Impacts of long‐term environmental variability on diapause phenology of coastal copepods in Tokyo Bay, Japan

Abstract

Many common and abundant copepods in coastal areas adapt to complex environments through diapause (physiological dormancy) by laying resting eggs. However, the response mechanisms of these species' phenology to environmental changes is poorly understood, especially the influence of both climatic and anthropogenic changes. Using monthly time series data for zooplankton in Tokyo Bay, Japan, from 1981 to 2010, we investigated phenological and quantitative changes in the dominant species Acartia omorii, Centropages abdominalis, and Labidocera rotunda in response to climatic and hydrographic variation in this semienclosed eutrophic coastal area. The first two species produce resting eggs in the warm season and the latter in the cold season. Decreasing abundance and increasing resting egg periods were observed for A. omorii and C. abdominalis, and the reverse for L. rotunda. Time series analysis revealed a possible mechanism driving these phenologic shifts. Wintertime warming of the water column associated with climate variability driven by the Pacific Decadal Oscillation index, followed by rapid development of summertime stratification and the formation of hypoxic bottom water layers, were responsible for the early initiation and delayed termination of the resting egg period for cold-water species. The warming trend in Tokyo Bay, possibly induced by inflow of warm oceanic water due to anthropogenic factors, caused these phenologic changes in the resting period and subsequently affected zooplankton abundance. These results suggest that the multiple stressors caused by climate change and other anthropogenic impacts can affect regional zooplankton communities in coastal areas.

Copepod Embryonic Dormancy: “An Egg Is Not Just an Egg”

“…Several studies have reported induction of diapause egg production as adverse environmental conditions are approaching (e.g., Kiørboe and Nielsen, 1994;Guerrero and Rodríguez, 1998;Tachibana et al, 2019). The free-swimming copepod biomass declines at a certain time of the year to a negligible level.…”

“…This enables free-living species to disappear from the plankton during the winter (e.g., Uye and Fleminger, 1976;Norrbin, 1991;Kiørboe and Nielsen, 1994;Wesche et al, 2007) and return in the spring (Marcus, 1984). However, resting eggs can also be used to cope with unfavorable summer conditions (Uye, 1985;Marcus, 1989;Tachibana et al, 2019), along with other unfavorable environmental conditions, such as high predation pressure (Hairston, 1996).…”

“…At present, the different life stages, pelagic and benthic, are studied as two different compartments and not as a holistic life cycle concept. In reality, we do not know for certain what happens when we describe annual population dynamics of copepod populations with resting eggs in their life cycles (e.g., Sullivan and McManus, 1986;Kiørboe and Nielsen, 1994;Guerrero and Rodríguez, 1998;Tachibana et al, 2019). We just make our best assumptions when interpreting life cycle characteristics, on the basis of numerical correlations between seasonal abundance of free-swimming adult individuals, resting eggs in the sediment, and past winter or summer blooming of propagules.…”

Effects of temperature and phytoplankton community composition on subitaneous and resting egg production rates of Acartia omorii in Tokyo Bay

“…A. omorii probably forms diapause eggs in early summer. Recently, Tachibana et al 29 reported that the decadal mean abundance of A. omorii for the 2000s decreased by 58.7% from the 1980s. The shift in production from subitaneous to resting eggs was due to changes in abiotic factors, such as water temperature.…”

Functional shifts in estuarine zooplankton in response to climate variability

“…Environmental changes, such as warming and decrease in salinity, have been shown to affect zooplankton body size negatively (Daufresne, Lengfellner, & Sommer, 2009; Mäkinen, Vuorinen, & Hänninen, 2017). Elevated temperature can also extend the season by postponing its end (Tachibana, Nomura, & Ishimaru, 2019), shown as cladocerans producing their resting eggs later due to warming (Chen & Folt, 1996). Fish larvae and their recruitment to the population can be especially impacted if the quality of their food community, that is, zooplankton decreases substantially (Arula, Ojaveer, & Klais, 2014; Edwards & Richardson, 2004).…”