107
4 Spawning Aggregations in Reef Fishes; Ecological and Evolutionary Processes
continued feeding would be expected for many resident spawning species. In contrast
the less predictable nature of food sources for transient spawning carnivores suggests
that they may be capital breeders relying on reserves accumulated over periods prior
to reproduction, especially as their body form and anatomy allows the development
of a very large ovarian mass compared to body mass. Partitioning reproduction into
a few large episodes requires the ability to store the nutrients necessary to nourish the
development of large numbers of hydrated oocytes (the last stage before spawning).
Resident spawners with extended seasonal reproductive periods (Ross 1983 ;
Robertson 1991 ; Craig 1998 ; Bushnell et al. 2010 , Chap. 12.20 ) that cover a range
of seasonal and oceanic environments contrast strongly with transient spawners
which reproduce at a limited number of times and places. Focusing reproductive
outputs in this way may allow females to better anticipate the future larval environment. Indeed, van Woesik ( 2010 ) has identifi ed such a proxy linking mass spawning
in corals to a specifi c environmental feature, wind fi elds. In the case of reef fi sh
aggregations a similar linkage between timing of transient spawning events and a
general environmental signal has yet to be identifi ed. However in temperate environments matching of spawning to a seasonally driven cycle of productivity and
hydrodynamic features is well-established (Sinclair 1988 ) .
4.6 Conclusions
The main conclusion of this chapter is that spawning aggregations have most
probably evolved to enhance egg and larval survival through rapid advection of
reproductive products away from the adult environment. The ecological distinctions
between resident and transient spawners refl ect differences in size and nutritional
ecology but not life histories. Size, structural and nutritional constraints limit the
acquisition of a transient spawning phenology to larger species, primarily those
with a carnivorous nutritional ecology and the capacity to develop very large ovarian
masses (i.e. high GSIs) fueled through an investment in stored energy. In addition
the differences in timing and frequency of reproductive episodes in resident and
transient spawners represent the spreading of recruitment risk in the former and
matching of spawning to favourable larval environments in the latter. By limiting
the spawning periodicity to a restricted number of episodes some tropical reef fi sh
appear to be converging towards their cold-temperate counterparts where spawning
is restricted to periods that match predictable environmental cycles. These arguments implicitly reject the idea that larval retention and self recruitment are the
result of selective pressures applicable to reef fi shes generally. In some species,
especially those with highly specifi c recruitment sites and adult environments, retention of individuals would be advantageous. In others, wide dispersal and colonizing of
new environments may be benefi cial.
A number of predictions follow. Transient spawning will be restricted to those
species above a size threshold of ~40 cm FL with an alimentary anatomy and body
form that provides for the development of a large ovarian mass. There is a phyloge-
4 Spawning Aggregations in Reef Fishes; Ecological and Evolutionary Processes
continued feeding would be expected for many resident spawning species. In contrast
the less predictable nature of food sources for transient spawning carnivores suggests
that they may be capital breeders relying on reserves accumulated over periods prior
to reproduction, especially as their body form and anatomy allows the development
of a very large ovarian mass compared to body mass. Partitioning reproduction into
a few large episodes requires the ability to store the nutrients necessary to nourish the
development of large numbers of hydrated oocytes (the last stage before spawning).
Resident spawners with extended seasonal reproductive periods (Ross 1983 ;
Robertson 1991 ; Craig 1998 ; Bushnell et al. 2010 , Chap. 12.20 ) that cover a range
of seasonal and oceanic environments contrast strongly with transient spawners
which reproduce at a limited number of times and places. Focusing reproductive
outputs in this way may allow females to better anticipate the future larval environment. Indeed, van Woesik ( 2010 ) has identifi ed such a proxy linking mass spawning
in corals to a specifi c environmental feature, wind fi elds. In the case of reef fi sh
aggregations a similar linkage between timing of transient spawning events and a
general environmental signal has yet to be identifi ed. However in temperate environments matching of spawning to a seasonally driven cycle of productivity and
hydrodynamic features is well-established (Sinclair 1988 ) .
4.6 Conclusions
The main conclusion of this chapter is that spawning aggregations have most
probably evolved to enhance egg and larval survival through rapid advection of
reproductive products away from the adult environment. The ecological distinctions
between resident and transient spawners refl ect differences in size and nutritional
ecology but not life histories. Size, structural and nutritional constraints limit the
acquisition of a transient spawning phenology to larger species, primarily those
with a carnivorous nutritional ecology and the capacity to develop very large ovarian
masses (i.e. high GSIs) fueled through an investment in stored energy. In addition
the differences in timing and frequency of reproductive episodes in resident and
transient spawners represent the spreading of recruitment risk in the former and
matching of spawning to favourable larval environments in the latter. By limiting
the spawning periodicity to a restricted number of episodes some tropical reef fi sh
appear to be converging towards their cold-temperate counterparts where spawning
is restricted to periods that match predictable environmental cycles. These arguments implicitly reject the idea that larval retention and self recruitment are the
result of selective pressures applicable to reef fi shes generally. In some species,
especially those with highly specifi c recruitment sites and adult environments, retention of individuals would be advantageous. In others, wide dispersal and colonizing of
new environments may be benefi cial.
A number of predictions follow. Transient spawning will be restricted to those
species above a size threshold of ~40 cm FL with an alimentary anatomy and body
form that provides for the development of a large ovarian mass. There is a phyloge-