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Along the eastern coast of the northern Adriatic (Kopar Bay), there are 12 submarine springs called Žumrove kotanje, known since the seventeenth century. The springs are depressions (pockmarks) with steep flanks, which lie on the sea-bottom from a depth of 17.2 to 23.1 m and even reach 11 m in depth. The warm, sulfur-rich water erupts at irregular intervals, destabilizing the sediments on the sea-bottom and the organisms that live there. Little is known about the benthic foraminifera in this environment or how these peculiar conditions affect the viability of benthic habitats. We study the foraminiferal distribution in 1-cm-thick surface sediment samples collected by divers at two springs and compare them to the mineralogical, geochemical, and lithological characteristics of the sediment. Three categories of indices were considered: biodiversity (species richness, Shannon H’, dominance), Ammonia-Elphidium (IAE), and sensitive-tolerant species occurrences (Foram-AMBI, EcoQs). The study revealed moderately diverse, species-rich benthic foraminiferal assemblages, with densities as high as 524 specimens per 1 g of dry sediment. With 40 benthic species, the species richness fits well with the distribution of a typical shallow-water benthic foraminiferal fauna in the eastern Adriatic. “Living” foraminifera occur in statistically satisfactory quantities only in one sample. For this reason, the foraminiferal interpretation was based on the total (stained + unstained tests) assemblages obtained from 300 randomly picked individuals. Representatives of the genera Ammonia and Elphidium, known to tolerate a broad range of salinity, temperature, oxygen concentration, and low pH, dominated all assemblages. We document that “living foraminifera” are present in at least one spring. IAE values reached 73.17% in total assemblages and 76.47% in biocenosis in sediment with a low concentration of total carbon. This inverse trend between organic carbon concentration, diversity, and IAE indices could be a product of resuspension sediments leading to increased release of nutrients into the overlying water column and negatively affecting oxygen concentration in depressions. A positive correlation was observed between IAE and EcoQs and Foram-AMBI indices. This research was supported by the Croatian Science Foundation (IP 2019-04-5775) and by the Slovenian Research Agency, Program Group Geoenvironment and geomaterials (P1-0195).

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Benthic Foraminifera Distribution Around Submarine Sulfur Springs: Case Study from the Northern Adriatic

  • 会议论文

  • 发表日期：

    2025年

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  • Vlasta Ćosović,
  • Rahela Šanjek,
  • Eric Hadžić,
  • Mihovil Rakarić,
  • Željko Ištuk,
  • Ante Horvat,
  • Kaja Šušmelj,
  • Branko Čermelj,
  • Dénes Szieberth,
  • Boštjan Rožič,
  • Petra Žvab Rožič

摘要

Along the eastern coast of the northern Adriatic (Kopar Bay), there are 12 submarine springs called Žumrove kotanje, known since the seventeenth century. The springs are depressions (pockmarks) with steep flanks, which lie on the sea-bottom from a depth of 17.2 to 23.1 m and even reach 11 m in depth. The warm, sulfur-rich water erupts at irregular intervals, destabilizing the sediments on the sea-bottom and the organisms that live there. Little is known about the benthic foraminifera in this environment or how these peculiar conditions affect the viability of benthic habitats. We study the foraminiferal distribution in 1-cm-thick surface sediment samples collected by divers at two springs and compare them to the mineralogical, geochemical, and lithological characteristics of the sediment. Three categories of indices were considered: biodiversity (species richness, Shannon H’, dominance), Ammonia-Elphidium (IAE), and sensitive-tolerant species occurrences (Foram-AMBI, EcoQs). The study revealed moderately diverse, species-rich benthic foraminiferal assemblages, with densities as high as 524 specimens per 1 g of dry sediment. With 40 benthic species, the species richness fits well with the distribution of a typical shallow-water benthic foraminiferal fauna in the eastern Adriatic. “Living” foraminifera occur in statistically satisfactory quantities only in one sample. For this reason, the foraminiferal interpretation was based on the total (stained + unstained tests) assemblages obtained from 300 randomly picked individuals. Representatives of the genera Ammonia and Elphidium, known to tolerate a broad range of salinity, temperature, oxygen concentration, and low pH, dominated all assemblages. We document that “living foraminifera” are present in at least one spring. IAE values reached 73.17% in total assemblages and 76.47% in biocenosis in sediment with a low concentration of total carbon. This inverse trend between organic carbon concentration, diversity, and IAE indices could be a product of resuspension sediments leading to increased release of nutrients into the overlying water column and negatively affecting oxygen concentration in depressions. A positive correlation was observed between IAE and EcoQs and Foram-AMBI indices. This research was supported by the Croatian Science Foundation (IP 2019-04-5775) and by the Slovenian Research Agency, Program Group Geoenvironment and geomaterials (P1-0195).