Ulva and its components as potential stimulants in aquaculture feeds: chemosensory response of a valuable sea urchin species 

Abstract

Ulva is close to becoming popular due to its suitability as potential feedstock production and for food items. However, there is a general lack of studies on the aversion or acceptability of this green alga by marine organisms, in particular on its role as a chemoattractant and/or phagostimulant activity. Here we tested the effect of Ulva and other biochemicals as potential chemostimulating compounds for a valuable sea urchin species Paracentrotus lividus, selected as model species for our tests. Sea urchins’ chemical sensitivity was estimated by the analysis of movements of spines, pedicellariae, tube feet, and individual locomotion, using an innovative bioassay. Our results showed that all forms of Ulva (fresh, defrosted, and fragmented) resulted in an effective stimulus, evoking in sea urchins strong responses with robust activation of spines and tube feet, where the defrosted one was the most stimulating. Among the amino acids tested, glycine, alanine, and glutamine produced a significant response, highlighting for the latter a concentration-response relationship. Sea urchins responded to glucose, not to fructose and sucrose. Spirulina resulted as the most effective stimulus, acting in a dose-dependent manner. These results first indicate the role of Ulva and its most representative compounds as chemostimulant for such herbivore species. From an applied point of view, the presence of potential Ulva's feed-related compounds, acting as chemoattractants (to reduce food searching time) and/or feeding stimulants (to stimulate ingestion), would improve the several applications of Ulva in the formulation of the feeds for sustainable aquaculture.