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    Middle Caranum copepods

    •  Gaetanus variabilis

      粒子食性種:particle-eating species, 全長:full length

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    Life-history analysis of copepods

      • The life history of copepods (when born and when dead) is known for species distributed primarily in the surface layer (0-200 m).


      • On the other hand, there is little information on the life history of copepods distributed in the middle layer (200-1000 m depth).


      • Copepods, like other crustaceans, molts and grows. As the number of segments and legs increases with each molting, observing them reveals what stage of development of the species.

      • Neutral copepods levels of Gaetanus variabilis appearing in planktonnet samples collected stratified up to a depth of 2000 m were counted at each developmental stage.



      Life history schematic is provided by the American Marine Atmosphere Agency HP.



      Above is a picture of the North Prius 6th (N1-N6) and Copopodite 6th (C1-C6) of copepods's Eucalanus bungii dominated off the coast of Kushiro on the same scale. In planktonnet, C1-C6 are mainly collected. C4-C6 are divided into males and females according to their morphology.


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    Middle-Layer copepods Life History of Gaetanus variabilis (1)


    • 出現個体数:number of appearance individuals, 水深:water depth, 夜:night, 昼:daytime, 水温:water temperature, 表層クロロフィルa:Surface chlorophyll a, 全発育段階:all developmental stages

      Gaetanus variabilis was distributed at depths of 500-1000 m throughout the year. On the other hand, it was found that there is a seasonality in the number of individuals appearing at all stages of development. The difference in distribution depth between day and night was not clear. In the offshore Kushiro (Oyashio area) where we went for the survey, a clear bloom of phytoplankton occurred in the surface layer from April to June.　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

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    Middle-Layer copepods Life History of Gaetanus variabilis (2)

    •  表層クロロフィルa:surface Chlorophyll a, 出現個体数:number of appearance individuals, 雌個体に占める割合:proportion of female individuals, 雄個体に占める割合:proportion of male individuals, 予想産卵期:Expected spawning season







      Looking at the number of individuals appearing at each developmental stage, it can be seen that there are many C1 stages from June to August.

      A separate egg-nauplius rearing experiment revealed that it takes 51 days for egg hatching and nauplii development under the field environment.

      Taking these into account, it was found that the reproduction (egg laying) of this species almost coincided with the high season of chlorophyll a in the surface layer.


      Growth from C1 to C3 could be traced clearly.


      After C4, this species has different developmental times in both sexes, and females spend a long time in C6 (parental adult).


      Expediting a long time in the adult state of a female is an advantageous life history strategy in that it rapidly shifts to egg laying in response to an increase in the number of food particles settling from the surface layer.

    • [Open Access] Yamaguchi & Ikeda, 2000, Marine Biology URL
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    Gastrointestinal contents of mid-layer copepods Gaetanus variabilis


    • 中心目珪藻:Centroorder diatoms, 有鐘繊毛虫:Tintinnid, 珪質鞭毛虫:Silicoflagellate

      Gastrointestinal contents of female adults collected from 600-700 m water depths were predominantly occupied by surface-derived sediment particles.

    • Yamaguchi et al., 2007, La mer URL
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    Methods for observing gastrointestinal contents of copepods


    • 消化管内容物:gastrointestinal contents, 内容物が出る:contents come out, 上をなぞる:trace over, 片方を抑えて:hold one side, 内容物のみにした後に少しほぐす:After only the contents are loosened a little, 横より:from the side, 上より:from above, 後ろから取っていく:take from behind, 切る:cut, 腸管を傷つけないようにCephulosomeをはがす:Peel off the Cephulosome so as not to damage the intestinal tract, 走査型電子顕微鏡:Scanning electron microscope


      The digestive tract contents are desalted, filtered through a filter, dehydrated, and coated with gold before being observed by electron microscopy.

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    Vertical sedimentation trafficking and feeding and shedding of copepods

    • 水深:water depth, カイアシ類:Copepods, 摂餌:feeding, 排泄:excretion, 沈降粒子:sedimentation particles, 分解:decomposition, 消費:consumption,カイアシ類の摂餌:feeding of copepods
       














      Sedimented particles that have fallen into the 0-4000 m water depth pass through three paths in each of the eight water depths.

      One is direct settling (downward arrow),
      Second, consume by copepods (left arrow),
      The third is microbial degradation consumption (right arrow).

      A mean of 32% of the precipitated particles were found to be consumed by copepods in water depths of 0-4000 m.



    • Yamaguchi et al., 2002, Deep Sea Research Part I URL
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    Summary

      • The long time spent by females in their parental adulthood may be an advantageous life history strategy in that they are rapidly transferred to regeneration in response to increasing sedimentation particles from the superficial layer.

      • The main spawning period of deep-sea species coincided with the surface phytoplankton bloom, which was considered to reflect the fact that the supply of precipitated particles to the deep sea was large in the surface phytoplankton bloom period.

      • In this study, deep-sea species (Gaetanus variabilis) had different growth rates in males and females, and females spent a long time in parental adulthood.

      • The long time spent by females in their parental adulthood may be an advantageous life history strategy in that they are rapidly transferred to regeneration in response to increasing sedimentation particles from the superficial layer.

      • The long time spent by females in their parental adulthood may be an advantageous life history strategy in that they are rapidly transferred to regeneration in response to increasing sedimentation particles from the superficial layer.

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    【Related courses】

    Research Introduction Marine Biology