Diverse thermotolerant assemblages of benthic foraminiferal biotas from tropical tide and rock pools of eastern Africa

Abstract

Tropical tide and rock pools are extreme environments with regard to temperature. They undergo diurnal heating and constitute natural laboratories to assess the fate of marine calcifiers under scenarios of global change. This study focuses on benthic foraminiferal assemblages from tide and rock pool sites from eastern Africa as “natural” laboratories to document the diverse spectrum of foraminiferal biotas potentially capable to succeed under conditions of future global warming. To date, the majority of foraminiferal thermal tolerance data have been compiled from laboratory experiments, anthropogenically heat-polluted or extreme hydrothermal vent areas. A total of 111 species of benthic foraminifera were recorded within the tide pool samples. Perforate species were most abundant (up to 84%), followed by porcellaneous taxa (up to 45%), while agglutinated species were only rare (up to 5%). Larger benthic foraminifera represented between 30 and 75% of the total assemblages with 8 observed genera. Species richness varied between 23 and 63 species per sample. The foraminiferal communities of most sites were dominated by larger perforate taxa such as Neorotalia calcar and Amphistegina spp., followed by a variety of small miliolid taxa (54 species) and small rotaliids (27 species). The surprisingly high foraminiferal species richness suggests that a large range of shallow-water benthic taxa appear to be capable to tolerate exposure to diurnally occurring temperature extremes (35°–>40°C). The large spectrum of benthic taxa recorded provides insight into potential acclimatization capacities of foraminiferal assemblages with regard to ongoing ocean warming and projected temperature changes. We infer that calcification in heat-tolerant benthic foraminifera, a group of productive carbonate producers, is more widespread than previously thought and will continue in future decades when water temperatures are significantly elevated. Tolerance to thermal stress is imperative for intertidal foraminifera and assemblages from tropical rock and tide pools appear to be less susceptible to future change. This capacity is central to the resilience to rising ocean temperatures and dictates how warming affects these delicate environments. Intertidal foraminiferal assemblages could potentially act as source populations for restocking and to mitigate detrimental effects of global change.