Seasonal changes in body size and oil sac volume of three planktonic copepods, Paracalanus parvus (Claus, 1863), Pseudocalanus newmani Frost, 1989 and Oithona similis Claus, 1866, in a temperate embayment: what controls their seasonality?

Abstract

Seasonal changes in body size (prosome length: PL) and oil sac volume (OSV) of the three most numerically abundant copepods in Ishikari Bay, northern Sea of Japan, Paracalanus parvus (Claus, 1863), Pseudocalanus newmani (Frost, 1989) and Oithona similis (Claus, 1866), were studied using monthly samples collected through vertical hauls of a 100-μm mesh NORPAC net from March, 2001 to May, 2002. Seasonal changes in PL were common for the three species and were more pronounced during a cold spring. PL was negatively correlated with temperature, and this relationship was described well using the Bělehrádek equation. Seasonal changes in OSV exhibited a species-specific pattern: i.e., OSV was greater during a warm summer for P. parvus and was greater during a cold spring for P. newmani and O. similis. The OSV peak period corresponded with the optimal thermal season of each species. The relative OSV to prosome volume of the small copepods (0.6-0.8%) was substantially lower than that of the large copepods (20-32%). These facts suggest that the oil sac of small copepods is not used for overwintering or diapauses or during periods of food scarcity but is instead used as the primary energy source for reproduction, which occurs during the optimum thermal season of each species.

Seasonal changes in taxonomic, size composition, and Normalised Biomass Size Spectra (NBSS) of mesozooplankton communities in the Funka Bay, southwestern Hokkaido: Insights from ZooScan analysis

“…Consequently, the numerically dominant small copepods reproduce, and growth takes place simultaneously in the biomass-dominant large copepods such as Neocalanus spp. (Yamaguchi & Shiga 1997, Shimada et al 2012, Arima et al 2014a, 2014b, Kitamura et al 2016. In this study, the numerically dominant taxa were "other Copepoda".…”

Temperature-dependent egg production and egg hatching rates of small egg-carrying and broadcast-spawning copepods Oithona similis, Microsetella norvegica and Microcalanus pusillus

“…Egg-producing females were present at least from March to August ( O. similis and M. pusillus ) and from May to August ( M. norvegica ) in Balsfjord, which is in accordance with the long reproductive periods described in previous studies ( Dvoretsky and Dvoretsky, 2009b ; Norrbin, 1991 ; Svensen et al., 2018 ). Small copepods do not accumulate large lipid reserves ( Arima et al., 2014 ; Norrbin, 1991 ), contrasting with larger diapausing, and sometimes capital-breeding, copepods ( Conover, 1988 ; Sainmont et al., 2014 ; Varpe et al., 2009 ). Smaller copepod species typically rely on continuous feeding to fuel their reproduction ( Norrbin, 1991 ; Svensen et al., 2019 ); i.e.…”