196
P.L. Colin
benthic juvenile colour pattern. The pelagic juvenile stage (also called “pre-settlement”)
may persist for some time if a suitable settlement environment is not found. Pelagic
juveniles are usually ready to settle from the plankton and take up benthic life.
The benthic juvenile stage – The young fi sh takes up life on the bottom and quickly
acquires normal juvenile coloration. Any adaptations for pelagic life are quickly lost.
This stage is also termed “post-settlement”.
7.4 Dynamics of Life History Stages and Events
Aside from the developmental stages, there are a number of critical life history
events during pelagic life, and failure to transition through these results in high
mortality of a given larval cohort. ELH for all reef fi shes can potentially be divided
into early, middle and late stages. The early starts at fertilization, ends with the
initiation of notochord fl exion and can be characterized by multiple critical events,
including fi rst feeding and swim bladder infl ation. During the middle stage the caudal
and other fi n supporting elements become complete, some specialized structures
(which potentially enhance survival) become fully developed, and signifi cant vertical
movements in pelagic environments may occur. Rapid growth during this stage
appears to be important in eventual success in recruitment and early benthic life.
The late stage (also termed the “settlement stage”) starts at the transition to a pelagic
juvenile, loss of specialized structures, enhancement of swimming ability and the
potential to use sound, olfactory or other cues to navigate towards suitable settlement
habitats, followed by settlement to a benthic existence. During all stages larvae are
moving, either by drifting or by actively swimming (and navigating?), and may be
selecting a given depth, perhaps on a diel schedule. Once ready to feed, they need to
do so continually (with interruptions at night?). The negative consequences of
failing to do so are probably more important in the early stages. They must avoid
predators at all times.
7.4.1 The Start of Pelagic Life – Aspects of the Early Stages
After spawning, egg and yolk sac larva mortality can potentially be high if conditions
of turbulence, salinity, temperature and light are unsuitable, as demonstrated in
culture studies. Ellis et al ( 1997 ) reported that low turbulence, high light and high
salinity were optimal for survival of larval Nassau grouper, Epinephelus striatus ,
from hatching to fi rst feeding. Increased survival under high versus low (to zero)
light intensity points to possible relationships between light intensity (affecting
behaviour through phototaxis and swimming activity), diel timing, and size at fi rst
feeding, which may extend throughout ELH. Finally, larvae in completely static
water had a less than 1% hatching success suggesting that exceptionally calm seas
P.L. Colin
benthic juvenile colour pattern. The pelagic juvenile stage (also called “pre-settlement”)
may persist for some time if a suitable settlement environment is not found. Pelagic
juveniles are usually ready to settle from the plankton and take up benthic life.
The benthic juvenile stage – The young fi sh takes up life on the bottom and quickly
acquires normal juvenile coloration. Any adaptations for pelagic life are quickly lost.
This stage is also termed “post-settlement”.
7.4 Dynamics of Life History Stages and Events
Aside from the developmental stages, there are a number of critical life history
events during pelagic life, and failure to transition through these results in high
mortality of a given larval cohort. ELH for all reef fi shes can potentially be divided
into early, middle and late stages. The early starts at fertilization, ends with the
initiation of notochord fl exion and can be characterized by multiple critical events,
including fi rst feeding and swim bladder infl ation. During the middle stage the caudal
and other fi n supporting elements become complete, some specialized structures
(which potentially enhance survival) become fully developed, and signifi cant vertical
movements in pelagic environments may occur. Rapid growth during this stage
appears to be important in eventual success in recruitment and early benthic life.
The late stage (also termed the “settlement stage”) starts at the transition to a pelagic
juvenile, loss of specialized structures, enhancement of swimming ability and the
potential to use sound, olfactory or other cues to navigate towards suitable settlement
habitats, followed by settlement to a benthic existence. During all stages larvae are
moving, either by drifting or by actively swimming (and navigating?), and may be
selecting a given depth, perhaps on a diel schedule. Once ready to feed, they need to
do so continually (with interruptions at night?). The negative consequences of
failing to do so are probably more important in the early stages. They must avoid
predators at all times.
7.4.1 The Start of Pelagic Life – Aspects of the Early Stages
After spawning, egg and yolk sac larva mortality can potentially be high if conditions
of turbulence, salinity, temperature and light are unsuitable, as demonstrated in
culture studies. Ellis et al ( 1997 ) reported that low turbulence, high light and high
salinity were optimal for survival of larval Nassau grouper, Epinephelus striatus ,
from hatching to fi rst feeding. Increased survival under high versus low (to zero)
light intensity points to possible relationships between light intensity (affecting
behaviour through phototaxis and swimming activity), diel timing, and size at fi rst
feeding, which may extend throughout ELH. Finally, larvae in completely static
water had a less than 1% hatching success suggesting that exceptionally calm seas