204
P.L. Colin
Hensley et al. ( 1994 ) found that bluehead wrasse tended to group-spawn at sites that
potentially offer advantages for off-reef transport of eggs, however, the benefi ts
were only evident over the short term.
Nearly all pelagic reef fi sh eggs are very slightly positively buoyant after
fertilization (see Chap. 5 ) and this buoyancy is helpful in keeping them in the water
column where they can be dispersed and advected away from predators. Under
extremely calm conditions eggs might rise and rest upon the water surface, something that happens in aquaria, and potentially exposes them to incident UV radiation.
Some temperate fi sh eggs are known to have UV blocking compounds (Chioccara
et al. 1980 ; Plack et al. 1981 ) , but these have not been investigated for tropical
reef fi sh pelagic eggs. Hamner et al. ( 2007 ) found that, for pelagic eggs (largely
surgeonfi shes, parrotfi shes and wrasses) spawned near the surface at a site 80 m
downcurrent and about 10 min after spawning, 90% of eggs were in the top 4 m of
the water column with 60% of these in the top metre. On windy days with surface
waves, fi sh eggs and zooplankton fl owing off the reef would mix deeper, with greater
under-sampling if plankton nets are moored at the surface.
7.5 Life in the Pelagic Environment – Aspects
of the Middle Stage
The middle phase of ELH is characterized by an increase in swimming ability,
which allows easier control of vertical distribution, necessary for selection of depth
during a daily cycle, and food capture to maintain rapid growth to increase survival.
Armsworth ( 2001 ) points out that, if possible, it is much more effi cient to use vertical
changes in position to move into water layers where advection will carry a larva
towards a “desired point” than to actually swim the entire distance toward that point.
The increased swimming ability is a result of swim bladder infl ation, development
of caudal supporting elements, and increasing development and strength of fi ns.
There is also greater ability to avoid predators through growth of anti-predator
structures (fi n spines, head and body spination) and better swimming. Finding
enough food consistently is a critical factor, both for fast growth and to prevent
starvation as food reserves are slight. Schooling is unlikely. There is ample evidence
of shifts in vertical distribution of larvae between day and night, with nocturnal
periods characterized by shallower distributions. Vertical distributions can also
modify dispersal trajectories.
7.5.1 Development of Specialized Structures
Specialized structures in larval reef fi shes include elongate dorsal, anal and pelvic
fi n spines, elaborate head spination, and fi n-rays with bulbous growths, with such
structures limited to a single or a few families. Specialized growth includes highly
P.L. Colin
Hensley et al. ( 1994 ) found that bluehead wrasse tended to group-spawn at sites that
potentially offer advantages for off-reef transport of eggs, however, the benefi ts
were only evident over the short term.
Nearly all pelagic reef fi sh eggs are very slightly positively buoyant after
fertilization (see Chap. 5 ) and this buoyancy is helpful in keeping them in the water
column where they can be dispersed and advected away from predators. Under
extremely calm conditions eggs might rise and rest upon the water surface, something that happens in aquaria, and potentially exposes them to incident UV radiation.
Some temperate fi sh eggs are known to have UV blocking compounds (Chioccara
et al. 1980 ; Plack et al. 1981 ) , but these have not been investigated for tropical
reef fi sh pelagic eggs. Hamner et al. ( 2007 ) found that, for pelagic eggs (largely
surgeonfi shes, parrotfi shes and wrasses) spawned near the surface at a site 80 m
downcurrent and about 10 min after spawning, 90% of eggs were in the top 4 m of
the water column with 60% of these in the top metre. On windy days with surface
waves, fi sh eggs and zooplankton fl owing off the reef would mix deeper, with greater
under-sampling if plankton nets are moored at the surface.
7.5 Life in the Pelagic Environment – Aspects
of the Middle Stage
The middle phase of ELH is characterized by an increase in swimming ability,
which allows easier control of vertical distribution, necessary for selection of depth
during a daily cycle, and food capture to maintain rapid growth to increase survival.
Armsworth ( 2001 ) points out that, if possible, it is much more effi cient to use vertical
changes in position to move into water layers where advection will carry a larva
towards a “desired point” than to actually swim the entire distance toward that point.
The increased swimming ability is a result of swim bladder infl ation, development
of caudal supporting elements, and increasing development and strength of fi ns.
There is also greater ability to avoid predators through growth of anti-predator
structures (fi n spines, head and body spination) and better swimming. Finding
enough food consistently is a critical factor, both for fast growth and to prevent
starvation as food reserves are slight. Schooling is unlikely. There is ample evidence
of shifts in vertical distribution of larvae between day and night, with nocturnal
periods characterized by shallower distributions. Vertical distributions can also
modify dispersal trajectories.
7.5.1 Development of Specialized Structures
Specialized structures in larval reef fi shes include elongate dorsal, anal and pelvic
fi n spines, elaborate head spination, and fi n-rays with bulbous growths, with such
structures limited to a single or a few families. Specialized growth includes highly