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.

Development of zygote for seed production of Sargassum swartzii in India

“…Effect of salinity The optimum salinity for the regeneration of receptacles from vesicles and tertiary leaves in the present study was 30-40 psu, which is in agreement with earlier reports for S. swartzii (Sukumaran and Kaliaperumal 2000), S. muticum (Steen 2004;Kerrison and Le 2016), S. ilicifolium (Subbarangaiah et al 2012), and S. vulgare (Appa Rao et al 2014). According to these studies, highest egg fertilization and egg release are observed at 30 and 40 psu salinity.…”

“…s w a r t z i i w a s o p t i m a l a t 4 5 μ m o l photons m −2 s −1 . Similar results have been reported in S. thunbergii in China (Zhao et al 2008) and S. muticum in Scotland (Kerrison and Le 2016). This optimal irradiance is lower than that reported for S. muticum by Hales and Fletcher (1990) (175 μmol photons m −2 s −1 ) and by Cao et al (2008) (60-100 μmol photons m −2 s −1 ), and higher than reported for S. ilicifolium by Appa Rao et al (2014) (9 μmol photons m −2 s −1 ).…”

“…That is why inhibition of receptacle regeneration happened at salinities below 25 psu. Kerrison and Le (2016) observed oospore release in all salinities from 10 to 30 psu; however, in our study, lower (15 psu) and higher (55 psu) salinities inhibited the regeneration of receptacles. According to Steen (2004), the growth rate of germlings of S. muticum decreased in salinities below 25 psu, and he also stated that low salinity could be a physiological barrier for the expansion of the alga in natural beds.…”

“…Germling developmental stages In the present study, S. swartzii oospore and germling dimensions are similar to S. thunbergii (Zhao et al 2008) and S. horneri (Pang et al 2009) in China and S. muticum (Kerrison and Le 2016) in Scotland. This species has the eight nuclei-one egg type, a quite common pattern found in members of Sargassaceae, and followed similar developmental stages including formation of multicellular germlings with abundant rhizoids within 48 h of fertilization (Fletcher and Fletcher 1975;Zhao et al 2008;Kerrison and Le 2016).…”

“…(Umamaheswara Rao and Kaliaperumal 1976;De Wreede 1978;Fletcher 1989, 1990;Sukumaran and Kaliaperumal 2000;Zhao et al 2008;Kerrison and Le 2016). In the Mandapam coastal region, surface seawater temperature is in the range of 27-32°C and does fluctuate much (Sukumaran and Kaliaperumal 2000;Veeragurunathan et al 2015aVeeragurunathan et al , 2015b.…”