台灣綠島透光層與中光層珊瑚礁生態系之造礁珊瑚入添與相依底棲群聚研究

Abstract

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Coral reefs are currently threatened by anthropogenic disturbances and climate change, stimulating interest in determining whether mesophotic reefs can act as a refuge from disturbances and help replenish deteriorated shallow reefs. We characterize and quantify spatial-temporal patterns of variation in the recruitment of scleractinian corals, defined in terms of diversity, structure and composition, and associated benthic assemblages in euphotic and mesophotic zones in Green Island, Taiwan. Artificial units of recruitment were immersed at shallow (15m) and mesophotic (40m) zones, during 2016-2018 and seasonal and long-term patterns of recruitment were examined. Deep neural networks were used to analyze photographs of settlement plate communities and quadrats of benthic communities at shallow and mesophotic depths, in order characterize the structure and composition benthic communities at juvenile and adult life stages, providing strong evidence for structuration across bathymetric zones and between life stages. 451 coral recruits, comprising 37 taxa and spanning 13 coral families were located using fluorescent censusing, and identified by barcoding the mt-COI, ORF and PaxC regions. Several depth-generalist taxa were identified, however unique recruit assemblages not found in shallow reefs were found recruiting within the mesophotic zone. Abundant recruitment and distinctive recruit communities within the mesophotic zone support the hypothesis that these reefs are acting as viable reproductive sources. This research provides a unique assessment of recruitment in a region where mesophotic reefs are understudied. We show that Taiwanese mesophotic reefs host recruit assemblages which are abundant, diverse, and distinctive from altiphotic reefs. Our results are consistent with the hypothesis of mesophotic reefs acting as a reproductive refuge for shallow water communities.