Aspects of the life history of the soft coral Efflatounaria sp. on Davies Reef, Great Barrier Reef

Stereophotography was used to study life history characteristics of Efflatounaria sp. at two sites at Davies Reef on the Great Barrier Reef, between December 1980 and June 1982. Site 1 was located on a patch reef about 200 m long on the leeward margin of the lagoon which had a comparatively high density of Efflatounaria sp.. Site 2 was located on a similar patch reef approximately 1 km away, within the lagoon but close to the leeward margin and had a lower density of Efflatounaria sp..Plots (1 m²) were established at about 5 m and 10 m below low water datum on hard substrate. At Site 1, plots were set up with both high densities (much greater than 50 colonies per square metre) and low densities (less than 20 colonies per square metres) of Efflatounaria sp.. At Site 2 only low density plots could be established. In addition, 'empty' plots (1 m² and 9 m²) were set up at 10 m depth at both sites. At Site 1, all Efflatounaria sp. colonies were completely removed from these plots using a knife. At Site 2, these plots were originally devoid of the species. Two replicate were established for each of the above treatments.Plots were photographed at intervals of about 2 months from December 1980 to June 1982, using twin Nikonos cameras and flashes mounted on a 105 em high frame constructed of aluminium and PVC piping. Four pairs of centrally overlapping photographs were taken of each square metre, each pair showing an area 70 x 60 cm. Using a stereoscope, maps were drawn for each plot recording the continued existence, appearance or disappearance of individual colonies and stolons. The precise numbers of colonies and stolons in dense clumps and the presence of very small colonies (less than 2 cm across) were checked by visual inspection underwater. Gonad development was also monitored following collection of approximately 40 colonies at 5-10 m from Site 1, at monthly intervals (more frequently in early summer). Reproductive condition was assessed by dissection and from histological sections. Additional field observations were made in summer 1981, principally at Site 1. In this study, vegetative propagation, natality and mortality rates, and some aspects of sexual reproduction in the soft coral, Efflatounaria sp. were investigated, to determine characteristics of the species' life history and possible reasons for its great abundance in some areas. In the xeniid genus Efflatounaria, vegetative propagation by means of stolon-like outgrowths occurs. Stolons usually arise from near the base of a branch or from the colony stalk. Sometimes series of several daughter colonies are formed, interlinked by straight or divided stolons. The stolons may bear polyps and are then usually attached to the substrate throughout their length.

本研究采用立体摄影术（Stereophotography），于1980年12月至1982年6月期间，在大堡礁（Great Barrier Reef）戴维斯礁（Davies Reef）的两处样地开展艾弗特软珊瑚属未定种（Efflatounaria sp.）的生活史特征研究。样地1设于潟湖（lagoon）下风侧边缘一处长约200米的斑礁（patch reef）上，该区域艾弗特软珊瑚属未定种的种群密度相对较高；样地2设于距离样地1约1公里的另一处相似斑礁上，该斑礁位于潟湖内部但紧邻下风侧边缘，其艾弗特软珊瑚属未定种的种群密度较低。研究团队在硬质底质上，于低潮基准面（low water datum）下5米与10米水深处设置了面积为1平方米的样方。在样地1中，设置了种群密度分别为高密度（每平方米远多于50个珊瑚群落）与低密度（每平方米少于20个珊瑚群落）的两类样方；而样地2仅可设置低密度样方。此外，在两处样地的10米水深处均设置了“空白”样方（面积分别为1平方米和9平方米）：样地1的空白样方中，所有艾弗特软珊瑚属未定种的群落均以刀具彻底清除；样地2的空白样方原本就未分布该物种。上述每种处理方式均设置了2个重复样方。1980年12月至1982年6月期间，以约每2个月1次的频率对样方进行拍摄：采用两台尼康诺斯（Nikonos）水下相机，搭配安装于由铝制与PVC管材搭建的105厘米高支架上的闪光灯。每个1平方米样方拍摄4组中心重叠的立体照片，每组照片覆盖的区域为70×60厘米。借助立体镜（stereoscope），为每个样方绘制样图，记录单株珊瑚群落与匍匐茎（stolon）的存续、出现或消失情况。对于密集簇生的群落和匍匐茎的精确数量，以及直径小于2厘米的微型群落的存在情况，通过水下目视检查进行核实。另外，研究团队于样地1的5-10米水深处采集约40个珊瑚群落，以约每月1次的频率（初夏时期采样频率更高）监测其性腺发育情况；通过解剖与组织切片来评估其生殖状态。1981年夏季还开展了额外的野外观测，观测地点主要为样地1。本研究针对软珊瑚艾弗特软珊瑚属未定种的营养繁殖（vegetative propagation）、出生率（natality）、死亡率（mortality）以及有性生殖的若干特征展开调查，旨在明确该物种的生活史特征，以及其在部分区域种群数量极多的潜在原因。在肉芝软珊瑚科（Xeniidae）的艾弗特软珊瑚属中，物种通过类匍匐茎的突起开展营养繁殖。匍匐茎通常萌发于分枝基部或群落柄部，有时会形成由若干子群落构成的连续结构，这些子群落通过直连或分叉的匍匐茎相互连接。匍匐茎可生长出珊瑚虫，此时其通常全程附着于底质之上。