Spawning and sexual reproduction in the octocoral, Sarcophyton elegans (Cnidaria: Alcyonacea), from Lizard Island, Great Barrier Reef

Two study sites were chosen at Lizard Island, in shallow areas with a high abundance of the soft coral, Sarcophyton elegans. Site A was located on Loomis Reef at the western entrance to the Lizard Island lagoon and Site B was located on a small wave-exposed patch reef near South Island. At each site, three 1x10 m belt transects were laid down end to end. Transects were located parallel to the direction of the current in order to examine the effects of spawning by upstream colonies on the reproductive behaviour of downstream colonies. The position of each Sarcophyton elegans colony within the belt transects was recorded and in December 1991, the basal circumference of the stalk of each colony within the transects was measured to determine colony size distribution.In October 1991, prior to the spawning season, the mesenteries of each colony within all transects were examined by making a small incision in the polypary and the sex of each colony was recorded. The reproductive state of each colony was recorded monthly between October 1991 and January 1994. Spawning activity was monitored between October 1991 and February 1992, August 1992 and February 1993 and August 1993 and January 1994. The spatial distribution of immature, mature and spawned mesentaries in individual polyparies was investigated by making incisions at several points along the radius of the polypary and examining the exposed mesentaries. A colony was recorded to have released its gametes when ripe gametes were recorded as present during a sampling event and absent in the next sampling event. Detailed studies of the timing of gamete release within transects was also carried out at Site A only.Fifty colonies of different size classes were collected outside the transects prior to the spawning season in 1992, to determine the minimum colony size at which sexual maturity is reached. The basal circumference of the stalk of each colony was measured and each colony was sectioned in the laboratory and examined under a light microscope to detect the presence of gametes. Histological samples of the smaller colonies were also prepared and examined for gametes.To determine the length of the gametogenic cycle, small pieces of tissue were excised from the polypary of 10 large male and 10 large female marked colonies, located outside the transects. Tissue samples were collected on an approximately monthly basis between October 1991 and January 1994. The samples were preserved, decalcified and the diameters of the oocytes and spermaries were measured under a compound microscope. Paraffin sections from each sample were stained with hematoxylin and eosin for histological examination to determine the stage of gonadal development. This research was undertaken to describe the sex ratio, gametogenesis and mode of sexual reproduction in the common octocoral species, Sarcophyton elegans, which is found in shallow lagoons and on reef flats throughout the Great Barrier Reef.

本研究在蜥蜴岛（Lizard Island）选取两处研究样地，两处均为优雅肉芝软珊瑚（Sarcophyton elegans）丰度较高的浅海区域。A样地位于蜥蜴岛潟湖西侧入口的卢米斯礁（Loomis Reef），B样地则位于南岛附近一处受波浪影响的小型斑礁。在每个样地中，沿首尾相接的方式布设3条1×10米的带状样带（belt transects），样带布设方向与海流平行，以探究上游珊瑚群体产卵对下游群体繁殖行为的影响。记录每条带状样带内每株优雅肉芝软珊瑚群体的位置，并于1991年12月测量样带内各群体的茎基周长，以明确珊瑚群体的大小分布特征。1991年10月，即产卵季之前，研究人员通过在每个珊瑚群体的珊瑚体（polypary）上做小型切口，检查所有样带内各群体的隔膜（mesenteries），并记录其性别。1991年10月至1994年1月期间，每月记录各珊瑚群体的繁殖状态。产卵活动的监测分为三个时段：1991年10月至1992年2月、1992年8月至1993年2月，以及1993年8月至1994年1月。通过沿珊瑚体径向多个点位做切口并观察暴露的隔膜，研究单个珊瑚体中未成熟、成熟以及已产卵隔膜的空间分布特征。若某次采样中检测到成熟配子（gametes），而下一次采样中未再检出，则记录该珊瑚群体已释放配子。仅在A样地开展了样带内配子释放时间的详细研究。1992年产卵季前，在样带外采集了50株不同大小等级的优雅肉芝软珊瑚群体，以确定达到性成熟所需的最小群体尺寸。测量各群体的茎基周长，并在实验室中将群体切片，通过光学显微镜观察是否存在配子；同时还制备了小型群体的组织学样本，用于配子检测。为确定配子发生周期（gametogenic cycle）的时长，研究人员从样带外标记的10株大型雄性群体和10株大型雌性群体的珊瑚体上切取小块组织。1991年10月至1994年1月期间，约每月采集一次组织样本。样本经固定、脱钙处理后，在复合显微镜下测量卵母细胞（oocytes）与精巢（spermaries）的直径；将每个样本的石蜡切片用苏木精-伊红（hematoxylin and eosin）染色，开展组织学检查以确定性腺发育阶段。本研究旨在描述优雅肉芝软珊瑚（Sarcophyton elegans）的性比、配子发生过程及有性繁殖模式，该物种为广泛分布于大堡礁（Great Barrier Reef）全域浅海潟湖及礁坪的常见八放珊瑚（octocoral）物种。