Does the embryonic response to temperature and salinity by four species of Caribbean sea urchins parallel the reproductive synchrony?

Abstract

Populations of four species of sea urchins, Lytechinus variegatus, Echinometra lucunter, Echinometra viridis and Tripneustes ventricosus, overlap in distribution on the shallow insular shelf of southwest Puerto Rico yet they exhibit distinctly different degrees of reproductive synchrony. Populations of L. variegatus and T. ventricosus possess gravid individuals for many months of the year while the Echinometra species have a synchronous spawning period with gravid individuals present only for the two fall months that coincide with the sea temperature maximum. These species all broadcast spawn and possess planktotrophic larvae. Little is known about the response of the embryos and larvae of these species to the environment. Perhaps the embryos of those species with highly synchronous reproduction are more sensitive to physical factors that those of the less synchronous ones. To determine developmental responses to temperature and salinity, a 3x3 factorial experiment over a temperature range of 20 to 30° C and a salinity range of 31.5 to 38.5 ‰ was performed for each species. Developmental stage was measured at 3h intervals for 48h. Response surface analysis of cleavage stages revealed that all species were more sensitive to temperature than salinity in the ranges tested and that the most synchronous species were most responsive to temperature differences. At the blastula stage, the least synchronous L. variegatus and T. ventricosus exhibit the broadest and narrowest lethal limits, respectively; while the more synchronous Echinometra species exhibit intermediate ones. Environmental influences seem to be manifested at a number of sites during the developmental process.

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