Barrier by a passively drifting object will be at least 87 days; given that 

 currents vary temporally and also decline as the near-shore environment is 

 reached, a minimum estimate of 100 days is probably more realistic. Yet, 

 apparent pelagic durations of nine trans-Pacific species examined range from 48 

 to only 83 days, averaging 24.8 days less than a reasonable minimum. None of 

 the 302 specimens we examined had a larval duration longer than 87 days, 

 suggesting that, even if one includes individual variation in larval competance, 

 few if any species are likely to cross the barrier under normal circumstances. 

 Our tentative conclusion, therefore, is that such colonization takes place only 

 during periods when the countercurrent is unusually strong, i.e., during El 

 Nino-type events (Wyrtki, 1965). If so, then we would predict that, following 

 the recent very strong El Nino event in 1982-83 (see Gill and Rasmussen, 1983; 

 Philander, 1983), unusually large numbers of new recruits of Indo-West Pacific 

 species should be present on Eastern Pacific reefs. 



ACKNOWLEDGMENTS 



We thank A. Gronell and N. Wolf for discussions of this work as it 

 progressed, W. N. McFarland for providing unpublished material for our examination, 

 L. Bell, D. Bellwood, P. L. Colon, G. Dingerkus, R. Greenfield, A. Gronell, J. 

 T. Moyer, P. F. Sale, and D. Williams for providing specimens, and S. Blaber 

 and J. Stevens for comments on an earlier version of this paper. 



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