Latitudinal distribution of chaetognaths in winter along the 137°E meridian in the Philippine Sea

Abstract

Latitudinal distributions of pelagic chaetognaths from 3–34°N along the 137°E meridian in the Philippine Sea in winter from 1967 to 1995 were studied using the data of oceanographic observations by the Japan Meteorological Agency. Zooplankton was collected at almost every latitudinal degree in every winter (mid-January to early-February) by vertical hauls of a 0.33-mm mesh NORPAC net from 150-m depth. Twenty-six chaetognath species, including four mesopelagic species, were recorded. Flaccisagitta enflata was most abundant, comprising 25%, on average, of the chaetognath community, followed by Serratosagitta pacifica and Pterosagitta draco. The community structure was analyzed according to the following five areas along the survey line: Japan coast area (JC), Kuroshio Current area (KC), subtropical area (ST), North Pacific Equatorial Current area (NEC), and North Pacific Equatorial Counter Current area (NECC). The dominant species were S. pacifica and Mesosagitta minima in JC, Pseudosagitta lyra and Pt. draco in KC and ST, and F. enflata in NEC and NECC. The cluster analysis revealed that the community was generally more similar among the samples from the same area than those from different areas except for KC and ST, which were not separated into different cluster groups. This suggests that the chaetognath communities are location-specific. Multiple comparisons of the mean densities of 17 common species among these areas revealed six distribution types, i.e. JC type, JC-KC type, KC-ST type, NEC-NECC type, NECC types, and bimodal type. Possible mechanisms determining the distribution types, especially the bimodal distribution, are discussed in terms of environmental factors.