Larval Swimming Behavior Research Articles

Vertical swimming behavior in larvae of the Florida stone crab, Menippe mercenaria

Vertical swimming behavior in larvae of the Florida stone crab, Menippe mercenaria

Larval Fish Swimming Behavior Alters Dispersal Patterns From Marine Protected Areas in the North-Western Mediterranean Sea

Most demersal fishes undergo a dispersal phase as larvae, which strongly influences the connectivity among adult populations and, consequently, their genetic structure and replenishment opportunities. Because this phase is difficult to observe directly, it is frequently simulated through numerical models, most of which consider larvae as passive or only vertically migrating. However, in several locations, including the Mediterranean Sea, many species have been shown to swim fast and orient. Here we use a Lagrangian model to study connectivity patterns among three Mediterranean Marine Protected Areas (MPAs) and compare simulations in which virtual larvae are passive to simulations in which oriented swimming is implemented. The parameterization of behavior is based on observations for two groups of species of the family Sparidae: species with small larvae (i.e. 9-11 mm), displaying a maximum swimming speed of 6 cm s-1 and a pelagic larval duration of 13-19 days (e.g. Diplodus annularis L., Oblada melanura L.) and species with large larvae (i.e. 14-16 mm), displaying a maximum swimming speed of 10 cm s-1 and a PLD of 28-38 days (e.g. Spondyliosoma cantharus L.). Including larval behavior in the model i) increased the overall proportion of successful settlers, ii) enhanced self-recruitment within the MPAs, but also iii) increased the intensity and iv) widened the export of eggs and larvae (recruitment subsidy) from the MPAs; overall, it significantly changed connectivity patterns. These results highlight the need to gather the observational data that are required to correctly parameterize connectivity models.

Neurobehavioral effects of 1,2-propanediol in zebrafish (Danio rerio)

The use of electronic cigarettes (e-cigarettes) is increasing despite insufficient information concerning their long-term effects, including the effects of maternal e-cigarette use on pre- and postnatal development. Our previous study demonstrated that developmental exposure to 1,2-propanediol (a principal component of e-cigarette liquid) affected early development of zebrafish, causing reduced growth, deformities, and hyperactive swimming behavior in larvae. The current study extends assessment of the developmental toxicity of 1,2-propanediol by examining additional long-term behavioral effects. We demonstrate that embryonic/larval exposure of zebrafish to 1,2-propanediol (0.625% or 1.25%) not only affected behavioral parameters in the larvae, but also caused persisting behavioral effects in adults after early developmental exposure. Additional parameters, including neural and vascular development in larvae, stress response in adults, and concentration of neurotransmitters dopamine and serotonin in adult brain were examined, in order to explain the behavioral differences. These additional assessments did not find 1,2-propanediol exposure to significantly affect Tg(Neurog1:GFP) or the transcript abundance of neural genes (Neurog1, Ascl1a, Elavl3, and Lef1). Vascular development was not found to be affected by 1,2-propanediol exposure, as inferred from experiments with Tg(Flk1:eGFP) zebrafish; however, transcript abundance of vascular genes (Flk1, Vegf, Tie-2, and Angpt1) was decreased. No statistically significant changes were noted for plasma cortisol or brain neurotransmitters in adult fish. Lastly, analysis of gene transcripts involved with 1,2-propanediol metabolism (Adh5, Aldh2.1, and Ldha) showed an increase in Adh5 transcript. This is the first study to demonstrate that developmental exposure to 1,2-propanediol has long-term neurobehavioral consequences in adult zebrafish, showing that e-cigarettes contain substances potentially harmful to neurodevelopment.

Illicit drug ketamine induces adverse effects from behavioral alterations and oxidative stress to p53-regulated apoptosis in medaka fish under environmentally relevant exposures.

With increasing problems of drug abuse worldwide, aquatic ecosystems are contaminated by human pharmaceuticals from the discharge of hospital or municipal effluent. However, ecotoxicity data and related toxic mechanism for neuroactive controlled or illicit drugs are still lacking, so assessing the associated hazardous risk is difficult. This study aims to investigate the behavioral changes, oxidative stress, gene expression and neurotoxic or apoptosis effect(s) in larvae of medaka fish (Oryzias latipes) with environmentally relevant exposures of ketamine (KET) solutions for 1-14 days. KET exposure at an environmentally relevant concentration (0.004μM) to 40μM conferred specific patterns in larval swimming behavior during 24h. At 14 days, such exposure induced dose- and/or time-dependent alteration on reactive oxygen species induction, the activity of antioxidants catalase and superoxide dismutase, glutathione S-transferase and malondialdehyde contents in fish bodies. KET-induced oxidative stress disrupted the expression of acetylcholinesterase and p53-regulated apoptosis pathways and increased caspase expression in medaka larvae. The toxic responses of medaka larvae, in terms of chemical effects, were qualitatively analogous to those of zebrafish and mammals. Our results implicate a toxicological impact of waterborne KET on fish development and human health, for potential ecological risks of directly releasing neuroactive drugs-containing wastewater into the aquatic environment.

Ontogenetic Differences in Swimming Behavior of Fish Exposed to the Harmful Dinoflagellate Cochlodinium polykrikoides

AbstractBlooms of the ichthyotoxic dinoflagellate Cochlodinium polykrikoides present both lethal and sublethal threats to coastal marine organisms. Because prior studies of this harmful algal bloom (HAB) species have focused on its acute toxic effects on fish, there remains a limited understanding of the sublethal effects on the swimming behavior of fish when exposed to these blooms. We conducted a video‐based laboratory assessment of the effects of C. polykrikoides exposures on larval and juvenile fish swimming behavior. Juvenile and larval life stages of three forage species common to the U.S. East Coast were examined: wild Atlantic Silversides Menidia menidia, hatchery‐reared Inland Silversides M. beryllina, and hatchery‐reared Sheepshead Minnow Cyprinodon variegatus. Results showed that juvenile Atlantic Silversides and Inland Silversides exposed to C. polykrikoides concentrations of 102 cells/mL swam significantly further distances in comparison with their baseline (control) behavior. In an ecosystem context, the results of this research support field‐based studies demonstrating that when blooms of this HAB species are present, the relative abundance of fish declines (i.e., the fish presumably detect the blooms and swim away after exposure). Conversely, juvenile Sheepshead Minnow exhibited no increased swimming behavior when exposed, supporting previous studies indicating that this species is more resistant to C. polykrikoides toxicity. Importantly, no behavioral changes were found in experiments with larval conspecifics (i.e., Inland Silversides and Sheepshead Minnow), suggesting that younger life stages, which lack developed gills and olfactory systems, may be unable to detect the dinoflagellate. This clear ontogenetic difference implies that for certain fish species, reaching later life stages may provide a refuge to HAB toxicity.Received March 26, 2017; accepted June 5, 2017 Published online August 9.2017

Light stimulates swimming behavior of larval eastern oysters Crassostrea virginica in turbulent flow

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 571:109-120 (2017) - DOI: https://doi.org/10.3354/meps12106 Light stimulates swimming behavior of larval eastern oysters Crassostrea virginica in turbulent flow Jeanette D. Wheeler1,6,*, Elaine Luo2, Karl R. Helfrich3, Erik J. Anderson4,5, Victoria R. Starczak1, Lauren S. Mullineaux1 1Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 2Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON M5S3B3, Canada 3Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA 4Department of Mechanical Engineering, Grove City College, Grove City, PA 16127, USA 5Applied Ocean Physics and Engineering Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA6Present address: Institute of Environmental Engineering, Department of Civil, Environmental, and Geomatic Engineering, ETH Zürich, 8093 Zurich, Switzerland *Corresponding author: jwheeler@whoi.edu ABSTRACT: Planktonic larvae of the eastern oyster Crassostrea virginica are able to regulate their vertical position in the water, but the environmental cues responsible for this regulation, particularly in turbulent settings, remain unclear. We quantified swimming responses of late-stage oyster larvae in a grid-stirred turbulence tank to determine how light affects the swimming behavior of larvae over a range of hydrodynamic conditions similar to their natural coastal environments. We used particle image velocimetry and larval tracking to isolate larval swimming from local flow and to quantify 3 behavioral metrics: vertical swimming direction, proportion of larvae diving, and proportion of larvae swimming helically. We compared these metrics across turbulence levels ranging from still water (ε = 0 cm2 s-3) to estuarine-like conditions (ε = 0.4 cm2 s-3) in light and dark. At all turbulence levels, light had no effect on the proportion of upward swimming larvae, but elicited detectable increases in the proportion of helical swimming and diving behaviors. We further examined the effect of light and turbulence on specific characteristics of helical trajectories, and found that these environmental cues induce changes to both vertical and horizontal velocities of helically swimming larvae, changing the helix geometry. The increased prevalence of these behaviors in light likely plays an ecological role: increased diving in light (in conjunction with turbulence) is a potential mechanism to enhance settlement success, while changes to helical swimming in light may serve an anti-predatory function. Together, these behaviors provide insight into potentially complex larval responses to multiple simultaneous environmental cues. KEY WORDS: Larval invertebrate ecology · Larval swimming · Environmental cues · Hydrodynamics Full text in pdf format Supplementary material PreviousNextCite this article as: Wheeler JD, Luo E, Helfrich KR, Anderson EJ, Starczak VR, Mullineaux LS (2017) Light stimulates swimming behavior of larval eastern oysters Crassostrea virginica in turbulent flow. Mar Ecol Prog Ser 571:109-120. https://doi.org/10.3354/meps12106 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 571. Online publication date: May 17, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Exposure to 1,2-Propanediol Impacts Early Development of Zebrafish (Danio rerio) and Induces Hyperactivity.

The use of electronic cigarettes (e-cigarettes) is increasing as an alternative to tobacco burning cigarettes; however, their safety remains to be fully determined. The long-term effects of e-cigarettes are unknown, including the effects of maternal e-cigarette use on pre- and postnatal development. Additional research on the safety of e-cigarettes is needed. Especially useful would be information from high- and moderate-throughput economic model systems. This study investigates the effects of 1,2-propanediol, which was identified as the main component of e-cigarette liquid, on early development of zebrafish (an in vivo high-throughput model system that was recently proposed for the study of tobacco cigarette and e-cigarette toxicity). Zebrafish embryos were exposed to 1.25% or 2.5% 1,2-propanediol from 6 to 72 h post-fertilization (hpf). We show that exposure to 1,2-propanediol did not significantly affect mortality. Hatching success was significantly lower in 2.5% 1,2-propanediol-exposed embryos at 48 hpf, but at 72 hpf no significant differences were noted. Moreover, exposure to 1,2-propanediol reduced growth and increased the incidence of string heart, pericardial edema, and yolk sac edema. Most importantly, developmental exposure to 1.25% 1,2-propanediol caused hyperactive swimming behavior in larvae. This study demonstrates that 1,2-propanediol has adverse impacts on early development in zebrafish.

Investigation of larval settlement pathways in the marine bryozoan, Bugula neritina

Bugula neritina is a sessile marine bryozoan with a pelagic larval stage. Larvae frequently settle on boat hulls, facilitating the introduction of B. neritina to bays and estuaries worldwide. Adrenergic agonists, such as norepinephrine, inhibit larval settlement in a variety of marine invertebrate species, including B. neritina. Light also inhibits larval settlement of B. neritina, yet the underlying mechanisms by which light and adrenergic compounds exert their effects on larvae are largely unknown. Octopamine is considered the invertebrate analog of norepinephrine, and may be one endogenous compound involved in larval settlement pathways. In this study, we investigated the effects of norepinephrine and the adrenergic antagonist phentolamine on larval settlement, and found that norepinephrine inhibited larval attachment and increased larval swimming behavior, while phentolamine increased larval attachment and decreased larval swimming behavior. We used fluorescent labeling and immunocytochemistry to localize sensory system components, and found that larvae possess adrenergic-like receptors and octopamine-like immunoreactivity. We also exposed larvae to phentolamine in both dark and light conditions, and found that light inhibited larval attachment, but phentolamine blocked those inhibitory effects. Based on these results, we put forth a putative mechanistic explanation for the effects of both light and adrenergic compounds on B. neritina larval settlement behavior. This study sheds light on previously unknown pathways underlying larval settlement behavior of bryozoans, and may aid in the development of effective, non-toxic biofouling control strategies.

Reversal of pentylenetetrazole-altered swimming and neural activity-regulated gene expression in zebrafish larvae by valproic acid and valerian extract.

RationaleEthnopharmacology has documented hundreds of psychoactive plants awaiting exploitation for drug discovery. A robust and inexpensive in vivo system allowing systematic screening would be critical to exploiting this knowledge.ObjectiveThe objective of this study was to establish a cheap and accurate screening method which can be used for testing psychoactive efficacy of complex mixtures of unknown composition, like plant crude extracts.MethodsWe used automated recording of zebrafish larval swimming behavior during light vs. dark periods which we reproducibly altered with an anxiogenic compound, pentylenetetrazole (PTZ). First, we reversed this PTZ-altered swimming by co-treatment with a well-defined synthetic anxiolytic drug, valproic acid (VPA). Next, we aimed at reversing it by adding crude root extracts of Valeriana officinalis (Val) from which VPA was originally derived. Finally, we assessed how expression of neural activity-regulated genes (c-fos, npas4a, and bdnf) known to be upregulated by PTZ treatment was affected in the presence of Val.ResultsBoth VPA and Val significantly reversed the PTZ-altered swimming behaviors. Noticeably, Val at higher doses was affecting swimming independently of the presence of PTZ. A strong regulation of all three neural-activity genes was observed in Val-treated larvae which fully supported the behavioral results.ConclusionsWe demonstrated in a combined behavioral-molecular approach the strong psychoactivity of a natural extract of unknown composition made from V. officinalis. Our results highlight the efficacy and sensitivity of such an approach, therefore offering a novel in vivo screening system amenable to high-throughput testing of promising ethnobotanical candidates.Electronic supplementary materialThe online version of this article (doi:10.1007/s00213-016-4304-z) contains supplementary material, which is available to authorized users.

A biophysical model to assess the trade-off between larval recruitment and catch in southern Australia's largest prawn fishery

Data from stock assessment surveys, published research and climate sensors were linked to model the interaction between fishing, physical‐oceanographic processes and spatial patterns of larval settlement for western king prawn [Penaeus (Melicertus) latisulcatus]. This information was used to evaluate the trade‐off between larval recruitment and catch during fishing periods that demand high prices but coincide with spawning. Total rates of larval settlement were maximized when tidal currents and atmospheric physical‐forcing components were coupled with simulations of larval swimming behaviour under average gulf temperatures. Average gulf temperatures sustained longer larval durations and increased larval settlement rates by over 12% compared with warmer gulf conditions simulated under a scenario of global warming. Reproductive data coupled with outputs from the biophysical model identified consistent inter‐annual patterns in the areas contributing to larval settlement success. Areas located in the north‐east, and central‐west of the fishery, consistently contributed to over 40% of all larvae reaching a settlement in each year. Harvest sensitivity analyses indicated that changes in the spatial patterns of pre‐Christmas fishing could lead to improvements in overall rates of the larval settlement while maintaining or improving the levels of catch. Future studies to refine the model inputs relating to physical processes, larval behaviour and mortality rates for P. latisulcatus coupled with surveys of juvenile prawn abundance to ground truth the modelled predictions, would allow stock recruitment relationships to be more closely examined and inform adaptive management of the fishery in the future.

Relationship between larval settlement, alongshore wind stress and surface temperature in a numerical model of the central California coastal circulation

Author(s): Drake, PT; Edwards, CA; Morgan, SG | Abstract: Variations in larval settlement in coastal upwelling regions such as the California Current System (CCS) have been attributed to variations in physical forcing at various time and space scales, but existing findings are often conflicting and fail to explicitly consider larval transport and swimming behavior. Using virtual larvae in a realistic simulation of the CCS, temporal relationships between wind stress, temperature and nearshore settlement in central California are explored for several vertical swimming behaviors, given a pelagic larval duration (PLD) of 20 to 22 d. A robust negative correlation between upwelling-favorable, PLD-averaged wind stress and settlement was found at timescales of days to years for larvae exposed to the surface boundary layer (SBL), while settlement for larvae that remain below the layer throughout development is increased, and their overall settlement is ∼2 to 20 times higher. A 20 d running mean of the wind stress can account for 52 to 86% of logit-transformed settlement variance over the 6 yr study period. Wind stress and settlement are coherent at all intra-annual periods greater than the PLD. Monthly climatological cycles of PLD-averaged wind stress and transformed settlement are nearly identical for behaviors exposed to the SBL and constitute ∼80% of the monthly variance. Monthly anomalies of wind stress and settlement are also significantly correlated. Nearshore surface temperature is also well correlated with settlement, but significantly less so than wind stress on both seasonal and intra-seasonal timescales. Other PLDs ranging from 10 to 40 d displayed similar results. Physical forcing in this model is found to dominate intrinsic eddy variability in driving settlement.

Effects of larval swimming behavior on the dispersal and settlement of the eastern oyster Crassostrea virginica

Effects of larval swimming behavior on the dispersal and settlement of the eastern oyster Crassostrea virginica

Developmental exposures to waterborne abused drugs alter physiological function and larval locomotion in early life stages of medaka fish

Environmental pollution by neuroactive pharmaceuticals from wastewater discharge is a major threat to aquatic ecosystems. However, the ecotoxicologic effect of waterborne abused drugs remains unclear. Embryos of medaka fish (Oryzias latipes) were exposed to aqueous solutions of 2 hallucinogenic drugs, ketamine (KET) and methamphetamine (MET) (0.004–40μM) to assess developmental toxicity, oxidative stress and behavioral alteration in early life stages. The environmentally relevant concentration (0.004μM) of both KET and MET significantly delayed blood circulation and hatching time in embryos and altered larval swimming behavior (e.g., maximum velocity and relative turn angle). KET and MET induced similar oxidative stress responses in embryos, which were unrecoverable in hatchlings in drug-free solutions. Early life exposure to the 2 drugs conferred distinct patterns in larval locomotion: KET induced hyperactivity and a less tortuous swimming path, but MET-treated larvae showed hypoactivity and a clockwise swimming direction at high doses. The alteration in locomotor responses were generally similar in mammals and zebrafish. We report sensitive biomarkers (e.g., heartbeat, hatching and swimming behavior) by developmental stage of medaka that reflect environmentally relevant exposures of abused drugs. They could be useful for ecological risk assessment of waterborne neuroactive drugs. The toxicity results implicate a potential ecotoxicological impact of controlled or abused drugs on fish development and populations in aquatic environments.

Persisting effects of a PBDE metabolite, 6-OH-BDE-47, on larval and juvenile zebrafish swimming behavior

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants that are widely detected in the environment, biota, and humans. In mammals, PBDEs can be oxidatively metabolized to form hydroxylated polybrominated diphenyl ethers (OH-BDEs). While studies have examined behavioral deficits or alterations induced by exposure to PBDEs in both rodents and fish, no study to date has explored behavioral effects from exposure to OH-BDEs, which have been shown to have greater endocrine disrupting potential compared to PBDEs. In the present study, zebrafish (Danio rerio) were exposed during embryonic and larval development (0–6days post fertilization, dpf) to a PBDE metabolite, 6-hydroxy, 2,2′,4,4′ tetrabromodiphenyl ether (10–50nM) and then examined for short and long-term behavioral effects. Exposed zebrafish tested as larvae (6dpf) showed an altered swimming response to light–dark transitions, exhibiting hypoactivity in light periods compared to control fish. When fish exposed from 0–6dpf were tested as juveniles (45dpf), they showed an increased fear response and hyperactivity in response to tests of novel environment exploration and habituation learning. These results demonstrate that early life exposure to a PBDE metabolite can have immediate or later life (more than a month after exposure) effects on activity levels, habituation, and fear/anxiety.

Assessment of ichthyotoxicity and anthropogenic contamination in the surface waters of Kenting National Park, Taiwan.

Millions of tourists visit Kenting National Park (KNP) in southern Taiwan every year, causing great amount of sewage discharges in this area. This study aimed to assess the impact of sewage on KNP surface waters using zebrafish embryo-larval bioassays combined with chemical analyses of pharmaceuticals and personal care products (PPCPs). Surface water samples were collected monthly from May to October in 2010. During the monthly bioassays, zebrafish embryos were exposed to the water samples for 144 h. Hatchability, embryonic heart rate, larval survival rate, and deformities were recorded. Larval swimming behavior was also digitally quantified at the end of exposure. Significant decreases in hatchability and larval survival rate were observed at all sites. Both hatchability and larval survival rate were negatively correlated with nitrite and ammonia concentrations in the water. The field water had little effect on embryonic heart rate and morphology. However, lower swimming speeds and activity levels were observed in the larvae, suggesting neurobehavioral toxicity of the surface waters. The general detection frequency of the 28 target PPCPs was 75%. High levels of some PPCPs, particularly caffeine, N,N-diethyl-3-methylbenzamide (DEET), and nonylphenol, were measured in the water samples. Our results show that surface waters in KNP have been strongly impacted by human activities, resulting in lethal and behavioral toxicities in developing fish.

Modification of the larval swimming behavior in Oikopleura dioica, a chordate with a miniaturized central nervous system by dsRNA injection into fertilized eggs.

Using RNA interference, we have selectively perturbed neurotransmitter-related features of the larval swimming behavior of Oikopleura dioica, a tunicate with a central nervous system comprising about 130 neurons. We injected dsRNA into fertilized eggs to knockdown the expression of the genes, respectively, encoding ChAT (choline acetyltransferase) and GAD (glutamic acid decarboxylase), enzymes critical for the biosynthesis of acetylcholine and GABA. These two neurotransmitters have conserved roles during evolution, particularly within chordate motor systems, where they mediate respectively neuromuscular and central inhibitory signals. In Oikopleura, interference with ChAT expression prevented the normal bidirectional, propagating tail movement characteristic of swimming, permitting only repeated unilateral tail bends. Proper swimming was never observed, and the resting period between episodes of activity was lengthened. This phenotype is most likely caused by the reduction of transcription observed for both the targeted ChAT gene and the VAChT gene (Vesicular Acetylcholine Transporter), both genes being transcribed from the same operon. Interference with GAD expression led to an uncoordinated version of swimming with a spiral movement trajectory, but with episodes similar in duration and cycle frequency to those of normal swimming. Our results suggest locomotor functions for ChAT and GABA that are more subtle than previously proposed for tunicates and opens the way for a genetic dissection of Oikopleura neuronal circuits, which are likely to be among the most simplified in the chordate phylum.

Modeling larval connectivity of the Atlantic surfclams within the Middle Atlantic Bight: Model development, larval dispersal and metapopulation connectivity

To study the primary larval transport pathways and inter-population connectivity patterns of the Atlantic surfclam, Spisula solidissima, a coupled modeling system combining a physical circulation model of the Middle Atlantic Bight (MAB), Georges Bank (GBK) and the Gulf of Maine (GoM), and an individual-based surfclam larval model was implemented, validated and applied. Model validation shows that the model can reproduce the observed physical circulation patterns and surface and bottom water temperature, and recreates the observed distributions of surfclam larvae during upwelling and downwelling events. The model results show a typical along-shore connectivity pattern from the northeast to the southwest among the surfclam populations distributed from Georges Bank west and south along the MAB shelf. Continuous surfclam larval input into regions off Delmarva (DMV) and New Jersey (NJ) suggests that insufficient larval supply is unlikely to be the factor causing the failure of the population to recover after the observed decline of the surfclam populations in DMV and NJ from 1997 to 2005. The GBK surfclam population is relatively more isolated than populations to the west and south in the MAB; model results suggest substantial inter-population connectivity from southern New England to the Delmarva region. Simulated surfclam larvae generally drift for over one hundred kilometers along the shelf, but the distance traveled is highly variable in space and over time. Surfclam larval growth and transport are strongly impacted by the physical environment. This suggests the need to further examine how the interaction between environment, behavior, and physiology affects inter-population connectivity. Larval vertical swimming and sinking behaviors have a significant net effect of increasing larval drifting distances when compared with a purely passive model, confirming the need to include larval behavior.

Mechanisms of nearshore retention and offshore export of mussel larvae over the Agulhas Bank

Ecological connectivity is critical for population dynamics but in many benthic species it is complicated by a planktonic larval phase, whose dispersal remains poorly understood. Using a plankton pump, we examine the distribution of intertidal mussel larvae along three axes: alongshore, cross-shelf and by depth during a large scale (600km) cruise over the Agulhas Bank off southern Africa in August/September 2010. As a general pattern, higher veliger abundances were found close to the coast. Our analyses of the nearshore flow, estimated from ADCP data and the vertical distribution of larvae, show that onshore larval retention may be mediated by active vertical swimming through the water column guided by light and wind-induced turbulence. A massive offshore export of larvae off St Francis Bay was, however, observed during an Agulhas Current meander which influenced inner shelf waters. We hypothesize that, by increasing and homogenizing flow, the Agulhas Current may erase the effects of larval vertical positioning on onshore retention and transport larvae offshore. Our study highlights the need to integrate the effects of complex, region-specific physical dynamics with the swimming behaviour of larvae in order to explain their spatial distribution, population connectivity and the consequences for population dynamics.

A question of homology for chordate adhesive organs.

The larvae of aquatic vertebrates sometimes possess a transient, mucus-secreting gland on their heads. The most studied of these organs is the Xenopus cement gland. The tadpoles use it to attach to plants or to the water surface, supposedly to hide from predators and save energy before they can swim or feed. Moreover their gland, being innervated by trigeminal fibres, also mediates a locomotor stopping response when the larvae encounter an obstacle. We have described an equivalent organ on the head of the teleost Astyanax mexicanus, that we have called the casquette because of its shape and position on the larval head. The casquette is transient, sticky, secretes mucus, is innervated by the trigeminal ganglion, has an inhibitory function on larval swimming behavior, and expresses Bmp4 and Pitx1/2 during embryogenesis. Here we further discuss the nature of the equivalence between the frog cement gland and the fish casquette, and highlight the usefulness of non-conventional model species to decipher developmental and evolutionary mechanisms of morphological variations.

The ontogeny of larval swimming behavior in the crab Hemigrapsus sanguineus: Implications for larval transport

Many estuarine crab species are exported from this habitat at spawning and are physically transported to coastal waters where they undergo zoeal development. Later, they recruit back to the adult habitat as megalopae. Larval behavior within the context of wind-driven coastal circulation contributes to this process. The present study tested whether the crab Hemigrapsus sanguineus, an invasive species to the mid-Atlantic coast of the United States as well as in Europe, possesses behavioral responses to exogenous cues (gravity and light) and endogenous rhythms that would facilitate this scenario. Throughout larval development, H. sanguineus zoeae were negatively buoyant. In a laboratory test chamber, early stage (Z1) larvae displayed a strong negative geotaxis in darkness which resulted in surface swimming that was not offset by behavioral responses to light exposure. These Z1 stage larvae also possessed an endogenous tidal rhythm in swimming activity that was in phase with ebb tides in the spawning habitat and was independent of light exposure. These behaviors are consistent with export of larvae from estuarine to coastal waters where larval development occurs. Intermediate (Z3) and late (Z5) stage larvae exhibited a predominant negative geotaxis and surface swimming, with some zoeae showing positive geotaxis and/or sinking in the Z5 stage. Visual spectral sensitivity of eyes in Z3 larvae peaked between 450 and 510nm, with a secondary peak evident at short-wavelengths (~370nm). In both the Z3 and Z5 stages, larvae descended in response to light exposure, as expected under a negative feedback model of depth regulation common among crab larvae. Photoresponse thresholds of 5.8×1012 and 1.2×1014 photons m−2s−1 for Z3 and Z5 stage larvae, respectively, predict both stages to be in the lower water column during the day. After molting to megalopae, H. sanguineus display positive geotaxis and/or sinking in darkness and lack a phototactic response, consistent with settlement in the adult benthic habitat. Thus, larvae of the invasive crab H. sanguineus possess endogenous rhythms and behavioral responses to environmental cues that are similar to those observed in successful native species with a similar coastal larval development pattern.