The potential of fiddler crabs for secondary productivity of mangroves

Mangroves are well-recognized productive environments that perform important ecological functions such as nursery areas for marine life, coastline protection, carbon sequestration, and the production of fishery resources. Despite the productivity of mangroves being a highly valuable ecosystem service, studies on this subject are mainly concentrated on primary production. However, most economically important fish species benefit from the secondary productivity of mangroves, as they feed on organisms that are lower in the trophic levels. In Brazilian mangroves, fiddler crabs have the potential to be one of the main contributors to secondary production due to their high abundance and generalist distribution. Fiddler crabs produce pelagic larvae that develop in coastal environments adjacent to mangroves and therefore constitute a food resource for planktivorous fish. Although the contribution of fiddler crabs to secondary productivity is not yet well understood, it could be affected by climate change, as these crustaceans are sensitive to temperature variations. The aim of this study was to estimate the secondary productivity of fiddler crab larvae in the Santos/São Vicente estuary. For this, the presence of ovigerous females and the ambient temperature in populations of four species of fiddler crabs were monitored ( <i>Leptuca uruguayensis, L. leptodactyla, L. thayeri</i><i> </i>and <i>Minuca rapax</i>)<i>.</i> In the laboratory, larval production per species was estimated and it was tested whether the fertility of females is affected by increasing temperature. The density of fiddler crab larvae in coastal waters was evaluated according to distance from the coast and season. This study aimed to elucidate the ecological and economic importance of mangroves and to assess how climate change affects one of their most characteristic ecosystem services—productivity.

红树林（Mangroves）是公认的高生产力生态系统，具备多项关键生态功能，包括作为海洋生物的育苗栖息地、海岸线防护、碳汇（carbon sequestration）以及渔业资源产出。尽管红树林的生产力是极具价值的生态系统服务，但相关研究多集中于初级生产力（primary production）。然而，多数具有经济价值的鱼类依赖红树林的次级生产力（secondary productivity）获益，因为它们以营养级更低的生物为食。在巴西的红树林中，招潮蟹（fiddler crabs）因种群丰度高、分布范围广，有望成为次级生产力的主要贡献者之一。招潮蟹会产生浮游幼体（pelagic larvae），这些幼体在红树林毗邻的沿岸环境中发育，因此成为浮游食性鱼类（planktivorous fish）的食物来源。尽管招潮蟹对次级生产力的贡献目前尚不明晰，但其作为甲壳动物（crustaceans）对温度变化敏感，因此其贡献可能受气候变化影响。本研究旨在估算桑托斯/圣维森特河口的招潮蟹幼体的次级生产力。为此，研究人员监测了4种招潮蟹——<i>Leptuca uruguayensis</i>、<i>L. leptodactyla</i>、<i>L. thayeri</i>以及<i>Minuca rapax</i>）的怀卵雌性个体（ovigerous females）存在情况与环境温度。在实验室中，研究人员估算了各物种的幼体产出量，并测试了雌性个体的繁殖力（fertility）是否随温度升高而受到影响。同时，研究人员根据离岸距离与季节，评估了沿岸水域中招潮蟹幼体的种群密度。本研究旨在阐明红树林的生态与经济重要性，并评估气候变化如何影响其最具代表性的生态系统服务之一——生产力。