Trophic gauntlet effects on fisheries recovery: a case study in Sansha Bay, China

Abstract

Low biological productivity causes ecosystem energy deficiency. Bottom-up drivers and trophic bottlenecks are potential reasons for unsuccessful fishery recovery. Sansha Bay is an important spawning and nursery ground for migratory fish in the East China Sea (ECS). There is significant mariculture in this area, but stock enhancement programs and seasonal fishery closures have failed to recover populations of the commercially important species, Larimichthys crocea. We wonder figure out the potential reason of unsuccessful L. crocea resource in recent 30 years. In this study, the trophic status of L. crocea, the food source proportions of L. crocea and zooplankton, and the food web structure and functioning of Sansha Bay was analyzed.A high nutrient low chlorophyll phenomenon was observed: this prevented harmful algal blooms, and phytoplankton growth was restrained by intensive macroalgal culture, resulting in a low abundance of zooplankton in Sansha Bay. Phytoplankton was the most important food source of zooplankton, and zooplankton was the greatest food source of juvenile L. crocea. Analyzed L. crocea suffered from starvation, and relative fatness varied among seasons. Crucially, most of the phytoplankton was not used efficiently in the Sansha Bay ecosystem. This study suggests that trophic bottleneck, caused by food limitation, is a potential reason for unsuccessful fishery recovery in enclosed bay with macroalgal culture.

Stable Isotope Analysis of Food Web Structure and the Contribution of Carbon Sources in the Sea Adjacent to the Miaodao Archipelago (China)

“…All the samples were collected by a random sampling method. The sediment was collected with a grab sediment sampler (5L: 305 × 150 × 480 mm), and the SOM samples were collected approximately 1 cm from the surface layer of the sediment [15]. POM samples (2.5 L) were collected from the sea surface layer (0.5 m below the sea surface), and prefiltered through 200 μm mesh sieves to remove large inorganic particles and zooplankton [15].…”

“…Before performing δ 13 C analysis on SOM samples and small crustaceans from whole individuals, the samples were processed to remove the influence of inorganic carbon [20]. These isotope samples were divided into two halves; one half was treated with acid (1 The sediment was collected with a grab sediment sampler (5L: 305 × 150 × 480 mm), and the SOM samples were collected approximately 1 cm from the surface layer of the sediment [15]. POM samples (2.5 L) were collected from the sea surface layer (0.5 m below the sea surface), and prefiltered through 200 µm mesh sieves to remove large inorganic particles and zooplankton [15].…”

“…These isotope samples were divided into two halves; one half was treated with acid (1 The sediment was collected with a grab sediment sampler (5L: 305 × 150 × 480 mm), and the SOM samples were collected approximately 1 cm from the surface layer of the sediment [15]. POM samples (2.5 L) were collected from the sea surface layer (0.5 m below the sea surface), and prefiltered through 200 µm mesh sieves to remove large inorganic particles and zooplankton [15]. The prefiltered water samples were then passed through pre-combusted GF/F filters, and heated for 4 h at 450 • C for organic matter removal [16].…”

“…where R stands for 13 C or 15 N, and X stands for 13 C/ 12 C or 15 N/ 14 N. The analytical precision of the carbon and nitrogen isotopic values was better than 0.1‰ and 0.2‰, respectively. Through meta-analysis, Hussey (2014) established an empirical linear relationship between experimental ∆ 15 N and the value of δ 15 N in prey consumed [23].…”

“…It is unknown if the contribution of phytoplankton to the benthic food web in the sea adjacent to the island is still high because the food sources of many benthic organisms, invertebrates, and small fish cannot be directly analyzed through their stomach contents. For this purpose, we used carbon (δ 13 C: 13 C/ 12 C) and nitrogen (δ 15 N: 15 N/ 14 N) stable isotopes and Bayesian mixing models. Therefore, our study used the sea adjacent to the Miaodao Archipelago as the research area, and attempted to study the carbon contribution of different primary producers to consumers on the benthic food web from the perspective of stable isotopes.…”