37
2 Ecosystem Aspects of Species That Aggregate to Spawn
well-developed linear reefs as their primary migration pathways while traveling to
and from their spawning aggregation site (RSN unpublished data). These preliminary
data and Fig. 2.8 suggest that ecosystem based management initiatives and MPA
networks should not only prioritize protection of key geomorphological reef types
(i.e. reef pass channels, shelf edge reefs and promontories) but also consider the
relative importance of migratory pathways and other potential spawning habitat types
in maintaining high biological diversity, connectivity and ecosystem function.
2.4 Predator-Prey Dynamics and Other Ecological Processes
Within Functional Migration Areas
Migrations from home ranges to spawning aggregation sites represent short-term
and possibly substantial localized fl uctuations in fi sh biomass, as judged from numbers
of fi sh in some aggregations. Large aggregations of cubera snapper in Belize briefl y
attain estimated peak abundances of 4,000–10,000 individuals within the 1,000 m
2
spawning aggregation site (Heyman et al. 2005 ) . Spawning adults in Cuba averaged
about 80 cm and 8.5 kg (Claro and Garcia-Arteaga 2001 ) and if fi sh in Belize are of
similar size, the aggregations represent an estimated fi sh biomass of 3,400–8,500 kg
100 m
−2
. Several surgeonfi sh species in the Caribbean and Pacifi c can form even
larger aggregations exceeding an estimated 20,000 individuals (Robertson 1983 ;
Colin and Clavijo 1988 ) . These temporary peaks in fi sh biomass may affect food web
dynamics and energy transfer along migratory pathways and at spawning aggregation
sites through feeding, defaecation, predation and reproduction. For example, Hamner
et al. ( 2007b ) found that nearly 90% of zooplankton fl owing off a Palauan reef during
ebb tide was composed of fi sh eggs from spawning aggregations of a suite of species
(mostly surgeonfi shes and parrotfi shes but also wrasses-Labridae). High concentrations of spawning adults or fi sh eggs may attract a wide diversity of predators
attempting to take advantage of this temporary and predictable food source.
Most available information suggests that while predation on spawning adults
may be low, rates of predation on eggs after release are much higher, and can vary
considerably depending upon species and location (Robertson 1983 ; Moyer 1987 ;
Craig 1998 ; Sancho et al. 2000a ; Claydon 2004 ) . Although it is unknown what proportion of gametes contributes to the local food web, the energy gathered through
the regular feeding activities of adults across a large functional migration area and
exported in the form of millions of fertilized eggs could have a brief, yet important,
infl uence on energy and nutrient dynamics during spawning periods. A comparable
system is the synchronized mass spawning of corals in which the sudden increase of
organic matter is rapidly assimilated into the local food web and stimulates biological activity in adjacent benthic and pelagic environments (Guest 2008 ) . Herbivorous
fi shes may be especially important for the transfer of energy from benthic to pelagic
environments since they consume primary algal production and convert it to eggs
which are exported from the reef during daily spawning episodes (Patrick Colin
personal communication).
2 Ecosystem Aspects of Species That Aggregate to Spawn
well-developed linear reefs as their primary migration pathways while traveling to
and from their spawning aggregation site (RSN unpublished data). These preliminary
data and Fig. 2.8 suggest that ecosystem based management initiatives and MPA
networks should not only prioritize protection of key geomorphological reef types
(i.e. reef pass channels, shelf edge reefs and promontories) but also consider the
relative importance of migratory pathways and other potential spawning habitat types
in maintaining high biological diversity, connectivity and ecosystem function.
2.4 Predator-Prey Dynamics and Other Ecological Processes
Within Functional Migration Areas
Migrations from home ranges to spawning aggregation sites represent short-term
and possibly substantial localized fl uctuations in fi sh biomass, as judged from numbers
of fi sh in some aggregations. Large aggregations of cubera snapper in Belize briefl y
attain estimated peak abundances of 4,000–10,000 individuals within the 1,000 m
2
spawning aggregation site (Heyman et al. 2005 ) . Spawning adults in Cuba averaged
about 80 cm and 8.5 kg (Claro and Garcia-Arteaga 2001 ) and if fi sh in Belize are of
similar size, the aggregations represent an estimated fi sh biomass of 3,400–8,500 kg
100 m
−2
. Several surgeonfi sh species in the Caribbean and Pacifi c can form even
larger aggregations exceeding an estimated 20,000 individuals (Robertson 1983 ;
Colin and Clavijo 1988 ) . These temporary peaks in fi sh biomass may affect food web
dynamics and energy transfer along migratory pathways and at spawning aggregation
sites through feeding, defaecation, predation and reproduction. For example, Hamner
et al. ( 2007b ) found that nearly 90% of zooplankton fl owing off a Palauan reef during
ebb tide was composed of fi sh eggs from spawning aggregations of a suite of species
(mostly surgeonfi shes and parrotfi shes but also wrasses-Labridae). High concentrations of spawning adults or fi sh eggs may attract a wide diversity of predators
attempting to take advantage of this temporary and predictable food source.
Most available information suggests that while predation on spawning adults
may be low, rates of predation on eggs after release are much higher, and can vary
considerably depending upon species and location (Robertson 1983 ; Moyer 1987 ;
Craig 1998 ; Sancho et al. 2000a ; Claydon 2004 ) . Although it is unknown what proportion of gametes contributes to the local food web, the energy gathered through
the regular feeding activities of adults across a large functional migration area and
exported in the form of millions of fertilized eggs could have a brief, yet important,
infl uence on energy and nutrient dynamics during spawning periods. A comparable
system is the synchronized mass spawning of corals in which the sudden increase of
organic matter is rapidly assimilated into the local food web and stimulates biological activity in adjacent benthic and pelagic environments (Guest 2008 ) . Herbivorous
fi shes may be especially important for the transfer of energy from benthic to pelagic
environments since they consume primary algal production and convert it to eggs
which are exported from the reef during daily spawning episodes (Patrick Colin
personal communication).