Influence of environmental parameters on gametogenesis, spawning and embryo survival in the holothuroid Cucumaria frondosa

Abstract

The environmental control of reproductive processes is central to both fundamental and applied aspects of animal ecology. The present study experimentally assessed how environmental factors modulate gametogenesis and spawning and impact embryo development and survival in the holothuroid Cucumaria frondosa, a cold-water echinoderm with lecithotrophic development. Adults were exposed to three seawater temperatures, four photoperiod regimes, and two food concentrations during 120 days overlapping the natural gametogenic and spawning periods. Among all the treatments tested, exposure to ambient conditions of water temperature (−1 to 3 °C), photoperiod (8 to 13 h of light) and food concentration (3 × 103 ± 896 rotifers g−1 of sea cucumbers d−1) yielded the greatest reproductive output and embryo survival. At pre-spawning, males and females had the highest gonad index (~33%) and where filled with mature gametes. At spawning, females in ambient conditions released the highest number of oocytes (1.2 × 103 oocytes female−1) and yielded the highest embryo survival rates (21% at 20 days post fertilization). Individuals exposed to warmer water temperatures (6 and 12 °C) experienced delayed gametogenesis and did not spawn. Individuals under 24-h light, 24-h dark, and advanced (4 months) photoperiods showed delayed gametogenesis and low numbers of oocytes released; moreover, embryos died within 10 days post fertilization. Individuals fed with high food concentration (6 × 103 ± 982 rotifers g−1 of sea cucumbers d−1) showed similar results to ambient conditions, suggesting that increased food supply neither decreased nor enhanced reproductive output over the experimental period. This study sheds new light on the environmental drivers of reproductive success in C. frondosa, which is of value for developing conservation strategies and mariculture protocols in cold-water holothuroids with lecithotrophic development.