Vertical distribution of pelagic chaetognaths and feeding of Sagitta enflata in the Central Equatorial Pacific

ISSN： 1464-3774

Source： Journal of Plankton Research, Vol.18, Iss.5, 1996-05, pp. : 673-682

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Abstract

The vertical distribution and feeding of pelagic chaetognaths at 5°S, 160°W in the Central Equatorial Pacific were investigated using a series of 0–500 m vertical hauls with a VMPS net over a 24 h period between 6 and 7 October 1990. The total number of individuals per haul was between 370 and 688. Fourteen species in four genera were found at this station. The most abundant species was Sagitta enflata which comprised 32.4–61.1% of the individuals collected from the 0–500 m layer. Mesopelagic species made up 9.3–15.1% of the total number of individuals. Sagitta enflata and Pterosagitta draco were found in the upper part of the thermocline both by day and at night. The fraction of the population containing food items (FCF) of S.enflata in the 0–50 m layer varied between 4.8 and 12.5% (mean 10.8%) and feeding activity was highest between sunrise and noon. The percentages of Copepoda, Foraminifera, crustacean larvae, Chaetognatha, Pteropoda, Ostracoda, fish and unidentified material in the gut of S.enflata were 51.9,6.7,3.8,2.9,1.9,1.9 and 30.9%, respectively. Sagitta enflata consumed food organisms which were mainly between 0.5 and 1.0 mm in length. The daily feeding rate of S.enflata was 1.81 prey per individual, which was equivalent to 8.06 mg C m⁻² day⁻¹. This corresponded to ∼7.9% of the daily secondary production in the Central Equatorial Pacific.