Seagrass time-series analysis products, in Moreton Bay, Australia, with links to GeoTIFFs@en

The spatial and temporal dynamics of seagrasses have been well studied at the leaf to patch scales, however, the link to large spatial extent landscape and population dynamics is still unresolved in seagrass ecology. Traditional remote sensing approaches have lacked the temporal resolution and consistency to appropriately address this issue. This study uses two high temporal resolution time-series of thematic seagrass cover maps to examine the spatial and temporal dynamics of seagrass at both an inter- and intra-annual time scales, one of the first globally to do so at this scale. Previous work by the authors developed an object-based approach to map seagrass cover level distribution from a long term archive of Landsat TM and ETM+ images on the Eastern Banks (~200 km**2), Moreton Bay, Australia. In this work a range of trend and time-series analysis methods are demonstrated for a time-series of 23 annual maps from 1988 to 2010 and a time-series of 16 monthly maps during 2008-2010. Significant new insight was presented regarding the inter- and intra-annual dynamics of seagrass persistence over time, seagrass cover level variability, seagrass cover level trajectory, and change in area of seagrass and cover levels over time. Overall we found that there was no significant decline in total seagrass area on the Eastern Banks, but there was a significant decline in seagrass cover level condition. A case study of two smaller communities within the Eastern Banks that experienced a decline in both overall seagrass area and condition are examined in detail, highlighting possible differences in environmental and process drivers. We demonstrate how trend and time-series analysis enabled seagrass distribution to be appropriately assessed in context of its spatial and temporal history and provides the ability to not only quantify change, but also describe the type of change. We also demonstrate the potential use of time-series analysis products to investigate seagrass growth and decline as well as the processes that drive it. This study demonstrates clear benefits over traditional seagrass mapping and monitoring approaches, and provides a proof of concept for the use of trend and time-series analysis of remotely sensed seagrass products to benefit current endeavours in seagrass ecology.海草的时空动态在叶片至斑块尺度已得到充分研究，但在海草生态学领域，其与大空间尺度景观及种群动态的关联仍未明确。传统遥感方法缺乏足够的时间分辨率与一致性，难以妥善解决该问题。本研究采用两套高时间分辨率的专题海草覆盖度时间序列图，分别从年际和年内时间尺度探究海草的时空动态，是全球范围内首批在此尺度开展此类研究的工作之一。作者团队此前已开发一种面向对象的方法，基于澳大利亚莫顿湾东岸（约200平方千米）的长期Landsat TM与ETM+影像档案，绘制海草覆盖度分布情况。本研究针对1988年至2010年的23幅年度海草覆盖图时间序列，以及2008-2010年的16幅月度海草覆盖图时间序列，展示了一系列趋势与时间序列分析方法。研究揭示了关于海草长期存续的年际与年内动态、海草覆盖度变异、覆盖度变化轨迹，以及海草面积与覆盖度随时间的变化等方面的重要新认知。整体而言，东岸区域的海草总面积未出现显著下降，但其覆盖度状况却发生了显著退化。本研究对东岸区域内两个海草群落展开详细案例分析——这两个群落的海草总面积与覆盖度状况均出现下降，由此凸显了驱动其变化的环境与过程机制可能存在的差异。本研究展示了如何通过趋势与时间序列分析，结合海草的时空历史背景对其分布进行合理评估，该方法不仅能够量化变化幅度，还可刻画变化的类型。此外，本研究还展示了时间序列分析产物在探究海草兴衰过程及其驱动机制方面的应用潜力。相较于传统海草制图与监测方法，本研究展现出显著优势，并为利用遥感海草产品的趋势与时间序列分析服务于当前海草生态学研究提供了概念验证。