In this study, antifouling and antibacterial properties of polar, semi polar and non-polar bioactive compounds derived from the sea cucumber Holothuria leucospilota were investigated. A series comprising n-hexane, ethyl acetate and methanol extracts from four different organs of sea cucumber (body wall, gonad, digestive tract and respiratory tree) were investigated for their antibacterial and antifouling activity against two species of microalgae, larvae of barnacle Amphibalanus amphitrite and a non-target organism: larvae of Artemia salina. Results showed that the highest antibacterial activity was found in the ethyl acetate extract of body wall against Staphylococcus aureus with minimum inhibitory concentration (MIC) of 0.250 mg/mL. The MIC of ethyl acetate extract of body wall ranged between 0.062 and 0.250 mg/mL against two microalgal strains. All extracts showed moderate to low toxicity against larvae of barnacles. The most pronounced anti-barnacle activity was found in the ethyl acetate extract of body wall with median lethal concentration (LC 50) value of 0.049 mg/mL. Among the twelve extracts, the ethyl acetate extracts of body wall showed the maximum antibacterial and antifouling activities. The bioactive compounds of the ethyl acetate extract of the sea cucumber body wall were determined using gas chromatography coupled with mass spectrometry. Fatty acids and terpenes were the major compounds, which may be responsible for antibacterial and antifouling activity of the ethyl acetate extract of body wall of the sea cucumber H. leucospilota.

An important challenge to decrease the toxic effects of the common biocides in marine environments and to achieve suitable ecofriendly natural antifouling coatings is to find effective natural antifoulants and efficient biodegradable coatings. In this study, antifouling activities of nine bioactive extracts (non-polar to polar) from different organs of the sea cucumber Stichopus herrmanni were tested against five bacterial strains, barnacle and brine shrimp larvae. The ethyl acetate extract of the body wall showed the highest in-vitro antifouling activity including high antibacterial and anti-barnacle activities and low toxicity against the brine shrimp as non-target organism. Based on these results, 10 phr of the ethyl acetate extract from S.herrmanni was added to different coatings consisting of polycaprolactone (PCL)/polylactic acid (PLA) blends containing various compositions of PLA (0, 10, and 20 wt.%). Polyvinyl chloride panels were coated with the prepared antifouling coatings and immersed in seawater for three months. Panel coated with PCL 80% /PLA 20% containing 10 phr of the antifoulant (panel-5), showed the highest resistance against fouling settlement with fouling coverage of 41.66% (P < 0.05). In addition, the lowest fouling weight was measured in panel-5 as well (81.00 ± 9.85 g) (P < 0.05). These findings indicate the antibacterial and antifouling potential of semi-polar bioactive extracts from the S. herrmanni body wall as natural antifoulants, as well as the enhanced antifouling performance of PCL/the natural antifoulant coatings by adding PLA. Graphical Abstract