Understanding the functional role of large benthic foraminifera on coral reefs in a changing climate

Abstract

Concerns regarding the response of calcifying species in future warmer and more acidic oceans have been raised in many studies. In coral reefs, calcifiers such as large benthic foraminifera (LBFs) play an important role in carbon sequestration and generating carbonate sediments. This thesis documents the importance of LBFs in coral reef environments using satellite imagery in conjunction with ground-truthed photographs to characterize LBF habitats, and subsequently reef-scale biomass on a seasonal scale at One Tree Reef (OTR), Southern Great Barrier Reef. Based on previous models of entire reef metabolism, LBFs contribute approximately 3.9-5.4% of the carbonate budgets at OTR, a previously underappreciated carbon sink. LBF species such as Marginopora vertebralis are commonly associated as epiphytes on algae such as Halimeda tuna and Laurencia intricata, interacting on a physiological scale. When incubated in future conditions of ocean warming and acidification, the epiphyte M. vertebralis increased the resilience of H. tuna by decreasing bleaching rates of the host algae. While isolated M. vertebralis exhibited reduced growth in near future ocean acidification and warming, those in association with L. intricata exhibited growth and calcification rates similar to ambient conditions, increasing the resilience of M.vertebralis to stress. These data on LBF interactions with algal substrata were used to model reef scale carbonate production at Lizard Island Reef, demonstrating ecologically relevant experiments can refine estimates of carbonate production. Using LBFs as model organisms, important ecological questions of ecosystem resilience to stress through physiological buffering are addressed in this thesis. This is especially important as coral reefs are facing compounding anthropogenic stressors from global change, and provides examples that species interactions are crucial to resilience of calcifiers such as LBFs in a future ocean conditions.