38
R.S. Nemeth
The possible effect of aggregating species on food web dynamics can be grouped
into four categories: (1) feeding by aggregating fi sh on animals and plants residing
at spawning aggregation sites or along migration pathways; (2) predation by piscivores on migrating or spawning adults; (3) egg predation, and (4) other trophic
linkages. These will each be discussed below.
2.4.1 Feeding by Aggregating Species at Spawning Aggregation
Sites or Along Migration Pathways
Several differences exist between resident and transient aggregations with respect to
their possible infl uence on food-web dynamics at spawning aggregation sites.
Resident aggregations tend to be characterized by herbivorous or omnivorous species
(i.e. surgeonfi sh, parrotfi sh, wrasses, Appendix) that undergo daily short-distance
migrations from feeding grounds to spawning sites over prolonged seasonal cycles
(Fishelson et al. 1987 ; Colin and Clavijo 1988 ) . Since resident aggregating species
spend only brief periods of time each day at their spawning aggregation site, most
of their activity is focused on courtship and spawning and not feeding, as described
for striped bristletooth and twotone tangs ( Ctenochaetus striatus and Zebrasoma
scopas ) (Randall 1961 ) . However, some herbivorous species (e.g. surgeonfi sh, parrotfi sh) have been observed milling and grazing on benthic algae at certain points
along their spawning migration routes and during the brief periods between spawning
episodes at aggregation sites (Randall and Randall 1963 ; Robertson 1983 ; Mazeroll
and Montgomery 1998 ; Sancho et al. 2000b ) . These species may therefore infl uence
the relative abundance of benthic algae and coral cover at aggregation sites and
along migration routes.
By contrast, transient aggregators tend to be characterized by carnivorous and
piscivorous species (i.e. snappers, groupers) that migrate 10’s–100’s of kilometers
and spend days to weeks around their spawning aggregation sites (Garcia-Cagide
et al. 2001 ; Rhodes and Sadovy 2002a, b ; Heyman et al. 2005 ; Nemeth 2005 ;
Kadison et al. 2007, 2009 ; Nemeth et al. 2007 ) . During migration and aggregation
fi sh may continue to feed on other fi shes and invertebrates thus linking local food
webs within their functional migration areas (McCann et al. 2005 ) . Evidence of
transient aggregating species feeding on fi shes and invertebrates at aggregation sites,
however, is limited to a few incidental observations of predation and gut contents of
several grouper species. In Palau aggregating squaretail coralgrouper occasionally
attacked schools of small fusiliers (Caesionidae) and brown-marbled grouper was
observed eating a camoufl age grouper which aggregated at the same site (Johannes
et al. 1999 ) . During spawning aggregations of red hind in the Virgin Islands, disgorged gut contents commonly contained true crabs, hermit crabs, juvenile lobster
and small reef fi shes such as the slender fi lefi sh, Monacanthus tuckeri , and even
juvenile red hind (RSN unpublished data). Yellowfi n grouper, Mycteroperca
venenosa , stomach contents also contained a variety of reef fi shes such as yellowtail snapper, Ocyurus chrysurus , blackfi n snapper, Lutjanus buccanella , red hind,
R.S. Nemeth
The possible effect of aggregating species on food web dynamics can be grouped
into four categories: (1) feeding by aggregating fi sh on animals and plants residing
at spawning aggregation sites or along migration pathways; (2) predation by piscivores on migrating or spawning adults; (3) egg predation, and (4) other trophic
linkages. These will each be discussed below.
2.4.1 Feeding by Aggregating Species at Spawning Aggregation
Sites or Along Migration Pathways
Several differences exist between resident and transient aggregations with respect to
their possible infl uence on food-web dynamics at spawning aggregation sites.
Resident aggregations tend to be characterized by herbivorous or omnivorous species
(i.e. surgeonfi sh, parrotfi sh, wrasses, Appendix) that undergo daily short-distance
migrations from feeding grounds to spawning sites over prolonged seasonal cycles
(Fishelson et al. 1987 ; Colin and Clavijo 1988 ) . Since resident aggregating species
spend only brief periods of time each day at their spawning aggregation site, most
of their activity is focused on courtship and spawning and not feeding, as described
for striped bristletooth and twotone tangs ( Ctenochaetus striatus and Zebrasoma
scopas ) (Randall 1961 ) . However, some herbivorous species (e.g. surgeonfi sh, parrotfi sh) have been observed milling and grazing on benthic algae at certain points
along their spawning migration routes and during the brief periods between spawning
episodes at aggregation sites (Randall and Randall 1963 ; Robertson 1983 ; Mazeroll
and Montgomery 1998 ; Sancho et al. 2000b ) . These species may therefore infl uence
the relative abundance of benthic algae and coral cover at aggregation sites and
along migration routes.
By contrast, transient aggregators tend to be characterized by carnivorous and
piscivorous species (i.e. snappers, groupers) that migrate 10’s–100’s of kilometers
and spend days to weeks around their spawning aggregation sites (Garcia-Cagide
et al. 2001 ; Rhodes and Sadovy 2002a, b ; Heyman et al. 2005 ; Nemeth 2005 ;
Kadison et al. 2007, 2009 ; Nemeth et al. 2007 ) . During migration and aggregation
fi sh may continue to feed on other fi shes and invertebrates thus linking local food
webs within their functional migration areas (McCann et al. 2005 ) . Evidence of
transient aggregating species feeding on fi shes and invertebrates at aggregation sites,
however, is limited to a few incidental observations of predation and gut contents of
several grouper species. In Palau aggregating squaretail coralgrouper occasionally
attacked schools of small fusiliers (Caesionidae) and brown-marbled grouper was
observed eating a camoufl age grouper which aggregated at the same site (Johannes
et al. 1999 ) . During spawning aggregations of red hind in the Virgin Islands, disgorged gut contents commonly contained true crabs, hermit crabs, juvenile lobster
and small reef fi shes such as the slender fi lefi sh, Monacanthus tuckeri , and even
juvenile red hind (RSN unpublished data). Yellowfi n grouper, Mycteroperca
venenosa , stomach contents also contained a variety of reef fi shes such as yellowtail snapper, Ocyurus chrysurus , blackfi n snapper, Lutjanus buccanella , red hind,