9
1 Revisiting Spawning Aggregations: Defi nitions and Challenges
spawning of a schooling species (such as bumphead parrotfi sh, Bolbometopon
muricatum ) is predictable in time and space, the management implications are similar to those of a spawning aggregation.
1.4 Egg Types and Spawning Aggregations
Most coral reef fi shes release very small pelagic eggs (often near 1 mm diameter)
that fl oat to near the surface and then hatch about 24 h later (actual time can vary)
(Chap. 7 ). There are also many examples of reef fi shes that produce sinking eggs
that are either brooded in the mouth or attached to the substrate. These demersal
eggs often have a longer developmental period prior to hatching and are usually
guarded by one or both sexes. There are also a few examples of demersal egg
spawners that do not guard the eggs and a few examples of live-bearing reef fi shes
(brotulids). The overwhelming majority of species that aggregate to spawn release
a pelagic egg. However, an increasing number of demersal spawning aggregations
are being described. Demersal spawning aggregations can be further divided into
those that exhibit parental care triggerfi shes (Balistidae), damselfi shes
(Pomacentridae) and those that do not (e.g. rabbitfi sh). Parental care demersal
spawning aggregations can also be split into groups based upon whether the nest
is guarded by the male (e.g. brown puller, Chromis hypsilepis Gladstone 2007 ) ,
the female (e.g. Graneledone sp . (Drazen et al. 2003 ) or both sexes (e.g. triggerfi sh)) . Live bearers and mouth brooders are not known to form spawning aggregations (Chap. 4 ).
Past treatments of spawning aggregations have listed the relatively few demersal examples without consideration for potential functional differences between
this and pelagic spawning aggregations. All species that aggregate to spawn are
under selective pressure to choose spawning sites and/or times that maximize
recruitment. Species that aggregate to spawn demersal eggs have additional selective pressures, since demersal spawning sites must also provide a suitable substrate for egg adhesion and an environment that facilitates keeping the eggs clean
and oxygenated. There are also different selective pressures on demersal aggregating species that care for their eggs and those that do not. Parental care includes
guarding the nest from predators, fanning and cleaning; for demersal aggregations
without parental care, the spawning site must adequately provide these functions
in the absence of the parents. It is possible that the act of spawning in an aggregation has allowed the elimination of parental care for some species that spawn
demersal eggs, due to the fact that the density of eggs satiates local egg predators
(Domeier and Colin 1997 ) . Also, the absence of parental care would be more
likely for species that produce eggs that hatch shortly after spawning. For example, brown puller exhibits male parental care during a 4.5 day incubation period
(Gladstone 2007 ) , while rabbitfi sh demonstrate no parental care and the eggs
hatch in 25–32 h (Thresher 1984 ) . Time to hatching for the siganids is similar to
that of reef fi shes that spawn pelagic eggs.
1 Revisiting Spawning Aggregations: Defi nitions and Challenges
spawning of a schooling species (such as bumphead parrotfi sh, Bolbometopon
muricatum ) is predictable in time and space, the management implications are similar to those of a spawning aggregation.
1.4 Egg Types and Spawning Aggregations
Most coral reef fi shes release very small pelagic eggs (often near 1 mm diameter)
that fl oat to near the surface and then hatch about 24 h later (actual time can vary)
(Chap. 7 ). There are also many examples of reef fi shes that produce sinking eggs
that are either brooded in the mouth or attached to the substrate. These demersal
eggs often have a longer developmental period prior to hatching and are usually
guarded by one or both sexes. There are also a few examples of demersal egg
spawners that do not guard the eggs and a few examples of live-bearing reef fi shes
(brotulids). The overwhelming majority of species that aggregate to spawn release
a pelagic egg. However, an increasing number of demersal spawning aggregations
are being described. Demersal spawning aggregations can be further divided into
those that exhibit parental care triggerfi shes (Balistidae), damselfi shes
(Pomacentridae) and those that do not (e.g. rabbitfi sh). Parental care demersal
spawning aggregations can also be split into groups based upon whether the nest
is guarded by the male (e.g. brown puller, Chromis hypsilepis Gladstone 2007 ) ,
the female (e.g. Graneledone sp . (Drazen et al. 2003 ) or both sexes (e.g. triggerfi sh)) . Live bearers and mouth brooders are not known to form spawning aggregations (Chap. 4 ).
Past treatments of spawning aggregations have listed the relatively few demersal examples without consideration for potential functional differences between
this and pelagic spawning aggregations. All species that aggregate to spawn are
under selective pressure to choose spawning sites and/or times that maximize
recruitment. Species that aggregate to spawn demersal eggs have additional selective pressures, since demersal spawning sites must also provide a suitable substrate for egg adhesion and an environment that facilitates keeping the eggs clean
and oxygenated. There are also different selective pressures on demersal aggregating species that care for their eggs and those that do not. Parental care includes
guarding the nest from predators, fanning and cleaning; for demersal aggregations
without parental care, the spawning site must adequately provide these functions
in the absence of the parents. It is possible that the act of spawning in an aggregation has allowed the elimination of parental care for some species that spawn
demersal eggs, due to the fact that the density of eggs satiates local egg predators
(Domeier and Colin 1997 ) . Also, the absence of parental care would be more
likely for species that produce eggs that hatch shortly after spawning. For example, brown puller exhibits male parental care during a 4.5 day incubation period
(Gladstone 2007 ) , while rabbitfi sh demonstrate no parental care and the eggs
hatch in 25–32 h (Thresher 1984 ) . Time to hatching for the siganids is similar to
that of reef fi shes that spawn pelagic eggs.