Data from: A decline in molluscan carbonate production driven by the loss of vegetated habitats encoded in the Holocene sedimentary record of the Gulf of Trieste

Carbonate sediments in non-vegetated habitats on the NE Adriatic shelf are dominated by shells of molluscs. However, the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because (1) monitoring of ecosystems prior to the 20th century was scarce and (2) ecosystem history inferred from cores is masked by condensation and mixing. Here, based on geochronological dating of four bivalve species, carbonate production during the Holocene is assessed in the Gulf of Trieste, where algal and seagrass habitats underwent a major decline during the 20th century. Assemblages of sand-dwelling Gouldia minima and opportunistic Corbula gibba are time-averaged to > 1,000 years and C. gibba shells are older by >2,000 years than shells of co-occurring G. minima. This age difference is driven by temporally disjunct production of two species coupled with decimeter-scale mixing. Stratigraphic unmixing shows that Corbula gibba declined in abundance during the highstand phase and increased again in the 20th century. In contrast, one of the major contributors to carbonate sands, Gouldia minima, increased in abundance during the highstand phase, but declined to almost zero abundance over the past two centuries. G. minima and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top-core increments but are rare alive. Although G. minima is not limited to vegetated habitats, it is abundant in such habitats elsewhere in the Mediterranean Sea. This live-dead mismatch reflects the difference between highstand baseline communities (with soft-bottom vegetated zones and hard-bottom Arca beds) and present-day oligophotic communities with organic-loving species. Therefore, the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century. More than 50% of the shells on the seafloor in the Gulf of Trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats.亚得里亚海东北陆架无植被栖息地的碳酸盐沉积物以软体动物贝壳为主要组成。然而，该陆架及其他陆架在20世纪富营养化与过度捕捞发生前的软体动物碳酸盐生产速率仍未明确，原因有二：其一，20世纪前的生态系统监测资料极度匮乏；其二，通过岩芯反演得到的生态系统历史被沉积物凝缩与混合作用所掩盖。本研究基于4种双壳类的年代学测年结果，对的里雅斯特湾全新世时期的碳酸盐生产速率进行了评估——该区域的藻类与海草栖息地在20世纪经历了大规模衰退。栖息于沙质环境的Gouldia minima（Gouldia minima）与机会主义种Corbula gibba（Corbula gibba）的组合体时间平均年限超过1000年，且Corbula gibba贝壳的年代较同期共存的Gouldia minima贝壳老2000年以上。该年龄差异源于两个物种种群生产时间的不连续性，叠加分米级的沉积物混合作用。地层解混分析显示，Corbula gibba的丰度在高水位期呈下降趋势，20世纪又再度回升。与之相反，作为碳酸盐砂主要贡献者之一的Gouldia minima，其丰度在高水位期持续增加，但在过去两个世纪中已降至近乎零。G. minima与附着于大型藻类或海草的草食性腹足类在岩芯顶部层位中丰度较高，但现生个体却十分稀少。尽管G. minima并非严格局限于植被栖息地，但在地中海其他区域的此类栖息地中其种群丰度颇高。这种现生-死亡失配（live-dead mismatch）反映了全新世高水位期基线群落（包括软底植被带与硬底魁蛤床）与当前以嗜有机质物种为主的寡光群落之间的差异。因此，光照穿透率下降以及高软体动物生产速率的植被栖息地丧失，可追溯至19世纪。的里雅斯特湾海底超过50%的贝壳均来自藻类或海草栖息地中的异养碳酸盐生产体系（heterozoan carbonate factory），属于非活跃性生产来源。