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

Coralie Barth-Jensen,Marja Koski,Owen S Wangensteen,Camilla Svensen,Kim Præbel,Peter Glad,Øystein Varpe

doi:10.1093/plankt/fbaa039

Abstract

Reproductive rates of copepods are temperature-dependent, but poorly known for small copepods at low temperatures, hindering the predictions of population dynamics and secondary production in high-latitude ecosystems. We investigated egg hatching rates, hatching success and egg production of the small copepods Oithona similis and Microsetella norvegica (sac spawners) and Microcalanus pusillus (broadcast spawner) between March and August. Incubations were performed at ecologically relevant temperatures between 1.3 and 13.2°C, and egg production rates were calculated. All egg hatching rates were positively correlated to temperature, although with large species-specific differences. At the lowest temperatures, M. pusillus eggs hatched within 4 days, whereas the eggs from sac spawners took 3–8 weeks to hatch. The egg hatching success was ≤25% for M. pusillus, >75% for O. similis and variable for M. norvegica. The maximum weight-specific egg production rate (μg C μg−1 C d−1) of M. pusillus was higher (0.22) than O. similis (0.12) and M. norvegica (0.06). M. norvegica reproduction peaked at 6–8°C, the prevailing in situ temperatures during its reproductive period. The difference in reproductive rates indicates species-specific thermal plasticity for the three copepods, which could have implications for present and future population dynamics of the species in arctic fjords.

Highlights

Small copepods, such as the cosmopolitan Oithona spp., are numerically abundant (Ormanczyk et al, 2017; Poulsen and Kiorboe, 2006; Schnack-Schiel, 2001; Zamora-Terol et al, 2013), and can seasonally dominate copepod biomass at high latitudes (Arendt et al, 2013; Svensen et al, 2011)
We investigated the temperature-dependent responses of reproductive rates in O. similis, M. norvegica and M. pusillus, expecting that egg hatching rates of the three species will increase with temperature within their tolerance range
We provide egg hatching rate and egg hatching success data for three small and abundant copepod species

Summary

Introduction

Small copepods, such as the cosmopolitan Oithona spp., are numerically abundant (Ormanczyk et al, 2017; Poulsen and Kiorboe, 2006; Schnack-Schiel, 2001; Zamora-Terol et al, 2013), and can seasonally dominate copepod biomass at high latitudes (Arendt et al, 2013; Svensen et al, 2011) They are an important food source for early larval stages of fish and carnivorous zooplankton, and can serve as an alternative or complementary carbon source for older larval stages (Castellani et al, 2007; Grønkjær et al, 2018; Turner, 2004). Small copepods tend to have increased production in warmer and more stable surface waters (Coyle et al, 2008; Mäkinen et al, 2017)

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