The radionuclides released from the nuclear power plants (NPPs) during nuclear accidents can cause severe damage to the marine ecosystems. Strontium (Sr), cobalt (Co), and manganese (Mn) are among the main metal elements in the radionuclide wastes. Living macroalgae have been regarded as efficient materials to scavenge metal ions from polluted water bodies. Given the enormous amount of harvested Sargassum horneri biomass due to the outbreak of “golden tide” along the China’s coastline, this study aimed to evaluate its potential in removing Sr, Co, and Mn from seawater. The process, kinetics, and mechanisms of scavenging these metal elements were investigated in the present study. The interaction among these three nuclides during the removal process was also explored. The results showed that living S. horneri biomass was effective at scavenging Sr, Co, and Mn from seawater in both mono- and multi-nuclide contamination scenarios. Notably, the removal efficiency of S. horneri was found to be in the following order: Mn > Co > Sr. Furthermore, the biosorption kinetic data of living S. horneri for Sr, Co, and Mn removal were well described by both pseudo-first-order and pseudo-second-order kinetic models. The removal efficiency of S. horneri on any single nuclide could be influenced by the co-existence with other two nuclides and their concentrations.

Sargassum horneri is one of the most common seaweeds in China growing on solid substrates in the sublittoral zones along the Chinese coast. Large-scale drifting biomass of S. horneri has been reported in the Yellow Sea since 2010. Huge amount of the stranded biomass of this alga on the cultivation rafts of Pyropia yezoensis has drawn wide attention after damaging the local Pyropia farming industry. The original sources of the drifting biomass in the Yellow Sea remain unknown. In this study, 16 populations including three benthic and 13 drifting ones were sampled from the Yellow Sea and the East China Sea. Results of microsatellite analyses revealed that there were significant genetic differentiations among most of the investigated populations. Cluster analysis demonstrated that the drifting individuals from the same year, rather than from the same sampling locations, were clustered together. The existence of marked admixture in six populations also implies that the same drifting population could be of different origins. These results provide evidence suggesting that the drifting populations, in particular the populations occurring in different years, originated from multiple sources. Satellite imagery observation combined with genetic analyses of more benthic and drifting populations in the future are expected to elucidate, on a clearer level, the exact locations of the origin of the drifting populations.

In our trials, from 2007 to 2008, of mass production of seedlings of Hizikia fusiformis using synchronization techniques, problems of a “dark thalli” phenomenon and epiphytes contamination severely threatened the health of juvenile seedlings. In this investigation, we optimized conditions for improving the growth of juvenile seedlings. Seven string collectors were seeded with zygotes and a series of experiments were conducted including direct exposure to solar irradiance, co-culture with Ulva spp. and treatment with sodium hypochlorite. It was found that direct exposure to solar irradiance (maximum: 1 740 μmol photons/(m2·s)) for 2 h per day could efficiently enhance the growth of young seedlings and simultaneously inhibit the growth of epiphytic algae. In this treatment, 50-day old seedlings could reach an average of 0.44 cm in length and possess up to nine leaflets. However, a single treatment with 18-mmol/L sodium hypochlorite for 10 min severely harmed 15-day old seedlings. In comparison, weekly treatment with 2.2-mmol/L sodium hypochlorite for 10 min brought no apparent harm to seedlings and eliminated epiphytic algae efficiently. However, this treatment significantly increased the detachment rate of seedlings. Inoculating Ulva spp. onto the collector caused a dramatic decrease in the number of seedlings. However, the growth of the remaining seedlings appeared unhampered. All collectors except the control were daily sprayed with a high pressure water jet from the 8th day post fertilization. From the first day to 50th day, no “dark thallus” was observed on any of the seven collectors. We believe that well-timed daily exposure to solar irradiance would favor H. fusiformis in its early growing stages.

通过实验生物学方法,探讨了采用5℃条件保存的多细胞和两细胞状态羊栖菜（Hizikia fusiformis）受精卵的成活和发育情况。结果表明,相同保存和恢复培养条件下的羊栖菜受精卵,两细胞状态的死亡率明显高于多细胞状态。5℃条件保存60 h多细胞状态羊栖菜受精卵的死亡率均在10%左右,同样条件保存48 h两细胞状态受精卵死亡率高达75%。在异地运输羊栖菜受精卵或者胚胎完成苗种培育的过程中,应当同时考虑温度、运输时间以及受精卵的发育阶段等多个因素,才能取得比较好的实际效果。

As a large conspicuous intertidal brown alga, individuals of Sargassum horneri can reach a length of more than 7 m with a fresh weight of 3 kg along the coasts of the Eastern China Sea. The biomass of this alga as a vital component in coastal water ecology has been well documented. In recent years, a steady disappearance of the algal biomass along the once densely populated coastal areas of the Eastern China Sea has drawn attention in China. Efforts have been made to reconstruct the subtidal algal flora or even to grow the alga by use of long-lines. As part of the efforts to establish an efficient technique for producing seedlings of S. horneri, in this investigation a series of culture experiments were carried out in indoor raceway and rectangular tanks under reduced solar irradiance at ambient temperature in 2007–2008. The investigation demonstrated that: (1) sexual reproduction of S. horneri could be accelerated in elevated temperature and light climates, at least 3 months earlier than in the wild; (2) eggs of S. horneri had the potential to be fertilized up to 48 h, much longer than that of known related species; (3) suspension and fixed culture methods were both effective in growing the seedlings to the long-line cultivation stage; and (4) the life cycle of S. horneri in culture could be shortened to 4.5 months, thus establishing this alga as an appropriate model for investigating sexual reproduction in dieocious species of this genus.

Mariculture of the brown alga Hizikia fusiformis (Harvey) Okamura as an export-oriented human food has been there more for than 20 years in China. It is now one of the five major farmed algal species along the Chinese coast. Stable and sufficient supply of young seedlings for scaling up the cultivation has been a problem throughout the farming history of this species due to the unique dioecious life cycle and relatively short time window of sexual reproduction in nature. These two factors led to a practical difficulty in obtaining zygotes at identical developmental stage in viable amounts for seedling production. A key solution to this problem is to control the synchronization of the receptacle development and to realize the simultaneous discharge of male and female gametes, such that the fertilization rate could be greatly enhanced. Focusing on one of the farmed populations in this report, we present our results on mass production of seedlings using the synchronization technique on a large scale performed in 2007. Totally 5.5 hundred million embryos were obtained from 100 kg female sporophytes. The seedlings were raised up to 3.5 mm in length in greenhouse tanks over a month and were further grown in open sea for over 3 months at two experimental sites. The success of mass production of seedlings in this alga helped to lay the basis for future trials in other species in the genus of Sargassum that have identical life cycle.

文章报道了20052007年针对铜藻Sargassum horneri有性生殖规律所开展的研究结果,包括生殖托发生、卵的排放、受精卵的发育及其与环境因子的关系。选择了潮间带典型的生态环境定点观察有性繁殖的过程,提出"铜藻以有性生殖为主,残枝营养繁殖为辅,共同维系种群繁衍"的推论。进行了筏式栽培、人工采苗、育苗及附苗基质选择等试验,为未来铜藻工厂化育苗和开展潮下带铜藻种群的恢复提供了科学依据。

The reuse of holdfasts for regeneration of young seedlings or using wild juvenile plants as the seedling source has played the major role in commercial cultivation of the brown alga Hizikia fusiformis in East Asia over the past 20 years. The possibility of employing zygote-derived germlings for producing seedlings has been discussed in the literature, but has not yet become a reality. Three main obstacles have limited the use of zygotes as a main source of seedlings, (1) the dioecious nature of the algal life cycle which may lead to asynchronous male and female receptacle development and thus different timing of egg and spermatozoa expulsion, (2) the low attachment rate when using zygote-derived germlings with developed rhizoids from wild parental plants for seeding production, and (3) the problem of culturing young germlings in regions where water temperature is high in summer. In this investigation, shifting the timing of receptacle formation earlier than in nature was performed by tumbling the algae in a long-day tank (16-h light per day). Synchronization of egg and spermatozoa expulsion and thereafter fertilization were conducted in indoor tanks. Receptacle formation in constant long days could be shifted by 20 days earlier than in plants cultured on long lines in the open sea, or 1 month earlier than in plants growing on intertidal rocks. Synchronized expulsion of eggs and spermatozoon led to a high rate of fertilization. This was achieved by tumbling the male and female receptacle-bearing branchlets in the same tank at low density in high irradiance. In two independent trials, a total of 1,400,000 zygote-derived germlings were obtained from 620 g (fresh weight) female sporophytes. The germlings shed from the receptacles were at an identical developmental stage indicating high synchronization of expulsion of eggs and spermatozoon followed by fertilization. Approximately 63% (±9.6%) of the germlings were shed from the receptacle between 16 and 24 h after fertilization and 20% (±11.9%) remained on the receptacle for 3 days after fertilization. Germlings were seeded on string collectors before rhizoids started to elongate and the attachment efficiency was enhanced. Young seedlings reached 800 (±50) μm in length in 25 days at 25 °C before they were transferred to open sea cultivation. These results provide the basis of a practical way of seedling production by use of zygote-derived germlings in the commercial cultivation of H. fusiformis.