Development of symbiotic bacterial bioluminescence in a nearshore cephalopod,Euprymna scolopes

The small neritic cephalopod Euprymna scolopes possesses a large glandular light organ that contains the symbiotic luminous bacterium Vibrio fischeri. Adult and immature E. scolopes were caught in the evening with dip nets in shallow water along the shore of Kanohe Bay, Oahu, Hawaii, during late February 1984. The initiation of the symbiosis was investigated by rearing the cephalopods either in seawater taken from aquaria containing adult E. scolopes or in seawater with reduced bacterial concentrations due to filtration or due to absence of adults. Light production was measured during early development. Bioluminescence was not detected in E. scolopes immediately after hatching. Most individulas of E. scolopes that hatched into seawater containing, or previously exposed to, adults produced light within 24 h. Individuals that hatched into filtered seawater did not produce light. The data suggest that each generation aquires an infection from free-living bacteria rather than from the egg, and that light production is dependent on the nutritional state of the host. Access to an initial inoculum of free-living, luminous bacteria seems to be critical for establishing a successful symbiosis.     

Elevated temperature impairs onset of symbiosis and reduces survivorship in larvae of the Hawaiian coral, <Emphasis Type="Italic">Fungia scutaria</Emphasis>

Many corals obtain their obligate intracellular dinoflagellate symbionts from the environment as larvae or juveniles. The process of symbiont acquisition remains largely unexplored, especially under stress. This study addressed both the ability of Fungia scutaria (Lamarck 1801) larvae to establish symbiosis with Symbiodinium sp. C1f while exposed to elevated temperature and the survivorship of aposymbiotic and newly symbiotic larvae under these conditions. Larvae were exposed to 27, 29, or 31°C for 1 h prior to infection, throughout a 3-h infection period, and up to 72 h following infection. Exposure to elevated temperatures impaired the ability of coral larvae to establish symbiosis and reduced larval survivorship. At 31°C, the presence of symbionts further reduced larval survivorship. As sea surface temperatures rise, coral larvae exposed to elevated temperatures during symbiosis onset will likely be negatively impacted, which in turn could affect the establishment of future generations of corals.     

Transfer of symbiotic luminous bacteria from parental Leiognathus nuchalis to their offspring

Juveniles of Leiognathus nuchalis were raised from fertilized eggs for up to 60 d and examined for luminescence activity. Almost all juveniles raised separately from adults failed to produce detectable light. In contrast, a significant percentage (33 to 100%) of the juveniles became luminescent in less than 48 h when they were either kept with adults or inoculated with a homogenate of the adult light organs. The luminescence tended to increase with time after the treatments. These findings suggest that: (1) most of L. nuchalis offspring typically hatch and develop apo-symbiotically and (2) at least 45 d after hatching, juveniles can be infected with symbiotic luminous bacteria from the light organ of adult fish, and thereby gain the ability to produce light. Received: 16 February 1999 / Accepted: 21 September 1999     

Onset of symbiosis and distribution patterns of symbiotic dinoflagellates in the larvae of scleractinian corals

The establishment of symbiosis in early developmental stages is important for reef-building corals because of the need for photosynthetically derived nutrition. Corals spawn eggs and sperm, or brood planula larvae and shed them into the water. Some coral eggs or planulae directly inherit symbiotic dinoflagellates (Symbiodinium spp.) from their parents, while others acquire them at each generation. In most species examined to date, the larvae without dinoflagellates (aposymbiotic larvae) can acquire symbionts during the larval stage, but little is known regarding the timing and detailed process of the onset of symbiosis. We examined larval uptake of symbiotic dinoflagellates in nine species of scleractinian corals, the onset of symbiosis through the early larval stages, and the distribution pattern of symbionts within the larval host, while living and with histology, of two acroporid corals under laboratory conditions. The larvae acquired symbiotic dinoflagellates during the planktonic phase in all corals examined which included Acropora digitifera, A. florida, A. intermedia, A. tenuis, Isopora palifera, Favia pallida, F. lizardensis, Pseudosiderastrea tayamai, and Ctenactis echinata. The larvae of A. digitifera and A. tenuis first acquired symbionts 6 and 5 days after fertilization, respectively. In A. digitifera larvae, this coincided with the formation of an oral pore and coelenteron. The number of symbiotic dinoflagellates increased over the experimental periods in both species. To test the hypothesis that nutrients promotes symbiotic uptake, the number of incorporated dinoflagellates was compared in the presence and absence of homogenized Artemia sp. A likelihood ratio test assuming a log-linear model indicated that Artemia sp. had a significantly positive effect on symbiont acquisition. These results suggest that the acquisition of symbiotic dinoflagellates during larval stages is in common with many coral species, and that the development of both a mouth and coelenteron play important roles in symbiont acquisition.     

Primary co-culture as a complementary approach to explore the diversity of bacterial associations in marine invertebrates: the example of <Emphasis Type="Italic">Nautilus macromphalus</Emphasis> (Cephalopoda: Nautiloidea)

The recent application of molecular tools to address associations between bacteria and marine invertebrates has provided access to an immense diversity of unidentified microbes resistant to cultivation. However, the role of bacteria as partners in animal physiology remains unclear and in most cases difficult to investigate in the absence of adequate condition of cell growth and proliferation. In this work, we studied the reservoir of microbes associated with the excretory organs of Nautilus macromphalus as a model. Using the bacterial 16S RNA gene as a marker, we compared three complementary approaches for bacterial detection: bacterial DNA extraction from N. macromphalus tissues (“molecular approach”), strain isolation to provide a bacterial culture collection (“microbiological approach”) and finally, maintenance of N. macromphalus excretory organ cells with associated bacteria (“cellular approach”). Our results stress the potential of the “cellular approach” as a promising new tool as it promotes the detection of as yet uncultured β-proteobacteria and spirochaetes associated with N. macromphalus, and serves as a foundation for future studies describing potential roles that these bacteria may play in Nautilus.     

Larval ecology of the great barracuda, <Emphasis Type="Italic">Sphyraena barracuda</Emphasis>, and other sphyraenids in the Straits of Florida

The great barracuda (Sphyraena barracuda) is a widespread, ecologically and socioeconomically important coastal fish, yet very little is known about its larvae. We examined spawning and larval ecology of Western Atlantic sphyraenids using monthly ichthyoplankton samples collected over 2 years along a transect spanning the east–west axis of the Straits of Florida (SOF). Samples were dominated by the great barracuda (92.8%) and sennets (Sphyraena borealis and Sphyraena picudilla; 6.6%). While larval sennets and S. barracuda displayed similar vertical distributions (majority in upper 25 m), horizontal and temporal patterns of abundance suggested a spatial and temporal species replacement between larval S. barracuda and sennets that tracks adult ecology. The diet of both taxa consisted largely of copepods, with inclusion of fish larvae at 8 mm SL, and in S. barracuda alone, a switch in the wet season to exclusive piscivory by 12 mm SL (18 days post-hatch). A lack of piscivory in S. barracuda larvae captured in the dry season corresponded to slower larval growth than in the wet season. Larval growth was also related to size-at-hatch and larval age such that larvae that were larger at hatch or larger (older) at capture grew faster at earlier ages, suggesting faster larval growth, and indirectly larger hatch size, conveys a survival advantage. Unlike larval growth, instantaneous mortality rate did not differ with season, and no lunar cyclic patterns in spawning output were identified. Our results provide insight into the pelagic phase of sphyraenids and highlight the importance of both diet and hatch size to the growth and survival of fish larvae in low latitude oceanic environments.     

The relative contribution of dinoflagellate photosynthesis and stored lipids to the survivorship of symbiotic larvae of the reef-building corals

The long-distance dispersal of larvae provides important linkages between populations of reef-building corals and is a critical part of coral biology. Some coral planulae have symbiotic dinoflagellates (Symbiodinium spp.) that probably provide energy in addition to the lipids provisioned within the egg. However, our understanding of the influence of symbionts on the energy metabolism and survivorship of planulae remains limited. This study examines the relative roles of symbiotic dinoflagellate photosynthesis and stored lipid content in the survivorship of the developing stages of the corals Pocillopora damicornis and Montipora digitata. We found that survivorship decreased under dark conditions (i.e. no photosynthetic activity) for P. damicornis and M. digitata at 31 and 22 days after release/spawning, respectively. The lipid content of P. damicornis and M. digitata planulae showed a significant decrease, at a higher rate, under dark conditions, when compared with light conditions. When converted to energy equivalents, the available energy provided by the depletion of lipids could account for 41.9 and 84.7% of larval metabolism for P. damicornis (by day 31) and 38.4 and 90.1% for M. digitata (by day 21) under light and dark conditions, respectively. This finding indicates that not all energy requirements of the larvae are met by lipids: energy is also sourced from the photosynthetic activities of the symbiotic dinoflagellates within these larvae, especially under light conditions. In addition, the amounts of three main lipid classes (wax esters, triglycerides, and phospholipids) decreased throughout the experiment in the planulae of both species, with the wax ester content decreasing more rapidly under dark conditions than under light conditions. The observations that the planulae of both species derive considerable amounts of energy from wax esters, and that symbiotic dinoflagellates enable larvae to use their stores at lower rates, suggested that symbiotic dinoflagellates have the potential to extend larval life under light conditions.     

Host preference,site fidelity,and homing behavior of the symbiotically luminous cardinalfish,Siphamia tubifer (Perciformes: Apogonidae)

The sea urchin cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), is unusual among coral reef fishes for its use of bioluminescence, produced by symbiotic bacteria, while foraging at night. As a foundation for understanding the relationship between the symbiosis and the ecology of the fish, this study examined the diel behavior, host urchin preference, site fidelity, and homing of S. tubifer in June and July of 2012 and 2013 at reefs near Sesoko Island, Okinawa, Japan (26°38′N, 127°52′E). After foraging, S. tubifer aggregated in groups among the spines of the longspine sea urchin, Diadema setosum, and the banded sea urchin, Echinothrix calamaris. A preference for D. setosum was evident (P < 0.001), especially by larger individuals (>25 mm standard length, P < 0.01), and choice experiments demonstrated the ability of S. tubifer to recognize and orient to a host urchin and to conspecifics. Tagging studies revealed that S. tubifer exhibits daily fidelity to a host urchin; 43–50 and 26–37 % of tagged individuals were associated with the same urchin after 3 and 7 days. Tagged fish also returned to their site of origin after displacement; by day two, 23–43 and 27–33 % of tagged individuals returned from displacement distances of 1 and 2 km. These results suggest that S. tubifer uses various environmental cues for homing and site fidelity; similar behaviors and cues might be used by larvae for recruitment to settlement sites and for the acquisition of luminous symbiotic bacteria.     

Foraging behaviour of larval cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) at low light intensities

The ability to forage at low light intensities can be of great importance for the survival of fish larvae in a pelagic environment. Three-dimensional silhouette imaging was used to observe larval cod foraging and swimming behaviour at three light intensities (dusk ~1.36 × 10⁻³ W/m², night ~1.38 × 10⁻⁴ W/m² and darkness ~3.67 × 10⁻⁶ W/m²) at 4 different ages from 6 to 53 days post-hatch (dph). At 6 dph, active pursuit of prey was only observed under dusk conditions. Attacks, and frequent orientations, were observed from 26 dph under night conditions. This was consistent with swimming behaviour which suggested that turn angles were the same under dusk and night conditions, but lower in darkness. Cod at 53 dph attacked prey in darkness and turn angles were not different from those under other light conditions. This suggests that larvae are still able to feed at light intensities of 3.67 × 10⁻⁶ W/m². We conclude that larval cod can maintain foraging behaviour under light intensities that correspond to night-time at depths at which they are observed in the field, at least if they encounter high-density patches of prey such as those that they would encounter at thin layers or fronts.     

Temporal and spatial infection dynamics indicate recognition events in the early hours of a dinoflagellate/coral symbiosis

The obligate symbiotic relationship between dinoflagellates, Symbiodinium spp. and reef building corals is re-established each host generation. The solitary coral Fungia scutaria Lamarck 1801 harbors a single algal strain, Symbiodinium ITS2 type C1f (homologous strain) during adulthood. Previous studies have shown that distinct algal ITS2 types in clade C correlate with F. scutaria—Symbiodinium specificity during the onset of symbiosis in the larval stage. The present study examined the early specificity events in the onset of symbiosis between F. scutaria larvae and Symbiodinium spp., by looking at the temporal and spatial infection dynamics of larvae challenged with different symbiont types. The results show that specificity at the onset of symbiosis was mediated by recognition events during the initial symbiont—host physical contact before phagocytosis, and by subsequent cellular events after the symbionts were incorporated into host cells. Moreover, homologous and heterologous Symbiodinium sp. strains did not exhibit the same pattern of localization within larvae. When larvae were infected with homologous symbionts (C1f), ~70% of the total acquired algae were found in the equatorial area of the larvae, between the oral and aboral ends, 21 h after inoculation. In contrast, no spatial difference in algal localization was observed in larvae infected with heterologous symbionts. This result provides evidence of functional differences among gastrodermal cells, during development of the larvae. The cells in the larval equator function as nutritive phagocytes, and also appear to function as a region of enhanced symbiont acquisition in F. scutaria.     

Halogenated metabolites in two marine polychaetes and their planktotrophic and lecithotrophic larvae

This study investigated the occurrence and ontogenetic changes of halogenated secondary metabolites in planktotrophic and lecithotrophic larvae and adults of two common, infaunal polychaetes, Streblospio benedicti (Spionidae) and Capitella sp. I (Capitellidae), with different life-history traits. S. benedicti contains at least 11 chlorinated and brominated hydrocarbons (alkyl halides) while Capitella sp. I contains 3 brominated aromatic compounds. These halogenated metabolites are potential defense compounds benefiting both larvae and adults. We hypothesized that: (1) planktotrophic larvae contain halogenated metabolites because they are not protected by adult defenses, (2) quantitative and qualitative variation of planktotrophic larval halogenated metabolites parallels that of adults, and (3) brooded lecithotrophic larvae initiate the production of halogenated metabolites only after metamorphosis. To address these hypotheses, volatile halogenated compounds from polychaete extracts were separated using capillary gas chromatography and identified and quantified using mass spectrometry with selected ion monitoring. All four life stages (pre- and post-release larvae, new recruits, adults) of both S. benedicti and Capitella sp. I contained the halogenated metabolites previously identified from adults. This is the first report of halocompounds identified and quantified in polychaete larvae. Allocation of potential defense compounds to offspring varied as a function of species, feeding type and developmental stage. Pre-release larvae of S. benedicti with planktotrophic development contained the lowest concentration of total halogenated metabolites (1.75 ± 0.65 ng mm⁻³), post-release and new recruits contained intermediate concentrations (8.29 ± 1.72 and 4.73 ± 2.63 ng mm⁻³, respectively), and planktotrophic adults contained significantly greater amounts (28.9 ± 9.7 ng mm⁻³). This pattern of increasing concentrations with increasing stage of development suggests synthesis of metabolites during development. Lecithotrophic S. benedicti post-release larvae contained the greatest concentrations of halometabolites (71.1 ± 10.6 ng mm⁻³) of all S. benedicti life stages and developmental types examined, while the amount was significantly lower in new recruits (34.0 ± 15.4 ng mm⁻³). This pattern is consistent with a previously proposed hypothesis suggesting a strategy of reducing potential autotoxicity during developmental transitions. Pre-release lecithotrophic larvae of Capitella sp. I contained the highest concentration of total halogenated metabolites (1150 ± 681 ng mm⁻³), whereas the adults contained significantly lower total amounts (126 ± 68 ng mm⁻³). All concentrations of these haloaromatics are above those known to deter predation in previously conducted laboratory and field trials. As a means of conferring higher larval survivorship, lecithotrophic females of both species examined may be expending more energy on chemical defenses than their planktotrophic counterparts by supplying their lecithotrophic embryos with more of these compounds, their precursors, or with energy for their synthesis. This strategy appears common among marine lecithotrophic larval forms. Received: 14 July 1999 / Accepted: 20 January 2000     

Sulfide assimilation by ectosymbionts of the sessile ciliate, <Emphasis Type="Italic">Zoothamnium niveum</Emphasis>

We investigated the constraints on sulfide uptake by bacterial ectosymbionts on the marine peritrich ciliate Zoothamnium niveum by a combination of experimental and numerical methods. Protists with symbionts were collected on large blocks of mangrove-peat. The blocks were placed in a flow cell with flow adjusted to in situ velocity. The water motion around the colonies was then characterized by particle tracking velocimetry. This shows that the feather-shaped colony of Z. niveum generates a unidirectional flow of seawater through the colony with no recirculation. The source of the feeding current was the free-flowing water although the size of the colonies suggests that they live partly submerged in the diffusive boundary layer. We showed that the filtered volume allows Z. niveum to assimilate sufficient sulfide to sustain the symbiosis at a few micromoles per liter in ambient concentration. Numerical modeling shows that sulfide oxidizing bacteria on the surfaces of Z. niveum can sustain 100-times higher sulfide uptake than bacteria on flat surfaces, such as microbial mats. The study demonstrates that the filter feeding zooids of Z. niveum are preadapted to be prime habitats for sulfide oxidizing bacteria due to Z. niveum’s habitat preference and due to the feeding current. Z. niveum is capable of exploiting low concentrations of sulfide in near norm-oxic seawater. This links its otherwise dissimilar habitats and makes it functionally similar to invertebrates with thiotrophic symbionts in filtering organs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Symbiosis between bacteria and oceanic clonal sea star larvae in the western North Atlantic Ocean

Bacteria were present in the majority of clonal sea star bipinnariae (Luidia sp.) collected between June 1987 and August 1990 from oceanic populations in the subtropical western North Atlantic Ocean. Light and electron microscopy revealed dense aggregations of bacteria within lobes of the epidermal cuticle in the gastric region of larvae. Gram-negative rods and less-common elongate spiral bacteria were observed, always in close association with branching epidermal microvilli. Intact and partially digested bacteria occurred in vesicles and phagosomes within epidermal cells, a probable indication of phagocytotic activity by the host. The association of larvae of Luidia sp. and bacteria ranged widely on both geographical and temporal scales. During July and August 1988, larvae were abundant (1.6 to 11.1 m³) in the mixed surface layer (<10 to 100 m) of stations in the Gulf Stream, the Sargasso Sea and the North Equatorial Drift, and 96% (mean of 5 stations, n=8 to 10 larvae in each station) of the individuals surveyed harbored bacteria beneath their cuticle. In a single station on the Florida Current sampled during winter, spring, and summer months between 1989 and 1991, 79 to 90% of the larvae harbored bacteria. The incidence of symbiosis was higher in actively cloning larvae than in non-cloning larvae. This is the first documentation of a symbiosis in field populations of echinoderm larvae.     

Fine-scale observations of the predatory behaviour of the carnivorous copepod <Emphasis Type="Italic">Paraeuchaeta norvegica</Emphasis> and the escape responses of their ichthyoplankton prey,Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>)

Paraeuchaeta norvegica (8.5 mm total length) and yolk-sac stage Atlantic cod larvae (4 mm total length) (Gadus morhua) larvae were observed in aquaria (3 l of water) using silhouette video photography. This allowed direct observations (and quantitative measurement) of predator–prey interactions between these two species in 3-dimensions. Tail beats, used by cod larvae to propel themselves through the viscous fluid environment, also generate signals detectable by mechanoreceptive copepod predators. When the prey is close enough for detection and successful capture (approximately half a body-length), the copepod launches an extremely rapid high Reynolds number attack, grabbing the larva around its midsection. While capture itself takes place in milliseconds, minutes are required to subdue and completely ingest a cod larva. The behavioural observations are used to estimate the hydrodynamic signal strength of the cod larva’s tail beats and the copepod’s perceptive field for larval fish prey. Cod larvae are more sensitive to fluid velocity than P. norvegica and also appear capable of distinguishing between the signal generated by a swimming and an attacking copepod. However, the copepod can lunge at much faster velocities than a yolk-sac cod larva can escape, leading to the larva’s capture. These observations can serve as input to the predator–prey component of ecosystem models intended to assess the impact of P. norvegica on cod larvae.     

Luminous bacteria of a monocentrid fish (Monocentris japonicus) and two anomalopid fishes (Photoblepharon palpebratus and Kryptophanaron alfredi): population sizes and growth within the light organs,and rates of release into the seawater

The light organs of monocentrid and anomalopid fishes consist of bacteria-filled tubular invaginations of the epidermis which are connected to the surrounding seawater by ducts. We used the release of bacteria from the light organs to estimate bacterial rates of growth in the light organs. For one monocentrid fish (4 specimens of Monocentris japonicus collected at Jogashima, Japan in 1980) and for two anomalopid fishes (2 specimens each of Photoblepharon palpebratus collected at Sebu, Phillipines in 1981 and Grand Comore Island in 1975 and Kryptophanaron alfredi collected at Parguera, Puerto Rico in 1982) we measured rates of release of bacteria into the surrounding seawater and the bacterial population sizes in the light organs; from this information we calculated doubling times of bacteria in the light organs. In addition, we determined the luminescence of bacteria after their release into the seawater. For M. japonicus, two specimens released 1.1 to 6×10⁶ and 2×10⁷ bacteria h^–1, respectively; the light organs contained about 1.5×10⁸ bacteria. For P. palpebratus, one specimen released 2.2×10⁸ bacteria h^–1; a second specimen had light organs containing 5.2×10⁹ bacteria. For K. alfredi, one specimen released 7×10⁷ bacteria h^–1 and had light organs containing 5.6×10⁸ bacteria; a second specimen released 3.6×10⁷ bacteria h^–1 and had light organs containing 7.3×10⁸ bacteria. Bacterial doubling times in the light organs of these three fishes were variable and ranged from 7.5 to 135 h in M. japonicus and 8 to 23 h in the anomalopids. Bacteria released from M. japonicus into the seawater remained viable, but bacteria from all of the fishes soon ceased to emit light.     

Larval settlement in the serpulid polychaete Hydroides elegans in response to bacterial films: an investigation of the nature of putative larval settlement cue

Larval settlement in the marine polychaete Hydroides elegans (Haswell) is induced by certain bacteria in marine biofilms. The exact nature of the settlement cue that larvae of H. elegans receive from these bacteria remains unknown. In this study, we revealed some properties of the bacterially derived larval settlement cue by investigating the larval settlement inductive activity of two bacterial strains after various treatments. These two bacterial strains, Roseobacter sp. and an α-subclass Proteobacteria, are highly inductive to larval settlement of H. elegans. The larvae responded similarly to Roseobacter and Proteobacteria in all the larval settlement bioassays, suggesting that the larval settlement-inducing substances produced by these bacteria may share common characteristics. First of all, the larvae did not settle in the seawater conditioned by the bacteria attached as a film or by the bacteria that were freely suspended in seawater. The results suggest that the putative larval settlement cue is not released into seawater and, therefore, should be associated with the surface of the bacteria. Secondly, formaldehyde treatment entirely eliminated the larval settlement induction activity of the bacterial films, and streptomycin treatment reduced the percentage of larval settlement on the bacterial films in a concentration-dependent manner. Since both treatments can kill bacteria with little damage to the surface chemistry of bacterial cells, the decline in larval settlement is suggested be due to a reduction of the viable bacterial population in the bacterial films. In fact, the reduction of larval settlement in the streptomycin treatments coincided with the decrease in viable bacterial populations in broth cultures containing respective concentrations of streptomycin. These results suggest that the viability of Roseobacter and Proteobacteria is important to their settlement induction effect. Since the larval settlement induction activity of the bacterial strains appears to correlate with their viability, we suggest that the putative larval settlement cue is derived from a metabolic pathway in the bacteria and that the cue is exported to and concentrated at the extracellular polymer matrix of the bacterial cell, at which the larvae establish contact with the bacteria. The larval settlement cue may be highly susceptible to degradation so that a metabolically active bacterial film is needed to maintain the putative cue at a concentration that surpasses the threshold for induction of larval settlement. Received: 14 October 1998 / Accepted: 5 September 2000     

The effects of zooplankton swimming behavior on prey-capture kinematics of red drum larvae, <Emphasis Type="Italic">Sciaenops ocellatus</Emphasis>

Most marine fishes undergo a pelagic larval phase, the early life history stage that is often associated with a high rate of mortality due to starvation and predation. We present the first study that examines the effects of prey swimming behavior on prey-capture kinematics in marine fish larvae. Using a digital high-speed video camera, we recorded the swimming velocity of zooplankton prey (Artemia franciscana, Brachionus rotundiformis, a ciliate species, and two species of copepods) and the feeding behavior of red drum (Sciaenops ocellatus) larvae. From the video recordings we measured: (1) zooplankton swimming velocity in the absence of a red drum larva; (2) zooplankton swimming velocity in the presence of a red drum larva; and (3) the excursion and timing of key kinematic events during prey capture in red drum larvae. Two-way ANOVA revealed that: (1) swimming velocity varied among zooplankton prey; and (2) all zooplankton prey, except rotifers and ciliates, increased their swimming velocity in the presence of a red drum larva. The kinematics of prey capture differed between two developmental stages in S. ocellatus larvae. Hyoid-stage larvae (3–14 days old) fed on slow swimming B. rotundiformis (rotifers) while hyoid-opercular stage larvae (15 days and older) ate fast moving A. franciscana. Hyoid-opercular stage red drum larvae had a larger gape, hyoid depression and lower jaw angle, and a longer gape cycle duration relative to their hyoid-stage conspecifics. Interestingly, the feeding repertoire within either stage of red drum development was not affected by prey type. Knowledge of the direct relationship between fish larvae and their prey aids in our understanding of optimal foraging strategies and of the sources of mortality in marine fish larvae.     

Dissolved saxitoxin causes transient inhibition of sensorimotor function in larval Pacific herring (<Emphasis Type="Italic">Clupea harengus pallasi</Emphasis>)

Herring (Clupea harengus pallasi) spawning sites in Puget Sound, Washington overlap spatially and temporally with blooms of Alexandrium catenella, a toxic dinoflagellate species responsible for paralytic shellfish poisoning. Consequently, newly hatched herring larvae may be regularly exposed to the suite of dissolved paralytic shellfish toxins that are released into the water column from toxic cells during blooms. To date, virtually nothing is known about the impacts of these neurotoxins on early developmental stages of marine fish. In the present study, herring larvae at three ages, 0 days post hatch (dph), 4 dph, and 11 dph, were exposed to dissolved saxitoxin (STX) in 24-h and multi-day exposures. All larvae were examined for sensorimotor function (i.e. spontaneous swimming behavior and touch response). Significant reductions in spontaneous and touch-activated swimming behavior occurred within 1 h of exposure. EC₅₀s at 1 h of exposure were 1,500, 840, and 700 μg STX equiv. l⁻¹ for larvae introduced to STX at 0, 4, and 11 dph, respectively. This progressive age-specific increase in STX-induced paralysis suggests that older larvae were more sensitive to the toxin than younger larvae. Interestingly, herring larvae at all ages exhibited a significant degree of neurobehavioral recovery within 4–24 h of continuous exposure relative to the 1-h time point. This recovery of normal motor behaviors was not observed in previous studies with freshwater zebrafish (Danio rerio) larvae under the same continuous exposure conditions, suggesting that an adaptive detoxification or toxin sequestration mechanism may have evolved in some species of marine fish larvae. Our data reveal that (1) dissolved STX is bioavailable to marine finfish larvae, (2) the toxin is a paralytic agent with potencies that differ between developmental stages, and (3) STX-induced sensorimotor inhibition occurs rapidly but is transient in marine larvae. Collectively, these results suggest that dissolved algal toxins may have important sublethal effects on marine fish populations.     

Embryogenesis and larval biology of the ahermatypic scleractinian<Emphasis Type="Italic"> Oculina varicosa</Emphasis>

The ivory tree coral Oculina varicosa (Leseur, 1820) is an ahermatypic branching scleractinian that colonizes limestone ledges at depths of 6–100 m along the Atlantic coast of Florida. This paper describes the development of embryos and larvae from shallow-water O. varicosa, collected at 6–8 m depth in July 1999 off Fort Pierce, Florida (27°32.542 N; 79°58.732 W). The effect of temperature on embryogenesis, larval survival, and larval swimming speed were examined in the laboratory. Ontogenetic changes in geotaxis and phototaxis were also investigated. Embryos developed via spiral cleavage from small (100 µm), negatively buoyant eggs. Ciliated larvae developed after 6–9 h at 25°C. Embryogenesis ceased at 10°C, was inhibited at 17°C, and progressed normally at 25°C and 30°C. Larval survival, however, was high across the full range of experimental temperatures (11–31°C), although mortality increased in the warmest treatments (26°C and 31°C). Larval swimming speed was highest at 25°C, and lower at the temperature extremes (5°C and 35°C). An ontogenetic change in geotaxis was observed; newly ciliated larvae swam to the water surface and remained there for approximately 18 h, after which they swam briefly throughout the water column, then became demersal. Early larvae showed no response to light stimulation, but at 14 and 23 days larvae appeared to exhibit negatively phototactic behavior. Although low temperatures inhibited the development of O. varicosa embryos, the larvae survived temperature extremes for extended periods of time. Ontogenetic changes in larval behavior may ensure that competent larvae are close to the benthos to facilitate settlement. Previous experiments on survival, swimming speeds, and observations on behavior of O. varicosa larvae from deep-water adults indicate that there is no difference between larvae of the deep and shallow populations.Communicated by J.P. Grassle, New Brunswick     

Morphological evidence for vertical transmission of symbiotic bacteria in the viviparous sponge<Emphasis Type="Italic"> Halisarca dujardini</Emphasis> Johnston (Porifera,Demospongiae, Halisarcida)

All stages of vertical transmission of symbiotic bacteria, from the penetration into oocytes to the formation of rhagon, were investigated in the White Sea (Arctic) representatives of Halisarca dujardini Johnston (Demospongiae). Small populations of free-living specific symbiotic bacteria inhabit the mesohyl of H. dujardini. They are represented by a single morphotype of small spiral gram-positive bacteria. Vertical transmission of symbiotic bacteria between generations in sponges may occur in different ways. In the case of H. dujardini the bacteria penetrate into growing oocytes by endocytosis. A part of the bacteria plays a trophic role for oocytes and the other part remains undigested in membrane-bound vacuoles within the cytoplasm. In cleaving embryos bacteria are situated between the blastomeres or in the vacuoles. In the blastula all bacteria are disposed in the blastocoel. The symbionts are situated in intercellular spaces in free-swimming larvae and during metamorphosis. Symbiotic bacteria do not play any trophic role in the period of embryonic and postembryonic development of H. dujardini. No signs of destruction and digestion of bacteria were revealed at any stage of development.Communicated by O. Kinne, Oldendorf/Luhe