Non-lethal effects of ocean acidification on two symbiont-bearing benthic foraminiferal species

Abstract

We conducted experiments to assess the effect of elevated atmospheric carbon dioxide concentrations on survival, fitness, shell microfabric and growth of two species of symbiont-bearing coral-reef benthic foraminifera, using <i>p</i>CO<sub>2</sub> Ievels similar to those likely to occur in shallow marine pore waters in the decades ahead. Foraminifera were cultured at constant temperature and controlled <i>p</i>CO<sub>2</sub> (385 ppmv, 1000 ppmv, and 2000 ppmv) for six weeks, and total alkalinity and dissolved inorganic carbon were measured to characterize the carbonate chemistry of the incubations. Foraminiferal survival and cellular energy levels were assessed using Adenosine Triphosphate (ATP) analyses, and test microstructure and growth were evaluated using high resolution SEM and image analysis. Fitness and survival of <i>Amphistegina (A.) gibbosa</i> and <i>Archaias (A.) angulatus</i> were not directly affected by elevated <i>p</i>CO<sub>2</sub> and the concomitant decrease in pH and calcite saturation states (Ω<sub>c</sub> values) of the seawater (pH and Ω<sub>c</sub> values of 8.12, 7.86, and 7.50, and 5.4, 3.4, and 1.5, for control, 1000 ppmv, and 2000 ppmv, respectively). In <i>A. gibbosa</i>, a species precipitating low-Mg calcite, test growth was not affected by elevated <i>p</i>CO<sub>2</sub>, but areas of dissolved calcium carbonate were observed even though Ω<sub>c</sub> was >1 in all treatments; the fraction of test area dissolved increased with decreasing Ω<sub>c</sub>. Similar dissolution was observed in offspring produced in the 2000 ppmv <i>p</i>CO<sub>2</sub> treatments. In <i>A. angulatus</i>, whose tests are more-solubile high-Mg calcite, growth was greatly diminished in the 2000 ppmv <i>p</i>CO<sub>2</sub> treatment compared to the control. These non-lethal effects of ocean acidification – reduced growth in <i>A. angulatus</i>, and enhanced dissolution in <i>A. gibbosa</i> – may reflect differences in test mineralogy for the two species; the long-term ecological consequences of these effects are not yet known

Elevated CO2effects on morphology and survival rate in intertidal benthic foraminifera

“…The lower pH did not significantly affect the survival rate in agglutinated and tectinous benthic foraminifera but negatively impacted the survival rate in calcareous foraminifera (Bernhard et al, 2009a). The present study recorded noticeable mortality rates in all the three species with decreasing pH, similarly to the previous work of, Mclntyre Wressing et al (2011) who have reported that higher CO 2 concentration affects survival rate in Amphistegina gibbosa .…”

The O2, pH and Ca2+ Microenvironment of Benthic Foraminifera in a High CO2 World

“…This is represented in the literature showing unaffected or increased calcification rates in hyaline (low Mg-calcite: less soluble) and decreased rates in miliolid (high Mg-calcite: more soluble) species in response to elevated pCO 2 [70], [73], [76], [77]. These taxa specific differences are in line with previous studies on foraminiferal DIC uptake mechanism, showing almost linear increases in miliolid Amphisorus hemprichii and almost no change in Amphistegina lobifera in response to increasing DIC (and CO 3 2− ) concentrations in the OA range between 2 and 3 mM ([84], also discussed in [76]).…”

“…While most laboratory studies investigating calcification in symbiont-free foraminifera showed decreases in calcification rate [72], [74], [75], [82] larger photosymbiotic foraminifera show more variable responses [50], [70], [76], [77]. Also, experiments conducted under low and stagnant flow conditions exhibit mostly decreases in calcification rate [70], [72]–[75], [82], while experiments applying higher rates of turbulent mixing show variable responses on rates of calcification, net photosynthesis and respiration ([50], [76], [77], this study). Thus calcification responses seem to correlate to some extend with the experimental flow conditions as suggested for corals (reviewed in [83]).…”

The benthic foraminiferal community in a naturally CO<sub>2</sub>-rich coastal habitat of the southwestern Baltic Sea

“…In contrast, the fitness and survival of the symbiontbearing benthic foraminifera Amphistegina gibbosa and Archaias angulatus were not directly affected by elevated pCO 2 up to 2000 µatm (McIntyre-Wressnig et al, 2011). But it is important to note that during the whole six week incubation time, calc was supersaturated ranging from 5.4 to 1.5.…”

“…Seawater pH NBS , pCO 2 and omega for calcite ( calc ) were calculated by using the CO2Sys-program developed by Lewis and Wallace (1998) (Tables 2 and 3). Dissociation constants K 1 and K 2 were chosen according to Mehrbach et al (1973) as refitted by Dickson and Millero (1987) and the KHSO 4 dissociation constant after Dickson (1990).…”