205
7 Aggregation Spawning: Biological Aspects of the Early Life History
compressed, high dorsal-ventral aspect (deep-bodied) and very elongate, larval
form (leptocephalus) and often such larvae have been given distinctive names,
sometimes based on initially erroneous descriptions of them as separate genera
(acronurus, tholichthys). Specialized larvae and structures are found in many
families with aggregation, in both aggregating and non-aggregating species of those
families. Structures, such as spines (epinepheline groupers – Colin and Koenig
1996 , surgeonfi shes – Randall 1961 ) , may serve in predator deterrence, but the
functional use of these features is usually not apparent from studies of preserved
specimens. For example, the dorsal and pelvic fi n spines of epinepheline groupers
form early (starting as soon as 7 days post-hatching at a prefl exion notochord length
of only 3 mm) and grow rapidly, reaching their maximum length in another
7–10 days at 6–7 mm NL (Colin and Koenig 1996 ) . The spines are quite motile, can
be erected nearly vertical and their ends clearly marked with dark melanophores.
Their normal positions and angles combined with the location of the snout form a
tetrahedron, presumably presenting potential predators with a greatly increased
effective size of the larvae. Other examples of specialized structures occur in surgeonfi shes; a highly compressed deep body, nearly as deep as long, with formidable
dorsal and anal spines which increase its effective size. Once the caudal peduncle
spine forms (at about 17 mm TL) the larvae is called an “acronurus” until settlement
and metamorphosis.
Body form, without spines or other hard structures, may be modifi ed. The
leptocephalus is an elongate fl attened leaf-like larva found in eels (order
Anguilliformes) and a few primitive bony fi shes, such as bonefi shes and tarpon
(order Elopiformes). Some elopiform fi shes may spawn in aggregations. Bonefi shes
(Albulidae), for example, are reported to migrate through channels to spawn on
outer reef slopes, although they may engage in simple migratory spawning rather
than aggregate. At least one moray eel aggregates near the reef to spawn (Thresher
1984 ; Ferraris 1985 ) .
7.5.2 Growth and Feeding of Mid-stage Larvae
While much of the larval life between the transport immediately after spawning
away from the site and eventual appearance as recruits weeks later is largely
unknown, some recent techniques provide tools to examine this life period. The
occurrence of rings laid down, near daily, in otoliths of larvae has allowed precise
ageing of many species, while the chemistry of otoliths, particularly the presence of
stable isotopes, can indicate whether larvae have grown up in oceanic or near shore
environments (Patterson et al. 2005 ) . Hamilton et al ( 2008 ) used the occurrence of
lead isotopes in otoliths of T. bifasciatum to distinguish larvae which developed in
offshore (about 55%) and nearshore (about 45%) waters and followed their survival
during the fi rst month of benthic life which suggested different larval histories suffered differential mortality. Patterson and Swearer ( 2007 ) used elemental signatures
in otoliths to attempt to identify natal locations for an endemic and a widespread
species of wrasse with some success.
7 Aggregation Spawning: Biological Aspects of the Early Life History
compressed, high dorsal-ventral aspect (deep-bodied) and very elongate, larval
form (leptocephalus) and often such larvae have been given distinctive names,
sometimes based on initially erroneous descriptions of them as separate genera
(acronurus, tholichthys). Specialized larvae and structures are found in many
families with aggregation, in both aggregating and non-aggregating species of those
families. Structures, such as spines (epinepheline groupers – Colin and Koenig
1996 , surgeonfi shes – Randall 1961 ) , may serve in predator deterrence, but the
functional use of these features is usually not apparent from studies of preserved
specimens. For example, the dorsal and pelvic fi n spines of epinepheline groupers
form early (starting as soon as 7 days post-hatching at a prefl exion notochord length
of only 3 mm) and grow rapidly, reaching their maximum length in another
7–10 days at 6–7 mm NL (Colin and Koenig 1996 ) . The spines are quite motile, can
be erected nearly vertical and their ends clearly marked with dark melanophores.
Their normal positions and angles combined with the location of the snout form a
tetrahedron, presumably presenting potential predators with a greatly increased
effective size of the larvae. Other examples of specialized structures occur in surgeonfi shes; a highly compressed deep body, nearly as deep as long, with formidable
dorsal and anal spines which increase its effective size. Once the caudal peduncle
spine forms (at about 17 mm TL) the larvae is called an “acronurus” until settlement
and metamorphosis.
Body form, without spines or other hard structures, may be modifi ed. The
leptocephalus is an elongate fl attened leaf-like larva found in eels (order
Anguilliformes) and a few primitive bony fi shes, such as bonefi shes and tarpon
(order Elopiformes). Some elopiform fi shes may spawn in aggregations. Bonefi shes
(Albulidae), for example, are reported to migrate through channels to spawn on
outer reef slopes, although they may engage in simple migratory spawning rather
than aggregate. At least one moray eel aggregates near the reef to spawn (Thresher
1984 ; Ferraris 1985 ) .
7.5.2 Growth and Feeding of Mid-stage Larvae
While much of the larval life between the transport immediately after spawning
away from the site and eventual appearance as recruits weeks later is largely
unknown, some recent techniques provide tools to examine this life period. The
occurrence of rings laid down, near daily, in otoliths of larvae has allowed precise
ageing of many species, while the chemistry of otoliths, particularly the presence of
stable isotopes, can indicate whether larvae have grown up in oceanic or near shore
environments (Patterson et al. 2005 ) . Hamilton et al ( 2008 ) used the occurrence of
lead isotopes in otoliths of T. bifasciatum to distinguish larvae which developed in
offshore (about 55%) and nearshore (about 45%) waters and followed their survival
during the fi rst month of benthic life which suggested different larval histories suffered differential mortality. Patterson and Swearer ( 2007 ) used elemental signatures
in otoliths to attempt to identify natal locations for an endemic and a widespread
species of wrasse with some success.