Sea-nymphs

Members of the Family Nereididae are named after Nereus, a sea god and father of numerous sea nymphs. Sea-nymphs are among the most commonly encountered and widespread intertidal polychaete worms. Close to two dozen species live in the Pacific Northwest (at all depths). The intertidal species have been called ragworms. Upon attaining sexual maturity, nereids are well known for their precisely timed and choreographed “nuptial dance.” The worms respond to internal cues (hormones and biological rhythm) as well as external environmental triggers to reach maturity. The environmental cues include seasonal or lunar cycles, tidal fluctuations, temperature, day length, light intensity and even salinity. As if by magic, all members of a species are able to reach sexual maturity simultaneously, as specialized forms called epitokes, and swim to the surface for spawning at exactly the same time and same place. The accompanying photograph of an undetermined species shows two sea-nymph epitokes, also known as heteronereids, exhibiting their highly transformed bodies, which are swollen with either eggs or sperm. Body transformations include increased size of the parapodia (fleshy appendages), greater swimming musculature, development of paddle chaetae (bristles) and enlargement of the eyes. These eyes are “programmed” to day length and light intensity, so it is not surprising that the epitokes can be falsely triggered and attracted to nearshore lights. Stimulated by self-produced, partner-attracting pheromones (chemical signals), the heteronereids perform intimate nuptial dances, jettisoning eggs and sperm into the surrounding sea but in close proximity to their partners. So extreme are these spawning modifications, along with a tendency for gamete release to occur through ruptures in the body wall, that spawning is inevitably followed by death. After fertilization the developing, non-feeding larvae inhabit the water column, ultimately being dispersed by tides and currents. Depending on the species, the larvae spend from hours to months as part of the plankton before settling out and onto the bottom. After completing metamorphosis, juveniles begin the journey to adulthood. Most, but not all, species of sea-nymphs exhibit this type of life cycle.
In the Pacific Northwest, late winter and spring is a magical time, when the reproductive activities of plants and animals occur at a frenzied pace and result in cyclical plankton blooms. Dockside observers and divers are treated to an amazing array of organisms congregating and breeding at or near the surface. Many of the sea-nymphs (Family Nereididae) join in the activity with their own unique reproductive method of broadcast (free) spawning.