187
6 Oceanography of the Planktonic Stages of Aggregation Spawning Reef Fishes
of the reef and when it reaches a topographic break. Propagules that initially
remain in the fl ow attached to reef topography, greatly increase their chance of local
recruitment. Coastal boundary currents, lateral trapping in embayments, and eddies
are fl ow features associated with specifi c reef topography that act to retain aggregation-spawned propagules. Resident and transient spawning aggregations do not
form everywhere but only at specifi c locations and particular times of day, tide, and
year.
Resident fi sh aggregators spawn at ebb tide each day into the nearshore waters
that fl ow tidally back and forth along the face of the reef. Tides fl ush embayments
in the reef, but embayments also sequester water, plankton and fi sh larvae from
larger scale circulation by lateral trapping. Resident aggregation spawning fi shes
are mostly small herbivores that are common and occur everywhere on all coral
reefs, and they spawn frequently (Chap. 4 ).
Most transient fi sh aggregations are composed of large carnivorous fi shes that
are less abundant than resident species, often migrate long distances to form spawning
aggregations, but only spawn on ebb tides at dusk at the edge of the continental shelf
near topographic projections of the reef and then only for several days a year at a
particular phase of one or several lunar cycles (Chaps. 7 and 12 ). While some larvae
are ejected into large-scale offshore fl ows, other larvae are entrained into and
retained by topographic tidal eddies generated by reef promontories. Understanding
eddy dynamics is critical for evaluating larval survivorship for both resident and
transient aggregators; the precise location of fi sh spawning aggregations on a given
reef affects both retention and dispersal of larvae.
It is diffi cult to tell a priori if fi sh have spawned into a linear, coastal boundary
current or into a rotating, topographic eddy. Without additional information from
drifters or aerial images, these different fl ow regimens look exactly alike to a swimmer on the edge of the reef. While wakes behind shallow-water continental reefs are
different from those downstream of oceanic reefs and islands, they both aggregate
plankton for fi rst-feeding larvae via horizontal layering (thermoclines, chlorophyll
maxima, thin-layers) and vertical discontinuities (fronts and slicks).
Acknowledgements We have been aided greatly in our review by two books, Marine Populations…
An Essay on Population Regulation and Speciation by Michael Sinclair ( 1988 ), and Physical
Oceanographic Processes of the Great Barrier Reef by Eric Wolanski ( 2001 ) , and by various
reviews cited herein, particularly those by Sponaugle et al. ( 2002 ) and Cowen and Sponaugle
( 2009 ) . Data for Fig. 6.11 of water column temperature and chlorophyll concentrations were provided by Dan Rudnick of Scripps Institution of Oceanography through Offi ce of Naval Research
grants N00014-06-1-0776 and N00014-10-1-0273. Pat Colin drafted most of the fi gures, provided
editorial assistance and contributed signifi cantly to the chapter.
References
Alldredge AL, Hamner WM (1980) Recurring aggregation of zooplankton by the tidal current.
Estuar Coast Mar Sci 10:31–37
Appeldoorn RS, Hensley DA, Shapiro DY et al (1994) Egg dispersal in a Caribbean coral reef fi sh.
Thalassoma bifasciatum . II Dispersal off the reef platform. Bull Mar Sci 54:271–280
6 Oceanography of the Planktonic Stages of Aggregation Spawning Reef Fishes
of the reef and when it reaches a topographic break. Propagules that initially
remain in the fl ow attached to reef topography, greatly increase their chance of local
recruitment. Coastal boundary currents, lateral trapping in embayments, and eddies
are fl ow features associated with specifi c reef topography that act to retain aggregation-spawned propagules. Resident and transient spawning aggregations do not
form everywhere but only at specifi c locations and particular times of day, tide, and
year.
Resident fi sh aggregators spawn at ebb tide each day into the nearshore waters
that fl ow tidally back and forth along the face of the reef. Tides fl ush embayments
in the reef, but embayments also sequester water, plankton and fi sh larvae from
larger scale circulation by lateral trapping. Resident aggregation spawning fi shes
are mostly small herbivores that are common and occur everywhere on all coral
reefs, and they spawn frequently (Chap. 4 ).
Most transient fi sh aggregations are composed of large carnivorous fi shes that
are less abundant than resident species, often migrate long distances to form spawning
aggregations, but only spawn on ebb tides at dusk at the edge of the continental shelf
near topographic projections of the reef and then only for several days a year at a
particular phase of one or several lunar cycles (Chaps. 7 and 12 ). While some larvae
are ejected into large-scale offshore fl ows, other larvae are entrained into and
retained by topographic tidal eddies generated by reef promontories. Understanding
eddy dynamics is critical for evaluating larval survivorship for both resident and
transient aggregators; the precise location of fi sh spawning aggregations on a given
reef affects both retention and dispersal of larvae.
It is diffi cult to tell a priori if fi sh have spawned into a linear, coastal boundary
current or into a rotating, topographic eddy. Without additional information from
drifters or aerial images, these different fl ow regimens look exactly alike to a swimmer on the edge of the reef. While wakes behind shallow-water continental reefs are
different from those downstream of oceanic reefs and islands, they both aggregate
plankton for fi rst-feeding larvae via horizontal layering (thermoclines, chlorophyll
maxima, thin-layers) and vertical discontinuities (fronts and slicks).
Acknowledgements We have been aided greatly in our review by two books, Marine Populations…
An Essay on Population Regulation and Speciation by Michael Sinclair ( 1988 ), and Physical
Oceanographic Processes of the Great Barrier Reef by Eric Wolanski ( 2001 ) , and by various
reviews cited herein, particularly those by Sponaugle et al. ( 2002 ) and Cowen and Sponaugle
( 2009 ) . Data for Fig. 6.11 of water column temperature and chlorophyll concentrations were provided by Dan Rudnick of Scripps Institution of Oceanography through Offi ce of Naval Research
grants N00014-06-1-0776 and N00014-10-1-0273. Pat Colin drafted most of the fi gures, provided
editorial assistance and contributed signifi cantly to the chapter.
References
Alldredge AL, Hamner WM (1980) Recurring aggregation of zooplankton by the tidal current.
Estuar Coast Mar Sci 10:31–37
Appeldoorn RS, Hensley DA, Shapiro DY et al (1994) Egg dispersal in a Caribbean coral reef fi sh.
Thalassoma bifasciatum . II Dispersal off the reef platform. Bull Mar Sci 54:271–280