138
P.L. Colin
In the IWP some RA species (as well as various non-aggregating fi shes) spawn
along reef fronts during the few hours after high tide, migrating (as discussed previously) either to the seaward front or along the reef to channel edges (Fig. 5.14 ), and
start spawning as the tide begins to turn and move slowly off the reef (see Fig. 6.12).
In Palau such spawning locations and times did not always ensure offshore dispersal
of eggs; a portion of these moved back towards their natal reefs after low tide with
some being carried across the reef into lagoon environments (Hamner et al. 2007 ,
PLC unpublished data). For other IWP fi shes aggregating in tidal channels of
barrier reefs and atolls, spawning by various RA species occurs after high tide when
currents start moving out towards the open ocean (Bell and Colin 1986 ; Moyer 1989 ;
Craig 1998 ) .
Three factors affect the movement of eggs after spawning; the vertical movement
of eggs in the water column, diffusion of eggs as particles and the advection of
water containing eggs. These are discussed in more detail in Chaps. 6 and 7 , but it
is important to establish here that nearly all aggregating species have positively
buoyant eggs that both ascend slowly and diffuse outward from their release point.
Currents producing horizontal transport (advection) in reef areas where aggregations occur are produced by a number of mechanisms. Weather and sea swell effects
can also dominate shallow transport of eggs and larvae in lagoons, channel areas
and nearshore outer reefs (Sancho et al. 2000a ) .
The entrainment of eggs and larvae into oceanic circulation is uncertain and
appears somewhat location-specifi c. Certainly there is a mix of entrainment potential
Fig. 5.16 Current-following drifters started at 30 min intervals after high tide at a grouper aggregation
site at Ulong Channel (Ngerumakaol), Palau during aggregation were carried 1–1.5 km out to sea
by tidal jets created by falling tides. After low tide they stalled offshore as tidal currents came
to a stop
P.L. Colin
In the IWP some RA species (as well as various non-aggregating fi shes) spawn
along reef fronts during the few hours after high tide, migrating (as discussed previously) either to the seaward front or along the reef to channel edges (Fig. 5.14 ), and
start spawning as the tide begins to turn and move slowly off the reef (see Fig. 6.12).
In Palau such spawning locations and times did not always ensure offshore dispersal
of eggs; a portion of these moved back towards their natal reefs after low tide with
some being carried across the reef into lagoon environments (Hamner et al. 2007 ,
PLC unpublished data). For other IWP fi shes aggregating in tidal channels of
barrier reefs and atolls, spawning by various RA species occurs after high tide when
currents start moving out towards the open ocean (Bell and Colin 1986 ; Moyer 1989 ;
Craig 1998 ) .
Three factors affect the movement of eggs after spawning; the vertical movement
of eggs in the water column, diffusion of eggs as particles and the advection of
water containing eggs. These are discussed in more detail in Chaps. 6 and 7 , but it
is important to establish here that nearly all aggregating species have positively
buoyant eggs that both ascend slowly and diffuse outward from their release point.
Currents producing horizontal transport (advection) in reef areas where aggregations occur are produced by a number of mechanisms. Weather and sea swell effects
can also dominate shallow transport of eggs and larvae in lagoons, channel areas
and nearshore outer reefs (Sancho et al. 2000a ) .
The entrainment of eggs and larvae into oceanic circulation is uncertain and
appears somewhat location-specifi c. Certainly there is a mix of entrainment potential
Fig. 5.16 Current-following drifters started at 30 min intervals after high tide at a grouper aggregation
site at Ulong Channel (Ngerumakaol), Palau during aggregation were carried 1–1.5 km out to sea
by tidal jets created by falling tides. After low tide they stalled offshore as tidal currents came
to a stop