Summer vertical distribution of appendicularians in the central Cantabrian Sea (Bay of Biscay)

Abstract

The summer vertical distribution of appendicularian species was analysed at 22 stations in the central Cantabrian Sea by means of vertical tows covering the surface, thermocline and deep layers. According to their preference for shallower waters, the appendicularian species could be arranged on the series Oikopleura longicauda (Vogt), Oikopleura fusiformis (Fol), Fritillaria pellucida (Quoy & Gaimard) and Oikopleura rufescens (Fol), with Oikopleura dioica (Miiller) in an uncertain position, probably closer to the end of this series. Principal components and correlation analyses suggest that a temperature gradient causes this pattern, which agrees with previous findings made at very different temporal and spatial scales. By means of particle-size spectra, it is shown that those oikopleurids that prefer cold, deep waters, O. fusiformis and O. rufescens, co-vary with a coefficient of particle-size quality. The lower the temperature, the lower the proportion of small, ingestible particles to large inlet-filter-clogging particles. This is proposed as an important reason for the presence of inlet filters in oikopleurids.