Distribution of holothurian larvae determined with species-specific genetic probes

Identification of marine invertebrate larvae to the species level is often difficult due to morphological similarity and phenotypic plasticity. To study dispersal of morphologically indistinguishable holothurian larvae, we developed a simple detection protocol that uses a series of oligonucleotide probes for the 16S rRNA portion of the mitochondrial DNA genome; this protocol may be feasible for use onboard research vessels. Using our technique, we analyzed > 1,800 larvae from collections made during spring 1993 in the western Gulf of Maine. Of the three species present in the plankton, Cucumaria frondosa larvae dominated the samples, often comprising >90% of the larval pool and 95% of new recruits. Temporal differences in planktonic distribution suggest the southward transport of C. frondosa. The vertical distribution of larvae over time suggests that larvae are located primarily in the upper coastal waters. The presence of C. frondosa larvae in the coastal waters of New Hampshire represents a loss to recruitment because C. frondosa adults are extremely rare in this area.