The mean duration for trans-Pacific species is 62.2 days (S.D. = 11.4, N = 9). 

 The difference between these and the Hawaiian-inclusive species is not significant 

 (p = 0.13; Kolmolgorov-Smi rnov test, two-tailed), although the trend in the 

 data is both evident and consistent with predictions made elsewhere in the 

 literature (e.g., Rosenblatt and Walker, 1963). All but one trans-Pacific 

 species also is found in Hawaii. 



DISCUSSION 



Our results suggest that a general correlation between long pelagic larval 

 durations and broad geographic distributions is a valid assumption only when 

 applied to a relatively few species with exceptionally long-lived pelagic stages 

 (see also Thresher and Brothers, in press). In this respect, our conclusions 

 are strikingly similar to those of Thorson (1961), who surveyed the pelagic 

 durations and distributions of marine invertebrates. Thorson concluded that 

 only 20% of all bottom invertebrates with pelagic larvae have "true long-distance 

 larvae." These he defined as those with a planktonic life longer than 6 weeks. 

 Both of these figures are strikingly close to those we calculate for Indo- 

 Pacific coral-reef fishes, i.e., a threshold value of about 45 days, with 20.7% 

 of the species examined exceeding this value. The latter figure obviously 

 could be manipulated by adding species with high or low pelagic durations. We 

 strongly suspect, however, that this threshold value will remain robust as more 

 data are added. It is premature to draw strong conclusions without additional, 

 detailed work for other families of fishes and other phyla, but the surprisingly 

 close quantitative agreement between the current study and Thorson (1961) 

 suggests that some fundamental principle that applies across phyla may be 

 i nvol ved. 



Our data are also in substantial agreement with suggestions that geographically 

 isolated regions of the Indo-Pacific are colonized primarily by species with 

 longer than average pelagic developmental stages. This point has previously 

 been raised, particularly with respect to colonization of the Eastern Pacific 

 Faunal Province by Indo-West Pacific species, both for marine invertebrates 

 (e.g., Thorson, 1961; Dana, 1975; Zinsmeister and Emerson, 1979; Reaka, 1980) 

 and coral-reef fishes (Briggs, 1961, 1974; Rosenblatt and Walker, 1963; 

 Rosenblatt, 1967). Comparison of the minimum observed pelagic durations of 

 species that occur in Hawaiian waters and in the Eastern Pacific with the large 

 majority of species found only in the Central Pacific suggests that, although 

 an element of chance certainly is involved, under normal circumstances the 

 majority of Central Pacific species may not be capable of colonizing these 

 outlying areas. Moreover, even for those species that have colonized the 

 Eastern Pacific, such colonization may well be intermittent rather than 

 continuous, and dependent on the occurrence of unusual oceanographic conditions. 

 The minimum time required to cross the "Eastern Pacific Faunal Barrier" (see 

 Ekman, 1953) can be estimated from the distance between the likely source of 

 colonists, the Line Islands, and the westernmost point of the Eastern Pacific 

 faunal province, Clipperton Island, and peak reported values for the Equatorial 

 Countercurrent, the presumed route of colonization (e.g., Leis, 1983; Reaka and 

 Manning, 1980). The distance involved is approximately 5250 km, and normal 

 peak current velocities are in the range of 0.46 to 0.7 m sec - * (Wyrtki, 1965; 

 Tsuchiya, 1974). Consequently, normal transit time of the Eastern Pacific 



66 



