Temperature Effects on the Shell Growth of a Larger Benthic Foraminifer (sorites Orbiculus): Results from Culture Experiments and Micro X-ray Computed Tomography

Ocean warming is predicted to have negative impacts on marine calcifying organisms. Larger benthic foraminifers (LBFs) are single-celled marine organisms with calcareous shells, and the third-highest carbonate producer in clear, shallow-water, tropical and subtropical, regions. Previous studies have reported declining shell growth when cultured at higher temperatures, although the specific physical characteristics of shell growth remain unknown because their small size and complex shell structures make it difficult to measure shell growth in three dimensions. To evaluate the effect of seawater temperature on LBF growth, we cultured a porcelaneous LBF Sorites orbiculus under six different temperature conditions (19 degrees C-29 degrees C) and quantitatively measured their shell volume, weight, maximum diameter, and chamber number, using micro X-ray computed tomography (MicroCT). Shell growth of S. orbiculus expressed by shell weight and volume is optimal around 25 degrees C, declining at lower and higher temperatures. Changes in shell weight were associated with variations in shell volume, but not shell density. MicroCT observations indicated that changes in shell volume and weight might be caused by symbiont activity. Our results suggest that suppressed LBF growth is currently occurring in summer months and might be further exacerbated in the future by rising ocean temperatures.