147
5 Timing and Location of Aggregation and Spawning in Reef Fishes
5.8.4 Location and Height Above the Bottom of Spawning
Nearly all fi shes with planktonic eggs release their gametes some distance above the
bottom and the eggs are positively buoyant. Exceptions among aggregation spawners
are rabbitfi shes, triggerfi shes and damselfi shes (Pomacentridae). Some TA species,
such as cubera snappers (Heyman et al. 2005 ; Kadison et al. 2006 ) ascend, often
almost to the surface. Among RA species the humphead wrasse spawns as pairs
near the surface (Colin 2010 ) while the yellow and blueback fusilier, Caesio teres,
spawned as a large mass close to the surface (Bell and Colin 1986 ) . Various surgeonfi shes and parrotfi shes also spawn very close to the surface, but ascend from
only a few metres depth (Robertson 1983 ) . The ascent of fi shes (including most
aggregation spawners) above the bottom causes expansion of the swim bladder and,
as originally suggested by Randall and Randall ( 1963 ) , this may aid in expulsion of
the gametes at the top of the ascent. This expansion may also limit how high fi shes
can rise above the bottom, ascending only to a depth where expansion aids spawning, but not to the point of endangering the fi sh through loss of buoyancy control or
internal damage from overinfl ation.
For most species, benthic-based egg predators are believed to be the most
important factor favouring spawning at some height above the bottom. Thresher
( 1984 ) found that both large and small species spawning during the day released
their eggs at the same height above the bottom, but for those spawning at dusk,
larger species spawned higher in the water column. Due to positive buoyancy, it is
likely most pelagic reef fi sh eggs ascend up into the upper few metres of the water
column before hatching, even if released at 20–30 m depth. The egg ascent rates
measured have been 8.4–18.6 cm min
−1 for cubera snapper (Heyman et al. 2001 )
and 11 cm min
−1 for coney, Epinephelus fulvus (Colin 1992 ) . At these rates eggs
spawned at 10–20 m would reach the surface within a few hours, well before hatching.
Spiralling of rising and spawning fi sh may produce a vortex that helps the ascent of
eggs towards the surface (Heyman et al. 2005 ) . Advective mechanisms also tend to
transport eggs away from reefs and benthic based predators (usually at speeds much
faster than ascent rates), although changing tidal currents can later bring them
back towards natal areas (Hamner et al. 2007 ) . Other aspects of the fate of eggs and
larvae just after spawning are discussed in Chaps. 6 and 7 .
5.8.5 Multi-species Aggregations and Sites
The multi-species use of aggregation sites was fi rst reported by Smith ( 1972 ) who
noted in the Bahamas, based on fi sher information, that black groupers, Mycteroperca
bonaci, also used the same aggregation site (but at a different time) as Nassau
groupers. Subsequently Olsen and LaPlace ( 1979 ), Colin ( 1992 ) , Carter ( 1989 ) ,
Carter et al. ( 1994 ) , Whaylen et al. ( 2006 ) , Sala et al. ( 2001 ) , Starr et al. ( 2007 ) , and
Sadovy et al. ( 1994 ) reported use of aggregation sites by multiple grouper species
5 Timing and Location of Aggregation and Spawning in Reef Fishes
5.8.4 Location and Height Above the Bottom of Spawning
Nearly all fi shes with planktonic eggs release their gametes some distance above the
bottom and the eggs are positively buoyant. Exceptions among aggregation spawners
are rabbitfi shes, triggerfi shes and damselfi shes (Pomacentridae). Some TA species,
such as cubera snappers (Heyman et al. 2005 ; Kadison et al. 2006 ) ascend, often
almost to the surface. Among RA species the humphead wrasse spawns as pairs
near the surface (Colin 2010 ) while the yellow and blueback fusilier, Caesio teres,
spawned as a large mass close to the surface (Bell and Colin 1986 ) . Various surgeonfi shes and parrotfi shes also spawn very close to the surface, but ascend from
only a few metres depth (Robertson 1983 ) . The ascent of fi shes (including most
aggregation spawners) above the bottom causes expansion of the swim bladder and,
as originally suggested by Randall and Randall ( 1963 ) , this may aid in expulsion of
the gametes at the top of the ascent. This expansion may also limit how high fi shes
can rise above the bottom, ascending only to a depth where expansion aids spawning, but not to the point of endangering the fi sh through loss of buoyancy control or
internal damage from overinfl ation.
For most species, benthic-based egg predators are believed to be the most
important factor favouring spawning at some height above the bottom. Thresher
( 1984 ) found that both large and small species spawning during the day released
their eggs at the same height above the bottom, but for those spawning at dusk,
larger species spawned higher in the water column. Due to positive buoyancy, it is
likely most pelagic reef fi sh eggs ascend up into the upper few metres of the water
column before hatching, even if released at 20–30 m depth. The egg ascent rates
measured have been 8.4–18.6 cm min
−1 for cubera snapper (Heyman et al. 2001 )
and 11 cm min
−1 for coney, Epinephelus fulvus (Colin 1992 ) . At these rates eggs
spawned at 10–20 m would reach the surface within a few hours, well before hatching.
Spiralling of rising and spawning fi sh may produce a vortex that helps the ascent of
eggs towards the surface (Heyman et al. 2005 ) . Advective mechanisms also tend to
transport eggs away from reefs and benthic based predators (usually at speeds much
faster than ascent rates), although changing tidal currents can later bring them
back towards natal areas (Hamner et al. 2007 ) . Other aspects of the fate of eggs and
larvae just after spawning are discussed in Chaps. 6 and 7 .
5.8.5 Multi-species Aggregations and Sites
The multi-species use of aggregation sites was fi rst reported by Smith ( 1972 ) who
noted in the Bahamas, based on fi sher information, that black groupers, Mycteroperca
bonaci, also used the same aggregation site (but at a different time) as Nassau
groupers. Subsequently Olsen and LaPlace ( 1979 ), Colin ( 1992 ) , Carter ( 1989 ) ,
Carter et al. ( 1994 ) , Whaylen et al. ( 2006 ) , Sala et al. ( 2001 ) , Starr et al. ( 2007 ) , and
Sadovy et al. ( 1994 ) reported use of aggregation sites by multiple grouper species