Experimental analysis of the contribution of swimming and drifting to the displacement of reef fish larvae |
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Authors: | Email author" target="_blank">J?Derek HoganEmail author Camilo?Mora |
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Institution: | (1) Department of Biological Sciences, University of Windsor, 401 Sunset Ave., Windsor, ON, Canada, N9B3P4;(2) Present address: Leigh Marine Laboratory, University of Auckland, , New Zealand |
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Abstract: | The extent to which behaviour affects the dispersal of pelagic larvae in reef fishes has been a topic of major discussion
among marine ecologists. Here, we experimentally quantified the extent to which the displacement of late-stage larvae of Abudefduf saxatilis is due to active movement (i.e. swimming) and drifting. We consider drifting as the component of larval displacement accounted
for by the current. Drifting was quantified by comparing larval displacement to the displacement of passive particles in an
extended flow chamber that gave larvae the free choice of swimming (i.e. swim with or against the current or not swim at all).
We also determine whether drifting results from currents exceeding larval swimming capabilities or from the behavioural choice
of larvae of not to swim against adverse currents. To do this, we compare the speeds of larval swimming in the extended flow
chamber to those obtained in a smaller chamber in which larvae are behaviourally forced to swim due to space constraints and
a retaining fence (most available data on larval swimming is based on this sort of chamber). Within the extended chamber,
larvae tended to face the current and swim slower than it. This resulted in a net displacement increasingly determined by
drifting. We also found that in the extended chamber, larvae swam at speeds between one and six times slower than the speeds
they achieved in the “behaviourally modifying” smaller chamber. This suggests that the net displacement in the extended chamber
was in part due to the behavioural choice of the larvae of not to swim. The importance of this “behavioural drifting” is discussed
in terms of energy savings required for successful completion of the larval period and post-settlement survival. The idea
that larvae may modulate their swimming behaviour raises caution for the use of published data regarding swimming capabilities
of reef fish larvae when assessing the extent to which these fish actively affect their dispersal. |
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