**Acknowledgements**

A PhD fellowship (ref. SFRH/BD/62121/2009), supervised by author F.X.M., was granted to author H.M.A., under the auspices of ESF (III Quadro Comunitário de Apoio) and the Portuguese State. A postdoctoral fellowship (ref. SFRH/BPD/72777/2010), also supervised by author F.X.M., was granted to author A.C.G., under the auspices of ESF (III Quadro Comunitário de Apoio) and the Portuguese State. This work received partial financial support via projects OPTIC-ALGAE (PTDC/BIO/71710/2006) and MICROPHYTE (PTDC/EBB-EBI/102728/2008), both coordinated by author F.X.M., also under the auspices of ESF (III Quadro Comunitário de Apoio) and the Portuguese State. 
