ACCLIMATIZATION POTENTIAL OF AMPHISTEGINA SPP. AND THEIR SYMBIONTS TO LONG- AND SHORT-TERM THERMAL STRESS

Larger benthic foraminifers (LBF) are widely used to reconstruct modern and ancient marine environments due to their high diversity and specific niche requirements. This has made them a widely used bioindicator within coral reef ecosystems with which to assess ecosystem health. One of the major threats to coral reefs worldwide is thermal stress, which causes the loss of photosymbiotic algae, more commonly know as bleaching. Due to the projected future increase in sea surface temperatures (SST) photosymbiotic organisms are expected to be highly vulnerable. This phenomenon is more commonly known for corals, however it has been observed among LBF since the 1990’s. Therefore, it is important to understand how photosymbiotic marine organisms will adapt to an elevated intensity, duration, and frequency of thermal stress. To study the adaptation potential of photosymbiont bearing benthic foraminifera towards thermal stress and to identify the underlying mechanisms of acclimatization and recovery, experimental studies were conducted on the genus Amphistegina to assess chronic, unique and repetitive heat stress over four weeks. To monitor intra- and interspecific variations three populations from two different geographic regions (Florida Keys and Zanzibar) and depths (5 m and 20 m) were used. Specifically, growth, respiration, and cellular biomarkers (such as total antioxidant capacity against peroxyl radicals) were measured to understand the holobiont response, while photosynthesis, coloration, and chlorophyll a content were measured to determine the photosymbiotic algae response. Variations in these parameters indicate changes in symbiont biomass and fitness as well as enzymatic activities of the foraminiferal antioxidant defense system. These findings show alterations in the symbiotic relationship, such as bleaching, acclimatization and possible higher resilience to various combinations of stress events. Understanding these intra- and interspecific variations and acclimatization mechanisms is key to deciphering the range of responses in marine photosymbiotic organisms to global warming.