Recruitment Variability of Coral Reef Sessile Communities of the Far North Great Barrier Reef

One of the key components in assessing marine sessile organism demography is determining recruitment patterns to benthic habitats. An analysis of serially deployed recruitment tiles across depth (6 and 12 m), seasons (summer and winter) and space (meters to kilometres) was used to quantify recruitment assemblage structure (abundance and percent cover) of corals, sponges, ascidians, algae and other sessile organisms from the northern sector of the Great Barrier Reef (GBR). Polychaetes were most abundant on recruitment titles, reaching almost 50% of total recruitment, yet covered <5% of each tile. In contrast, mean abundances of sponges, ascidians, algae, and bryozoans combined was generally less than 20% of total recruitment, with percentage cover ranging between 15–30% per tile. Coral recruitment was very low, with <1 recruit per tile identified. A hierarchal analysis of variation over a range of spatial and temporal scales showed significant spatio-temporal variation in recruitment patterns, but the highest variability occurred at the lowest spatial scale examined (1 m—among tiles). Temporal variability in recruitment of both numbers of taxa and percentage cover was also evident across both summer and winter. Recruitment across depth varied for some taxonomic groups like algae, sponges and ascidians, with greatest differences in summer. This study presents some of the first data on benthic recruitment within the northern GBR and provides a greater understanding of population ecology for coral reefs.

评估海洋固着生物（marine sessile organism）种群动态的核心环节之一，是明确其在底栖生境（benthic habitat）中的补充模式。本研究针对大堡礁（Great Barrier Reef, GBR）北部海域，通过在不同水深（6 m与12 m）、季节（夏季与冬季）以及空间尺度（米至千米级）下连续布设的招募定植板（recruitment tile），量化了珊瑚、海绵、被囊动物、藻类及其他固着生物的招募群落结构（涵盖丰度与盖度两项指标）。多毛类（polychaetes）在定植板上丰度最高，占总招募量的近50%，但其单块定植板的盖度却不足5%。与之形成鲜明对比的是，海绵、被囊动物、藻类与苔藓虫（bryozoans）的总平均丰度通常不足总招募量的20%，单块定植板的盖度则介于15%~30%之间。珊瑚招募量极低，每块定植板仅能发现不足1个招募个体。对多尺度时空变异开展的分层分析（hierarchal analysis of variation）显示，招募模式存在显著的时空变异（spatio-temporal variation），但最高变异程度出现在本次检测的最低空间尺度（1 m，即定植板之间）。无论是类群丰度还是盖度，招募的时间变异在夏季与冬季均显著存在。部分分类类群（taxonomic group）如藻类、海绵与被囊动物的招募模式随水深存在显著差异，且该差异在夏季最为突出。本研究获取了大堡礁北部海域底栖生物招募的首批实测数据之一，增进了学界对珊瑚礁种群生态学的认知。