Decadal changes in intertidal biodiversity of the Benguela upwelling region

The southern Benguela upwelling region, one of the most productive coastal ecosystems globally, supports diverse intertidal communities and is strongly affected by strong oceanographic and climatic forces. However, this region has been facing various anthropogenic pressures, primarily caused by human activities in the past few decades, including climate change, commercial and subsistence harvesting, coastal development, and mining. These pressures have resulted in noticeable ecological changes, particularly in intertidal communities and changes in land use. Replication of historical surveys has allowed scientists to track and document these shifts, which helps them better understand the trends and shifts in biological communities. This thesis examines changes in coastal ecosystems over the past three decades through two complementary approaches, (1) through a fine- scale field resurvey of rocky intertidal shore communities and (2) through landscape-scale remote sensing data and spatial analysis of land cover changes along the west coast of South Africa.Intertidal resurveys conducted at 13 sites originally studied in 2001–2003 revealed significant community shifts by 2020–2021. Multivariate analyses indicated strong site-level differences, yet consistent temporal changes. Alien functional groups played a key role: Alien species played a key role: <i>Balanus glandula</i> showed a positive association with the periwinkle <i>Afrolittorina knysnaensis</i>, while <i>Mytilus galloprovincialis</i> declined at wave-exposed sites but increased in sheltered habitats. The arrival of the alien mussels <i>Semimytilus patagonicus</i> marked one of the most striking changes, alongside declines in native limpets and mussels, reduced grazing intensity increased algal cover, pointing to possible trophic restructuring.Land use land cover analyses (1990-2020) highlighted substantial habitat alteration along the west coast, particularly linked to agricultural expansions, urban growth, mining and extractive industries. Three case studies, Verlorenvlei, the Alexcor mining area, and the Tormin Mine were selected a priori to represent distinct and dominant forms of anthropogenic landscape change in the region, including wetland contraction and both historical and recent large-scale coastal mining. The case studies showed a concerning water loss at Verlorenvlei (a Ramsar-listed wetland) and major landscape transformation around the Alexcor and Tormin mines, including vegetation loss, wetland degradation and altered sediment flows. These findings demonstrate the extent and spatial pattern of anthropogenic landscape transformation along the west coast over the past three decades.The combination of these two chapters offers a wide-ranging, multidisciplinary assessment of decadal changes in anthropogenic pressures and their impacts on the ecology of southern Benguela coastal ecosystems. By linking biodiversity patterns in rocky intertidal zones with spatial land cover dynamics onshore, the thesis demonstrates how localised disturbances, such as the harvesting of limpets altering grazer population structure, or mining-driven land cover change reshaping coastal landscapes, contribute to broader socio-ecological change across the land-sea interface. The study’s findings highlight the importance of sustained long-term ecological monitoring and the protection of critical habitats, such as estuarine coastal wetlands. There is an urgent need to implement integrated coastal zone management in South Africa, given the vulnerability of coastal ecosystems to both local and regional disturbances. The research highlights the necessity for repeat surveys to accurately track ecological change, especially under the ongoing anthropogenic impacts and climate change pressure.

本格拉南部上升流区（southern Benguela upwelling region）是全球生产力最高的近岸生态系统之一，孕育着多样的潮间带群落（intertidal communities），同时受强劲的海洋学与气候学过程强烈调控。然而近数十年来，该区域面临多重人为压力，主要源自人类活动，包括气候变化、商业性与自给性捕捞、沿岸开发以及采矿活动。这些压力已引发显著的生态变化，尤以潮间带群落与土地利用变化最为突出。对历史调查的重复开展，使科学家得以追踪并记录这些变化，进而更好地解析生物群落的演变趋势与格局偏移。

本研究通过两种互补方法，解析过去三十年间近岸生态系统的变化：其一为对岩相潮间带海岸群落开展的高精度野外重测；其二为针对南非西海岸土地覆盖变化的景观尺度遥感（remote sensing）数据分析与空间分析（spatial analysis）。

对2001–2003年曾开展调查的13个点位进行潮间带重测后发现，至2020–2021年，群落结构已发生显著偏移。多变量分析结果显示，点位间存在显著差异，但时间维度上的变化趋势具有一致性。外来功能群发挥了关键作用：布氏藤壶（Balanus glandula）与滨螺（Afrolittorina knysnaensis）呈现正相关关系；而地中海贻贝（Mytilus galloprovincialis）在浪蚀生境中种群数量下降，但在遮蔽型生境中却有所增加。外来贻贝巴塔哥尼亚半贻贝（Semimytilus patagonicus）的入侵是最显著的变化之一，与此同时本土帽贝与贻贝种群数量下降、牧食压力降低导致藻类盖度上升，这暗示群落营养结构可能已发生重构。

1990–2020年的土地利用与土地覆盖分析显示，南非西海岸的生境已发生大规模改变，尤以农业扩张、城镇增长、采矿与采掘业活动相关的变化最为显著。研究预先选取三个案例研究区域——弗洛伦弗莱（Verlorenvlei）、亚历科罗（Alexcor）矿区与托尔明（Tormin）矿区——以代表该区域内典型且占主导地位的人为景观变化类型，包括湿地萎缩以及历史与近期的大规模沿岸采矿活动。案例研究结果显示，作为拉姆萨尔湿地的弗洛伦弗莱出现了令人担忧的水体流失问题；亚历科罗与托尔明矿区周边则发生了大规模景观转型，包括植被丧失、湿地退化与沉积物输运格局改变。上述研究结果阐明了过去三十年间南非西海岸人为景观转型的范围与空间分布格局。

本研究的两个章节相结合，对人为压力的年代际变化及其对本格拉南部近岸生态系统生态学特征的影响开展了多维度、多学科的综合评估。通过将岩相潮间带的生物多样性格局与陆域空间土地覆盖动态相结合，本研究揭示了局部扰动——如帽贝捕捞改变牧食者种群结构、采矿驱动的土地覆盖变化重塑沿岸景观——如何推动海陆界面更广泛的社会-生态变化。本研究结果凸显了长期持续生态监测与关键生境（如河口沿岸湿地）保护的重要性。鉴于沿岸生态系统易受局地与区域扰动影响，南非亟需推行整合式沿岸带管理方案。本研究同时强调，需开展重复调查以精准追踪生态变化，尤其在当前人为影响与气候变化压力持续加剧的背景下。