) the presence of unidentified inducers found in the adult habitat and (2) the presence of cefined organic compounds. Axenic planulae and buds were unable to settle and complete metamorphosis in autoclaved artificial or natural seawater from the North Sea when maintained without food, but continued swimming while decreasing in size and protein content, eventually dying within three months. When maintained in autoclaved seawater from the Red Sea, between 25 and 46% of the planulae and 4 and 11% of the buds metamorphosed within 30 d. Axenic solutions of cholera toxin, thyroid stimulating hormone, and pancreatic casein hydrolysate peptides in artificial seawater induced morphogenic development of 20 to 100% of planulae and buds within 2 to 18 d. The natural inducer(s) in Red Sea seawater, though unidentified, may have characteristics similar to the large proteins and small peptide inducers used in this study. Planulae and buds older than 20 d metamorphosed sooner and responded to lower concentrations of pancreatic casein hydrolysate peptides than younger individuals. This may be a physiological mechanism for enhancing metamorphosis and survival in nature. The data show that settlement and metamorphosis can be induced by solutions of cholera toxin and thyroid stimulating hormone, suggesting that, as in mammalian systems, the mechanism of action of these chemicals may involve cyclic adenosine monophosphate (cAMP) as an intermediate messenger. However, dibutyric cAMP, which is capable of passing through membranes and functioning normally inside the cell, did not induce metamorphosis of buds, and the levels of intracellular cAMP in buds and larvae typically increased slowly during induction of metamorphosis, unlike the high and rapid increases associated with cAMP-mediated biochemical events in mammalian cells. These results suggest that the observed cAMP changes seen were associated with metamorphic development, but not with the triggering mechanism.     

Induction of settlement and metamorphosis in the sand dollarEchinarachnius parma: Evidence for an adult-associated factor

Larvae of the northern sand dollarEchinarachnius parma (Lamarck), reared from adults collected from Eagle Head, Nova Scotia, Canada, in 1988 and 1989, metamorphose in significantly greater numbers on sand conditioned by adults than on non-conditioned sand. The metamorphic factor has a molecular weight < 1000 and is destroyed by heating. Larvae are capable of sensing this cue in the water column under static conditions. Substrata of varying particle size and surface texture can be conditioned by adults to induce metamorphosis. Substrata conditioned in the dark, and conditioned sand treated with antibiotics also induce metamorphosis suggesting that the factor is not produced by adult-associated bacteria or microflora. In nature, this adult-associated factor may direct settlement of larvae to established sand dollar beds resulting in the aggregated distribution of this species.     

Where are larvae of the vermetid gastropod <Emphasis Type="Italic">Dendropoma maximum</Emphasis> on the continuum of larval nutritional strategies?

This study evaluated whether larvae of the Indo-Pacific vermetid gastropod Dendropoma maximum are obligate planktotrophs, or whether they exhibit an intermediate feeding strategy. Experiments were conducted in Moorea, French Polynesia (149°50′W, 17°30′S), Sep–Oct 2009, to examine D. maximum larval growth and metamorphic responses to different diets and amounts of food. Dendropoma maximum larvae required particulate food to undergo metamorphosis, but were able to survive and grow in the absence of food for up to 20 days. Larvae in Low and Unfed food treatments exhibited phenotypic plasticity by growing a larger velum (the larval feeding structure) compared with those in high food. Unfed D. maximum larvae had a slower initial growth rate; however, by 11-day post-hatch fed and unfed larvae had converged on the same mean shell height (553 μm), which was only 10% larger than the initial size at hatching. Therefore, although the nutritional strategy of D. maximum larvae is best described as obligate planktotrophy, it appears to approach an intermediate feeding strategy.     

Morphological and functional development of larval and juvenile Limanda yokohamae (Pisces: Pleuronectidae) reared in the laboratory

Morphological and behavioural aspects in larval development need to be studied in detail to understand the early life history better, and to gain a comprehensive knowledge on early life stages for fish species important in aquaculture and fisheries. In the present study, larvae of Limanda yokohamae (Günther) were reared to observe their behavioural development, and to obtain specimens for studying the morphological features and the intestinal development at Ohno, Hiroshima, Japan, in 1987. Swimming activity was monitored at several larval stages, and swimming speed was recorded until settlement and after-feeding behaviour was initiated. A slight increment of swimming speed was observed with larval growth. Larvae changed their swimming behaviour from surface waters to the bottom of the rearing tank when their eyes began to move. Morphological development of pigmentation patterns, fin development, squamation and the development of the digestive tract were described and illustrated in detail to characterize development stages, especially those relating to metamorphosis. During metamorphosis, growth ceased and rapid changes in allometric growth were accompanied by differentiation of the digestive tract. After metamorphosis there was steady growth, allometric growth achieved a constant value, and both the scales and digestive organs were fully formed. Metamorphosis was therefore a crucial developmental milestone, including a critical phase during which survival potential was lowered.     

Morphological and behavioral alterations induced by endocrine disrupters in amphibian tadpoles

Developmental toxicity effects of endocrine disrupter chemicals, acephate and cypermethrin were studied in Bufo melanostictus tadpoles. Thirty developing eggs of B. melanostictus were exposed to each concentration (0.01, 0.05, 0.1, 0.5, and 1?µg?L^?1) of acephate or cypermethrin in the laboratory (temperature: 23?±?1°C; photoperiod: 11.5–12.5?h). Eggs maintained in conditioned water alone served as controls. After hatching, larvae were fed on boiled spinach until the completion of metamorphosis. In control group, larvae that hatched on 3rd day were heavily pigmented, voracious feeders, and active swimmers; in these tadpoles, hind limb and forelimb-buds emerged on 16th and 24th day and metamorphosis was complete on 32nd day. Eggs exposed to acephate also hatched on 3rd day but larvae exhibited deformities such as, (i) tail distortions, (ii) laterally crooked trunk, (iii) decreased pigmentation, (iv) inactivity, (v) peeling of the skin, and (vi) delay in emergence of limbs and completion of metamorphosis. Cypermethrin-exposed eggs exhibited a delay (4–8 days) in hatching, there was no mortality, deformities in tail, trunk and head region, delay in the emergence of limbs, and completion of metamorphosis were evident. The demonstrated data indicate that these pesticides interfere with amphibian development when present in the aquatic system.     

Effect of Ca2+ on survival and development of metamorphosing bonefish (Albula sp.) leptocephali

Bonefish (Albula sp.) larvae (leptocephali) from the Gulf of California complete metamorphosis in ˜10 d in natural seawater (35‰S; Ca²⁺ conc = 10.5 mM). The increase in ossification that occurs near the end of the non-feeding metamorphic period, in addition to the ability of larvae to complete metamorphosis in dilute seawater (8‰ S) prompted the present study, where the effects of varying the external calcium ion concentration, [Ca²⁺]_e, of artificial seawater (ASW) on the survival, development and internal (whole-body) calcium ion content, (Ca²⁺)_i, of unfed metamorphosing larvae were investigated. Early-metamorphosing larvae placed in␣ASW, where [Ca²⁺]_e = 10.1 mM, survived for up to 10 d and developed normally without exogenous nutrients. In shorter-term experiments (4 to 5 d), no differences in survival were found for larvae in ASW with [Ca²⁺]_e rang-ing from 1.5 to 10.1 mM. However, in Ca²⁺-free ASW, most larvae died within 27 h and no larvae survived more than 42 h; the median lethal time (LT₅₀), and its 95% confidence limits, were 14.5 (10.0 to 20.9) h. High mortality (81% after 20 h) also occurred in 1.0 mM Ca²⁺ ASW, but 2 of 16 larvae tested survived for 96 h. The 96 h median tolerance limit (TL_M), corrected for control mortality, was 1.2 mM Ca²⁺. In natural seawater, larval (Ca²⁺)_i remained relatively constant ( = 0.419 mg larva⁻¹)␣in early- and intermediate-metamorphosing larvae, and then increased to a mean value of 0.739 mg larva⁻¹ in advanced larvae, indicating that Ca²⁺ was␣taken up from the medium at this stage; the increase in (Ca²⁺)_i corresponded to the period of ossification of the vertebral column. Internal (whole-body) magnesium ion content (Mg²⁺)_i showed no significant change during metamorphosis ( = 0.089 mg larva⁻¹). No significant differences in (Ca²⁺)_i were found in advanced larvae in natural seawater and those in ASW, with [Ca²⁺]_e ranging from 2.0 to 10.1 mM. However, clearing and staining revealed that ossification of the vertebral column had not yet occurred in advanced larvae from 2.0 to 10.1 mM Ca²⁺ ASW. Also, low [Ca²⁺]_e (1.0 to 2.0 mM) usually produced deformed larvae that swam erratically, at times showing “whirling” behavior. Received: 21 August 1996 / Accepted: 26 August 1996     

Waterborne chemical compounds in tropical macroalgae: positive and negative cues for larval settlement

Settlement sites of marine invertebrate larvae are frequently influenced by positive or negative cues, many of which are chemical in nature. Following from the observation that many shallow-water, Hawai'ian marine macroalgae are free of fouling by sessile invertebrates, we predicted that the algae are chemically protected and dependent on either surface-bound or continuously released soluble compounds to deter settling invertebrate larvae. To address the importance of waterborne algal compounds, we experimentally determined whether larvae of two of Hawai'i's dominant hard-surface fouling organisms, the polychaete tube worm Hydroides elegans and the bryozoan Bugula neritina, would settle in the presence of waters conditioned by 12 species of common Hawai'ian macroalgae (representing the Phaeophyta, Chlorophyta, Rhodophyta and Cyanophyta). The results included a full spectrum of biological responses by each larval species to waterborne algal compounds. Larval responses to conditioned water were consistent for each algal species, but the outcomes were not predictable based on the taxonomic relationships of the algae. For example, among the species of Phaeophyta examined, different conditioned waters were: (1) toxic, (2) inhibited settlement, (3) simulated settlement, or (4) had no effect, compared to larvae in control dishes containing filtered seawater. Additionally, larval responses to aged (24 h) conditioned waters could not be predicted from the results of assays run with conditioned waters utilized immediately after preparation. Finally, settlement by larvae of one species did not predict outcomes of tests for the other species. Four of 12 shallow-reef Hawai'ian macroalgae tested released compounds into surrounding waters that immediately killed or inhibited settlement by both H. elegans and B. neritina (toxic: Dictyota sandvicensis; inhibitory: Halimeda discoidea, Sphacelaria tribuloides, Ulva reticulata); the remaining 8 algal species prevented settlement by one of these fouling organisms but for the other had no effect or, in some cases, even stimulated settlement     

Effects of elevated temperature on larval settlement and post-settlement survival in scleractinian corals, <Emphasis Type="Italic">Acropora solitaryensis</Emphasis> and <Emphasis Type="Italic">Favites chinensis</Emphasis>

We examined the effects of elevated temperature under different exposure periods on larval settlement and post-settlement survival in scleractinian corals, Acropora solitaryensis and Favites chinensis. In the first experiment with the subtropical coral, A. solitaryensis, the numbers of larvae settling and those dead were examined daily for 5 days at 20, 23 (ambient), 26 and 29°C conditions. Larval settlement of A. solitaryensis was initially greater at higher temperature conditions, but the peak in number of settled larvae shifted from 29 to 26°C by day 5, due to ca. 90% post-settlement mortality at 29°C condition. In order to determine the effects under short-term exposure, larvae of F. chinensis were exposed to 27 (ambient), 31 or 34°C only for one hour in the second experiment. The number of larvae settling for 24 h after the exposure and their survivorship over subsequent week was monitored in the ambient temperature condition. Larvae of F. chinensis exhibited greater settlement at higher temperature treatments and constantly low post-settlement mortalities (< ca. 17%) in all temperature treatments, resulting in the highest number of settled larvae at 34°C treatment. These results suggested two different effects of elevated temperature on the early stages of recruitment process of scleractinian corals; (1) the positive effect on larval settlement and (2) the negative effect on post-settlement survival under prolonged exposure.     

Experimental evidence for direct nutrient assimilation by the lophophore of articulate brachiopods

The uptake of inorganic and non-nutritive organic molecules has been compared with uptake of nutritive molecules by the articulate brachiopod Terebratalia transversa (Sowerby). Only minimal uptake of Na₂ ¹⁴CO₃ and ¹⁴C-urea was observed, while ¹⁴C-glucose was concentrated extensively. After administration of a dilute solution of ¹⁴C-glucose over timed intervals, whole organ counts and autoradiographs showed that labelled material was accumulated along the exposed ciliated epidermal tissue of the lophophore and mantle and concentrated along the peritoneal lining of the coelom even before appearing in the gastrointestinal tract. The presence or absence of bacteria had little discernible effect upon extent and rate of uptake. The uptake experiments suggest that the lophophore not only creates an inhalent and exnalent current as is common in other filter-feeders, but also appears to be adapted for extraction of dilute nutrients in seawater. This ability of the lophophore to extract nutrients may help explain the evolutionary trend of the lengthening of the articulate lophophore and the reduction of the intestine to a short blind-ended gut.This work was supported by National Science Foundation Grant GB-20067.     

Larval settlement and metamorphosis of the mussel <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> in response to biofilms

Biofilms were allowed to develop on glass slips immersed 1.0–1.5 m below the sea surface in Tachibana Bay, Nagasaki, Japan, for different periods of time from November 2003 to January 2005. The effects of age, immersion month, dry weight, bacterial and diatom densities of these biofilms on the settlement and metamorphosis of pediveliger larvae of the mussel Mytilus galloprovincialis were investigated in the laboratory. Furthermore, biofilms were subjected to various treatments to investigate the nature of the settlement and metamorphosis cue in the biofilm. Pediveliger larvae of the mussel settled and metamorphosed in response to biofilms. Settlement and metamorphosis to the post-larval stage significantly increased with the biofilm age. In addition, the biofilm activity varied depending on the immersion month (season), e.g., for biofilms with the same age, those immersed between June and August had higher activities than those immersed between November and March. The activity of the biofilm also positively correlated with the dry weight, bacterial and diatom densities. These three quantitative parameters of the biofilm were significantly affected by the film age but were not affected by the immersion month, suggesting that other parameters (e.g., community structures, extracellular products) also affected the inductive activity of the biofilm. The fixative agents (formalin and glutaraldehyde), heat, ethanol, ultraviolet irradiation and antibiotics treatments of the biofilm resulted in significant reduction or loss of its inductive activity. The survival of bacterial cells in the treated films where activities were either reduced or lost also decreased significantly. No settlement and metamorphosis were obtained when larvae were exposed to the conditioned water of the biofilm. Thus, larvae of M. galloprovincialis settled and metamorphosed in response to a cue produced by living bacteria in the biofilm. The cue may be a bacterial extracellular product which was susceptible to the above treatments.     

Delayed growth of mussel (Mytilus edulis) and scallop (Pecten maximus) veligers at low temperatures

Veliger larvae of Mytilus edulis (L.) from Menai Straits, North Wales, were maintained for up to 2 mo during 1981 at 5°C and then grown on to metamorphosis at 17°C. Larvae so treated showed similar low mortality and equivalent spat production to control larvae. Growth rate at 17°C was less in treated larvae than in controls, but treated larvae grew a little during the period at low temperature. Larvae of Pecten maximus (L.) from the Irish Sea suffered high mortality at low temperature but larvae surviving 2 wk at 8°C could be grown on to spat at 17°C. The longevity of M. edulis larvae is discussed in relation to the genetic homogeneity of adult populations around the UK.     

Comparison of larval development and growth of the sea cucumberActinopyga echinites: Ovary-induced ova and DTT-induced ova

AdultActinopyga echinites (Jaeger) were collected from northern Taiwan in September 1989. Oocytes were induced to mature by bathing them in ovary juice (ovary-induced ova) or in 10^–2 M dithiothreitol (DTT-induced ova). The percentage of germinal vesicle breakdown (GVBD) increased from 0.4 to 6.4% in the former treatment and to 84% in the latter. After artificial fertilization, the embryos were cultured in seawater (35 S) at 25 to 28°C. Larvae were fed with the algaIsochysis aff.galbana at 10^4–5 cells/ml. Larvae from ovary-induced ova developed faster (18 d to the doliolaria stage) and grew to a larger size (1.13 mm length) than those from DTT-induced ova (20 d to the doliolaria stage and 0.62 mm in length). On the twelfth day, larvae from ovary-induced ova bear lipid spheres. The number of spheres is positively correlated with larval size. Lipid spheres may provide nutrient reserves for larvae during metamorphosis.     

Effects of duration of larval swimming period on early colony development in Bugula stolonifera (Bryozoa: Cheilostomata)

Laboratory experiments with larvae of the cheilostome bryozoan Bugula stolonifera Ryland, 1960 assessed the time to settlement in the presence of a constantly available polystryrene substrate, the development of competence for metamorphosis, and the effects of the duration of swimming period on early colony development. Sexually mature colonies of B. stolonifera were collected on 11 and 18 September 1987; 2 and 18 August, 1988; and 6, 12, 19, and 26 September 1988, from Eel Pond (Woods Hole, Massachusetts, USA) and were maintained at 20°C. In the presence of a constantly available substrate, cumulative percent settlement curves were sigmoid, with 75% of larvae settled in 3.2±0.5 h. Typically, 50% of the larvae settled in less than 3 h and 95% settled in 6.1±1.2 h. The number of settled individuals that developed feeding ancestrulae by 3 d and the number that developed first-feeding autozooids by 6 d was assessed as a function of duration of larval swimming. Individuals which were kept swimming for 8 and 10 h after hatching developed significantly more slowly to the ancestrula and autozooid stages in 13 out of 14 experiments than did larvae that swam 2 or 6 h. This is the first report for any bryozoan that prolongation of the larval free-swimming period affects the rate of colony development.