Our next feature from the ICES/PICES Zooplankton Production Symposium is from Sanae Chibae who spoke to participants about retrospective zooplankton study.
The retrospective study of zooplankton has been recognized as an effective method to understand marine ecosystem variability since the 1990s, coinciding with the launch of GLOBEC. Though initially driven by the needs of ecosystem-based management for sustainable fisheries, long-term zooplankton change study has been expanding its goals toward wider perspectives in recent decades, such as ecosystem responses to climate and anthropogenic changes, plankton roles in regional and global biogeochemical cycles, and biodiversity conservation.
Three major steps in retrospective approaches are: 1. from correlation to mechanism2. from biomass to species/functional level breakdown3. from regional process to global comparison.
In the 1990s, many studies revealed significant correlations between zooplankton biomass and climate indices, such as the North Atlantic Oscillation and the North Pacific Decadal Oscillation. However, to understand the mechanisms and ecological and biogeochemical consequences of the detected variations in zooplankton, species level and/or functional level breakdowns are necessary. While zooplankton time-series collected in a standard sampling method for more than a couple of decades are rare, the Continuous Plankton Recorder survey and CalCOFI program have conducted species level analysis on over 50 years of observation data and have greatly increased our knowledge on long-term marine ecosystem changes in the North Atlantic and eastern North Pacific by the mid-2000s.
The Odate Collection dataset is one of the few extensive zooplankton time-series. Those samples were collected in the waters around Japan by multiple organizations for various purposes since the 1950s and complied by Dr. Kazuko Odate of Tohoku National Fisheries Research Institute, Japan Fisheries Research and Education Agency (FRA). The initial Odate dataset is circa 17000 samples covering 1951-1990, which are available online. The FRA has continued to collect and curate zooplankton samples quasi-monthly after 1990 until present. The total number of biomass data, including the original Odate data, surpassed 87000 by 2015, among which over 4,800 samples have been analyzed at species level. Although no online access is available, those data are recorded following the international standard (Darwin Core) format.
Using those species level data, we have studied how ecosystem structures in the western North Pacific changed responding to climatic forcing, in particular, the North Pacific Decadal Oscillation (PDO). The scientific outcome includes phenological change and latitudinal shift of dominant copepods, Neocalanus species, which were driven by the decadal warm-cool cycle related to PDO. As mentioned above, one of the recent trends in the retrospective study is basin to global scale synthesis of long-term ecosystem changes. We have conducted collaborative studies with international counterparts, and participated in some international projects aiming for global comparison of long-term zooplankton variation. Those collaborative researches revealed, for example, the seesaw pattern in its decadal phenology between eastern and western North Pacific, influence of the climate - ocean currents dynamics on its biogeography over the North Pacific, and global distribution pattern on its species diversity. More recently, those data are used for future habitat projection of commercially important fish species, and solving the fundamental questions of ecology such as the mechanism of formation of functional diversity distribution.
Today, the ocean science community recognizes the benefits of long-term zooplankton data, and there is an increasing demand for global integration and sharing of the data, with which various international projects are trying to develop ecosystem/biodiversity indicators for climate change study, fisheries, biodiversity conservation, and other sustainable development purposes. Meanwhile, many existing zooplankton time-series are struggling to continue observation efforts, some have even terminated due to budgetary cuts.
No observation means no data, and no returns to society. We, the science community, should speak out more and more to the public on the significance of zooplankton time-series observation.
Odate Collection - data distribution map. Image: NOAA COPEPOD.