Review articleCultivation of seaweed Gracilaria in Chinese coastal waters and its contribution to environmental improvements
Introduction
Approximately 1000 seaweed species globally distributed, from cold, temperate to tropical zones, are economically valuable [1]. Those seaweeds play very important roles in sustaining the biodiversity and ecological functions in marine ecosystems [2]. More than 100 species of Gracilaria have been described in the world, and they grow mostly in temperate, subtropical and tropical zones [3], [4]. Historically, seaweeds are harvested from nature. However, seaweed cultivation has significantly grown rapidly since the early 20th century due to the continuously rising demand for food and industry. Several species of algae have been cultivated for many years, especially Pyropia (formerly referred to as Porphyra), Saccharina (formerly referred to as Laminaria), and Nostoc for food, Gloipeltis for colloidal substances and Gracilaria for feedstuffs and agar materials [5].
Cultivation of seaweed is one type of aquaculture. Now, aquaculture is growing fastest in the food production sector, and its average annual growth rate reached 8.3% between 1970 and 2009, compared to that of 4.9% for poultry, 2.9% for pig, and 1.8% for sheep and goats [6]. China has had the highest mariculture production in the world for over 20 years, and has remained one of the most important contributors to the world aquaculture production. For example, its mariculture production in 2010 reached 14.82 million t and accounted for 44.2% of the world's total production [7].
The rapid development of mariculture has resulted in an increasing release of nitrogen (N) and phosphorus (P) into the mariculture and its surrounding ecosystems. For example, Troell et al. [8] found that more than half of nutrients originated from marine fish culture systems, with the contribution of P, carbon (C) and N approximating 85%, 80–88% and 52–95%, respectively. Excess feed and fecal wastes of cultivated animals settle to the bottom through the water column, and then are incorporated into sediments, where the remineralization of particulate organic matter may cause an increase in dissolved inorganic nutrient concentrations. Increased discharge of organic pollutants from aquaculture farms may lead to various adverse effects to local environments, such as eutrophication, anoxia, loss of biodiversity, and coastal-water pollution [8], [9].
Mixing cultivation, which incorporates seaweeds into animal mariculture systems, has long proven to be the most promising approach for mitigating the pollution of the surrounding environment by aquaculture operations. Accordingly, seaweed cultivation has been carried out for decades and has grown rapidly in China and other countries [8], [10], [11], [12]. The seaweeds cultivated at an industrial scale include many species, such as Saccharina, Pyropia, Undaria, and Gracilaria species in China.
This paper reviews the history and presents the status of Gracilaria cultivation, its potential environmental importance as eco-materials, and its role in maintaining healthy mariculture ecosystems in the Chinese coastal waters.
Section snippets
Species diversity of the genus Gracilaria and its distribution in China
There are more than 30 species in the genus Gracilaria in China [1], [13]. They distribute in the coastal waters from Liaoning in the north to Hainan in the south of China (Table 1). Species diversity of Gracilaria is higher in the south than in the north, and almost 50% of Gracilaria species are found in Guangdong and Hainan Provinces in the southern China. In the genus Gracilaria, the most economically important species is Gracilaria lemaneiformis based on the recent 10-year documentation,
Gracilaria cultivation
The artificial cultivation of Gracilaria began in the 1950s in China, but then the production was low. For example, the production of Gracilaria tenuistipitata and other Gracilaria species was about 500 t (fresh weight) per year in the late 1950s. By the end of the 1980s, the area for Gracilaria cultivation in South China reached 2000 ha, with an annual yield of 3000 t (dry weight) [1].
The cultivation history of Gracilaria in China may be divided into 2 stages. From the 1950s to 2000, the main
Main environmental factors influencing Gracilaria cultivation
Several key environmental factors have been identified to affect Gracilaria cultivation, including light, temperature, salinity, nutrients, cultivation depth, water movement, and herbivorous fish and epiphytes.
Bioremediation potential of Gracilaria for environmental improvement
As an efficient nutrient pumper, Gracilaria may be used in integrated aquaculture systems to reduce eutrophication, control red tides, remediate contaminants and sequestrate CO2 [11], [12], [23], [39], [40]. All those will contribute to the improvement of coastal water environments. Seaweeds also create habitats, providing shelters and serving as feeding/nursery grounds for many organisms, which helps protect the diversity of marine organisms [41], [42]. Furthermore, seaweed aquaculture beds
Final considerations and conclusions
Mariculture has undergone a rapid development in China during the last three decades. The annual production reached 14, 823,008 t in 2010, making China the largest mariculture producer in the world. As the production increases, the nutrient concentrations of mariculture waters in China have been continuously rising for several decades [20]. Because Gracilaria species are environmentally friendly and economically important, the cultivation of these seaweeds at an industrial scale has been
Acknowledgments
This research was supported by the National Natural Science Foundation of China (U1301235, 41173079) and the Chinese Special Fund for Agro-scientific Research in the Public Interest (201403008). Our special thanks are given to Prof. Yingzhong Tang (Institute of Oceanology, Chinese Academy of Sciences, China), Dr. Kevin G. Sellner (Chesapeake Research Consortium, USA), Prof. Charles Yarish and Prof. Senjie Lin (University of Connecticut, USA), and Prof. Dinghui Zou (South China University of
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