小竹山岛海洋牧场区营养盐分布特征及增养殖适宜性探究

营养盐作为海水生物的基本生源要素，其含量与分布显著影响渔业资源分布与渔业活动。为了探究海洋牧场生态环境分布状况，并为海洋牧场的开发管理提供科学指导，于2017年12月—2018年9月对小竹山岛海洋牧场区进行4个航次的季度调查，分析并讨论了该海区营养盐分布特征，并针对虾夷扇贝(Patinopecten yessoensis)和深水网箱增养殖活动，选取海水营养水平指数、叶绿素a浓度、温度、盐度、水深和底质类型等指标，对增养殖适宜性进行了探究。结果显示，活性磷酸盐(DIP)浓度为冬季>夏季>秋季>春季，浓度值分别为0.032、0.021、0.017和0.015 mg/L。无机氮(DIN)浓度为秋季>冬季>夏季>春季，浓度值分别为0.26、0.21、0.20和0.18 mg/L。DIP和DIN浓度在4个季节间差异明显，但季节内分布均匀。受到地形坡度和人工鱼礁投放的影响，在人工鱼礁投放区域的中下层水体有较高的营养盐浓度。增养殖适宜性结果显示，虾夷扇贝增养殖适宜性指数在冬季和夏季较高，适宜在海洋牧场西部区域进行增养殖活动。深水网箱增养殖适宜性指数在夏季和秋季较高，也适宜在西北区域进行增养殖活动。由于人工鱼礁投放改善了生态环境，除西北海域外，在人工鱼礁投放区域附近出现较高的增养殖适宜性指数。海水营养盐分布与增养殖活动适宜性评价可为提高海洋牧场增殖效率、促进可持续发展及开发提供科学依据与参考。

Distribution characteristics of nutrients and suitability for aquaculture in marine ranching of Xiaozhushan Island

In recent years, marine ranching has become an essential measure for restoring the marine ecological environment and promoting the development of fisheries. The ecological effects of artificial reefs are complex. In addition to providing shelter from predators and living space, artificial reef modules can also affect nutrient transport for vertical water columns by altering the current flow and entraining nutrients, thereby influencing the surrounding biological production available to organisms and proliferating local fishery resources. During the construction process of marine ranching, nutrients are the essential biogenic elements of marine organisms. Their concentration and distribution significantly affect the distribution of fishery resources and anthropogenic activities. Understanding the spatial distribution characteristics of nutrients can provide a reference for adjusting the construction and layout of different functional areas in marine ranching. At present, marine ranching in China mainly focuses on fishery multiplication and leisure industrialization, and the comprehensive utilization efficiency of marine ranching is not high, therefore, allowing the extensive development of marine ranching. However, as an essential part of marine pasture construction, aquaculture activities often lack scientific planning, and exploring the scientific and reasonable layout of aquaculture activities is still in the preliminary stage. This is reflected in the lack of scientific investigations and demonstrations before aquaculture activities. At the same time, the aquaculture varieties are relatively single, leading to poor aquaculture activities. To explore the distribution of nutrients and provide scientific guidance for the development and management of marine ranching, four quarterly surveys were conducted from December 2017 to September 2018 in the marine ranching adjacent to Xiaozhushan Island. Distribution maps of different water layers and profiles of nutrients were generated, and the distribution characteristics were analyzed and discussed. Then, the suitability evaluation method was adopted to explore the suitability of scallop (Patinopecten yessoensis) culturing and deep-sea cages, which are the two main aquaculture activities in marine ranching. Nutrient level index, Chl a concentration, temperature, salinity, water depth, and sediment type were selected as evaluation indexes. The results showed that the seasonal variation of dissolved inorganic phosphorus (DIP) concentration from high to low was winter, summer, autumn, and spring (0.032, 0.021, 0.017, and 0.015 mg/L, respectively). The dissolved inorganic nitrogen (DIN) concentration was seen to decrease seasonally from autumn through winter, summer, and spring (0.26 mg/L, 0.21 mg/L, 0.20 mg/L, and 0.18 mg/L, respectively). The concentrations of DIP and DIN were both significantly different across the four seasons. Still, the distribution was uniform in different seasons. Due to the influence of terrain slope and placement of artificial reefs, the nutrient concentration was higher in the middle and deeper depths close to the area of artificial reef placement. For different seasons, the suitability evaluation results indicated a spatial-temporal instruction in which the suitability index of P. yessoensis culturing was higher in winter and summer. It was prone to be conducted in the west of certain sea areas. However, the suitability index was low in the autumn. Throughout the year, the suitability index of P. yessoensis was higher in the northwest of marine ranching. It was higher in summer and autumn, and it was also suitable for the northwestern region. The suitability index was low in winter. Throughout the year, the suitability index of deep-sea water was higher in the northwest region of marine ranching. One possible reason is the silt sediment in the northwestern area with deep water. A higher suitability index for aquaculture appeared near the area of artificial reef placement for different seasons. Artificial reef is an essential part of the marine ranching area of Xiaozhushan Island and its adjacent areas. However, the placement area of artificial reefs was small, and additionally, the influence of artificial reefs was not included in the suitability evaluation in the present study. As a result, the suitability index of the artificial reef is not high throughout the year, which can be further discussed in the future. Exploring the distribution pattern of water nutrients and evaluating the suitability of aquaculture activities can provide scientific evidence and reference for improvement of stock enhancement, sustainable development, and exploitation of marine ranching. It can also provide a basis for exploring the distribution of marine ranching ecological environments and utilization management.