engleski

Fidelity of (paleo)ecological interpretation based on studies living and dead benthic foraminiferal assemblages: A case study from the northeastern Adriatic shelf (Koper bay, Slovenia)

Benthic foraminifera collected in coastal to deep-marine environments are widely used for (paleo) ecological interpretations. The use of oraminifera as proxies for ecological parameters requires the necessary study of living foraminifera to assess their ecology and test geochemistry. It is necessary to define the original environmental conditions, which is almost impossible in the case of coastal and transitional marine settings due to human activities. A good alternative is to study sedimentary records (Alves Martinis et al., 2019). Comparison of living (LA) and dead (DA) assemblages is not straightforward because of the role of taphonomic processes in preservation of DAs. The studies of benthic foraminiferal assemblages from different locations along the eastern Adriatic coast show a low percentage of stained tests. The samples were collected from different habitats (intertidal salt marshes, bays and lagoons and open marine settings), with different sampling techniques (gravity corers, Eckman grabs or simple manual sampling by divers), at different depths (from 0.3 to 44 m), and from spring to late autumn during the last two decades. The question arises what conclusion we can draw from the discrepancies between LAs and DAs. Should we study the total (TA), or the living or dead assemblages? For biomonitoring, the FOMIBO protocol is clear (Schönfeld et al., 2012), only living. Since, the inner part of the shelf, where most studies were conducted (Popadić et al., 2013 ; Vidović et al., 2014 and references), is considered a dynamic area (waves, currents) where the sedimentary processes prevent the development of large LAs and strongly influence the preservations of DAs, the TAs seemed to contain most of the information and therefore were analyzed. This study compared the composition and biodiversity indices of TAs, DAs and LAs from two 10 cm long sediment cores KPF1 and REF (surface 0 – 2 cm and 4 – 6 cm, and due to a low number of specimens in the surface interval for REF the 2-4 cm interval was analysed) recovered from 13.6 and 18.5 m water depths in August 2014 in Koper Bay (NE Adriatic Sea). The DAs have higher diversity than LAs, while TAs have the highest. The LAs show lower values of species richness and the larger values of the Fisher and Evenness indices. In general, the lower discrepancy occurs when the values of Shannon-Weaver H’ diversity and Simpson 1 - D dominance indices are compared between three types of assemblages. When stained tests were rare, the differences between the indices values were large, indicating the role of depositional processes in preservation and accumulation of empty tests. The study showed that interpretation of ecological condition based on biodiversity indices was highly variable when stained tests accounted for less than 10% of the total assemblages. Although the LAs show the small number of species, the indices suggesting environmental stability, heterogeneity and dominance are similar except for evenness (a small number of tests means that 90% of species are represented by single specimen). The interpretation presented in this study was carried out in the context of investigations within the BREEMECO project founded by the Croatian Scientific Foundation IP- 2019-04-5775. The sampling was taken by the technical support of National Institute of Biology, Marine Biology Station in Piran.

Species diversity indices, Stained foraminiferal assemblages, Un-stained foraminiferal assemblages

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