Progress in Fishery Sciences (Feb 2023)
Distribution Characteristics of Nutrients and Suitability for Aquaculture in Marine Ranching of Xiaozhushan Island
Abstract
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.
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