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

This study examines the distribution patterns and feeding ecology of chaeto gnaths in the Catalan Sea in relation to mesoscale features along an inshor e-offshore gradient. The study was conducted during two different periods o f the year: late spring of 1995 and late summer of 1996. The two periods di ffered in hydrographic conditions and mesoscale processes, which affected t he distribution patterns of the different species of chaetognaths found. Th e diet of the chaetognaths was mainly composed of copepods and differed bet ween species. Prey size was not always strongly related to chaetognath size and for certain species, there was an overlap in prey size spectrum. Troph ic niche breadth ton a ratio scale) appeared to be constant with growth. In gestion 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 ap peared to be extremely low (<1%), but it became more relevant when the spec ies and prey size specificity of the chaetognaths was taken into account.