Response of benthic foraminifera to pH changes: Community structure and morphological transformation studies from a microcosm experiment

Abstract

Abstract Marine calcifying organisms, such as foraminifera, are threatened by the declining pH in the modern ocean. Benthic foraminifera are abundant, widespread and occur in diverse populations in the intertidal environment. However, to date, no studies have been conducted on the response of the intertidal foraminiferal community to pH under laboratory culture experiment. In this study, we cultured the entire foraminiferal community with the natural sediments from the intertidal area of the Yellow Sea at five pH values (8.5, 8.0, 7.5, 7.0 and 6.5, NBS scale). After four months' incubation, all living specimens (stained by rose-Bengal) were picked and identified. A total of 2246 living benthic foraminiferal specimens belonging to 15 species were analyzed, among which 1962 individuals were cultured and 284 ones were sampled before culturing. We calculated the community parameters under different pH, which showed both foraminiferal abundance and species richness decreased with the decline in pH. We analyzed the response of three foraminiferal taxa with different test types (hyaline, porcelaneous and agglutinated). The hyaline (e.g., Ammonia aomoriensis) and porcelaneous (e.g., Quinqueloculina seminula) foraminifera showed significant positive correlation with pH. In contrast, the agglutinated taxa (e.g., Ammoglobigerina globigeriniformis) showed significant negative response. For detecting the response of individual species to pH, body size and abnormal morphology of dominant species were measured and analyzed. Morphometric analysis of 1919 specimens showed the maximum length of hyaline and porcelaneous species decreased under low pH treatments (