Comparative study on the efficiency of two plankton nets for the quantitative estimation of appendicularians (Chordata, Tunicata)

Resumen

Appendicularians collected from a coastal station located at 5°S and 36°W, northeast Brazil, were studied. Eight daytime and eight night samples were collected from the 0-10 m layer. Two samples were taken simultaneously using 53 pm and 200 pm mesh plankton nets. Oikopleura cornutogastra, O. dioica, O. longicauda, and O. rufescens were the main species present in the samples. The efficiency of both nets was compared for the quantitative estimation of these species. All the appendicularians were classified into three maturity stages: immature, intermediate, and mature. Their densities were compared using a randomized complete blocks ANOVA design with net level as the main plot. Only immature O. dioica were underestimated when a 200 pm mesh net was used (P=0). Immature individuals of the remaining species were equally captured by both nets (P>0.05). O. longicauda and, to a lesser extent. O. dioica, were the dominant species. All samples showed a high proportion of immature animals, indicating an active reproduction of all the species.