Quasi‐decadal periodicities in growth and production of the copepod Eodiaptomus japonicus in Lake Biwa, Japan, related to the Arctic Oscillation

Abstract

Copepods are important secondary producers that support higher trophic levels in aquatic food webs. Large-scale climate events such as climate oscillations and global warming force on physical and chemical conditions in aquatic ecosystems might regulate copepod production through physiological and biochemical processes. We evaluated how large climatic and anthropogenic events impacted secondary production of copepods in Lake Biwa, the largest lake in Japan. We determined demographic traits such as body size, growth rate, biomass and production of the dominant copepod Eodiaptomus japonicus in this lake over four decades . To evaluate in situ food conditions and estimate growth and production for this omnivorous species, we firstly defined a size-based food index (f), that is the ratio of in situ body size to ideal body size in adult females. Values of f were mostly < 1 even during eutrophication (1970s to the early 1980s), suggesting that this copepod continuously suffered from a food shortage in this lake. Quasi-decadal periodicities were detected in f, growth and production (but not biomass) for this copepod throughout the study period. These periodicities were correlated with the Arctic Oscillation, implying that long-term trends in climate could regulate copepod food availability and production. This correlation weakened after 1990, which might be due to a regime shift in lake water temperature, which increased abruptly in the mid-1980s. Global warming might now be disrupting historical quasi-decadal periodicity in growth and production of copepods in Lake Biwa.

Sedimentary DNA can reveal the past population dynamics of a pelagic copepod

“…As shown in the present study, the sedDNA concentrations of E. japonicus markedly increased more than 3-fold during the 2000s compared to those before the 1990s, which significantly correlated with their production and biomass. The production of E. japonicus greatly increased more than approximately 2-fold in the 2000s, mainly due to the decline of predation effect (Liu et al ., 2021), which occurred in parallel with their temporal increase of specific growth rate and subitaneous eggs. These facts support that copepod sedDNA can be applied as a powerful tracking tool for reconstruction of their production and biomass related to the intensity of spawning activity.…”

“…1g, h). Long-term monthly data sets of biomass, specific growth rate, and population production in previous studies were referred to (Liu et al ., 2021; Liu et al ., 2020b). The calculation methodology is summarized in Supplementary Table S4; detailed descriptions are provided in previous studies (Liu et al ., 2015; Liu et al ., 2021; Liu et al ., 2020b).…”

“…Long-term monthly data sets of biomass, specific growth rate, and population production in previous studies were referred to (Liu et al ., 2021; Liu et al ., 2020b). The calculation methodology is summarized in Supplementary Table S4; detailed descriptions are provided in previous studies (Liu et al ., 2015; Liu et al ., 2021; Liu et al ., 2020b). Briefly, biomass (g dry weight m -2 ) was calculated as the product of the population density (individuals m -2 ) with the mean body dry-weight (g individual -1 ).…”

“…Previous studies have shown that global warming decreases copepod abundance (Garzke et al ., 2015). Also, large-scale climate events showing oscillation cycles over decades, such as the Pacific Decadal Oscillation and Arctic Oscillation, regulate ocean temperature and consequently affect copepod biomass and production (Peterson & Schwing, 2003; Chiba et al ., 2006; Liu et al ., 2021). Information about long-term copepod population dynamics is urgently required to achieve better fish management and to understand how large-scale climatic events influence aquatic ecosystems.…”

“…In Lake Biwa (Japan), one of the world’s ancient lakes (Hampton et al ., 2018), regular zooplankton surveys have been intensively conducted since 1965 (Hsieh et al ., 2011; Liu et al ., 2020b). Moreover, the long-term demographic traits of the pelagic dominant copepod Eodiaptomus japonicus , such as biomass, population growth rate, and production, have been determined from 1971 to 2010 with experimental and microscopic observations (Liu et al ., 2015; Liu et al ., 2021; Liu et al ., 2020b). E. japonicus produces both subitaneous and resting eggs; the historical variation of resting egg concentration was recovered from sediment archives up to 60 years ago (Liu et al ., 2020a).…”