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retention in a bay occurs when water and plankton are trapped on the inshore side
of the long shore fl ow, and it is one of the most important topographic mechanisms
for retention of materials such as pollutants or larvae near reefs (Wolanski 2001 ) .
Lateral trapping can be seen clearly at Cid Island in the Whitsunday Island, Australia
(Fig. 6.6 , redrawn from Hamner and Hauri 1977 ) . Archambault et al. ( 1998 )
demonstrated lateral trapping for small embayments, as have McCulloch and Shanks
( 2003 ) and Shanks et al. ( 2003 ) .
Cross shore tidal jets disrupt coastal boundary currents but their disturbance
often does not completely interrupt alongshore fl ow unless the jet is particularly
Fig. 6.5 Movement of current drifters on three different days released at a resident spawning
aggregation site in the Ulong Reef embayment. Palau, at 30 min intervals. Drifters took somewhat
different paths each day. Some became entrained within the coastal boundary layer while others
reversed direction on the fl ood tide and advected east towards and across the barrier reef (Colin and
Hamner, unpublished data)