Rising sea surface temperatures and extreme heat waves are affecting symbiont-bearing tropical calcifiers such as corals and Large Benthic Foraminifera (LBF). In many ecosystems, parallel to warming, global change unleashes a host of additional changes to the marine environment, and the combined effect of such multiple stressors may be far greater than those of temperature alone. One such additional stressor, positively correlated to temperature in evaporation-dominated shallow-water settings is rising salinity. Here we used laboratory culture experiments to evaluate the combined thermohaline tolerance of one of the most common LBF species and carbonate producer, Amphistegina lobifera. The experiments were done under ambient (39 psu) and modified (30, 45, 50 psu) salinities and at optimum (25 °C) and warm temperatures (32 °C). Calcification of the A. lobifera holobiont was evaluated by measuring alkalinity loss in the culturing seawater, as an indication of carbonate ion uptake. The vitality of the symbionts was determined by monitoring pigment loss of the holobiont and their photosynthetic performances by measuring dissolved oxygen. We further evaluated the growth of Peneroplis (P. pertusus and P. planatus), a Rhodophyta bearing LBF, which is known to tolerate high temperatures, under elevated salinities. The results show that the A. lobifera holobiont exhibits optimal performance at 39 psu and 25 °C, and its growth is significantly reduced upon exposure to 30, 45, 50 psu and under all 32 °C treatments. Salinity and temperature exhibit a significant interaction, with synergic effects observed in most treatments. Our results confirm that Peneroplis has a higher tolerance to elevated temperature and salinity compared to A. lobifera, implying that a further increase of salinity and temperatures may result in a regime shift from Amphistegina- to Peneroplis-dominated assemblages.
Bibliographical noteFunding Information:
This study represents part of the Ph.D. thesis of the senior author in the Department of Geological and Environmental Sciences at the Ben-Gurion University of the Negev. We are thankful to Yael Kenigsberg, Yahel Eshed, Doron Pinko, and Sneha Manda for their assistance in the fieldwork and Gad Rahicman and Sneha Manda for their assistance in the lab. This study was supported by the German Federal Ministry of Education and Research (BMBF), and the Israeli Ministry of Science, Technology and Space (MOST), (grant nos. 3-15275 and 3-15274 ) and the Israel Science Foundation (grant no. 941/17 ). SAP wishes to thank the Israeli Ministry of Science, Technology and Space (MOST) for their continued support of the ADSSC. We acknowledge the support provided to Chen Kenigsberg by High-Tec scholarship of the Kreitman School of Advanced Graduate Studies and the Mediterranean Sea Research Center of Israel (MERCI).
- Calcification rates
- Global warming
- Large Benthic Foraminifera
- Net photosynthesis
- Salinity rise