LAUSR

Simple Summary Sea urchins are key in the trophic cascades of benthic communities. They also possess physiological characteristics of low digestibility. Thus, we explored the relationship between the indicators (digestive enzymes activities and the gut emptying) and molecules (TRPA1 and 5-HT) related to digestive physiology in the sea urchin Strongylocentrotus intermedius. The results in the present study indicate that digestive enzyme activities and gut emptying are correlated with the TRPA1 and 5-HT in the gut of S. intermedius. This novel finding not only is important for understanding the low food digestibility of sea urchins but provides an entry point to further investigate the molecular details of digestive physiology of sea urchins. Abstract The energetic link in the benthic community is based on physiological characteristics of the low food absorption efficiency of sea urchins. Low food absorption efficiency of sea urchins is correlated with the activity of digestive enzymes and the duration of food in their gut. Thus, the digestive enzymes activities (pepsin and amylase enzyme activities) and gut emptying are important indicators in assessing nutrient digestion and absorption in sea urchins. In the present study, the relationship between these indicators and molecules related to digestive physiology were quantified in sea urchins. We found (1) an inter-regulatory relationship existed between Transient receptor potential cation channel, subfamily A, member 1 (TRPA1), and serotonin (5-hydroxytryptamine; 5-HT) in the gut of Strongylocentrotus intermedius; (2) digestive enzyme activities were negatively correlated with the TRPA1 and concentration of 5-HT in the gut of S. intermedius; (3) gut emptying rate was positively correlated with TRPA1 and concentration of 5-HT in the gut of S. intermedius. The present study revealed that the digestion and absorption of food are correlated with the TRPA1 and 5-HT in the gut of S. intermedius, which provides valuable information about the digestive physiology of sea urchins. This novel finding is relevant to understanding the low food digestibility of sea urchins. It also provides valuable information to the digestive physiology of sea urchins, which are key to maintaining the stability of food webs in the marine ecosystem.