209
7 Aggregation Spawning: Biological Aspects of the Early Life History
of their planktonic lives. Four of the families with the highest average swimming
speeds have aggregating species (surgeonfi shes, rabbitfi shes, snappers, emperors).
Despite this capability late in larval life, larvae of these same families are weak
swimmers early in larval life. For example, Fisher ( 2005 ) examined swimming ability
in 10 species of reef fi shes, but only one, the brown surgeonfi sh, Acanthurus
nigrofuscus , had a pelagic egg (also an aggregation spawner). The brown surgeonfi sh at hatching were the slowest swimmers with a value near zero (Fisher 2005 ,
Fig. 2) refl ecting the feeble ability of yolk sac larvae to distribute themselves or
control their depth. Overall she found that larval reef fi shes (minus brown surgeonfi sh)
increase their swimming speed in an essentially linear relationship with age (for the
species examined) and that during the latter half of larval life they swim suffi ciently
well to be able to infl uence their location in relation to average currents near reefs.
The vast increase in swimming capability with growth needs to be put into the
perspective of the entire ELH in that larvae with pelagic eggs will spend roughly the
fi rst half of their larval life without the ability to swim against average currents.
Once they have the capability to swim robustly, their location in the ocean could be
quite far from any shallow water habitat.
7.6.3 Do Aggregation-Spawning Species Recruit
as Large Cohorts?
If large numbers of propagules are started simultaneously from a limited number of
locations via aggregation spawning, does this produce a corresponding pulse of
recruitment by a large settlement-ready cohort at the end of pelagic life? It would
seem the prospects for large recruitment pulses from aggregation spawning, particularly from TAs, would be high. For resident aggregators, which often have lengthy
spawning seasons, it seems less likely recruitment would be pulsed, unless survival
of some cohorts are enhanced by processes during pelagic life. There is some limited
evidence to support such a conclusion, but the connections between aggregation
spawning and the occurrence of large cohorts is far from certain. Large pulses of
recruitment might be produced by non-aggregation spawners which have a short
spawning season. Such would probably be indistinguishable from aggregation spawning recruitment pulses. Differential survival in the pelagic stage among fi shes which
spawn would also tend to produce recruitment in large cohorts. Interestingly,
some capture-based aquaculture fi sheries are based on catching large pulses of settlement phase larvae (Sect. 8.2.3 ).
There are records of large recruitment pulses for reef fi shes; many from aggregation
spawning species or families. Such are known in surgeonfi shes, groupers, wrasses,
tetraodontiform fi shes, bigeyes (Priacanthidae), Moorish idols (Zanclidae) and rabbitfi shes (Fig. 7.6 ). In a large recruitment pulse, high numbers of settlement-ready
fi shes appear over just a few days and, based on locations where such pulses have
been sampled, recruit over reef crests (Dufour and Galzin 1993) in the Indo-Pacifi c,
through tidal channels from offshore waters (Keener et al 1988 ; Shenker et al. 1993 ;
7 Aggregation Spawning: Biological Aspects of the Early Life History
of their planktonic lives. Four of the families with the highest average swimming
speeds have aggregating species (surgeonfi shes, rabbitfi shes, snappers, emperors).
Despite this capability late in larval life, larvae of these same families are weak
swimmers early in larval life. For example, Fisher ( 2005 ) examined swimming ability
in 10 species of reef fi shes, but only one, the brown surgeonfi sh, Acanthurus
nigrofuscus , had a pelagic egg (also an aggregation spawner). The brown surgeonfi sh at hatching were the slowest swimmers with a value near zero (Fisher 2005 ,
Fig. 2) refl ecting the feeble ability of yolk sac larvae to distribute themselves or
control their depth. Overall she found that larval reef fi shes (minus brown surgeonfi sh)
increase their swimming speed in an essentially linear relationship with age (for the
species examined) and that during the latter half of larval life they swim suffi ciently
well to be able to infl uence their location in relation to average currents near reefs.
The vast increase in swimming capability with growth needs to be put into the
perspective of the entire ELH in that larvae with pelagic eggs will spend roughly the
fi rst half of their larval life without the ability to swim against average currents.
Once they have the capability to swim robustly, their location in the ocean could be
quite far from any shallow water habitat.
7.6.3 Do Aggregation-Spawning Species Recruit
as Large Cohorts?
If large numbers of propagules are started simultaneously from a limited number of
locations via aggregation spawning, does this produce a corresponding pulse of
recruitment by a large settlement-ready cohort at the end of pelagic life? It would
seem the prospects for large recruitment pulses from aggregation spawning, particularly from TAs, would be high. For resident aggregators, which often have lengthy
spawning seasons, it seems less likely recruitment would be pulsed, unless survival
of some cohorts are enhanced by processes during pelagic life. There is some limited
evidence to support such a conclusion, but the connections between aggregation
spawning and the occurrence of large cohorts is far from certain. Large pulses of
recruitment might be produced by non-aggregation spawners which have a short
spawning season. Such would probably be indistinguishable from aggregation spawning recruitment pulses. Differential survival in the pelagic stage among fi shes which
spawn would also tend to produce recruitment in large cohorts. Interestingly,
some capture-based aquaculture fi sheries are based on catching large pulses of settlement phase larvae (Sect. 8.2.3 ).
There are records of large recruitment pulses for reef fi shes; many from aggregation
spawning species or families. Such are known in surgeonfi shes, groupers, wrasses,
tetraodontiform fi shes, bigeyes (Priacanthidae), Moorish idols (Zanclidae) and rabbitfi shes (Fig. 7.6 ). In a large recruitment pulse, high numbers of settlement-ready
fi shes appear over just a few days and, based on locations where such pulses have
been sampled, recruit over reef crests (Dufour and Galzin 1993) in the Indo-Pacifi c,
through tidal channels from offshore waters (Keener et al 1988 ; Shenker et al. 1993 ;