Department of Marine Ecosystem Science, Atmosphere and Ocean Research Institute, The University of Tokyo

The world ocean is dominated by various drifting organisms referred to as plankton. While each plankton species is unique in its morphology, ecology, and evolutionary history, each also has various relationships with co-occurring species and its environment, and plays major roles in biological production and biogeochemical cycles in the ocean. In recent years, it has become apparent that global-scale environmental changes and disruptions to marine ecosystems by human activities are closely linked to changes in plankton communities. 

Our group focuses on investigating marine plankton and micronekton to understand their biology, ecology, and roles in biogeochemical cycles in the ocean.

Microorganisms are the firstly appeared living entities on Earth. While most of the ocean is characterized by high salinities, low nutrients, low temperatures and high pressures, marine bacteria have evolved to adapt to such physicochemical factors, and have become distributed throughout the ocean. In addition, microbes have developed various interactions with other microbes and higher organisms. These interactions have also contributed to species diversification on Earth. Bacteria, known as degraders, convert organic matter into water and carbon dioxide. Although particulate organic matter can be consumed by animals, dissolved organic matter (DOM) is utilized mostly by bacteria. As DOM is one of the largest global reservoirs of organic materials, clarification of bacterial functions is of primary importance in understanding the mechanisms of the global carbon cycle. Our group seeks to clarify the biological characteristics, functions, and ecological contributions of marine microorganisms by introducing new approaches in combination with molecular techniques and newly developed various devices.

Deep-sea reducing environments including hydrothermal vent fields and

cold seep areas harbor faunal communities with an extraordinary large biomass that depend on primary production by chemosynthetic bacteria. As most animal species of the chemosynthesis-based communities are endemic and highly adapted to the specific conditions, they provide unique opportunities to investigate evolutionary processes, adaptation and dispersal in the deep sea. Our current studies on these animals include genetic population analyses and species- and higher-level phylogenies based on mitochondrial and nuclear gene sequences. We are also studying the early development and dispersal mechanisms of the vent endemics and other deep-sea species by rearing pelagic larvae and analyzing the chemical composition of gastropod shells. The Sea of Japan is a semi-closed sea connected with neighboring seas by shallow and narrow straits and thought to have experienced environmental deterioration during the last glacial maximum. In order to evaluate the effects of past and recent climatic changes on marine ecosystems, we are comparing the genetic population structures of various benthic animals along Japanese coasts. Another research focus in our research group is the biogeography of snails on tidelands — a marine environment that has been severely damaged by reclamation and pollution. Obtained results would provide significant implications to the estimation of future environmental changes.