Planktonic foraminifera are unicellular marine zooplankton with calcite shells. Important characteristics of planktonic foraminifera include the preservability of calcite shells as microfossils in sediments and the recordability of environmental and ecological information as their shells were calcified. Some planktonic foraminifera species have been found to possess an endosymbiotic relationship with algae, known as “photosymbiosis.” Overall, photosymbiosis is an evolutionary and nutritionally important ecology, and it also plays an important role in understanding the Earthʼs surface system in terms of material cycling and carbon cycling in particular. In this paper, I briefly review the current knowledge on planktonic foraminifera and photosymbiosis and outline the studies we have conducted so far with focus on the extraction of photosymbiotic signals and the biological phenomena concerning photosymbiosis. Finally, I discuss the prospects of further research on photosymbiotic marine protistan plankton.

Transport processes in coastal oceans are important for understanding mass transport between land and ocean. Investigations of mixing processes are essential to reveal the transport processes. This paper presents mixing processes due to internal tides and the associated mass transport, on the basis of field observations and numerical simulations conducted by the author who is a recipient of Okada Prize from the Oceanographic Society of Japan, 2022. The Yowing Ocean Data Acquisition (YODA) Profiler, has been developed to observe small scale dynamics and mixing processes in coastal oceans. Results from the profiler revealed mixing in river plumes and breaking of nonlinear internal tides on a shallow slope. Breaking of internal tides results in strong turbulent mixing, sediment resuspension and generation of intermediate nepheloid layers in Otsuchi Bay, Japan. It was found that vertical mixing was enhanced by a collision of a receding internal tide and a subsequent run-up nonlinear internal bore on a gentle slope. In addition, numerical models were developed to investigate internal tides breaking. Large scale oceanic numerical models showed enhanced diurnal internal tides caused by a resonance of Kelvin waves around islands over the Izu-Ogasawara Ridge and strongly enhanced the internal tide energy flux toward the upstream of the Kuroshio owing to an interaction of the Kuroshio and tides. This study also applies methods established in oceanic studies to analysis of mixing processes in a lake.