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J.H. Choat
snappers and groupers are predominantly carnivores on benthic invertebrates and on
fi shes, with a shift to increased piscivory with increase in size (Wainwright and
Bellwood 2002 ) . These groups are highly opportunistic feeders foraging over a
wide range of habitats, feeding modes that are more likely to be sustained during
migratory episodes than grazing on a shallow benthic biota. Thus maximum size,
body architecture and trophic biology interact to constrain the migratory behaviour
and episodic reproduction of transient spawning species to the larger carnivorous
groups. In this context the infl uence of predation on the formation of spawning
aggregations is unclear and requires additional study of size-dependent rates of
predation on fi sh that make up spawning aggregations.
Is a classifi cation of resident and transient spawners based on size and nutritional
ecology linked to particular demographic and life history variables? In a second analysis the parameters maximum life span, the form of the growth curve (indeterminate
or asymptotic) and reproductive ontogeny (gonochorism or protogynous hermaphroditism) were investigated (Fig. 4.3b ). Fishes with asymptotic growth patterns will
achieve maximum size early in life while those with indeterminate curves continue
to grow over most of their life span. The different growth curves will require different patterns of investment in somatic and reproductive growth and could be an
important driver of spawning patterns. The proportion of primary males in the population was used as an estimate of the importance of two distinctive patterns of sexual
ontogeny, gonochorism and protogynous hermaphroditism. Protogynous species
(most parrotfi shes and groupers) would have a relatively low proportion of primary
males compared to gonochorists.
Unlike the previous analysis which separated groups based on size, foraging and
trophic variables the analysis based on demographic and life history variables
retrieved different and more diffuse groupings (Fig. 4.3b ). The assemblage was
partitioned primarily by the pattern of sexual ontogeny with the relatively small
surgeonfi shes grouping with snappers and the gonochoristic Nassau grouper , while
a second grouping consisted of protogynous groupers and parrotfi shes. The species
that grouped by a protogynous sexual ontogeny also exhibited indeterminate growth
patterns. Most of the gonochoristic species, including the snappers and surgeonfi shes, displayed asymptotic growth curves reaching the maximum size early in life
and with limited growth following sexual maturity. There was a trend of increasing
life span with the greatest ages achieved by the smaller surgeonfi shes and the largest
snappers and groupers (both Epinephelus and Mycteroperca spp . ), and low maximum
ages in parrotfi shes and groupers of the genus Plectropomus . The main conclusion
of the analysis was that basic demographic and life history features do not refl ect the
different spawning modes.
In summary the capacity of reef fi shes to form large spawning aggregations
appears to be governed by basic rules of size, trophic ecology and anatomy. The
resultant spawning patterns emerge as combinations of lineages that have little in
common with respect to demography and life histories. As long as the groups shared
basic properties of size, nutritional ecology and anatomy they manifested the same
spawning behaviours regardless of whether they were protogynous or gonochoristic, or with short or long generation times. The ecological analysis also suggested
J.H. Choat
snappers and groupers are predominantly carnivores on benthic invertebrates and on
fi shes, with a shift to increased piscivory with increase in size (Wainwright and
Bellwood 2002 ) . These groups are highly opportunistic feeders foraging over a
wide range of habitats, feeding modes that are more likely to be sustained during
migratory episodes than grazing on a shallow benthic biota. Thus maximum size,
body architecture and trophic biology interact to constrain the migratory behaviour
and episodic reproduction of transient spawning species to the larger carnivorous
groups. In this context the infl uence of predation on the formation of spawning
aggregations is unclear and requires additional study of size-dependent rates of
predation on fi sh that make up spawning aggregations.
Is a classifi cation of resident and transient spawners based on size and nutritional
ecology linked to particular demographic and life history variables? In a second analysis the parameters maximum life span, the form of the growth curve (indeterminate
or asymptotic) and reproductive ontogeny (gonochorism or protogynous hermaphroditism) were investigated (Fig. 4.3b ). Fishes with asymptotic growth patterns will
achieve maximum size early in life while those with indeterminate curves continue
to grow over most of their life span. The different growth curves will require different patterns of investment in somatic and reproductive growth and could be an
important driver of spawning patterns. The proportion of primary males in the population was used as an estimate of the importance of two distinctive patterns of sexual
ontogeny, gonochorism and protogynous hermaphroditism. Protogynous species
(most parrotfi shes and groupers) would have a relatively low proportion of primary
males compared to gonochorists.
Unlike the previous analysis which separated groups based on size, foraging and
trophic variables the analysis based on demographic and life history variables
retrieved different and more diffuse groupings (Fig. 4.3b ). The assemblage was
partitioned primarily by the pattern of sexual ontogeny with the relatively small
surgeonfi shes grouping with snappers and the gonochoristic Nassau grouper , while
a second grouping consisted of protogynous groupers and parrotfi shes. The species
that grouped by a protogynous sexual ontogeny also exhibited indeterminate growth
patterns. Most of the gonochoristic species, including the snappers and surgeonfi shes, displayed asymptotic growth curves reaching the maximum size early in life
and with limited growth following sexual maturity. There was a trend of increasing
life span with the greatest ages achieved by the smaller surgeonfi shes and the largest
snappers and groupers (both Epinephelus and Mycteroperca spp . ), and low maximum
ages in parrotfi shes and groupers of the genus Plectropomus . The main conclusion
of the analysis was that basic demographic and life history features do not refl ect the
different spawning modes.
In summary the capacity of reef fi shes to form large spawning aggregations
appears to be governed by basic rules of size, trophic ecology and anatomy. The
resultant spawning patterns emerge as combinations of lineages that have little in
common with respect to demography and life histories. As long as the groups shared
basic properties of size, nutritional ecology and anatomy they manifested the same
spawning behaviours regardless of whether they were protogynous or gonochoristic, or with short or long generation times. The ecological analysis also suggested