Bathymetric distribution of chaetognaths and their association with water masses off the coast of Valparaiso, Chile

The bathymetric distribution of chaetognaths was studied at an oceanic stat ion located 14 nautical miles off Valparaiso. During an annual cycle betwee n July 1994 and September 1995, vertical samples of plankton were taken bet ween 0 and 900 m depth. Temperature, salinity and dissolved oxygen showed t emporal and spatial fluctuations within the surface layer (0-100 m), mainly affected by Subantarctic Water and in certain periods by Subtropical Water . Between 150 and 400 m low dissolved oxygen content and higher salinity we re found, characteristic of Equatorial Subsurface Waters, and between 400 a nd 800 m Antarctic Intermediate Water, characterized by its higher content of dissolved oxygen and lower temperature and salinity was present. Fifteen species of chaetognaths were identified: Sagitta bierii, S. enflata, S, mi nima, S. pacifica, S. lyra, S. planctonis, S. marri, S. macrocephala, S. ma xima, S. decipiens, S. tasmanica, S. gazellae, Krohnitta subtilis, Eukrohni a hamata and E. fowleri. The most abundant and frequent species were Sagitt a enflata, S. bierii and Eukrohnia hamata. The greatest density of chaetogn aths was confined to the 0-200 m water column and the species diversity gra dually decreased from the epiplanktonic to the mesoplanktonic domain. The v ertical distribution of the chaetognaths showed a strong association with t he water masses present. The epipelagic species (0-200 m) S. enflata, S. bi erii, S. minima and Krohnitta subtilis are associated mainly with Subantarc tic Water and occasionally with Subtropical Water; the mesopelagic species (200-1000 m) S. lyra, S. planctonis, S. macrocephala, S. marri and E. fowle ri are associated with Equatorial Subsurface Water and Antarctic Intermedia te Water. There is another species assemblage of broad bathymetric distribu tion (0-900 m) consisting of E. hamata, S. decipiens and S. maxima, which d oes not show a distinctive association with a given water mass. E hamata is an indicator species of upwelling events off the Chilean coast, showing an association with waters of low temperatures, greater salinity, and low con tents of dissolved oxygen, which are characteristic of Equatorial Subsurfac e Water. (C) 2000 Elsevier Science Ltd. All rights reserved.