214
P.L. Colin
citing Johannes ( 1981 ) . While this might seem a useful comparison to fi sh aggregation
spawning, the similarities are limited. Many species of stony corals release sperm
and egg bundles over a period ranging from a few minutes to as much as an hour
relying on eventual mixing and fertilization in the water column. Corals do not, in
the sense of reef fi shes, aggregation spawn, as they can not migrate to a spawning
area, but release gametes over their entire range within a reef area. The sex products
are quite buoyant, compared to pelagic fi sh eggs, and quickly form slicks on the
surface that are carried by currents or waves. Wolanski and Hamner ( 1988 ) point out
that “coral eggs are larger and more buoyant than most other eggs from animals that
have a planktonic stage and will tend to fl oat even in areas of downwelling” and that
waves disperse larvae across the water’s surface. Coral spawn can be thought of
more as an oil slick on the surface, than the discrete fertile eggs of fi shes which
might be distributed in the upper few metres of water (Hamner et al. 2007 ) . Only
later (many hours to a few days) do the fertile eggs transform into larvae which
leave the surface and swim in the water column for a short larval life, in some only
a few days. It might also be relevant that no reef fi sh is known to synchronize its
spawning with that of stony corals.
Some crabs and lobsters are probably the invertebrates whose reproductive and
larval lives are most comparable to those of reef fi shes. This similarity was also
noted by Arvedlund and Kavanagh ( 2009 ) who stated “almost all demersal tropical
teleost fi shes have pelagic larvae that may disperse, in common with most tropical
marine decapod larvae”. For crabs and lobsters, their already fertilized eggs hatch to
swimming larvae, often en masse , live in the water column, and have to feed and
fi nd settlement habitat at the end of the larval life; all comparable to reef fi shes. In
Palau, Hamner et al. ( 2007 ) found on some days very large numbers of crab larvae
among zooplankton normally dominated by planktonic fi sh eggs largely from aggregation spawning. The mass larval release of terrestrial coconut and Coenobitide
hermit crabs are similar to aggregation spawning of reef fi shes. As detailed by
Fletcher ( 1993 ) ovigerous coconut crabs with already fertilized eggs move to shore.
“Spawning” takes place after sunset when high tide corresponds with dusk, usually
on a semi-lunar pattern with the fi rst and last quarters of the moon. Coconut crabs
go through 4–5 larval stages requiring 15–28 days, depending on temperature, and
the fi nal larval stage must fi nd a terrestrial environment into which to recruit and
emerge from the ocean. Marine crabs are similar, however, although they may
release their larvae anywhere in the ocean. The oceanographic mechanisms that
might tend to concentrate or enhance survival of fi sh larvae also affect crab and
spiny lobster larvae (Eggleston et al. 1998 ) .
7.7 What Do We Know About ELH for Aggregation
Spawning Fishes?
While knowledge of the larval biology of coral reef fi shes has advanced signifi -
cantly in the last decade, much of it concerns species with demersal eggs, such as
damselfi shes, or small fi shes with pelagic eggs (e.g. bluehead wrasse) with little
P.L. Colin
citing Johannes ( 1981 ) . While this might seem a useful comparison to fi sh aggregation
spawning, the similarities are limited. Many species of stony corals release sperm
and egg bundles over a period ranging from a few minutes to as much as an hour
relying on eventual mixing and fertilization in the water column. Corals do not, in
the sense of reef fi shes, aggregation spawn, as they can not migrate to a spawning
area, but release gametes over their entire range within a reef area. The sex products
are quite buoyant, compared to pelagic fi sh eggs, and quickly form slicks on the
surface that are carried by currents or waves. Wolanski and Hamner ( 1988 ) point out
that “coral eggs are larger and more buoyant than most other eggs from animals that
have a planktonic stage and will tend to fl oat even in areas of downwelling” and that
waves disperse larvae across the water’s surface. Coral spawn can be thought of
more as an oil slick on the surface, than the discrete fertile eggs of fi shes which
might be distributed in the upper few metres of water (Hamner et al. 2007 ) . Only
later (many hours to a few days) do the fertile eggs transform into larvae which
leave the surface and swim in the water column for a short larval life, in some only
a few days. It might also be relevant that no reef fi sh is known to synchronize its
spawning with that of stony corals.
Some crabs and lobsters are probably the invertebrates whose reproductive and
larval lives are most comparable to those of reef fi shes. This similarity was also
noted by Arvedlund and Kavanagh ( 2009 ) who stated “almost all demersal tropical
teleost fi shes have pelagic larvae that may disperse, in common with most tropical
marine decapod larvae”. For crabs and lobsters, their already fertilized eggs hatch to
swimming larvae, often en masse , live in the water column, and have to feed and
fi nd settlement habitat at the end of the larval life; all comparable to reef fi shes. In
Palau, Hamner et al. ( 2007 ) found on some days very large numbers of crab larvae
among zooplankton normally dominated by planktonic fi sh eggs largely from aggregation spawning. The mass larval release of terrestrial coconut and Coenobitide
hermit crabs are similar to aggregation spawning of reef fi shes. As detailed by
Fletcher ( 1993 ) ovigerous coconut crabs with already fertilized eggs move to shore.
“Spawning” takes place after sunset when high tide corresponds with dusk, usually
on a semi-lunar pattern with the fi rst and last quarters of the moon. Coconut crabs
go through 4–5 larval stages requiring 15–28 days, depending on temperature, and
the fi nal larval stage must fi nd a terrestrial environment into which to recruit and
emerge from the ocean. Marine crabs are similar, however, although they may
release their larvae anywhere in the ocean. The oceanographic mechanisms that
might tend to concentrate or enhance survival of fi sh larvae also affect crab and
spiny lobster larvae (Eggleston et al. 1998 ) .
7.7 What Do We Know About ELH for Aggregation
Spawning Fishes?
While knowledge of the larval biology of coral reef fi shes has advanced signifi -
cantly in the last decade, much of it concerns species with demersal eggs, such as
damselfi shes, or small fi shes with pelagic eggs (e.g. bluehead wrasse) with little