Sea cucumbers reduce nitrogen, bacteria and transparent exopolymer particles in Anemonia sulcata aquaculture tanks

Traditional aquaculture produces wastewater with high nutrient and organic matter concentrations. Poly‐culture can improve this problem including “extractive species” such as sea cucumbers along with the primary species. The influence of sea cucumbers on transparent exopolymer particles (TEP) (i.e. biofilm precursors) has not been previously explored. Here, we monitored during 1 year the concentration of nutrients, total organic carbon (TOC), particulate organic matter (POM), TEP, chlorophyll‐a and bacteria in two tanks of 50,000 L. One tank only contained Anemonia sulcata, whereas the other tank also included holothurians. To complement these time‐series, we performed three short‐term experiments in smaller (300 L) tanks. Three tanks contained A. sulcata plus Holothuria tubulosa (+H treatment) and other four tanks contained only A. sulcata (−H treatment). In the time‐series, we found that the concentration of ammonium, nitrate, TOC, POM, TEP and bacteria in the effluent of the tank with holothurians was lower than in the effluent of the tank without holothurians. The three experiments confirmed that the holothurians reduced significantly nitrates, bacterial abundance and TEP concentration. Therefore, these invertebrates can control bacterial proliferation and prevent biofilm formation minimizing likely the risk of outbreak of pathogenic bacteria and improving the hygiene of the tanks.