An Ecological Perspective on Short-Term Heat Exposure Experiments with Marine Calcifying Organisms from the Western Arabian Gulf Region: Insights into a Summer Heatwave Scenario

Frequent occurrences of high-temperature records have become commonplace during the summer seasons in regions adjacent to the western Arabian Gulf, such as Bahrain, Saudi Arabia, and Qatar. On a daily basis, the fluctuation in daytime and nighttime temperatures, along with varying afternoon temperatures, poses a potential threat to organisms inhabiting intertidal and shallow water environments, whether residing above the substrate or submerged beneath. Surprisingly, there has been no prior scientific investigation into the resilience of these coastal communities, especially from a non-anthropocentric perspective, focusing on the marine calcifying organism that inhabits one of the world's most extreme marine environments. To address this gap, we aimed to determine the upper thermal limits of intertidal calcifying benthic organisms in the western Arabian Gulf region. For this purpose, we selected three representative species among the diverse inhabitants, comprising two gastropod species and one ostracod species. These specimens were subjected to controlled environmental conditions inside a thermal incubator over a short-term period (three hours), with temperature exposures ranging from 40°C to 60°C. We considered different scenarios that replicated their natural ecological conditions: full exposure, partial exposure, and full coverage/submerged underwater. Our comprehensive results revealed that different gastropod species exhibited varying levels of resilience to higher thermal exposure, depending on the scenario (heat comma temperature/HCT ranged between 39°C-48.5°C versus 42.1°C-44.1°C). In contrast, the ostracod displayed remarkable tolerance to higher temperatures than the gastropod specimens before succumbing to complete mortality or entering a comatose state (temperature range of 39.1°C-53.5°C). Furthermore, post-exposure recovery demonstrated that higher heat exposure substantially prolonged the recovery time. In the case of the gastropod specimens subjected to the highest thermal exposure, no successful recovery was observed. Our findings underscore the importance of conducting ecological experiments that involve prolonged exposure to high temperatures. However, it is imperative to recognize that even short-term periods of elevated temperatures can have fatal implications for the target organisms. This is particularly relevant in light of the ongoing warming trend and the recording of extreme temperatures in our regional area in the western Arabian Gulf, which may eventually be deemed a potential "kill zone" during the peak of summer seasons within a short timeframe.