Behaviour that influences dispersal and connectivi

Authors: Jeffrey M Leis Kelly J Wright Rebecca N Johnson

Publish Date: 2007/09/05

Volume: 153, Issue: 1, Pages: 103-117

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Abstract

Determining the scale of larval dispersal and population connectivity in demersal fishes is a major challenge in marine ecology Historically considerations of larval dispersal have ignored the possible contributions of larval behaviour but we show here that even young small larvae have swimming orientation and vertical positioning capabilities that can strongly influence dispersal outcomes Using young 11–15 days relatively poorly developed 8–10 mm larvae of the pomacentrid damselfish Amblyglyphidodon curacao identified using mitochondrial DNA we studied behaviour relevant to dispersal in the laboratory and sea on windward and leeward sides of Lizard Island Great Barrier Reef Behaviour varied little with size over the narrow size range examined Critical speed was 275 ± 10 cm s−1 309 BL s−1 and in situ speed was 136 ± 06 cm s−1 Fastest individuals were 446 and 250 cm s−1 for critical and in situ speeds respectively In situ speed was about 50 of critical speed and equalled mean current speed Unfed larvae swam 172 ± 29 h at 8–10 cm s−1 520 ± 86 km and lost 25 wet weight over that time Vertical distribution differed between locations modal depth was 25–50 and 100–125 m at leeward and windward sites respectively Over 80 of 71 larvae observed in situ had directional swimming trajectories Larvae avoided NW bearings with an overall mean SE swimming direction regardless of the direction to nearest settlement habitat Larvae made smaller changes between sequential bearings of swimming direction when swimming SE than in other directions making it more likely they would continue to swim SE When swimming NW 62 of turns were left more than in other directions which would quickly result in swimming direction changing away from NW This demonstrates the larvae knew the direction in which they were swimming and provides insight into how they achieved SE swimming direction Although the cues used for orientation are unclear some possibilities seemingly can be eliminated Thus A curacao larvae near Lizard Island on average swam into the average current at a speed equivalent to it could do this for many hours and chose different depths in different locations These behaviours will strongly influence dispersal and are similar to behaviour of other settlementstage pomacentrid larvae that are older and largerIt is a pleasure to acknowledge the skilful field assistance of Marcus Gregson Amanda Hay Klaus Heubert and Tom Trnski As always the staff of the Lizard Island Research Station made our work possible and our stay pleasant and productive Ash Fowler and Tom Mullaney provided essential assistance with the otoliths and Iain Suthers provided laboratory facilities Suzanne Bullock inked Fig 2 and she Michelle Yerman and Greer Howarth provided editorial assistance The research was supported by ARC grant DP0345876 to JML and by the Australian Museum KJW was supported by an Australian Postgraduate Award from the University of New South Wales

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