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48 Larvae orientation in situ Divers observation does not allow to investigate cues Experimental methods are limited to near-reef orientation Studying orientation cues in situ and throughout ontogeny the scope of these results is limited due to methodological constraints, as detailed hereafter. Following larvae on scuba allows for observation of their natural swimming behaviours, both horizontally and vertically, in an open environment with apparently insignificant influence by the presence of divers. However, scuba diving restricts the duration and depth of the observations as well as the size of the study specimen, particularly when visibility is reduced. Therefore, this method has only been used for day-time observations of the late, pre-settlement stages of coral reef fishes in clear coastal waters. In addition, this method is impractical for manipulating and inferring the cues potentially used for orientation. Alternatively, the experimental methods have provided direct evidence that sound 115 or chemical 103 cues influence the orientation of reef fishes. Because these studies rely on the use of some kind of fixed device toward which larvae are attracted, they operate in shallow water habitats and/or on late stage larvae. They are designed to identify the cues involved during settlement and not for investigating large-scale navigation during the pelagic phase of reef fishes. In summary, the existing methods provide valuable information on the orientation of late-stage larvae relative to a limited set of coastal water cues. However, fish are known to develop swimming capacities early 25 ; hence, orientation of young individuals is potentially influential to the connectivity between adult populations. The behaviour of younger larvae in the pelagic environment is still completely unknown and may involve other cues, such as magnetic or electric fields, sun position, swell and waves 146 . Current methods are not appropriate to tackle these questions. Here, we present a device aimed at assessing the orientation of all larval stages directly in the pelagic environment, while conserving some control over environmental cues. Larvae embedded in oceanic waters have no apparent frame of reference for detecting the direction of the current 146 . Therefore the device is designed to drift with the current, and contains a circular behavioural arena in which a larva is filmed. The larva used for the experiment is thus exposed to sensory cues as a free larva would. Its trajectory is extracted from the movie recording and analysed through circular statistics to detect orientation behaviour. Simplicity, extendibility, and ease of use were major foci during the design of this instrument, while avoiding limitations in detecting and measuring orientation behaviour and manipulating proximal cues. We describe the observation methodology and present a proof of concept using data collected with late stage reef larvae.
Materials and Procedures 49 2.2 Materials and Procedures 2.2.1 Materials The OWNFOR (Orientation With No Frame Of Reference) apparatus is built upon a hollow cylindrical frame (130.8 cm height, 45.7 cm diameter) made of four aluminium bars and three aluminium rings (1.25 cm thick) welded together (Figure 2.1). Eight smaller bars, to which four strong nylon fabric sheets (130.8 cm × 29.20 cm) are secured, protrude diametrically outward from the cylinder and should lock the apparatus in the surrounding water mass. The bottom of the frame holds a cylindrical arena (12 cm height, 38 cm diameter) made of two round pieces of transparent acrylic (1.25 cm thick), secured by transparent plastic bolts. The bolts are placed outside of the arena so that the specimen cannot seek refuge behind them. The periphery of the arena is closed by 300 µm Nytex® mesh attached with Velcro® bands. The arena is entirely symmetrical to minimise visual reference for the larvae enclosed within. At the top of the frame, an Ikelite Underwater Systems housing contains a Sony Handycam DCR-PC350® camcorder aimed down at the arena, a diving compass, and a white reference mark over a black plastic disc. This DV camera has very good low-light performance and all filming is done in available light. Frames measure 720 × 576 pixels A symmetric cylindrical frame . . . . . . drifting with the current Record larval trajectories on video . . . Figure 2.1 3D representation of the observation apparatus
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À mon étoile.
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vi Résumé La plupart des organism
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viii Abstract Most demersal marine
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x Table des matières 1.3.3 Simple
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xii Table des matières 6.2.3 Examp
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xiv Liste des figures 4.6 Distribut
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Page 20 and 21: 2 Introduction La survie des larves
Page 22 and 23: 4 Introduction Limitation par le re
Page 24 and 25: 6 Introduction Les courants déterm
Page 26 and 27: 8 Introduction où m est le taux de
Page 28 and 29: 10 Introduction biologique simple.
Page 30 and 31: 12 Introduction Le milieu lui-même
Page 32 and 33: 14 Introduction Figure I.6 Schémat
Page 34 and 35: 16 Introduction obstacles technique
Page 36 and 37: 18 Introduction Figure I.8 Prédict
Page 38 and 39: 20 Introduction I.5 La biologie des
Page 40 and 41: 22 Introduction du fonctionnement d
Page 42 and 43: 24 Introduction L’objectif de cet
Page 44 and 45: 26 Behaviour in models 1.1 Introduc
Page 46 and 47: 28 Behaviour in models Using mean p
Page 48 and 49: 30 Behaviour in models 1.3 Vertical
Page 50 and 51: 32 Behaviour in models . . . bring
Page 52 and 53: 34 Behaviour in models of measured
Page 54 and 55: 36 Behaviour in models Additive dis
Page 56 and 57: 38 Behaviour in models In situ stud
Page 58 and 59: 40 Behaviour in models Operational
Page 60 and 61: 42 Behaviour in models Effects on p
Page 62 and 63: 44 Behaviour in models begins is no
Page 64 and 65: 46 Behaviour in models 1.10 Conclus
Page 68 and 69: 50 Larvae orientation in situ . . .
Page 70 and 71: 52 Larvae orientation in situ optio
Page 72 and 73: 54 Larvae orientation in situ if >
Page 74 and 75: 56 Larvae orientation in situ Table
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Page 78 and 79: 60 Larvae orientation in situ 2.A A
Page 80 and 81: 62 Behaviour of settling fishes at
Page 87 and 88: Chapter 4 Biophysical correlates in
Page 89 and 90: Methods 71 4.2 Methods 4.2.1 Sampli
Page 91 and 92: Methods 73 Three rotations were com
Page 93 and 94: Methods 75 test really focuses on w
Page 95 and 96: Results 77 Figure 4.3 Mean of insta
Page 97 and 98: Results 79 Figure 4.5 Perspective v
Page 99 and 100: Results 81 Table 4.1 Abundances of
Page 101 and 102: Results 83 Figure 4.8 Distribution
Page 103 and 104: Results 85 Figure 4.10 Concentratio
Page 105 and 106: Discussion 87 Figure 4.11 Compariso
Page 107 and 108: Discussion 89 But the most likely e
Page 109 and 110: Acknowledgements 91 This evidence a
Page 111 and 112: Chapter 5 Ontogenetic vertical “m
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The statistical analysis of vertica
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Methods 101 80, 55, 30 m (Figure 4.
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Methods 103 same station were likel
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Results 105 Figure 5.2 Univariate r
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Results 107 5.4.3 Ontogenetic shift
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Results 109 Figure 5.5 Violin plot
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Discussion 111 5.5 Discussion 5.5.1
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Discussion 113 expression of differ
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Chapter 6 Oceanography vs. behaviou
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Introduction 117 a good description
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A general modelling framework for l
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The balance between feeding and pre
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Oriented swimming and passive advec
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General discussion 161 such integra
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General discussion 163 6.5.2 Why se
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General discussion 165 such as the
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General discussion 167 energeticall
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Acknowledgements 169 Therefore: •
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172 Conclusion Un environnement pé
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174 Conclusion global sur la connec
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176 Conclusion l’intérêt est po
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178 Conclusion La différence entre
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180 Conclusion Mieux décrire la di
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182 Conclusion Comme tout comportem
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184 Undescribed Chaetodonthidae Fig
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186 Undescribed Chaetodonthidae Fig
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188 Bibliographie [12] Cushing DH.
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190 Bibliographie [39] Johnson MW.
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192 Bibliographie [71] Paris CB, Co
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194 Bibliographie [99] Lara MR. Mor
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196 Bibliographie [127] Masuda R, S
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198 Bibliographie [157] Holbrook SJ
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200 Bibliographie [187] Bowen B, Ba
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202 Bibliographie [218] Oxenford HA
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204 Bibliographie [246] Wellington
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206 Bibliographie [276] Sargent RC,
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208 Bibliographie [308] Greenberg D
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210 Remerciements solides pour ces
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212 Remerciements tri des larves de
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214 Remerciements Évidemment, tout
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