Plankton are tiny, microscopic marine organisms that represent the very bottom of the food chain. Some are photosynthetic and others graze on bacteria and other plankton, but no plankton species can move against ocean currents.
As a primary food source in the ocean, marine ecosystems rely on ocean mixing to distribute plankton and form aggregates that function as food for other plankton and organisms higher on the food chain.
The growth of photosynthetic plankton, or phytoplankton, is affected by climate change through differences such as rising upper ocean temperatures and reduced vertical mixing, affecting the amount of food generated in this lowest link in the food chain. Importantly, climate change also alters turbulent mixing of the oceans, affecting the availability of phytoplankton in the marine ecosystem.
Despite the importance of plankton availability in the ocean, only short-term time-series data were available to characterize plankton abundance and variety and ocean mixing over time. No high-frequency observations were available to calculate ocean mixing and plankton characteristics over timespans of weeks to months, which are necessary to characterize seasonal, annual and long-term mixing processes.
To address this issue, a group of researchers funded by JST CREST deployed the cabled marine Oshima Coastal Environmental data Acquisition Network System (OCEANS) observatory in 20 m of water off the coast of Oshima Island in Japan. The OCEANS observatory was equipped with a variety of highly sensitive instruments; including temperature, depth, turbidity and fluorescence sensors, a photosynthetically active radiation (PAR) sensor, a wave height gauge, and a Continuous Particle Imaging Classification System (CPICS); to observe plankton abundance at a high sampling rate between August 2014 and September 2018.
The researchers published their study on March 6 in the journal Ocean-Land-Atmosphere Research .
“[The OCEANS observatory allowed us to study h]ow… plankton diversity change[s] over [a much longer period of] time and … the statistical characteristics of its variability,” said Hidekatsu Yamazaki, emeritus professor at Tokyo University of Marine Science and Technology and first author of the research paper.
Specifically, the researchers focused on two 4-month segments (October 2014 to January 2015 and October 2015 to January 2016) from a 4-year dataset. The researchers found clear differences in ocean temperature and salinity between 2014/2015 and 2015/2016, with increasing average temperature (19.7 °C vs. 20.8 °C) and decreasing average salinity (34.4 parts per thousand vs. 33.7) in 2015/2016 compared to 2014/2015.
The CPICS primarily identified large plankton and aggregates in ocean water as expected, along with smaller varieties of plankton, fecal matter and mineral particles. A total of 33 different groups of organisms were detected during the study. Aggregates made up the majority of the particles detected in both 2014/2015 (77% of particles) and 2015/2016 (73%). Zooplankton, or plankton that graze on other plankton or bacteria, were the second-most abundant particles in the analysis, representing 10% of 2014/2015 and 22% of particles in 2015/2016, while phytoplankton made up 6% and 3% of particles, respectively.
The abundance of plankton and other nutrients in the ocean is critical as the base of the marine food chain. The researchers found that aggregate abundance correlated with turbulent energy dissipation rate in this study in short-term analyses of less than one day. In contrast, long-term changes in aggregate abundance and plankton diversity were not influenced by ocean turbulence.
“We found that time series of plankton diversity exhibit a pink noise spectrum, characterized by a slope of approximately −1,” said Yamazaki. This data suggests that plankton and marine aggregate abundance is instead governed by a self-organized system with nonlinear dynamics. This observation aligns with the diurnal vertical migration of some types of zooplankton, which enhances surface diversity as some deep-dwelling plankton ascend at night.
Overall, the study identified correlations between turbulence, plankton diversity and aggregate abundance in marine coastal regions over longer time periods, providing new insights into marine ecosystems. “Our next step is to investigate how plankton diversity is linked to ecosystem dynamics and underlying biological and physical processes,” said Yamazaki.
Silvana B. Penninck, Leandro T. De-La-Cruz and Rubens M. Lopes from the Department of Biological Oceanography in the Oceanographic Institute at the University of São Paulo in São Paulo, Brazil; Gabriel Freitas from the School of Marine Resources and Environment at Tokyo University of Marine Science and Technology in Tokyo, Japan; Marika Takeuchi from Ocean BioGeosciences at the National Oceanography Centre in Southampton, UK; and Mamoru Tanaka from the Department of Civil Engineering at Tokyo University of Science in Tokyo, Japan also contributed to this research.
This work was financially supported by JST CREST grant number JPMJCR12A6.
Ocean-Land-Atmosphere Research
Observational study
High-Frequency Observations of Plankton and Particle Abundance from a Cabled Observatory Off Japan
6-Mar-2026
There are no conflicts of interest to declare.