Data from: Seagrass on the brink: decline of threatened seagrass Posidonia australis continues following protection

Seagrasses are in decline globally due to sustained pressure from coastal development, water quality declines and the ongoing threat from climate change. The result of this decline has been a loss of coastal productivity, a reduction in critical fisheries habitat and increased erosion. Attempts to slow this decline have included legislative protection of habitat and direct restoration efforts. Monitoring the success of these approaches requires tracking changes in the abundance of seagrasses, but such monitoring is frequently conducted on large scales that lack the sensitivity to detect changes in time. Here, we used high resolution aerial imagery to quantify the change in meadows dominated by Posidonia australis over five years at 14 sites in five estuaries in south-eastern Australia. Australia has some of the world's most diverse and extensive seagrass meadows, but the widely distributed P. australis has a slow growth rate, recovers poorly after disturbance, and suffers runaway attrition if the conditions for recovery are not met. In 2010, after declines of 12-57% between the 1940s and 1980s, P. australis was listed as a threatened ecological community in New South Wales. We quantified changes in area at fine scales and, where loss was observed, describe the general patterns of temporal decline within each meadow. Our results demonstrate that seagrass meadows dominated by P. australis underwent declines of ~ 2-40% total area at our study sites between 2009 and 2014. In the iconic Sydney Harbour, our analyses suggest that P. australis meadows are declining at an average rate greater than 10% yr-1, exceeding the global rate of seagrass decline. Highlighting these alarming declines across the study region should serve as means to prioritise management action and review the effectiveness of legislative listing as a method to limit impacts at an ecosystem level.

全球海草床正面临全球性衰退，其驱动因素包括沿海开发带来的持续压力、水质恶化，以及气候变化带来的长期威胁。这种衰退已导致沿海生产力下降、重要渔业栖息地缩减，以及海岸侵蚀加剧。为延缓这一衰退进程，相关举措已涵盖海草栖息地的立法保护与直接修复工作。评估这些措施的成效需要追踪海草种群丰度的变化，但当前此类监测往往在大尺度下开展，难以具备及时检测种群变化所需的灵敏度。本研究依托高分辨率航空影像，对澳大利亚东南部5个河口的14个监测位点开展了为期5年的定量分析，以明确以澳大利亚波喜荡草（Posidonia australis）为优势种的海草床的面积变化情况。澳大利亚拥有全球物种多样性最高、分布范围最广的海草床之一，但分布广泛的澳大利亚波喜荡草生长速率缓慢，受干扰后恢复能力极差，且若恢复条件无法满足，其种群将出现失控性衰减。在1940年代至1980年代期间其种群衰减幅度达12%-57%后，澳大利亚波喜荡草于2010年被新南威尔士州列为受威胁生态群落。本研究以精细尺度量化了海草床的面积变化，并针对出现衰退的海草床，阐述了其随时间衰减的一般模式。研究结果显示，2009年至2014年间，本研究监测位点内以澳大利亚波喜荡草为优势种的海草床总面积衰减幅度约为2%-40%。在标志性的悉尼港，本研究分析显示澳大利亚波喜荡草海草床的年均衰减速率超过10%，这一速度远超全球海草床的平均衰退速率。揭示研究区域内这些触目惊心的海草床衰退现象，可为优先开展管理行动提供依据，并有助于评估立法保护措施在生态系统层面限制海草衰退的实际成效。