Influence of competitors on sterol production by the sponge Desmapsamma anchorata, in the marine community of Bananal in Baía da Ilha Grande (RJ) B. A. Fernandes, Y C.S.F. Vançato, J. M.T. Santos, M. R. Marques, B. G. Fleury

Abstract

Marine natural products are chemical substances originating from numerous organisms, and are generally involved in chemical defense processes. Among them, the poriferous Desmapsamma anchorata stands out , known for producing several secondary metabolites. However, these substances can vary within the same species, according to the biotic and abiotic characteristics of the habitat. In this way, 5 colonies of D. anchorata from the Bananal locality, in Ilha Grande Bay (RJ), were used in this study for intrapopulation evaluation of the variation in the production of the sterol stigmasterol, in relation to its competitors for space. The dried colonies were extracted, with the help of ultrasound, with the organic solvent methanol for subsequent analysis. The community surrounding the D. anchorata colonies were evaluated by photography using the CPCe 4.1 software, while the production of this sterol, in organic extracts, was analyzed semi-quantitatively by gas chromatography coupled to high-resolution mass spectrometry. Benthic communities around D. anchorata colonies were predominantly composed of 37.4% zoanthid Palythhoa caribaerum and 25.6% mat-forming algae. The average stigmasterol concentration was 19.4% in D. anchorata colonies. Regression analyzes of stigmasterol concentration and the most abundant benthic organisms were performed. Only the percentage of P. caribaerum coverage showed a significant positive relationship (p=0.03) with the abundance of stigmasterol produced by D. anchorata. Sterols are structurally present in all living beings, and can also act directly in the defense of organisms. P. caribaeorum is considered a major competitor for space and can affect the growth of sessile organisms around it, including corals and sponges. The positive relationship between stigmasterol concentration in D. anchorata and the abundance of P. caribaeorum may indicate the production of chemical defense by the sponge in competition with this zoanthid.