Combined effects of warming and ocean acidification on coral reef Foraminifera Marginopora vertebralis and Heterostegina depressa

Abstract

Warming and changes in ocean carbonate chemistry alter marine coastal ecosystems at an accelerating pace. The interaction between these stressors has been the subject of recent studies on reef organisms such as corals, bryozoa, molluscs, and crustose coralline algae. Here we investigated the combined effects of elevated sea surface temperatures and pCO 2 on two species of photosymbiont-bearing coral reef Foraminifera: Heterostegina depressa (hosting diatoms) and Marginopora vertebralis (hosting dinoflagellates). The effects of single and combined stressors were studied by monitoring survivorship, growth, and physiological parameters, such as respiration, photochemistry (pulse amplitude modulation fluorometry and oxygen production), and chl a content. Specimens were exposed in flow-through aquaria for up to seven weeks to combinations of two pCO 2 (*790 and *490 latm) and two temperature (28 and 31°C) regimes. Elevated temperature had negative effects on the physiology of both species. Elevated pCO 2 had negative effects on growth and apparent photosynthetic rate in H.depressa but a positive effect on effective quantum yield. With increasing pCO 2 , chl a content decreased in H. depressa and increased in M. vertebralis. The strongest stress responses were observed when the two stressors acted in combination. An interaction term was statistically significant in half of the measured parameters. Further exploration revealed that 75 % of these cases showed a synergistic (= larger than additive) interaction between the two stressors. These results indicate that negative physiological effects on photosymbiont-bearing coral reef Foraminifera are likely to be stronger under simultaneous acidification and temperature rise than what would be expected from the effect of each of the stressors individually.

An updated synthesis of the observed and projected impacts of climate change on the chemical, physical and biological processes in the oceans

“…Synergistic negative effects have been observed on the growth, survival, fitness, calcification and development of organisms (Padilla-Gamino et al, 2013;Vehmaa et al, 2013;Gaitán-Espitia et al, 2014;Gobler et al, 2014;Hyun et al, 2014;Mackenzie et al, 2014b;Madeira et al, 2014;Maugendre et al, 2014Roy et al, 2014;Schram et al, 2014;Rosa et al, 2014a,b;Schmidt et al, 2014a). In some cases, hypoxic conditions have been observed to mediate the negative effects of ocean acidification (Mukherjee et al, 2013).…”

Variation in sensitivity of large benthic Foraminifera to the combined effects of ocean warming and local impacts

“…Reef-dwelling LBFs are vulnerable and consequently threatened by these pressures253435. Our study demonstrates that exposure to reduced light levels and inorganic nutrient enriched seawater at environmentally relevant concentrations reduces the resistance of A. lobifera to temperature stress, leading to greater declines in survivorship and fecundity, and increased bleaching frequency and changes in chl a concentration.…”

Polymorphic adaptations in metazoans to establish and maintain photosymbioses

“…Of the 150 foraminiferan families, 10% are hosts of algal symbionts (Lee & Anderson, 1991). Benthic foraminiferans either establish symbioses with Symbiodinium (Schmidt, Kucera & Uthicke, 2014) or, as in Sacoglossa, retain only the chloroplasts from their algal prey (Bernhard & Bowser, 1999;Pillet et al, 2011;Pillet & Pawlowski, 2012). Planktonic foraminiferans, however, mainly associate with the dinoflagellate Pelagodinium, a sister taxon of Symbiodinium (Decelle et al, 2015).…”