Small copepods matter: population dynamics of Microsetella norvegica in a high-latitude coastal ecosystem

Abstract

We investigated the population dynamics of a small and little-studied harpacticoid copepod, Microsetella norvegica, in a sub-Arctic Norwegian fjord (Balsfjord 69°N). We sampled with a 90 μm mesh WP-2 net and a 20 L Go-Flo bottle and found that the WP-2 under-sampled all juvenile stages. The abundance and biomass were high, peaking in June with 9349 × 10³ ind. m⁻² and 1678 mg C m⁻². Microsetella were most abundant in the surface, but females and males demonstrated a distinct migration to below 50 m from October to March. Consistently, individual female body carbon content was highest in October (0.39 μg C ind⁻¹) and lowest in March (0.18 μg C ind⁻¹). Males were present throughout the year, and females with eggs were found from April to September. The average clutch size was 11 ± 2 eggs female⁻¹, and our study supports the observation that females can release their egg sac before the eggs have hatched, possibly to produce a new one. With its high abundance and biomass, a flexible reproductive strategy and specialized feeding preferences, M. norvegica is likely a key species in high-latitude coastal ecosystems.