An integrative investigation of sensory organ development and orientation behavior throughout the larval phase of a coral reef fish

The dispersal of marine larvae determines the level of connectivity among populations, influences population dynamics, and affects evolutionary processes. Patterns of dispersal are influenced by both ocean currents and larval behavior, yet the role of behavior remains poorly understood. Here we report the first integrated study of the ontogeny of multiple sensory systems and orientation behavior throughout the larval phase of a coral reef fish—the neon goby, Elacatinus lori. We document the developmental morphology of all major sensory organs (lateral line, visual, auditory, olfactory, gustatory) together with the development of larval swimming and orientation behaviors observed in a circular arena set adrift at sea. We show that all sensory organs are present at hatch and increase in size (or number) and complexity throughout the larval phase. Further, we demonstrate that most larvae can orient as early as 2 days post-hatch, and they swim faster and straighter as they develop. We conclude that sensory organs and swimming abilities are sufficiently developed to allow E. lori larvae to orient soon after hatch, suggesting that early orientation behavior may be common among coral reef fishes. Finally, we provide a framework for testing alternative hypotheses for the orientation strategies used by fish larvae, laying a foundation for a deeper understanding of the role of behavior in shaping dispersal patterns in the sea

Optical 3D-storage in sol-gel materials with a reading by Optical Coherence Tomography-technique

We report on the recording of 3D optical memories in sol-gel materials by using a non-linear absorption effect. This effect induces a local change of the optical properties of the material which is read and quantified with a high resolution full-field Optical Coherence Tomography setup. It is the first time that this technique is used for this purpose. Data recording was performed by focused picosecond (ps) single-pulse irradiation at 1064 nm with energy densities of 10 and 33 J/cm2 per pulse.Comment: 19 pages, 7 figure

Impact of Biological Variability on the Dispersal of Coral Reef Fish Larvae: A Study of Early Life Behaviors and Group Dispersal

Demersal coral reef fish all share a complex life cycle, with a demersal phase as juvenile and adults, and a pelagic larval phase. This larval phase is thought to disperse offspring, connecting distant fish populations and influencing meta-population dynamics. Accurately estimating the connectivity between fish populations is important for the conservation, protection, and managements of coral reef fish; however, this estimation remains a difficult and challenging task. During dispersal, fish larvae are transported by the currents but actively modify their trajectories to improve their odds for survival/settlement. Studies conducted on pre-settlement stage larvae have shown that they use their swimming and sensory abilities to detect environmental cues and orient toward their settlement grounds. Although the behaviors of coral reef fish larvae have been the topic of many studies, there are still a lot of open questions concerning their early life stage and the development of their behavioral abilities. This dissertation attempts to fill this gap by documenting the beginning of the life of reef fish larvae and quantifying the impact of biophysical interactions after hatching and during development. This dissertation is divided in four parts: a description of coral reef fish hatching strategies, a quantification of the potential for cohesive dispersal, a study of the impact of biological uncertainties on estimates of connectivity, and a study of the impact of orientation behaviors on estimates of connectivity. In the first part of this work, following in situ observations, we describe the hatching strategies of demersal coral reef fish. These observations lead us to investigate whether larvae disperse in cohesive groups. With numerical models developed to quantify biophysical interactions, we demonstrate that with certain swimming strategies, fish larvae could counteract micro-scale turbulence and maintain group cohesion. Then, we implemented larval behaviors in a biophysical model to account for larval active swimming during dispersal. The simulated larval behaviors rely on empirical parameters to model biological traits and behaviors --such as mortality, swimming abilities and orientation-- and modulate larval settlement and dispersal forecasts. These parameters are, however, uncertain because they are poorly constrained by observations and vary naturally between individuals. We construct and use a polynomial chaos surrogate to quantify the impacts of these uncertain biological parameters on estimates of larval connectivity. We then highlight the uncertainties associated with the mechanisms used by fish larvae to orient and quantify their impact on the dispersal of a model fish species. Finally, we discuss the early life behaviors and their impact on connectivity estimates, and we propose different methods that can be used to quantify and reduce uncertainties.</p

Environmental conditions and paternal care determine hatching synchronicity of coral reef fish larvae

For all fishes, hatching is a short but crucial event, and the conditions under which it occurs considerably influence the success of the larvae. For coral reef fish, hatching is even more important because it marks the beginning of the dispersal phase. The timing of hatching dictates the conditions that the larvae will encounter, potentially influencing their survival and dispersal. Despite this importance, very few studies have looked at hatching of marine fishes in the natural environment because of important technical constrains. In this study, we directly examined the temporal pattern of hatching during the night. Using remote night vision cameras and infrared lights to avoid disturbances, we successfully documented in situ hatching events of three coral reef fish species, all benthic brooders (Abudefduf saxatilis, Stegastes partitus, and Elacatinus lori). Hatching timing, rate, and duration were computed from the observations, and highlight different hatching strategies used by the fish species. The analysis of the fish behaviors shows that the males display parental care beyond the incubation period of the eggs and increase activity during the hatching events. With this study, we can relate the hatching events to the environmental context, giving us a better understanding of the factors influencing the beginning of the larval phase. These observations highlight the benefit of in situ studies to better understand the characteristics and potential consequences of hatching

Hydrodynamic and biological constraints on group cohesion in plankton

•Fish larvae and plankton have the abilities to actively counteract the dispersive effects of micro-scale turbulence and could maintain group cohesion.•Some fish larvae could form groups early on in development.•Specific swimming strategies would help maintain group cohesion.•Migration to low turbulence regions should enhance group cohesion.•Behavioral experiments should be done in natural turbulent environment. The dynamics of plankton in the ocean are determined by biophysical interactions. Although physics and biotic behaviors are known to influence the observed patchiness of planktonic populations, it is still unclear how much, and if, group behavior contributes to this biophysical interaction. Here, we demonstrate how simple rules of behavior can enhance or inhibit active group cohesion in plankton in a turbulent environment. In this study, we used coral-reef fish larvae as a model to investigate the interaction between microscale turbulence and planktonic organisms. We synthesized available information on the swimming speeds and sizes of reef fish larvae, and developed a set of equations to investigate the effects of viscosity and turbulence on larvae dispersion. We then calculated the critical dispersion rates for three different swimming strategies – cruise, random-walk, and pause-travel – to determine which strategies could facilitate group cohesion during dispersal. Our results indicate that swimming strategies and migration to low-turbulence regions are the key to maintaining group cohesion, suggesting that many reef fish species have the potential to remain together, from hatching to settlement. In addition, larvae might change their swimming strategies to maintain group cohesion, depending on environmental conditions and/or their ontogenic stage. This study provides a better understanding of the hydrodynamic and biological constraints on group formation and cohesion in planktonic organisms, and reveals a wide range of conditions under which group formation may occur

Quantitative uncertainty estimation in biophysical models of fish larval connectivity in the Florida Keys

International audienceThe impacts of seven uncertain biological parameters on simulated larval connectivity in the Florida Keys are investigated using Polynomial chaos surrogates. These parameters describe biological traits and behaviours-such as mortality, swimming abilities, and orientation-and modulate larval settlement as well as dispersal forecasts. However, these parameters are poorly constrained by observations and vary naturally between individual larvae. The present investigation characterizes these input uncertainties with probability density functions informed by previous studies of Abudefduf saxatilis. The parametric domain is sampled via ensemble calculations, then a polynomial-based surrogate is built to explicitly approximate the dependence of the model outputs on the uncertain model inputs, which enables a robust statistical analysis of uncertainties. This approach allows the computation of probabilistic dispersal kernels that are further analyzed to understand the impact of the parameter uncertainties. We find that the biological input parameters influence the connectivity differently depending on dispersal distance and release location. The global sensitivity analysis shows that the interactions between detection distance threshold, orientation ontogeny, and orientation accuracy, are the dominant contributors to the uncertainty in settlement abundance in the Florida Keys. Uncertainties in swimming speed and mortality, on the other hand, seem to contribute little to dispersal uncertainty

Table_1_Combined biophysical and genetic modelling approaches reveal new insights into population connectivity of New Zealand green-lipped mussels.xlsx

Understanding how ocean currents affect larval transport is crucial for understanding population connectivity in sessile marine invertebrates whose primary dispersal opportunity occurs during the pelagic larval stage. This study used Lagrangian particle tracking experiments to examine population connectivity in New Zealand green-lipped mussels (Perna canaliculus) at the national scale. Predicted patterns of larval dispersal were compared to published multi-locus microsatellite data of observed population genetic structure. Estimates of oceanographic circulation correlated significantly with FST, and we conclude that hydrodynamic processes are important in driving genetic connectivity. However, no evidence was found for an oceanographic barrier to gene flow south of Cook Strait, an important feature of genetic structure observed across several marine invertebrate species. Discrepancies between genetic and biophysical data may be explained by several factors including the different timescales of connectivity described by the two methods and the impact of localised ecological conditions and corresponding adaptations in genetic structure not captured by the bipohysical model. Population genetic analyses provide empirical data on realised connectivity and Lagrangian particle tracking experiments reveal information about directionality and asymmetry of connections that often cannot be determined by molecular analyses alone, thus a multidisciplinary approach is recommended.</p