22
R.S. Nemeth
2.1 Introduction
Throughout reef ecosystems many fi shes utilize a reproductive strategy that requires
migration to specifi c sites where courtship and spawning commence and fertilized
eggs or larvae are released into local water masses. The reproductively mature adults
that spawn at aggregation sites may represent the primary source of reproductive
effort for a species (Shapiro et al. 1993 ) . Therefore each spawning aggregation may
have a strong infl uence on the replenishment of participating populations.
Migration and subsequent spawning by aggregating species provide an important
and largely overlooked ecological component of connectivity within marine ecosystems, due to fi sh movements, habitat use and interspecifi c interactions. Since most
reef-associated fi shes have limited adult movements, connectivity at larger spatial
scales has typically referred to the genetic exchange among local marine populations
via larval dispersal (Cowen et al. 2000 ; Cowen 2002 ; Sale 2004 ) . However, recent
biophysical models of larval dispersal suggest that spatial structure of successful
larval exchange for a variety of reef fi sh species can be as little as 10–100 km
(Cowen et al. 2006 ) . On the other hand, the adults of many species within at least
fi ve families (snooks-Centropomidae, ladyfi shes-Elopidae, snappers-Lutjanidae,
groupers-Serranidae, porgies-Sparidae) of reef-associated fi shes annually swim these
distances, or greater, when migrating from home ranges to their spawning aggregation sites (Nemeth 2009 , Table 4). The extent of genetic mixing at fi sh spawning
aggregations (FSA) among adults who have migrated from an area encompassing
100’s of square kilometers is unknown but is highly relevant to understanding population structure and for management, and therefore requires greater attention when
addressing issues of population connectivity. However, because information on the
genetic relatedness of fi sh in spawning aggregations is scant (Rhodes et al. 2003 ) ,
this chapter will focus primarily on spatial scales of adult connectivity in aggregating species and on the ecological interactions that occur along migration pathways and at spawning aggregation sites. Moreover, ecosystem based management
(EBM) requires a good understanding of the ecology and behaviours of target species
(Garcia et al. 2003 ) , to fully explore different management scenarios.
Because aggregating species include many large carnivorous (i.e. groupers, snappers,
jacks-Carangidae) and numerous herbivorous (i.e. surgeonfi shes-Acanthuridae,
parrotfi shes-Scaridae) fi shes of high commercial and ecological value, they play an
important role in ecosystem function and fi sheries economics. For example, the
Nassau grouper ( Epinephelus striatus ) was an important commercial species until
aggregation fi shing nearly eliminated it from many locations throughout the
Caribbean (Olsen and LaPlace 1978 ; Sadovy 1997 ; Sala et al. 2001 ; Aguilar-Perera
2006 ) . Although the substantial decline in Nassau landings and subsequent loss of
revenue has long been documented (Sadovy 1994, 1997 ; Sadovy and Eklund 1999 ;
Claro et al. 2001 ) , the broad ecological importance of this single species has only
recently been realized. Stallings ( 2008 ) found that Nassau grouper facilitated higher
rates of recruitment and maintained higher biological diversity of small reef fi shes
by indirectly structuring food webs through the consumption of secondary predators
R.S. Nemeth
2.1 Introduction
Throughout reef ecosystems many fi shes utilize a reproductive strategy that requires
migration to specifi c sites where courtship and spawning commence and fertilized
eggs or larvae are released into local water masses. The reproductively mature adults
that spawn at aggregation sites may represent the primary source of reproductive
effort for a species (Shapiro et al. 1993 ) . Therefore each spawning aggregation may
have a strong infl uence on the replenishment of participating populations.
Migration and subsequent spawning by aggregating species provide an important
and largely overlooked ecological component of connectivity within marine ecosystems, due to fi sh movements, habitat use and interspecifi c interactions. Since most
reef-associated fi shes have limited adult movements, connectivity at larger spatial
scales has typically referred to the genetic exchange among local marine populations
via larval dispersal (Cowen et al. 2000 ; Cowen 2002 ; Sale 2004 ) . However, recent
biophysical models of larval dispersal suggest that spatial structure of successful
larval exchange for a variety of reef fi sh species can be as little as 10–100 km
(Cowen et al. 2006 ) . On the other hand, the adults of many species within at least
fi ve families (snooks-Centropomidae, ladyfi shes-Elopidae, snappers-Lutjanidae,
groupers-Serranidae, porgies-Sparidae) of reef-associated fi shes annually swim these
distances, or greater, when migrating from home ranges to their spawning aggregation sites (Nemeth 2009 , Table 4). The extent of genetic mixing at fi sh spawning
aggregations (FSA) among adults who have migrated from an area encompassing
100’s of square kilometers is unknown but is highly relevant to understanding population structure and for management, and therefore requires greater attention when
addressing issues of population connectivity. However, because information on the
genetic relatedness of fi sh in spawning aggregations is scant (Rhodes et al. 2003 ) ,
this chapter will focus primarily on spatial scales of adult connectivity in aggregating species and on the ecological interactions that occur along migration pathways and at spawning aggregation sites. Moreover, ecosystem based management
(EBM) requires a good understanding of the ecology and behaviours of target species
(Garcia et al. 2003 ) , to fully explore different management scenarios.
Because aggregating species include many large carnivorous (i.e. groupers, snappers,
jacks-Carangidae) and numerous herbivorous (i.e. surgeonfi shes-Acanthuridae,
parrotfi shes-Scaridae) fi shes of high commercial and ecological value, they play an
important role in ecosystem function and fi sheries economics. For example, the
Nassau grouper ( Epinephelus striatus ) was an important commercial species until
aggregation fi shing nearly eliminated it from many locations throughout the
Caribbean (Olsen and LaPlace 1978 ; Sadovy 1997 ; Sala et al. 2001 ; Aguilar-Perera
2006 ) . Although the substantial decline in Nassau landings and subsequent loss of
revenue has long been documented (Sadovy 1994, 1997 ; Sadovy and Eklund 1999 ;
Claro et al. 2001 ) , the broad ecological importance of this single species has only
recently been realized. Stallings ( 2008 ) found that Nassau grouper facilitated higher
rates of recruitment and maintained higher biological diversity of small reef fi shes
by indirectly structuring food webs through the consumption of secondary predators