Environmental factors on egg liberation and germling production of Sargassum muticum

Abstract

Sargassum muticum is a successful invasive Phaeophyte macroalga, which has colonized from Norway to the Mediterranean in Europe and from Alaska to the Bay of Mexico on the American Atlantic coast. It is also being evaluated as a commercial crop within its native range, SE Asia. Understanding its reproductive tolerance will improve our understanding of its invasive potential and allow optimal germling production for commercial cultivation. Egg liberation, fertilization and germling production were monitored in fertile branchlets collected from Great Cumbrae, Scotland, UK. These were incubated under a range of conditions as follows: photon flux densities (20–150 μmol photons m⁻² s⁻¹), salinity (0–70 psu), temperature (10–30 °C) and desiccation in either the sun (5–60 min) or the shade (15–120 min). The optimum conditions to maximize germling production were found to be a 15–30 min desiccation period in the shade, followed by immersion into normal salinity seawater at 20 °C and 50–100 μmol photons m⁻² s⁻¹. This information could be useful for the development of a cultivation industry within its native range. An interactive effect was seen between temperature and light intensity with germling production favoured in high light and low temperature (10–15 °C, 100–150 μmol photons m⁻² s⁻¹) and vice versa (25–30 °C, 20–50 μmol photons m⁻² s⁻¹). Whilst its salinity and desiccation tolerance agree with previous investigations 40 years ago, the lower temperature optimum of 20 °C (previously 25 °C) may indicate selection for lower temperature reproduction within the UK population. This may accelerate its invasion northward into Scotland.