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.

细枝鹿角珊瑚（Acropora tenuis，采自磁岛）和多孔鹿角珊瑚（Acropora millepora，采自戴维斯礁）群体的配子，是在水槽中产卵后收集的。为开展摄食实验，从汤斯维尔附近的近岸珊瑚礁采集了多种珊瑚群体（指状鹿角珊瑚Acropora digitifera、美丽鹿角珊瑚Acropora formosa、宽星鹿角珊瑚Acropora latistella、Acropora secali、Acropora verweyi、丛生盔形珊瑚Galaxea astreata、粗糙角蜂巢珊瑚Goniastrea aspera、潘多拉角孔珊瑚Goniopora pandoraensis、松枝扁脑珊瑚Platygyra pini）及两种海鸡头（瘤形帕拉海葵Palythoa tuberculosa、Zoanthus属1号种Zoanthus sp.1）。摄食实验在缓水流的流动室中进行。实验始于幼虫3日龄时，持续至自由游泳幼虫数量因实验、附着和/或变态而耗尽——这些过程在产卵后约11天（细枝鹿角珊瑚）或13天（多孔鹿角珊瑚）发生。实验在白天或夜间进行，具体取决于各捕食性珊瑚物种的水螅体扩张时间：潘多拉角孔珊瑚和丛生盔形珊瑚倾向于日间扩张、夜间收缩，而大多数蜂巢珊瑚科（faviids）物种和鹿角珊瑚属（Acropora spp.）仅在夜间扩张。记录了物种、生长形态（亚块状、块状、分枝状、匍匐茎连接的单水螅体）；活跃摄食的珊瑚和海鸡头造成的幼虫消耗百分比（D）；2小时暴露后的对照组（N0）数据。计算了不同珊瑚属（含或不含海鸡头）间存活幼虫数量的差异显著性水平，以及两种幼虫间的差异显著性水平。研究表明（若实验室实验能反映野外实际情况），珊瑚幼虫在浮游期后期——即变为负浮力并寻找适宜附着位点时——面临极高的捕食风险。非鹿角珊瑚属（non-acroporid）珊瑚的捕食导致的礁区幼虫死亡，可能显著影响高珊瑚覆盖率礁区的补充率。然而，在低珊瑚覆盖率区域，珊瑚捕食的影响微不足道，而该区域的成功珊瑚补充对扰动后的恢复至关重要。本研究探究了若干硬珊瑚和海鸡头物种在流动室实验条件下捕食珊瑚幼虫的能力。由于硬珊瑚占据礁区的大部分区域，其摄食行为和食物选择性（无论是无差别捕食，还是回避亲缘类群的繁殖体）可能会影响礁区的补充率。由于石珊瑚（scleractinian corals）在许多珊瑚礁中占据大部分区域，其摄食行为和食物选择性（无论是无差别捕食，还是回避亲缘类群的繁殖体）可能会影响礁区的补充率。仅将实验期间珊瑚持续扩张的实验组纳入分析，导致各物种的重复次数不均。测试了多种鹿角珊瑚，但由于成功实验组数量少且所有物种的响应一致较弱，后续将所有鹿角珊瑚物种的数据合并分析。