CHLOROPLAST-SEQUESTERING BENTHIC FORAMINIFERA INHABITING HIGH ARCTIC DEEP-SHELF SEDIMENTS

Recent studies show that chloroplasts sequestered by benthic foraminifera may aid their fitness in low oxygen to anoxic habitats. Such sequestration of chloroplasts, or “kleptoplasty”, has been documented in about a dozen foraminifera species, mostly from mudflats and other shallow-water habitats where sunlight is available. Kleptoplasty in deeper-water benthic foraminifers is less commonly documented. The exact role of kleptoplasts in aphotic (dark) habitats remains enigmatic. Here, we expand the list of known kleptoplastidic benthic foraminifers from deeper waters where little to no sunlight penetrates. While studying the ecology and physiology of benthic foraminiferal communities in Arctic methane-emission sites and their surroundings, we noted that multiple species sequester chloroplasts. Here, we report that Buccella frigida, Nonionellina labradorica, Elphidium clavatum (S4) and, perhaps, Robertinoides sp. sequester what appear to be diatom chloroplasts from a ~381-m deep area near a gas hydrate pingo off southern Svalbard, where sediments were collected via coring using the manipulator of a remotely operated vehicle (ROV). Specimen fitness (viability) was determined using cellular ultrastructural analysis with Transmission Electron Microscopy (TEM). While it is well established that N. labradorica and multiple Elphidium species are kleptoplastidic, this is the first report of kleptoplasty for Buccella frigida and Robertinoides sp. Because the available Robertinoides specimens had somewhat degraded cytoplasm, we cannot definitively establish their kleptoplasty; if so, we believe this is the first documentation of an aragonitic kleptoplastidic benthic foraminifer. Importantly, there was no universal distinction between kleptoplasty and gas-hydrate environmental conditions, meaning the kleptoplastidic specimens occurred in both seep-associated and control (non-seep) settings. Results show that kleptoplasty is more widespread in foraminifera than previously thought and that the phenomenon also occurs in high latitudes and may occur in aragonite-bearing benthic foraminifers. Funded by AKMA (Advancing Knowledge in Methane in the Arctic, project 287869), NORCRUST (255150), the French program Make Our Planet Great Again, US NSF 1634469 & WHOI Investment in Science Program.