Utility of salps as a baseline proxy for food web studies
Résumé
In recent years, pelagic tunicates (mostly salps, but potentially doliolids, appendicularians and pyrosomes as well)have been used in isotopic studies as a baseline consumer (trophic position 2) when recreating food web dynamicsto overcome the challenges of using particulate organic matter (POM). While pelagic tunicates are continuous filterfeeders, recent evidence has shown that they have selective feeding behaviors, and preferentially assimilate certainparticles. In this review, we combine available stable isotope data for POM and pelagic tunicates and identify thattrophic enrichment in 13C and 15N relative to POM is highly variable, and suggests tunicates prefer to consumesmaller, heterotrophic organisms. Here we propose that it is not appropriate to consider pelagic tunicates as representativefirst level consumers in the classical pelagic food web in stable isotope analyses. Rather it needs acknowledgmentthat they are members of the microbial food web, and thus reflect an alternate food chain.