As pointed out in Chap. 1, a variety of options for producing biofuels from marine biomass have been suggested, such as biofuels from Macrocystis pyrifera or giant kelp (Wilcox 1982; Bungay 2004), Laminaria (Hornetal. 2000; Chopin etal. 2001) and Dunaliella (Ben-Amotz et al. 1982). Dunaliella has been found more suitable to cultivation in open ponds (Joint et al. 2002; Ugwu et al. 2008). As to Macrocystis pyrifera, it seems doubtful whether the energy balance for biofuel can be positive (Bungay 2004).

Near-shore cultivation of macroalgae is substantial (Neushul and Wang 2000; Wikfors and Ohno 2001; Chopin et al. 2001; Critchley et al. 2006; Troell et al.

2006) . For Gracilaria in Taiwanese coastal waters, average yields of 4Mgha-1 year-1 (dry weight) have been reported (van der Meer 1983). Yields of commer­cial Eucheuma cultivation in the Philippines, Indonesia and Kiribati are about 6 Mg (dry weight) ha-1 year-1 (Ask and Azanza 2002). Such yields suggest relatively low solar energy conversion efficiencies if compared with cultivated terrestrial plants (see Table 2.1). Cultivation is vulnerable to invasions of competing algae and her­bivores, and major interventions may be necessary to limit losses in such cases (Buschmann et al. 2001; Ask and Azanza 2002; Neill et al. 2006). As pointed out in Chap. 1, prices for cultivated macroalgae are high, and thus it is hard to see the emergence of a practical large-scale biomass-from-the-sea-for-transport-fuel scheme based on macroalgae cultivation (Neushul and Badash 1998; Buschmann etal. 2001).