Predation on coral larvae by corals from the Great Barrier Reef

Gametes from colonies of the coral Acropora tenuis (from Magnetic Island) and from Acropora millepora (from Davies Reef) were collected after spawning in tanks. Colonies of several corals (Acropora digitifera, Acropora formosa, Acropora latistella, Acropora secali, Acropora verweyi, Galaxea astreata, Goniastrea aspera, Goniopora pandoraensis, Platygyra pini) and two zoanthids (Palythoa tuberculosa, Zoanthus sp.1.) species were collected from inshore reefs near Townsville for the feeding experiments. The feeding experiments were conducted in flow chambers at gentle water flow. They commenced when the larvae were 3 days old, and continued until the numbers of free-swimming larvae were depleted by the experiments, and by settlement and/or metamorphosis which occurred at about 11 days (Acropora tenuis) or 13 days (Acropora millepora) after spawning.Experiments were run at night or day, depending on the time of polyp expansion in each of the predating coral species: Goniopora pandoraensis and Galaxea astreata tended to expand during the day and often contracted at night, whereas most faviids and Acropora spp. only expanded at night. Species, growth form (submassive, massive, branching, stolon-connected solitary polyps); percent depletion of larvae by actively feeding corals and zoanthids (D); controls (N0) after 2-h exposure. Significance levels of difference between numbers of surviving larvae among coral genera (with and without zoanthids), and between the two species of larvae were calculated. The study shows that (if the laboratory experiments are indicative of events in thefield) coral larvae are at high predation risk during their final period in the plankton, when they become negatively buoyant and search for a suitable settlementlocation. Larval mortality around reefs due to predation by non-acroporid corals could significantly affect recruitment rates on reefs with high coral cover. However, predation by corals will be insubstantial in areas of low coral cover, where successful coral recruitment will have the greatest bearing for recovery after disturbance. The ability of some hard coral and zoanthid species to prey upon coral larvae under experimental conditions in flow chambers was investigated.Because hard corals occupy a large proportion of the reef area, their feeding behavior and food selectivity (be it indiscriminate predation, or avoidance of propagules from phylogenetically related taxa) are likely to contribute to affect recruitment rates on reefs. Because scleractinian corals occupy a large proportion of the area on many coral reefs, their feeding behavior and food selectivity (be it indiscriminate predation, or avoidance of propagules from phylogenetically related taxa) are likely to contribute to affect recruitment rates on reefs.Only runs in which the corals remained expanded throughout the experiment were included in the analyses, resulting in uneven numbers of replicates per species. Several species of Acropora were tested but data from all Acropora species were later combined due to the low number of successful runs and consistently weak responses in all species.

采集了来自磁岛（Magnetic Island）的轴孔珊瑚（Acropora tenuis）种群以及戴维斯礁（Davies Reef）的多孔鹿角珊瑚（Acropora millepora）种群在水族箱产卵后的配子。为开展捕食实验，从汤斯维尔附近的近岸礁盘采集了多种珊瑚：指形鹿角珊瑚（Acropora digitifera）、美丽鹿角珊瑚（Acropora formosa）、宽枝鹿角珊瑚（Acropora latistella）、Acropora secali、Verwey鹿角珊瑚（Acropora verweyi）、星状珊瑚（Galaxea astreata）、粗糙菊花珊瑚（Goniastrea aspera）、潘多拉牡丹珊瑚（Goniopora pandoraensis）、松叶珊瑚（Platygyra pini），以及两种鞘群海葵：疣状鞘群海葵（Palythoa tuberculosa）、未定种鞘群海葵（Zoanthus sp.1.）的种群。
捕食实验在缓流流水培养箱（flow chambers）中开展。实验于幼虫3日龄时启动，直至自由游泳幼虫因实验捕食、以及产卵后约11日（轴孔珊瑚）或13日（多孔鹿角珊瑚）发生的附着变态而耗尽为止。实验的开展时段依捕食性珊瑚的水螅伸展节律而定：潘多拉牡丹珊瑚与星状珊瑚多在日间伸展水螅，夜间常收缩；而多数菊珊瑚科（Faviidae）物种及鹿角珊瑚属（Acropora spp.）仅在夜间伸展水螅。
本研究记录了物种信息、生长型（亚块状、块状、分枝型、具匍匐茎的孤立水螅）、主动捕食的珊瑚与鞘群海葵对幼虫的捕食消耗率（D），以及暴露2小时后的对照组幼虫数量（N0）。同时计算了珊瑚属间（有无鞘群海葵分组）的存活幼虫数差异显著性，以及两种受试幼虫间的存活幼虫数差异显著性。
本研究表明，若实验室实验可反映野外实际情况，则珊瑚幼虫在浮游阶段的末期面临极高的捕食风险——此时它们失去浮游能力并寻找适宜的附着位点。在珊瑚盖度较高的礁盘，非鹿角珊瑚类群的捕食导致的幼虫死亡可能显著影响珊瑚的补充率。但在珊瑚盖度较低的区域，珊瑚捕食的影响可忽略不计，此时珊瑚成功补充对扰动后礁盘恢复的影响最为关键。
本研究探究了部分造礁珊瑚与鞘群海葵物种在流水培养箱的实验条件下捕食珊瑚幼虫的能力。由于造礁珊瑚占据了礁盘的大部分区域，其捕食行为与食物选择性——无论是无差别捕食，还是规避系统发育亲缘关系较近类群的繁殖体——均可能影响礁盘的珊瑚补充率。由于石珊瑚（Scleractinia）在多数珊瑚礁中占据大面积区域，其捕食行为与食物选择性（无差别捕食或规避亲缘关系较近类群的繁殖体）同样可能影响礁盘的珊瑚补充率。仅纳入实验全程中珊瑚始终保持水螅伸展状态的实验批次用于分析，因此各物种的重复样本数量并不均等。本研究测试了多种鹿角珊瑚，但由于成功实验批次较少且所有物种的响应均较弱，最终将所有鹿角珊瑚的数据合并分析。