Chaetognath assemblages in Bahía de Banderas, Mexico

The composition, distribution, and main assemblages of chaetognath species were examined throughout an annual cycle in Bahía de Banderas, Mexico. Zooplankton sampling was carried out during five seasons (1989 and 1991), using a 50 cm diameter and 1.5 m long conical net with a 505 μm mesh size. The abundance of chaetognaths in each season was subjected to a Factor Correspondence Analysis (FCA) in order to identify the main assemblages. A total of 4142 individuals was sorted out from samples, and seven species were identified: Sagitta euneritica (Alvariño, 1961), Sagitta neglecta Aida, 1897, Sagitta inflata Grassi, 1881, Sagitta bedoti Béraneck, 1895, Sagitta pacifica (Tokioka, 1940), Sagitta minima Grassi, 1881, and Krohnitta pacifica (Aida, 1897). Sagitta euneritica was the most abundant and widely distributed species throughout the study area. The FCA defined two chaetognath groups, the "euneritic assemblage" and the "mixed assemblage," whose differences were established mainly by relative species abundance, rather than composition. For most of the year, the "euneritic assemblage" occupied the area over the shelf, possibly reflecting an area of high secondary production.