Assessing the conservation status of Mediterranean coastal ponds: Checklist, ecological and functional diversity of diatom communities

Coastal ponds are peculiar and threatened habitats, considered biodiversity hotspots. In many ecosystems ponds can be a valuable resource for the conservation of freshwater biodiversity. The Castelporziano Presidential Estate is a Mediterranean protected area hosting numerous ponds which are suffering severe droughts and a general decline in number and hydroperiod length. Hydroperiod changes can be particularly relevant for biodiversity inhabiting ponds, in particular diatom communities. Here, for the first time, we evaluate the conservation status of Mediterranean ponds inside the Castelporziano Reserve. The aims of this research are to i) investigate the influence of environmental variables on diatom communities of ponds; (ii) analyse diatom community structure in function of species richness and competitive interactions; (iii) highlight the potential and effectiveness of diatom ecological guilds in supporting the interpretation of the ecological status of threatened small waterbodies. Overall, 122 diatom taxa in the 29 ponds were described. Nitzschia (18 species) was the most species-rich genus, followed by Gomphonema (14) and Navicula (13). 17 species were included in the Red List of endangered species. Intra-pond distance and anthropogenic impacts didn't influence diatom assemblages. On the contrary, diatom communities were influenced by altitude and the distance from the sea. Furthermore, temporary ponds showed the lowest values for Shannon, evenness and Simpson indexes Considering Beta-diversity, both Bray-Curtis and Jaccard dissimilarity matrices highlighted a large dissimilarity between sampling sites. Inter-variability between sites and intra-variability within the sites resulted both very low. Our results highlight that diatom species are not influenced by hydroperiod length. Moreover, a structured diatom community emerged, where segregation processes predominating over aggregation ones. Finally, the average water quality of the ponds, calculated using the EPI-D index, was described as “good”. This study represents the most complete checklist of diatom communities inside coastal ponds of Castelporziano, providing valuable insights into the effects of natural and anthropogenic influences on ponds conservation and management activities. However, spatial-temporal changes and anthropogenic impacts should be deeply investigated.Full article: https://doi.org/10.1016/j.csr.2024.105359滨海池塘是一类独特且受威胁的生境，被视为生物多样性热点区域。在多数生态系统中，池塘是保护淡水生物多样性的宝贵资源。卡斯泰尔波尔齐亚诺总统庄园（Castelporziano Presidential Estate）是一处地中海型保护区，其内分布有大量池塘，但这些池塘正遭受严重干旱，数量及水文周期（hydroperiod）长度均呈现普遍下降趋势。水文周期的变化对栖息于池塘中的生物，尤其是硅藻（diatom）群落，具有尤为关键的影响。 本研究首次对卡斯泰尔波尔齐亚诺保护区内的地中海型池塘的保护现状开展评估。本研究的目标如下：（一）探究环境变量对池塘硅藻群落的影响；（二）基于物种丰富度与种间竞争互作，分析硅藻群落结构；（三）阐明硅藻生态类群在解读受威胁小型水体生态现状方面的潜力与有效性。 本研究共记录29处池塘中的122个硅藻分类单元（taxa）。以菱形藻属（Nitzschia）物种最为丰富，共计18种，其次为异极藻属（Gomphonema，14种）与舟形藻属（Navicula，13种）。其中17个物种被列入濒危物种红色名录（Red List）。池塘内部距离与人为活动影响并未对硅藻集合群落产生显著作用。与之相反，硅藻群落的组成受到海拔高度与距海距离的显著影响。 此外，暂时性池塘的香农（Shannon）多样性指数、均匀度指数与辛普森（Simpson）多样性指数均为最低。就β多样性（Beta-diversity）而言，布雷-柯蒂斯（Bray-Curtis）相异度矩阵与雅卡尔（Jaccard）相异度矩阵均显示，各采样点间存在较大的群落组成差异。各采样点间的组间变异与单采样点内的组内变异均极低。 本研究结果表明，硅藻物种组成并未受到水文周期长度的显著影响。同时，研究发现存在结构化的硅藻群落，其中物种分隔过程相较于聚集过程占据主导地位。最终，通过EPI-D指数（EPI-D index）计算得到的池塘平均水质等级被评定为"good"。 本研究构建了卡斯泰尔波尔齐亚诺滨海池塘硅藻群落最为完整的名录，可为阐明自然与人为因素对池塘保护及管理活动的影响提供重要参考。但仍需深入探究时空动态变化与人为活动影响对该区域池塘生态的作用。 全文链接：https://doi.org/10.1016/j.csr.2024.105359