Ecology and Management of the Invasive Marine Macroalga Caulerpa taxifolia - Management of Invasive Weeds - page 289

Posidonia may be able to effectively compete with C. taxifolia in areas with limited
urban pollution, but C. taxifolia will win in polluted areas (Jaubert et al. 1999).
Williams and Grosholz (2002) found that in California, biomass of the seagrass
Ruppia maritima was 20 times lower if mixed with C. taxifolia than alone.

15.3.6 Secondary Chemistry and Predation

Many marine algae are defended from herbivory by a wide diversity of secondary
metabolites (e.g., Paul et al. 2001). Some green algae, including C. taxifolia , use an
activated defense system whereby damage from feeding or abrasion results in the
conversion of a stored secondary metabolite with minimal to moderate biological
activity into a product with greater bioactivity (Paul and Van Alstyne 1992). If dam-
aged, caulerpenyne, the dominant toxin in C. taxifolia , is transformed into a more
toxic and deterrent cytotoxic sesquiterpene, which has greater antifeedant, antibi-
otic, and antifouling properties (Paul and Fenical 1986; Paul et al. 1987; Jung and
Pohnert 2001). Reactive chemicals that are present within seconds after tissue dam-
age act locally as defensive metabolites during the relatively slow feeding process
by urchins or slugs (Sureda et al. 2006). Caulerpa taxifolia also has 10, 11-epoxy-
caulerpenyne and caulerpenynol, two minor sesquiterpenoids, taxifolials, and other
terpenes (Raffaelli et al. 1997; Paul 2002).
Caulerpenyne helps with wound response (Adolph et al. 2005) and is very unsta-
ble in seawater (Amade and Lemee 1998). Samples degraded by 50% in 4 h and
95% in 24 h (Amade and Lemee 1998). More caulerpenyne was found in blades
than stolons in C. taxifolia (Dumay et al. 2002) and content varied seasonally in the
Mediterranean (Amade and Lemee 1998), with the lowest concentrations in the
winter followed by a sharp increase in summer (Dumay et al. 2002). Additionally,
caulerpenyne content decreased with depth (Amade and Lemee 1998). Caulerpenyne
levels were greater in the aquarium strain than native strains (Guerriero et al. 1992)
and accounted for up to 1.3% of algal fresh weight or 2% + of algal dry mass (Paul
2002). Caulerpenyne was lethal in tropical waters to the sea urchin Lytechinus pic-
tus (fertilized eggs, sperm, larvae) and toxic to the damselfish Pomacentrus coru-
leus and Dascyllus aruanus (Paul and Fenical 1986). Lemee et al. (1993) found that
aquarium C. taxifolia whole extracts were toxic to mammals and eggs of the sea
urchin Paracentrotus lividus . However, Oxynoe olivacea , a Mediterranean sacoglos-
san opisthobranch, expands its diet to consume C. taxifolia after the alga invades an
area and uses caulerpenyne for self-protection by transforming caulerpenyne into
oxytoxin-2, the mollusc's main defensive metabolite (Cutignano et al. 2004;
Gianguzza et al. 2007).
Foraging behaviors and population structures of vertebrates and invertebrates
were negatively impacted by C. taxifolia in numerous studies (e.g., Boudouresque
et al. 1996; Relini et al. 1998; Davis et al. 2005). Densities and biomasses of fish
assemblages were significantly lower in Caulerpa -invaded Mediterranean Posidonia
beds (Francour et al. 1995; Harmelin-Vivien et al. 1999; Levi and Francour 2004;