Effects of temperature and light on the growth and reproduction of an endophytic pest alga Ectocarpus siliculosus (Ectocarpales) found in wild Gracilaria textorii (Gracilariales)

Abstract

The genus Gracilaria is an economically important macroalgae group that has been cultivated worldwide on a commercial scale. Epiphytic algae are commonly found in both natural and cultured Gracilaria and have become one of the major concerns in the Gracilaria aquaculture. In contrast to the wide reports of epiphytic pests, the endophytic algae inGracilaria have rarely been reported. In this study, we isolated the brown filamentous endophytic macroalgae Ectocarpus siliculosus from the host wild Gracilaria textorii to investigate its growth and reproduction capability under environmental changes. We studied the effects of various temperatures and light levels on growth and reproduction for 12 days. The results revealed that the highest growth rate (26.65 ± 1.78 day−1) of the endophytic pest E. siliculosus was at 25 °C and 50 μmol photons m−2 s−1. Furthermore, the gametangium/sporangium formation and gamete/spore release of the pest E. siliculosus preferred 20 °C with medium and high light intensities. In contrast, the worst performances of growth (3.34 ± 0.49 day−1) and reproduction (0.13 ± 0.09 gametangia/sporangia) occurred at the highest temperature (25 °C) and light level (100 μmol photons m−2 s−1). Our study indicate that optimal temperature can stimulate the rapid growth of E. siliculosus, and the strategy of living inside seaweed helps E. siliculosus avoid the excessive sunlight, which is especially critical for the ones inhabiting on the intertidal rocks. The physiological characteristics of endophytic E. siliculosus may help to inform the best pest management strategies for Gracilaria aquaculture.