Reproductive biology of two species of holothurian from the deep-sea order Elasipoda, on the Antarctic continental shelf

Antarctic shallow-water and deep-sea echinoderms are known to have seasonal gametogenic cycles linked to seasonal pulses of phytodetritus produced in surface waters. We suggest that phytodetritus reaching the Antarctic continental shelf may persist for longer timescales than in shallow OF deep waters as a result of the low temperatures, low flow velocities, and the relatively short descent. If this food source remains available for extended periods throughout the year, Antarctic continental shelf megabenthos may not entrain seasonal gametogenic periodicity. To explore the reproductive response of the elpidiid holothurians, Protelpidia murrayi and Peniagone vignoni, a seasonal series of samples were taken on the West Antarctic Peninsula (WAP) at depths of 550-600 m between November 1999 and March 2001. Gonad indices were measured, and gonad tissues were analysed using histological and image analysis techniques. Oocyte size-frequency distributions were constructed from measurements of oocyte diameter, and analysed to describe reproductive patterns. Histological analyses of gonads tissue from P. murrayi suggest that gametogenesis is synchronised and seasonal, with spawning occurring between March and June. The onset of vitellogenesis appears to be initiated and synchronised by the arrival of the phytodetritus pulse. While, oocyte size-frequency distributions of P. vignoni suggest that oogenesis is synchronous between individuals, and infer a seasonal variation in gametogenic intensity, with an increase in production of vitellogenic oocytes that may be associated with an increase in food supply. The seasonal series of oocyte size-frequency distributions suggests that spawning commenced during October and November. We propose that both P. murrayi and P. vignoni have opportunistic reproductive patterns. In P. murrayi, the distinct gametogenic response to the summer Antarctic-shelf food pulse may be well adapted to any trophic regime with a pulsed food supply. In contrast P. vignoni produces mature gametes all year round but capitalises on higher summer food flux by increasing the intensity of gamete production during this time. Therefore, although these species continue to feed during the austral winter and may gain sufficient energy to maintain basal metabolism and limited reproductive development, energetically more costly activities, such as high rates of vitellogenesis, may be reserved for the summer months when higher quality of food is available.

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