In freely spawning invertebrates, fertilization success or failure may have a major impact on recruitment and hence on population dynamics. Although the process of fertilization has been studied extensively at the cellular and molecular levels, the ecological question of how sperm encounter eggs remains largely unresolved. Shallow-water echinoderms use light and other environmental cues to synchronize their spawning. Many such cues are not available in the deep sea; indeed, mechanisms facilitating fertilization in low-density, deep-sea populations are completely unknown. Dr. Young and a collaborator has discovered numerous sperm modifications (large sperm head, dimorphic sperm, bipolar sperm, extensive energy stores) among deep-sea echinoids that could enhance fertilization success. Preliminary data also indicate that some deep-sea sperm remain viable for very long periods and that some adult echinoderms aggregate for breeding. These investigators propose a multidisciplinary, comparative study that relates gamete untrastructure and fertilization kinetics to the problem of sperm-egg encounter in the deep sea. The approach includes shallow-water in situ validation of equations that predict sperm concentration and fertilization success and a comparison of fertilization kinetics between tropical bathyal echinoderms and shallow-water temperate species living at the same temperature.
