Ensilage of seaweeds from an integrated multi-trophic aquaculture system

Abstract

This study aimed to evaluate the feasibility of ensiling preservation of three seaweed species (Gracilaria vermiculophylla, Ulva rigida and Saccharina latissima) produced in an integrated multi-trophic aquaculture system without or with a lactic acid bacteria inoculant after 24–48hours wilting. The course of silage fermentation for a storage period up to nine weeks was also studied. The characteristics of fresh seaweeds suggested ensiling to be challenging. Overall, seaweeds presented a pH above 7.0, low dry matter (DM) content, and a non-structural polysaccharides content (DM basis) ranging from 14% (U. rigida) to 43% (S. latissima). The highest buffering capacity was recorded for U. rigida while the fermentation coefficient was higher for S. latissima, lower for U. rigida, and intermediate for G. vermiculophylla. The ensiling of S. latissima resulted in a pronounced lactic acid formation and a lower pH in comparison to the red and green seaweed silages. The ensilage of U. rigida and of G. vermiculophylla failed to decrease pH below 5.0 up to nine weeks, fermentation products suggesting the occurrence of a heterolactic fermentation or the promotion of heterofermentative bacteria and clostridia growth, respectively. The use of a lactic acid bacteria inoculant prior to ensiling had only minor effects on fermentation. Composition of seaweeds was generally preserved by ensilage, but in vitro digestibility of G. vermiculophylla was severely reduced. More research is needed to test different inoculants and dosages, and to assess the effects of seaweed silages on animal feed intake and performance.