Quantifying energy fluxes and trophic dynamics to assess artificial reef restoration success: Evidence from Bohai Bay, China

Abstract

To achieve the established ecological restoration goals, habitat-based enhancement measures are commonly implemented by deploying artificial reefs, aiming to increase structure complexity and boost local production. In this study, using Juehua Island as case study, we investigated food web structure and energy fluxes to compare artificial reef habitat with natural ecosystems (seagrass bed and sediment substrate habitats surrounding). Our research revealed that seagrass beds exhibited the highest mean δ¹³C values and most complex topological properties of food web among trophic species, while artificial reefs had the largest mean δ¹⁵N values. Lateolabrax japonicus in seagrass beds had the highest trophic position (3.79), followed by Gobiidae in artificial reefs (3.45) and Sebastes schlegelii in sediment substrates (3.30). Species had a wide range of dietary sources, indicting the complex food web structure. Despite trophic transfer efficiency declined gradually with increasing trophic levels in artificial reefs, the presence of these reefs enhanced the $P/\bar{B}$ (production/biomass) ratio of phytoplankton (39 times higher than macroalgae), and significantly improved primary productivity. The seagrass bed habitat showed the highest energy flow in the food web at 69.37 g m⁻² yr⁻¹, followed by artificial reefs (4.23 g m⁻² yr⁻¹) and sediment substrate habitats (1.05 g m⁻² yr⁻¹). Across three habitats, energy flow from detritus to bivalves was dominant. Bivalvia and Zooplankton accounted for nearly 90 % of consumer biomass across all habitats, acting as key intermediaries between primary producers and higher consumers. The quantitative analysis of the food web structure and energy flow in the typical ecosystems of Juehua Island provided valuable scientific data to support the assessment of ecological effects, as well as protection and restoration of offshore ecosystems.