Chemical composition and energy content of deep-sea calanoid copepods in the Western North Pacific Ocean

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Condition factor index [CFI=1000×DW/(PL)3; DW: dry weight, PL: prosome length],water content, carbon (C), nitrogen (N), ash and energy content were determined on atotal of 69 copepod species caught from the mesopelagic (500-1000 m),upper-bathypelagic (1000-2000 m), lower-bathypelagic (2000-3000 m) andabyssopelagic (3000-5000 m) zones of the western subarctic Pacific. Resultant datawere grouped into these four sampling zones, four developmental stage/sex categories(C4, C5 and C6 females and males), three feeding types (carnivore, detritivore andsuspension feeder), or two reaction speed groups by the presence/absence of myelinatedsheath enveloping axons (fast and slow reacting species). Zone-structured datashowed the overall ranges were 3.8-4.6 mm for PL, 1.6-2.6 mg for DW, 21.4-25.0 forCFI, 75.0-78.6% of wet weight (WW) for water, 51.3-53.7% of DW for C, 7.7-8.8% ofDW for N, 6.2-7.0 (by weight) for C/N, 6.9-9.6% of DW for ash and 25.3-27.4 J mg-1DW for energy. Among these components, N and ash exhibited significantbetween-zone differences characterized by gradual decrease downward for the former,and only the upper-bathypelagic zone > abyssopelagic zone for the latter.Stage/sex-structured data showed no significant differences among them, but energycontent of C5 was higher than that of C6 females. From the analyses of feedingtype-structured data, carnivores were shown to have lower water, N, ash, but higher C,C/N and energy contents than suspension feeders do. Reaction speed-structured dataindicated that slow-reacting species have significantly higher water but lower CFI, C, Nand energy contents than fast-reacting species. Designating these grouping criteria, PLand DW as independent variables, the attributes of these variables to the CFI, chemicalcomposition or energy contents were evaluated by stepwise-multiple regression analysis,showing the most pronounced effect of suspension-feeder, followed by the presence ofmyelinated sheath, DW, C6 females and the abyssopelagic zone. Further analysis ofzone-structured data, by adding epipelagic copepod data from identical thermal habitats(Arctic/Antarctic waters), revealed a more marked decline in N content from theepipelagic zone to the abyssopelagic zone, accompanied by an increase in C/N ratiosdownward. The decline in N (=protein or muscle) contents with depth cannot be explained by the "visual interactions" hypotheses being proposed for the metabolism ofpelagic visual predators, but is consistent with the "predation-mediated selection"hypothesis for the metabolism of pelagic copepods.
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Chemical composition and energy content of deep-sea calanoid copepods in the Western North Pacific Ocean

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