Diversity of leptocephalus larvae around the island of Barbados (West Indies): relevance to regional distributions

Abstract

The cryptic nature of many elopomorph species and their occupation of minimally explored habitats have led to the underestimation of their importance as a component of regional bio- diversity. Additionally, it had led to their exclusion from studies that seek to resolve the processes and life history traits important in determining the geographic distributions of species. Collections of the larval stage of elopomorphs provide one means of addressing regional diversity in this taxa. Plankton tows around Barbados during 4 separate years collected 68 identifiable taxa of the leptocephalus lar- val form unique to elopomorphs. While most of these species have either been collected as adults in the Lesser Antilles or upcurrent in the Guyanas, there remained 11 species whose adults are not known from either biogeographic area, and 7 leptocephalus types of species not described as adults. To determine whether these leptocephali were likely to be the product of local spawning, or alterna- tively expatriates from the Guyanas, temporal patterns of length frequency distributions and abun- dance of each species were analyzed with respect to regional oceanographic conditions. High abun- dances and small leptocephali of species probably expatriated from the Guyanas were found to coincide with periods when North Brazil Current (NBC) rings were present around Barbados and locally produced coral reef fish larvae were flushed away from the sample area. Minimum size classes and high abundances of Lesser Antillean species were more sporadic over time. While this work does help establish the geographic distribution of a number of rare and less frequently encoun- tered species, it also highlights the lack of knowledge about elopomorph distributions that justifies their exclusion from biogeographic studies reliant on accurate fine-scale distribution patterns. How- ever, a comparison of species distributions across major biogeographic boundaries indicates that elopomorph species as a whole are more broadly distributed than perciform species, a pattern attrib- utable to many unique characteristics of their leptocephalus larval stage.