Smooth cordgrass (Spartina alterniflora), a potential food source for Apostichopus japonicus

The sea cucumber (Apostichopus japonicus) is becoming one of the most important fishery resources in Asia. Spartina alterniflora is a common invasive plant in China, that has not been effectively controlled or utilized. Some studies have shown that the organic detritus of S. alterniflora can be used by benthic animals. This study investigated the effects of the addition of S. alterniflora in the diet of juvenile A. japonicus on growth performance, digestive enzyme activity, non-specific immunity and gut microbiota. Powdered S. alterniflora and Sargassum polycystum were mixed in five proportions (0,100, 25,75; 50:50; 75:25; 100:0) along with muddy sediment (60% of total food) to create five different experimental diets for sea cucumbers. The results showed that specific growth rates (SGRs) improved with the addition of S. alterniflora, but did not increased with the increasing proportion of S. alterniflora. The increase in the ratio of S. alterniflora also improved the food conversion efficiency (FCE) of A. japonicus. The cellulase activity was highest in P20 group, which is a mixture of 20% S. alterniflora, 20% S. polycystum and 60% muddy sediment. Non-specific immune enzyme activity was not altered by the addition of S. alterniflora. In addition, the addition of S. alterniflora reduced the abundance of pathogenic bacteria and increased the abundance of bacteria associated with the degradation of high-molecular carbohydrates. The results of this study indicated that S. alterniflora could be a potential food source for A. japonicus and might be beneficial to A. japonicus growth. The findings of this study are important for the development of suitable feed for A. japonicus and the management and utilization of invasive plants.