ORIGINAL ARTICLE Terpenes from the Red Alga Sphaerococcus coronopifolius Inhibit the Settlement of Barnacles Veronica Piazza & Vassilios Roussis & Francesca Garaventa & Giuliano Greco & Vangelis Smyrniotopoulos & Constantinos Vagias & Marco Faimali Received: 16 October 2009 / Accepted: 30 November 2010 # Springer Science+Business Media, LLC 2010 Abstract In this study, we screened eight terpenes isolated from the organic extract of Sphaerococcus coronopifolius for their antifouling activity in order to find possible new sources of non-toxic or less toxic bioactive antifoulants. The anti-settlement activity (EC 50 ) and the degree of toxicity (LC 50 ) of S. coronopifolius metabolites was evaluated using larvae of the cirriped crustacean Amphibalanus (Balanus) amphitrite (cyprids and nauplii) as model organism. For five of eight tested metabolites EC 50 was lower than 5 mg/L. The most promising results were observed for bromos- phaerol (3), which expressed an EC 50 value of 0.23 mg/L, in combination with low toxicity levels (LC 50 >100 mg/L). The therapeutic ratio—an index used to estimate whether settlement inhibition is due to toxicity or other mechanisms— is also calculated and discussed. Keywords Antifouling . Marine natural products . Barnacle . Sphaerococcus coronopifolius Introduction Marine fouling affects a wide range of human activities in the aquatic environment and, especially in shipping, it is associated with economic loss due to speed reduction and higher costs both for fuel and for hull maintenance. Technological problems related to biofouling and methods for protecting surfaces have been widely discussed in the past few years (Omae 2003; Yebra et al. 2004; Chambers et al. 2006). The majority of vessels are protected by antifouling paints containing biocides (Almeida et al. 2007); the key property of a good antifouling biocide with respect to the environment is to be effective in preventing fouling, without causing persisting adverse environmental effects. The effects and behaviour of biocides used in antifouling paints have been extensively studied and the related data are available (see reviews: Thomas 2001; Thomas and Brooks 2010). Currently, a wide range of chemicals are used as antifouling biocides, governed by different regulations, depending on the legislation in each country. Copper, copper pyrithione, zinc pyrithione, TPBT, diuron, SeaNine 211, Irgarol 1051, chlorothalonil, cuprous thyocianate, Ziram, Zineb, naphthenic acid copper salts, tolyfluanid, Econea and capsaicin are just a few of the antifoulants in use. Nowadays, marine antifouling technology is at a crossroads: in September 2008, IMO banned the use of self-polishing tributyltin coatings, while there is an increasing opposition to the use of copper. Silicone-based fouling release technologies are providing an alternative solution, however they are relatively expensive and can be easily damaged (Swain et al. 2007). Preventing the settlement of fouling organisms in a non- toxic manner is the ideal solution; it is therefore necessary to investigate new avenues, which may be inspired by a biomimetic approach, studying structures and functions of biological systems as models for the design of antifouling solutions. Much effort has been directed to identify natural chemistries that may act as antifoulants (Pawlik 1992; Abarzua et al. 1999; Rittschof 2001; de Nys and Steinberg 2002; Burgess et al. 2003; Ralston and Swain 2009). In the V. Piazza (*) : F. Garaventa : G. Greco : M. Faimali Institute of Marine Science (ISMAR) CNR, via De Marini 6, 16149 Genoa, Italy e-mail: veronica.piazza@ge.ismar.cnr.it V. Roussis : V. Smyrniotopoulos : C. Vagias Department of Pharmacognosy and Chemistry of Natural Products, School of Pharmacy, University of Athens, Panepistimiopolis Zografou, Athens 15771, Greece Mar Biotechnol DOI 10.1007/s10126-010-9337-4