The coral reef-dwelling Peneroplis spp. shows calcification recovery to ocean acidification conditions

Abstract

Large Benthic Foraminifera are a crucial component of coral-reef ecosystems, which are currently threatened by ocean acidification. We conducted culture experiments to evaluate the impact of low pH on survival and test dissolution of the symbiont-bearing species Peneroplis spp., and to observe potential calcification recovery when specimens are placed back under reference pH value (7.9). We found that Peneroplis spp. displayed living activity up to 3 days at pH 6.9 (Ωcal < 1) or up to 1 month at pH 7.4 (Ωcal > 1), despite the dark and unfed conditions. Dissolution features were observed under low Ωcal values, such as changes in test density, peeled extrados layers, and decalcified tests with exposed organic linings. A new calcification phase started when specimens were placed back at reference pH. This calcification’s resumption was an addition of new chambers without reparation of the dissolved parts, which is consistent with the porcelaneous calcification pathway of Peneroplis spp. The most decalcified specimens displayed a strong survival response by adding up to 8 new chambers, and the contribution of food supply in this process was highlighted. These results suggest that porcelaneous LBF species have some recovery abilities to short exposure (e.g., 3 days to 1 month) to acidified conditions. However, the geochemical signature of trace elements in the new calcite was impacted, and the majority of the new chambers were distorted and resulted in abnormal tests, which might hinder the specimens’ reproduction and thus their survival on the long term.

Elements and Isotopes in Foraminifera

“…The moderately positive influence of CO 2 on calcification as observed here is in contrast with the response of the majority of marine calcifiers (Kroeker et al, 2013) and reports on the effect of CO 2 on larger benthic foraminifera (Doo et al, 2014). Although other studies have found mixed responses of large benthic foraminifera to elevated pCO 2 /reduced pH (McIntyre-Wressnig et al, 2013;Narayan et al, 2022) and showed that they are able to withstand periodic undersaturated conditions (Charrieau et al, 2022).…”

Impact of dissolved CO2 on calcification in two large, benthic foraminiferal species

“…The moderately positive influence of CO 2 on calcification as observed here is in contrast with the response of the majority of marine calcifiers [ 57 ] and reports on the effect of CO 2 on larger benthic foraminifera [ 58 ]. Although other studies have found mixed responses of large benthic foraminifera to elevated p CO 2 /reduced pH [ 17 , 59 ] and showed that they are able to withstand periodic undersaturated conditions [ 60 ]. Finally, Fujita et al [ 61 ] reported an optimum growth rate for three species of the large, high-Mg/Ca benthic foraminifera, similar to the pattern reported here.…”

Controls on Lithium Incorporation and Isotopic Fractionation in Large Benthic Foraminifera

“…In the dark treatments, this photosynthetic activity cannot counter low pH or low DIC conditions, which could therefore have affected the δ 7 Li values and Li/Ca ratios in the low pH and low DIC treatments. This finding is consistent with a culture study using the LBF Peneroplis spp., in which three days under lower pH and darker conditions were sufficient to affect the geochemical signatures of their tests [58].…”