“Climate Change Tiny Giants”: Ocean Warming and Acidification Changes: Response of Microfossils of the Anoxic Great Seas

Our results show that the severely organically enriched benthic environment of Flamengo Inlet and Florianopolis Bay (Sao Paulo and Santa Catarina states) have been recently invaded by the agglutinated foraminifera Trochammina hadai. The invasion in Flamengo Inlet occurred sometime before 2010, and by 2014–2015, the species has become one of the dominant faunal constituents at several locations. This species probably arrived in this region due the active commercial fishing and recreational boating traffic. Some questions remain unanswered and we still have to investigate exactly how it invaded into this embayment, and at what other locations in Brazil the species has been introduced. We do know that in Florianopolis North Bay, in the interface marine sediment-water, extremely low dissolved-oxygen values at the bottom waters associated with high percentage of total organic carbon, and low pH (high acidity) are better tolerated, by fauna of opportunists (Ammonia tepida and Buliminella elegantissima) and Trochammina hadai, than by other calcareous benthic foraminiferal species. Abundance of organic matter, low oxygen, with low pH are optimum for the fauna replacement and establishment of the invasive T. hadai, thereby enhancing its chances of proliferating. The invasive species is replacing calcareous benthic foraminifera, especially Elphidium genera, but needs further studies to find out if there are other genera being damaged as well. On the other hand species that thrive in high oxygen, that were found closer to the marine entrance towards the north of both environments, are responsible for bringing constant periodic natural oceanic water, renewing to both environments. We conclude that periods of hypoxia is unfavorable for bottom infauna where just the opportunists predominate in some central sites of both marine ecosystems severely affected at least by seasonal hypoxia.