Effects of ocean acidification on calcification of symbiont-bearing reef foraminifers

Abstract

Abstract. Ocean acidification (decreases in carbonate ion concentration and pH) in response to rising atmospheric pCO 2 is generally expected to reduce rates of calcification by reef calcifying organisms, with potentially severe implications for coral reef ecosystems. Large, algal symbiontbearing benthic foraminifers, which are important primary and carbonate producers in coral reefs, produce high-Mg calcite shells, whose solubility can exceed that of aragonite produced by corals, making them the "first responder" in coral reefs to the decreasing carbonate saturation state of seawater. Here we report results of culture experiments performed to assess the effects of ongoing ocean acidification on the calcification of symbiont-bearing reef foraminifers using a high-precision pCO 2 control system. Living clone individuals of three foraminiferal species (Baculogypsina sphaerulata, Calcarina gaudichaudii, and Amphisorus hemprichii) were subjected to seawater at five pCO 2 levels from 260 to 970 µatm. Cultured individuals were maintained for about 12 weeks in an indoor flow-through system under constant water temperature, light intensity, and photoperiod. After the experiments, the shell diameter and weight of each cultured specimen were measured. Net calcification of B. sphaerulata and C. gaudichaudii, which secrete a hyaline shell and host diatom symbionts, increased under intermediate levels of pCO 2 (580 and/or 770 µatm) and decreased at a higher pCO 2 level (970 µatm). Net calcification of A. hemprichii, which secretes a porcelaneous shell and hosts dinoflagellate symbionts, tended to decrease at elevated pCO 2 . Observed different responses between hyaline and porcelaneous species are possibly caused by the relative importance of Correspondence to: K. Fujita (fujitaka@sci.u-ryukyu.ac.jp) elevated pCO 2 , which induces CO 2 fertilization effects by algal symbionts, versus associated changes in seawater carbonate chemistry, which decreases a carbonate concentration. Our findings suggest that ongoing ocean acidification might favor symbiont-bearing reef foraminifers with hyaline shells at intermediate pCO 2 levels (580 to 770 µatm) but be unfavorable to those with either hyaline or porcelaneous shells at higher pCO 2 levels (near 1000 µatm).

Calcification in the planktonic foraminifera <i>Globigerina bulloides</i> linked to phosphate concentrations in surface waters of the North Atlantic Ocean

“…This is a factor that may explain the larger decrease of test weights between the last glacial maximum to present day conditions for G. bulloides (Barker and Elderfield, 2002;Moy et al, 2009) compared to the symbiotic G. ruber (de Moel et al, 2009), and the differences in response to [CO 2− 3 ] exhibited by these two species in the surface waters of the Arabian Sea (Beer et al, 2010a). However, a recent study by Fujita et al (2011) demonstrates that it is important to be careful when extrapolating these responses to future ocean acidification scenarios. The effects of increased pCO 2 on three species of symbiont-bearing reef foraminifers were examined, and although two of the species exhibited enhanced calcification at intermediate pCO 2 values, further increases beyond 970 µatm reduced calcification.…”

Effect of ocean acidification on the benthic foraminifera <i>Ammonia</i> sp. is caused by a decrease in carbonate ion concentration

“…Subjecting different species to the same method allows detection of species-specific effects, whereas the method effects can be assessed by subjecting the same species to different methods. Deconvolving species-specific differences was, for instance, possible in the study of Fujita et al (2011), where the responses to elevated pCO 2 of three foraminiferal species were studied. The difference in the response patterns has been speculated by these authors to be attributed to the different calcification pathways of hyaline and porcellanous species (e.g.…”

Ocean acidification induces biochemical and morphological changes in the calcification process of large benthic foraminifera

“…The effects of OA are likely to be widespread across a diversity of marine life [7]. The decline in calcite saturation state (V Ca ) results in reduced calcification and increased dissolution rates of major marine calcifiers such as corals, foraminifera, calcifying algae and some molluscs, with potentially severe implications for coral reef ecosystems [7,[8][9][10][11]. However, there is a lack of sufficient understanding of calcification mechanisms to explain species-specific differences observed in manipulative experiments [4,7,12].…”

“…The rate of calcification in LBF is highly affected by pH changes and decreases significantly when pH levels drop below 8.0 [22]. Several recent studies have explored the effects of OA on the growth, calcification and photobiology of LBF [10,11,[23][24][25][26]. Decline in pH can decrease shell weight [24], cause reduction in calcification rates [10,11,24,26 -28] and photosynthetic efficiency [27], and alter shell microfabric through dissolution of calcium carbonate crystals [25].…”