molecules Article Chemical Defense Mechanisms and Ecological Implications of Indo-Pacific Holothurians Elham Kamyab 1,* , Sven Rohde 1 , Matthias Y. Kellermann 1 and Peter J. Schupp 1,2,* 1 Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl-von-Ossietzky University Oldenburg, Schleusenstrasse 1, 26382 Wilhelmshaven, Germany;
[email protected] (S.R.);
[email protected] (M.Y.K.) 2 Helmholtz Institute for Functional Marine Biodiversity, University of Oldenburg, Ammerländer Heerstrasse 231, D-26129 Oldenburg, Germany * Correspondence:
[email protected] (E.K.);
[email protected] (P.J.S.); Tel.: +49-4421-944-100 (P.J.S.) Academic Editor: David Popovich Received: 14 August 2020; Accepted: 13 October 2020; Published: 19 October 2020 Abstract: Sea cucumbers are slow-moving organisms that use morphological, but also a diverse combination of chemical defenses to improve their overall fitness and chances of survival. Since chemical defense compounds are also of great pharmaceutical interest, we pinpoint the importance of biological screenings that are a relatively fast, informative and inexpensive way to identify the most bioactive organisms prior to further costly and elaborate pharmacological screenings. In this study, we investigated the presence and absence of chemical defenses of 14 different sea cucumber species from three families (Holothuriidae, Stichopodidae and Synaptidae) against ecological factors such as predation and pathogenic attacks. We used the different sea cucumber crude extracts as well as purified fractions and pure saponin compounds in a portfolio of ecological activity tests including fish feeding assays, cytotoxicity tests and antimicrobial assays against environmental pathogenic and non-pathogenic bacteria.