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Life-History Traits of a Small Cosmopolitan Copepod (Oithona similis) in the Barents Sea: A Review
Murmansk Marine Biological Institute of the Russian Academy of Sciences (MMBI RAS), 183038 Murmansk, Russia
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Biology 2026, 15(1), 27; https://doi.org/10.3390/biology15010027 (registering DOI)
Submission received: 20 October 2025
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Revised: 17 December 2025
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Accepted: 19 December 2025
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Published: 23 December 2025
(This article belongs to the Special Issue Feature Papers in 'Conservation Biology and Biodiversity' (2nd Edition))
Simple Summary
This review highlights the important role of the small copepod Oithona similis in the Arctic ecosystem, particularly in the Barents Sea amid ongoing warming. Oithona similis is a common planktonic species whose abundance and biomass vary across different water masses, with notable populations in coastal and Arctic waters. Despite contributing less to overall zooplankton biomass compared to other copepods, it can still represent a significant portion during certain seasons. Its reproductive activity and morphological characteristics differ regionally, influenced by environmental factors such as temperature, salinity, and chlorophyll levels. The species exhibits distinct populations across the southern, central, and northern parts of the sea, each with unique life cycle durations and reproductive patterns. The highest mortality rates occur in summer, driven by predation, parasitism, and competition. These findings underscore the species’ adaptability and the influence of environmental conditions on its biology. Understanding these dynamics is crucial, as Oithona similis plays a vital role in the Arctic food web, and its responses to climate change may have significant ecological implications in this rapidly changing region.
Abstract
This review synthesizes current knowledge on the biology and ecology of the small cyclopoid copepod Oithona similis, a prevalent planktonic species in the Barents Sea, during the period of Arctic warming since the early 2000s. The region serves as an effective model system for examining the influence of different water masses on Arctic zooplankton dynamics. The highest abundances and biomass of Oithona similis are observed in Murmansk Coastal Waters (MCW) and Arctic Waters (ArW). Although its contribution to total zooplankton biomass is generally lower than that of higher copepod taxa, it can account for up to 27–35% seasonally and regionally. Ovigerous females are most abundant in Novaya Zemlya Waters (NZW) and ArW. Egg production rates exhibit a decreasing trend from south to north across the sea. Morphometric analyses reveal an increase in prosome length for both sexes, while relative antenna size diminishes from the south (MCW) to the north (ArW). The highest mortality rates occur during summer, coinciding with peak abundances of Oithona similis, its predators, and parasites, as well as increased interspecific competition. Based on morphological and reproductive parameters, three distinct populations are delineated within the Barents Sea: southern (MCW), central (Atlantic Water/Barents Sea Water), and northern/eastern (ArW/NZW), with respective life cycle durations of 11–12, 9–10, and 11 months, and typically one to two generations per year. The primary environmental drivers influencing population abundance, biomass, size, and reproduction are temperature and salinity, while chlorophyll a concentration predominantly affects mortality rates.
