Reef fishes recruited at midwater coral nurseries consume biofouling and reduce cleaning time in Seychelles, Indian Ocean

In coral reef restoration, coral gardening involves rearing coral fragments in underwater nurseries prior to transplantation. These nurseries become fish-aggregating devices and attract biofouling. We hypothesised that: (1) the presence of corals at a nursery is critical to recruit fish assemblages and (2) the recruited fish assemblages control biofouling, reducing person-hours invested in nursery cleaning. Three midwater coral nurseries were deployed at 8 m depth for 27 months within the marine protected area of Cousin Island Special Reserve, Seychelles, Indian Ocean. Each nursery consisted of a 6 m×6 m PVC pipe frame, layered with a recycled 5.5-cm-mesh tuna net. Human cleaning effort was calculated based on daily dive logs. Nursery-associated fish assemblages and behaviour were video-recorded prior to harvesting corals after a 20-month growth period and seven months post-coral harvesting. The density (ind. m–2) of blue-yellow damselfish Pomacentrus caeruleus was 12–16 times higher when corals were present than when corals were absent at the nurseries. Fish assemblages recruited into the nurseries included three trophic levels, from herbivores to omnivores, in six families: Ephippidae, Pomacentridae, Labridae (Scarinae), Gobiidae, Siganidae and Monacanthidae. Higher abundance of large fish (total number of individuals) resulted in 2.75 times less person-hours spent in nursery cleaning. These results have important implications for cost-effective coral reef restoration.在珊瑚礁修复领域，珊瑚园艺（coral gardening）指在移植作业前，于水下苗圃中培育珊瑚断枝的技术手段。此类水下苗圃兼具鱼群聚集装置的功能，同时易滋生生物淤积（biofouling）。我们提出两项研究假设：其一，苗圃内珊瑚的存在对鱼类群落的招募具有关键作用；其二，招募至苗圃的鱼类群落可抑制生物淤积，进而减少用于苗圃清洁的人工工时。我们于印度洋塞舌尔库辛岛特别保护区（Cousin Island Special Reserve）内的海洋保护区（marine protected area）中，在8米水深处部署了3个中层海水珊瑚苗圃，整体实验周期为27个月。每个苗圃由6m×6m的PVC（聚氯乙烯）管材框架搭建而成，框架上铺设有网孔尺寸为5.5厘米的回收金枪鱼网。人工清洁工作量通过每日潜水日志进行统计核算。在珊瑚生长满20个月、收获珊瑚前，以及珊瑚收获后的第7个月，我们分别录制了与苗圃相关的鱼类群落及其行为的视频影像。当苗圃内存在珊瑚时，蓝黄雀鲷（Pomacentrus caeruleus）的密度（单位：ind. m⁻²）较无珊瑚状态下高出12至16倍。招募至该苗圃的鱼类群落涵盖6个科、3个营养级，涵盖从植食性到杂食性的多个类群，涉及的科分别为白鲳科（Ephippidae）、雀鲷科（Pomacentridae）、隆头鱼科（Labridae，鹦嘴鱼亚科Scarinae）、鰕虎鱼科（Gobiidae）、蓝子鱼科（Siganidae）以及单角鲀科（Monacanthidae）。大型鱼类的丰度（即总个体数）越高，苗圃清洁所耗费的人工工时便越少，仅为原水平的2.75分之一。上述研究结果对实现兼具成本效益的珊瑚礁修复工作具有重要的指导价值。