Distribution and trophic ecology of chaetognaths in the western Mediterranean in relation to an inshore-offshore gradient

Abstract

This study examines the distribution patterns and feeding ecology of chaetognaths in the Catalan Sea in relation to mesoscale features along an inshore-offshore gradient. The study was conducted during two different periods of the year: late spring of 1995 and late summer of 1996. The two periods differed in hydrographic conditions and mesoscale processes, which affected the distribution patterns of the different species of chaetognaths found. The diet of the chaetognaths was mainly composed of copepods and differed between species. Prey size was not always strongly related to chaetognath size and for certain species, there was an overlap in prey size spectrum. Trophic niche breadth (on a ratio scale) appeared to be constant with growth. Ingestion rates and predation pressure by chaetognaths did not follow a clear trend related to the mesoscale features in the area, such as the presence of a density front. The impact of chaetognaths on copepod standing stock appeared to be extremely low (<1%), but it became more relevant when the species and prey size specificity of the chaetognaths was taken into account.