Evidence against a mechanism of allelopathy in the green alga Chlorodesmis fastigiata

Abstract

Allelopathic macroalgae have been shown to have significant negative effects on corals via the transfer of toxic compounds. The interaction that takes place between allelopathic macroalgae and other algae, however, has not been studied in detail. Here, the effects of the allelopathic Chlorodesmis fastigiata on other macroalgae were analyzed. These effects were first tested on complete coral and macroalgal individuals over several days, then on small samples of the macroalgal species when exposed to isolated toxins. However, neither experiment found significant negative effects on either Sargassum mangarevense or Boodlea kaeneana due to the interaction between these algae and the toxin produced Berkeley, CA 94720 USA 6 7 Abstract. Allelopathic macroalgae have been shown to have significant negative effects on corals 8 via the transfer of toxic compounds. The interaction that takes place between allelopathic 9 macroalgae and other algae, however, has not been studied in detail. Here, the effects of the 10 allelopathic Chlorodesmis fastigiata on other macroalgae were analyzed. These effects were first 11 tested on complete individuals on multi-day time scales, then on small samples of the macroalgal 12 species exposed to isolated toxins over the scale of minutes. However, neither experiment found 13 significant negative effects on either Sargassum mangarevense or Boodlea kaeneana due to the 14 interaction between these algae and the toxin produced by C. fastigiata. Distribution and 15 abundance of C. fastigiata were also assessed around the island of Mo'orea in French Polynesia. 18Introduction 19 Coral reef health and conservation have become topics of much conversation in recent years. For 20 the most part, these discussions center around large-scale environmental changes such as climate 21 change and ocean acidification (Hoegh-Guldberg et al., 2007), increased sedimentation rates 22 (Rogers 1990), nutrient fluxes (Fabricius, 2005), and a rise in fishing pressure (Jackson et al. 23 2001). These negatively affect reef health and create an increased risk of colonization by 24 macroalgae (McCook, 1999). Some algae facilitate this colonization process via the transfer of 25 toxic nonpolar compounds directly onto the coral (Rasher and Hay, 2010;Rasher et al, 2011; 26 Bonaldo and Hay, 2014). Chlorodesmis fastigiata, commonly known as turtleweed, exemplifies 27 this allelopathic interaction and its diterpene toxins causes appreciable bleaching of sensitive 28 corals in merely a few days (Rasher and Hay, 2010;Rasher et al. 2011;Bonaldo and Hay 2014). 29It is not known exactly how the algal toxins function, but they may act by blocking 30 photosynthesis. Previous studies on aquatic and marine algae have shown that toxins produced by 31 algae can inhibit the light-dependent reactions of photosynthesis. (Patterson et al, 1979; Patterson 32 and Harris, 1983) This is especially true if the toxin is nonpolar and has a low molecular weight 33 (Leflaive and Ten-Hage, 2007; Smith and Thanh, 2007) such as is the case for the ...

Review POTENT PHARMACEUTICAL PRODUCTS FROM AQUATIC PLANTS – REVIEW

“…This toxin also kills corals on contacting alga [69]. The genus Halimeda, a calcareous macroalga contains less [70][71][72][73][74]. Diterpenes are antimicrobial and anti-inflammatory compounds (Tables 1 and 5).…”