Phenolic contents of two brown algae, Turbinaria ornata and Sargassum mangarevense on Tahiti (French Polynesia): interspecific, ontogenic and spatio-temporal variations

Abstract

To elucidate the possible implications of phenolic content in survival strategies of two tropical brown fucaleans, Tur- binaria ornata and Sargassum mangarevense, we deter- mined total phenolic contents in relation to ontogenic stages, and then followed spatio-temporal variations. Samples were collected at different sites and seasons. Both species exhibited low phenolic contents with, how- ever, some differences: levels were higher in the algae from grazer- and nutrient-rich sites, and during the aus- tral summer. Moreover, adults produced more phenolic compounds than immature stages. In addition, Turbinaria ornata had higher levels than Sargassum man- garevense. Parent thalli may exert an indirect protection of easily-grazed recruits which settle in close vicinity. The differences between species in protection of recruits would, therefore, derive from the respective species mor- phologies. A mechanical protection can be hypothesized in S. mangarevense because of its soft flexible thallus: plants can sweep around their base and, therefore, would need to produce less phenolics as a repellent than Turbinaria. On the other hand, due to its relatively tough texture, together with its upright-thallus, Turbinaria has a greater need to protect recruits by chemicals. The low phenolic content observed from thalli collected at the outer barrier reef may be explained by an exudation of phenolics after dessication.