159
Y. Sadovy de Mitcheson and P.L. Colin (eds.), Reef Fish Spawning Aggregations:
Biology, Research and Management, Fish & Fisheries Series 35,
DOI 10.1007/978-94-007-1980-4_6, © Springer Science+Business Media B.V. 2012
Abstract Aggregation spawning reef fi sh have planktonic (pre-fl exion) and nektonic
(post-fl exion) larval phases. Pelagic eggs hatch in about 24 h into non-motile, yolksac larvae and several days later into pre-fl exion larvae which feed actively and
control depth despite incomplete fi n development and limited motility. Thus, eggs,
yolk-sac and pre-fl exion larvae are all passive, planktonic drifters, yet they are not
necessarily fl ushed away by coastal currents into the open sea. Here we investigate
how the physics of near-shore fl ow features, such as diffusion of the initial spawning
cloud, tidal advection in coastal boundary currents and entrainment into tidal eddies,
interact with the complexities of reef topography to reduce offshore dispersion. We use
scale modelling to estimate dispersal via turbulence of gamete clouds for the fi rst
few days post-spawning. Thereafter, we emphasize empirical information from
tracked drifters released at spawning sites to evaluate alongshore tidal advection
and entrainment into tidal eddies. Larval behaviour is of great importance not only
to trajectories, but also because subtle depth adjustments by planktonic pre-fl exion
larvae permit contact with concentrated foods on density discontinuities or at
convergent fronts. This food source is critical for transformation from pre-fl exion
plankton into post-fl exion nektonic larvae.
W. M. Hamner (*)
Department Ecology and Evolutionary Biology , University California , Los Angeles , USA
e-mail: whamner@ucla.edu
J. L. Largier
Bodega Marine Laboratory , University of California , Davis , USA
e-mail: jlargier@ucdavis.edu
Chapter 6
Oceanography of the Planktonic Stages
of Aggregation Spawning Reef Fishes
William Marion Hamner and John Louis Largier
Y. Sadovy de Mitcheson and P.L. Colin (eds.), Reef Fish Spawning Aggregations:
Biology, Research and Management, Fish & Fisheries Series 35,
DOI 10.1007/978-94-007-1980-4_6, © Springer Science+Business Media B.V. 2012
Abstract Aggregation spawning reef fi sh have planktonic (pre-fl exion) and nektonic
(post-fl exion) larval phases. Pelagic eggs hatch in about 24 h into non-motile, yolksac larvae and several days later into pre-fl exion larvae which feed actively and
control depth despite incomplete fi n development and limited motility. Thus, eggs,
yolk-sac and pre-fl exion larvae are all passive, planktonic drifters, yet they are not
necessarily fl ushed away by coastal currents into the open sea. Here we investigate
how the physics of near-shore fl ow features, such as diffusion of the initial spawning
cloud, tidal advection in coastal boundary currents and entrainment into tidal eddies,
interact with the complexities of reef topography to reduce offshore dispersion. We use
scale modelling to estimate dispersal via turbulence of gamete clouds for the fi rst
few days post-spawning. Thereafter, we emphasize empirical information from
tracked drifters released at spawning sites to evaluate alongshore tidal advection
and entrainment into tidal eddies. Larval behaviour is of great importance not only
to trajectories, but also because subtle depth adjustments by planktonic pre-fl exion
larvae permit contact with concentrated foods on density discontinuities or at
convergent fronts. This food source is critical for transformation from pre-fl exion
plankton into post-fl exion nektonic larvae.
W. M. Hamner (*)
Department Ecology and Evolutionary Biology , University California , Los Angeles , USA
e-mail: whamner@ucla.edu
J. L. Largier
Bodega Marine Laboratory , University of California , Davis , USA
e-mail: jlargier@ucdavis.edu
Chapter 6
Oceanography of the Planktonic Stages
of Aggregation Spawning Reef Fishes
William Marion Hamner and John Louis Largier