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

Highlights

• Entire foraminiferal communities were successfully cultured under five pH treatments for four months.

• 2246 living individuals were analyzed to calculate the community parameters and 1919 specimens were measured to compare the morphological transformation.

• Hyaline and porcelaneous foraminifera showed significant positive correlations with pH, while the agglutinated taxa showed significant negative response.

• The test size of calcareous species showed an obvious decline with decreasing pH, which indicated these taxa were sensitive and vulnerable to ocean acidification.

• More deformed tests occurred under low pH conditions (<7.5).

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 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 (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 (<7.5) while that of agglutinated species increased. There were more deformed foraminiferal tests under low pH treatments. Our results demonstrate that benthic foraminifera are sensitive to pH decline which can cause a decline of community abundance and species richness, a reduction of dominant species of hyaline and porcelaneous types, and increase the chance of deformity. Among which, calcareous types are the first victims under low pH conditions.

Dong S., Lei Y., Li T. & Jian Z., in press. Response of benthic foraminifera to pH changes: community structure and morphological transformation studies from a microcosm experiment. Marine Micropaleontology. Article (subscription required).

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