Immunostimulatory effect of diet (Laminaria digitata and Mytilus edulis) in the edible sea urchin, Paracentrotus lividus

The edible sea urchin, Paracentrotus lividus, is an Atlanto-Mediterranean species that is of commercial interest for its gonads in Europe and Pacific/Asian countries. Laminaria digitata, a common food source for sea urchins, contains known compounds, which are beneficial to numerous organisms. The objective of this study was to determine whether using L. digitata as a food source for P. lividus had an immunomodulatory effect on the sea urchin. This work was carried out in the context of planning for future trials to assess the impact of potential immunostimulants on the sea urchin's immune function. This algal food source was compared to an animal food source (Mytilus edulis) and a starved group over 28 days. Monitoring of a range of immune parameters in this study (nitric oxide production, lysozyme activity, cell viability, and differential cell counts) indicated that the main parameter that was impacted on by different diets was nitric oxide production. L. digitata as a food source for P. lividus had a more significant effect on nitric oxide levels of the experimental animals compared to an alternative food source (M. edulis) or the starved group. Viable cell counts (cell viability) were not significantly different between the different treatments over the study period. However, in an assessment of different coelomocyte types and relative levels, amebocyte levels peaked much more rapidly in mussel-fed urchins compared to kelp-fed animals. Amebocytes are the first mobilized defense mechanism responsible for clotting and encapsulation and can contain an antibacterial agent known as echinochrome. In conclusion, this study demonstrates that foodstuffs, particularly L. digitata, being provided to sea urchins may impact on immune parameters and so should be considered when similar trials are being planned or data are being analyzed.