Herbivory and zonation of Sargassum spp. within fringing reefs of the central Great Barrier Reef

A series of transplant and caging experiments, using the macroalgae Sargassum spp., were carried out in Coolgaree (Challenger) Bay, Great Palm Island and Brook Island between December 1992 and January 1994.Seasonal effects were investigated in two experiments conducted on the landward edge of the coral dominated zone in Coolgaree Bay, Great Palm Island. In the first experiment, which commenced in December 1992, mixtures of 'mature phase' adult Sargassum species, predominantly Sargassum oligocystum and Sargassum tenerrimum, attached to coral rubble rocks, were collected in the Sargassum zone in Coolgaree Bay. The plants were counted, sorted into roughly even groups by frond numbers and three replicate groups were assigned randomly to each of four treatments in plots within the coral dominated zone. The treatments were: open (uncaged) transplant; transplant with cage; partial cage control; and a "return transplant" returned to the Sargassum zone. Frond densities were counted before allocation and at 1 and 3 months and categorised as numbers of primary laterals (fronds/plot) in four size classes (0 to 5 cm; 5 to 15 cm; 15 to 50 cm; >50 cm). After 3 months, the plants were retrieved, dried and weighed. In a similar experiment, initiated in July 1993, dormant plants with few fronds longer than 5 cm (none >15 cm) were used. These were retrieved, counted, dried and weighed in January 1994. Qualitative data collected included regular observations of plant condition, and observations of sites and mobile species composition at night and at different tide levels.A Sargassum recruitment experiment commenced on Great Palm Island in December 1992. Each plot in the coral dominated zone was chosen to include a large, flat block of carboniferous substrate (~0.5 m²), with no Sargassum or other fucalean macroalgae, and little or no live coral. Blocks were scraped and wire-brushed at the beginning of the experiment to remove most of the turf algae and sediments covering them. Three replicate plots were randomly assigned to each of three treatments: open (uncaged); caged; and partial cage control. Quantitative descriptions were made of algae on each block every 2 to 3 months until January 1994, when any Sargassum recruits were counted, dried and weighed.A within-reef transplant experiment commenced at Brook Island in mid-November 1992. Coral rocks, with mixtures of Sargassum oligocystum and Sargassum tenerrimum plants attached, were collected and counted. Five replicate groups of plants were randomly assigned to either Sargassum or coral patches. Plants were recounted, collected, dried and weighed after 1 month. Qualitative observations included plant condition and mobile species composition, the latter observed at night and at different tide levels.
This research was undertaken to test the importance of herbivory, physiological tolerance limits, and recruitment and dispersal in regulating the distribution and abundance of the genus Sargassum on nearshore fringing reefs of the central Great Barrier Reef.

1992年12月至1994年1月期间，研究团队于大堡礁中部的大棕榈岛库利加里（挑战者）湾与布鲁克岛，开展了一系列以大型藻类马尾藻属（Sargassum spp.）为研究对象的移植与笼养实验。
为探究季节效应的影响，研究人员在大棕榈岛库利加里湾以珊瑚为主的群落陆侧边缘，开展了两项相关实验。第一项实验于1992年12月启动：从库利加里湾的马尾藻分布区采集附着于珊瑚碎石上的“成熟型”成体马尾藻，优势类群为少孢马尾藻（Sargassum oligocystum）与细弱马尾藻（Sargassum tenerrimum）。先统计植株总数，按叶状体数量将其大致均分为若干组，随后将3组重复样本随机分配至珊瑚主导区样地的4种处理中，每种处理设置3个重复组，共设置4种处理：开放式（无笼）移植、带笼移植、半笼式对照，以及“回迁移植”（即移回原马尾藻分布区）。在分组前、实验开展后1个月与3个月时统计叶状体密度，并按叶状体的初级侧枝尺寸分为4个等级，以每样地的叶状体数量为统计单位，尺寸范围分别为0~5 cm、5~15 cm、15~50 cm及>50 cm。实验持续3个月后，回收所有植株，烘干并称量其干重。
第二项类似实验于1993年7月启动，采用叶状体长度极少超过5 cm（无个体长度超过15 cm）的休眠植株。该实验于1994年1月回收植株，统计其数量后烘干并称量干重。此外研究还收集了定性数据：定期观测植株生长状态，以及不同潮汐时段、夜间的样地与生境移动物种组成情况。
1992年12月，大棕榈岛启动了一项马尾藻定植实验。珊瑚主导区的每个样地均选取面积约0.5 m²的大型平坦石炭纪基质块，该区域无马尾藻或其他墨角藻目大型藻类，且活珊瑚覆盖率极低或无活珊瑚。实验开始前，对基质块进行刮擦与钢丝刷洗，以去除覆盖于表面的大部分草皮藻类（turf algae）与沉积物。随后将3组重复样地随机分配至3种处理：开放式（无笼）、带笼、半笼式对照。每2~3个月对每个基质块上的藻类群落进行定量描述，直至1994年1月，此时统计所有马尾藻定植幼苗的数量，烘干并称量其干重。
1992年11月中旬，布鲁克岛启动了一项礁内移植实验。采集附着有少孢马尾藻与细弱马尾藻混合种群的珊瑚碎石，统计植株数量。将5组重复植株随机分配至马尾藻分布区或珊瑚斑块生境中。实验开展1个月后，再次统计植株数量，回收样本并烘干称重。定性观测内容包括植株生长状态，以及不同潮汐时段、夜间的移动物种组成情况。
本研究旨在验证植食作用、生理耐受极限以及种群补充与扩散过程，对大堡礁中部近岸岸礁马尾藻属物种分布与丰度的调控作用。