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Environmental problems such as organic pollution and eutrophication caused by highly intensive mariculture activities constrain the sustainable and healthy development of industry. Therefore, it is necessary to quantify the nutrient dynamics of aquaculture animals in order to reduce the risk of environmental pollution. In this study, a discontinuous individual growth model of Portunus trituberculatus in an intensive mariculture pond of P. trituberculatus–Penaeus japonicus–Sinonovacula constricta was constructed based on a dynamic energy budget theory combined with the index of condition factor. This model better predicted the growth and molting behavior of P. trituberculatus, and an acceptable fit was obtained through model parameterization using the Add-my-Pet (AmP) method (mean relative error = 0.058, symmetric mean squared error = 0.007). Ten molts were simulated over 180 days and generally coincided with the recorded molt time points. Based on this model and P. trituberculatus populations, the dynamic processes of carbon, nitrogen, and phosphorus in ingestion, respiration, excretion, feces, residual feed, dead crabs, seeding, molt, and harvest were simulated. The carbon, nitrogen, and phosphorus ingested during the 180-day culture period were 4,938.57 kg ha-1, 1,255.88 kg ha-1, and 244.16 kg ha-1, respectively. Carbon, nitrogen, and phosphorus removal by harvest accounted for 1.06%, 1.03% and 0.62% of the total ingestion, respectively, while carbon, nitrogen, and phosphorus removal by dead crabs accounted for 6.84%, 6.63%, and 4.04%, respectively, and carbon, nitrogen, and phosphorus released from residual feed into the water accounted for 41.43% of the total feed. The accurate simulation of molting behavior and nutrient dynamics in this study provides a theoretical basis for molting risk prevention and environmental stress assessment of P. trituberculatus and provides basic modules and data support for the construction of the integrated mariculture ecosystem model.

In recent years, integrated pond aquaculture under controlled management has been crucial in improving the supply of aquatic products and ensuring food security. This study constructed two trophic models of integrated pond aquaculture ecosystems of Portunus trituberculatus–Penaeus japonicus (PP) and P. trituberculatus–P. japonicus–Sinonovacula constricta (PPS) using Ecopath with Ecosim software. The energy flows, ecosystem properties, and carrying capacities of the two ecosystems were analyzed and evaluated. The results showed that the ecotrophic efficiency values in the PP and PPS ecosystems were 0.962 and 0.954 for P. trituberculatus and P. japonicus and 0.952 for S. constricta. The effective trophic levels of P. trituberculatus and P. japonicus were 2.065 and 2.027 in the PP system, and those of P. trituberculatus, P. japonicus, and S. constricta were 2.057, 2.018, and 2.010 in the PPS system. The primary productivities of the PP and PPS ecosystems were 2623.79 and 2781.48 g/m2/240 days, with 2.13 and 37.83% of the energy flowing to trophic level II and 97.87 and 62.17% flowing to the detritus, respectively. The total energy of the detritus group was 2900.89 and 2372.98 g/m2/240 days, with 931.02 and 1505.35 g/m2/240 days flowing to trophic level II, respectively. The total primary production/total respiration ratio of the PPS ecosystem (1.632) was lower than that of the PP ecosystem (4.824), indicating that the former had a greater degree of exploitation. At the current feeding level, the carrying capacities of P. trituberculatus and P. japonicus were 65.15 and 47.62 g/m2 in the PP ecosystem, and those of P. trituberculatus, P. japonicus, and S. constricta were 64.96, 48.06, and 100.79 g/m2 in the PPS ecosystem, respectively. At adequate feeding levels, the carrying capacities of P. trituberculatus and P. japonicus were 83.76 and 48.52 g/m2 in the PP ecosystem and 81.82 and 53.44 g/m2 in the PPS ecosystem. The ecotrophic efficiency values and energy flow parameters of the two integrated pond aquaculture ecosystems indicated that S. constricta was a suitable collocation culture species for P. trituberculatus and P. japonicus, and there is room for further improvement in yields of this integrated aquaculture ecosystem.

Individual growth models can form the basis of population dynamics assessment and ecosystem model construction. In order to provide a basic module for an ecosystem model of an integrated marine aquaculture pond, an individual growth model was constructed for kuruma shrimp (Penaeus japonicus) based on dynamic energy budget (DEB) theory. The model was first parameterized based on a covariation method using the Add-my-Pet (AmP) procedure. The parametric estimation model underestimated the ultimate abdominal length for female shrimp, and the predicted values of other zero-variate parameters were generally consistent with observed values. The relative errors of the predicted and observed values of the univariate data set within three geographical regions showed acceptable goodness of fit. Parameter estimation achieved an overall goodness of fit with a mean relative error of 0.048 and a symmetric mean squared error of 0.066. A DEB model was constructed using the estimated parameters, and the goodness-of-fit indicators (R square, mean bias and absolute and relative root mean square error) showed that the model was able to reproduce the growth of kuruma shrimp in terms of total length and wet weight with high accuracy. The results provide data to support the subsequent development of integrated aquaculture management at the ecosystem level.

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In order to investigate the effects of razor clams (Sinonovacula constricta) on the food composition and isotopic niches of swimming crabs (Portunus trituberculatus) and kuruma shrimp (Marsupenaeus japonicus) in polyculture systems, this study analyzed 60 P. trituberculatus, 60 M. japonicus and 30 S. constricta to quantify the food sources, food source contributions, and isotopic niches of cultured organisms using 18S rDNA barcoding and stable isotope techniques. The results were as follows: (1) In the P. trituberculatus-M. japonicus (PM) polyculture system, the Sobs and Shannon-Wiener indices of the stomach contents of P. trituberculatus and M. japonicus were not significantly different (P > 0.05). In the P. trituberculatus-M. japonicus-S. constricta polyculture (PMS) system, the Sobs and Shannon-Wiener indices of the stomach contents of P. trituberculatus and M. japonicus were also not significantly different (P > 0.05), but the Sobs indices of P. trituberculatus in the PMS system were significantly higher than those in the PM system (P < 0.05), M. japonicus shows a similar pattern. (2) 18S rDNA barcoding analysis showed the dominant taxa in the stomach contents of both P. trituberculatus and M. japonicus in the PM system were Trebouxiophyceae, Embryophyta and Rotifera, and the food overlap between them was 0.8992, which was significant (Q > 0.6). In the PMS system, the dominant taxa in the stomach contents of P. trituberculatus were Chrysophyceae, Intramacronucleata, and Embryophyta, and in M. japonicus were Chrysophyceae, Embryophyta, and Bacillariophyceae, in this system the food overlap was 0.2061, which was not significant (Q < 0.6). (3) Stable isotope analysis suggested, in both systems, the main food sources of P. trituberculatus and M. japonicus were iced trash fish, zooplankton, phytoplankton, and organic particulate matter (POM). Iced trash fish accounted 77.67% of food sources for P. trituberculatus and 69.42% for M. japonicus in the PM system, and 60.82% and 57.60% in the PMS system. (4) The isotopic niche overlap between P. trituberculatus and M. japonicus was 5.69% in the PM system and 1.21% in the PMS system. These results suggested food competition between P. trituberculatus and M. japonicus, and S. constricta can reduce the competition and isotopic niche overlap, improve the contribution of food sources such as phytoplankton. Razor clams also serve to purify the water and improve the utilization of iced trash fish by filtering phytoplankton (51.10%), POM (32.25%), SOM (7.47%), and iced trash fish (9.18%). Thus, P. trituberculatus-M. japonicus-S. constricta is a healthy and sustainable culture model.