Earth and Ocean Sciences, School of Natural Sciences and Ryan Institute, National University of Ireland, Galway, H91 TK33, Ireland.
UMR 8227- Integrative Biology of Marine Models, CNRS, Station Biologique de Roscoff, Roscoff, France.
Harmful Algae. 2019 Jan;81:94-105. doi: 10.1016/j.hal.2018.11.015. Epub 2019 Jan 3.
Although nutrient enrichment of estuarine and coastal waters is considered a key factor for the development of green tides, the extent, distribution, and species composition of blooms vary among systems of similar nutrient loading, which compromises our ability to predict these events based on information about nutrient status alone. Additional factors may play a role in the control and development of macroalgal blooms. The identification of relevant scales of variation is a necessary prerequisite before explanatory models can be proposed and tested. In this study spatial and temporal patterns of biomass distribution were assessed for two Ulva morphologies in two Irish estuaries heavily affected by green tides (wet biomass >1 kg m during the peak bloom). Moreover, using genetic markers, the species composition of these green tides was assessed. Results revealed that these blooms were multi-specific, with Ulva prolifera, U. compressa and U.rigida the most frequent species. The species U. prolifera and U. compressa usually showed a tubular morphology, while U. rigida was mainly laminar. A seasonal succession common to both estuaries was also identified, with the bloom dominated by tubular species during spring and early summer, and co-dominated by tubular and laminar morphologies during late summer and autumn. Moreover, tubular and laminar morphologies exhibited different distribution patterns, with tubular morphologies varying at bigger spatial scales and higher biomass than the laminar. As tubular and laminar morphologies exhibited different distribution patterns, varying tubular morphologies along bigger spatial scales with higher biomass levels than the laminar. Considering that tubular morphologies were usually anchored to the sediment, while laminar Ulva were usually observed free-floating, these differences could explain a differential influence by water motion. An important annual and decadal variability in biomass levels of Ulva was observed, in the case of the Tolka estuary a noticeable increase over the last two decades. These findings should be considered for the development of management and monitoring strategies since the different habitat of laminar and tubular morphologies (anchored vs. free-floating) may play an important role in the balance of nutrients and biomass in the estuary, or determine the response to pollutant exposure. Furthermore, the presence of different species with different ecological requirements could favour the duration and extension of the bloom though temporal and spatial successions.
尽管富营养化被认为是赤潮形成的关键因素，但在营养负荷相似的系统中，赤潮的范围、分布和物种组成差异很大，这使得我们仅凭营养状况信息预测这些事件的能力受到了限制。其他因素可能在控制和发展大型藻类赤潮方面发挥作用。在提出和测试解释模型之前，确定相关的变化尺度是必要的前提。在这项研究中，评估了两个爱尔兰河口两种形态的浒苔生物量分布的时空模式，这两个河口受到赤潮的严重影响（高峰期湿生物量> 1 kg m）。此外，利用遗传标记评估了这些赤潮的物种组成。结果表明，这些赤潮是多物种的，其中最为常见的物种是孔石莼、石莼和刚毛藻。孔石莼和石莼通常呈管状形态，而刚毛藻则主要呈片状。还确定了两个河口共有的季节性演替，春末夏初以管状物种为主，夏末秋初则以管状和片状物种为主。此外，管状和片状形态表现出不同的分布模式，管状形态的分布范围更大，生物量更高。由于管状和片状形态表现出不同的分布模式，因此具有更高生物量的较大空间尺度上的变化管状形态比片状形态更为常见。考虑到管状形态通常固定在沉积物上，而片状的浒苔通常是自由漂浮的，这些差异可以解释水动力的不同影响。在托尔克河口，观察到浒苔生物量水平在过去二十年中明显增加，这表明存在重要的年度和十年间的变化。由于片状和管状形态的不同栖息地（固定的与自由漂浮的）可能在河口的营养物质和生物量平衡中发挥重要作用，或者决定对污染物暴露的反应，因此这些发现应在管理和监测策略的制定中加以考虑。此外，不同生态需求的不同物种的存在可能会通过时间和空间演替来延长赤潮的持续时间和范围。
