Seasonal abundance, population structure, sex ratio and gonad maturation of Metridia okhotensis Brodsky, 1950 in the Okhotsk Sea: analysis of samples collected by pumping up from deep water
In: CrustaceanaIn the Okhotsk Sea, the calanoid copepod Metridia okhotensis Brodsky, 1950 is the dominant component of zooplankton, accounting for 61% of the annual mean total pelagic copepods. Although this organism is important, little ecological information is available for M. okhotensis in the Okhotsk Sea because of the ice cover during winter, which prevents the collection of seasonal samples in this region. Here, we report the seasonal changes in the population structure, sex ratio and female gonad maturation of M. okhotensis. The data are from samples collected using water pumped from a depth of 350 m off Rausu Harbour in the Okhotsk Sea at 2-week intervals over a 2.5-year period. Due to the mesh size of the strainer (420 μm), M. okhotensis was collected from C3 to adults. The sex ratio of C5 (female : male) was approximately 1 : 1 throughout the year. In contrast, the sex ratio of C6 (adult) showed a clear seasonality, with males (C6M) occurring only from December to May and females (C6F) dominating during the other seasons. The gonad maturation of C6F was scored using five categories, and their composition also showed clear seasonality. From January to April, gonads developed rapidly from stage I (immature) to V (spawning). During the other seasons, the majority of C6F had immature gonads. Based on these data, we conclude that this species likely has a diapause phase for C6F, with immature gonads, and C5M from June to November. Moulting from C5M to C6M began in December. Accompanying the occurrence of C6M, C6F were fertilized from December to January. C6F underwent gonad maturation from January to April and performed primary reproduction from April to May. Thereafter, M. okhotensis entered diapause from June to November.
Dans la mer d’Okhotsk, le copépode calanoïde Metridia okhotensis est le composant dominant du zooplancton et représente 61% de la moyenne annuelle des copépodes pélagiques. Bien que cet organisme soit important, peu d’informations écologiques sont disponibles sur M. okhotensis dans la mer d’Okhotsk en raison de la couverture de glace durant l’hiver, qui empêche la collecte d’échantillons en toutes saisons dans cette région. Nous rapportons ici les changements saisonniers de la structure de la population, du sex-ratio, et de la maturation des gonades femelles de M. okhotensis. Les données ont été obtenues à partir d’échantillons collectés par pompage à une profondeur de 350 m au large du port de Rausu dans la mer d’Okhotsk, à des intervalles de deux semaines au cours d’une période de deux ans et demi. En raison du vide de maille utilisé (420 μm) pour la filtration, M. okhotensis a été récolté du stade C3 au stade adulte. Le sex-ratio des C5 (femelle : mâle) était approximativement de 1 : 1 tout au long de l’année. En revanche, le sex ratio des C6 (adultes) a montré une saisonnalité évidente, avec des mâles (C6M) présents seulement de décembre à mai et des femelles (C6F) dominantes aux autres saisons. La maturation des gonades des C6F a été classée en cinq catégories, et leur composition a montré aussi une saisonnalité nette. De janvier à avril, les gonades se développaient rapidement du stade I (immature) à V (reproduction). Au cours des autres saisons, la majorité des C6F présentaient des gonades immatures. Selon ces données, cette espèce avait probablement une phase de diapause chez les C6F avec des gonades immatures, et chez les C5M de juin à novembre. La mue de C5M à C6M a commencé en décembre. En présence des C6M, les C6F étaient fécondées de décembre à janvier. Les C6F réalisaient la maturation de leurs gonades de janvier à avril, puis la première reproduction d’avril à mai. Ensuite, M. okhotensis entrait en diapause de juin à novembre.
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| All Time | Past Year | Past 30 Days | |
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Seasonal abundance, population structure, sex ratio and gonad maturation of Metridia okhotensis Brodsky, 1950 in the Okhotsk Sea: analysis of samples collected by pumping up from deep water
In: CrustaceanaIn the Okhotsk Sea, the calanoid copepod Metridia okhotensis Brodsky, 1950 is the dominant component of zooplankton, accounting for 61% of the annual mean total pelagic copepods. Although this organism is important, little ecological information is available for M. okhotensis in the Okhotsk Sea because of the ice cover during winter, which prevents the collection of seasonal samples in this region. Here, we report the seasonal changes in the population structure, sex ratio and female gonad maturation of M. okhotensis. The data are from samples collected using water pumped from a depth of 350 m off Rausu Harbour in the Okhotsk Sea at 2-week intervals over a 2.5-year period. Due to the mesh size of the strainer (420 μm), M. okhotensis was collected from C3 to adults. The sex ratio of C5 (female : male) was approximately 1 : 1 throughout the year. In contrast, the sex ratio of C6 (adult) showed a clear seasonality, with males (C6M) occurring only from December to May and females (C6F) dominating during the other seasons. The gonad maturation of C6F was scored using five categories, and their composition also showed clear seasonality. From January to April, gonads developed rapidly from stage I (immature) to V (spawning). During the other seasons, the majority of C6F had immature gonads. Based on these data, we conclude that this species likely has a diapause phase for C6F, with immature gonads, and C5M from June to November. Moulting from C5M to C6M began in December. Accompanying the occurrence of C6M, C6F were fertilized from December to January. C6F underwent gonad maturation from January to April and performed primary reproduction from April to May. Thereafter, M. okhotensis entered diapause from June to November.
| All Time | Past Year | Past 30 Days | |
|---|---|---|---|
| Abstract Views | 186 | 36 | 2 |
| Full Text Views | 158 | 1 | 0 |
| PDF Views & Downloads | 13 | 2 | 0 |