Cryptic speciation in the stony octocoral Heliopora coerulea: temporal reproductive isolation between two growth forms

Abstract

Two growth forms of the stony blue octocoral Heliopora coerulea were recently shown to exhibit different genetic structures. In the present study, the reproductive timing of the two growth forms of the externally brooding blue coral was determined over a period of three years to examine the possible mechanism of cryptic speciation previously indicated by genetic data. During each monitoring year, in situ observations revealed external brooding of larvae in columnar colonies approximately one month earlier than their laminar counterparts. Ex situ larval collection during the first monitoring year showed larval release occurring around new moon to first quarter moon, with columnar colonies planulating in March and laminar colonies in April. These results indicate temporal reproductive isolation between the two growth forms, hence supporting the existence of cryptic species in the blue octocoral.