Substrate temperature as a primary control on meiofaunal populations in the intertidal zone: A dead zone attributed to elevated summer temperatures in eastern Bahrain

Summer temperatures in excess of 52°C, have been measured at the high tide mark in surficial substrates in the exposed areas of an intertidal mudflat in Bahrain. The incoming flood tide may have a temperature as high as 42°C. As a result, large swaths of the upper intertidal zone are barren of living meiofauna (e.g., foraminifera, ostracods, gastropods, and worms) during the hottest months of the year. Samples collected from the intertidal zone in August present only dead assemblages of foraminifera, ostracods, and gastropod shells. Dead assemblages of the foraminifer Peneroplis collected from the upper reaches of the intertidal zone consist largely of juvenile specimens, implying that the living populations, when present, do not reach maturity. The full range of living meiofaunal organisms is only observed in tidal channels that remain submerged during low tide. The presence of a summer dead zone for intertidal meiofaunal organisms is consistent with predictions of climate models that suggest portions of the Arabian Gulf may become too extreme to support eukaryotic life.