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

Artificial reefs have significantly altered ecological and environmental conditions compared with natural reefs, but how these changes affect sediment bacteria structure and function is unknown. Here, we compared the structure and function of the sediment bacterial community in the artificial reef area, the future artificial reef area, and the control area in Bohai Bay by 16S rRNA genes sequencing. Our results indicated that bacteria communities in the sediment were both taxonomically and functionally different between the reef area and control area. In the artificial reef area, the α-diversity was significantly lower, whereas the β-diversity was significantly higher. Functional genes related to chemo-heterotrophy, nitrate reduction, hydrocarbon degradation, and the human pathogens and human gut were more abundant, whereas genes related to the metabolism of sulfur compounds were less abundant in the artificial reef than in the control area. The differences in bacterial communities were primarily determined by depth in the artificial reef area, and by total organic carbon in the future reef area and control area. This study provides the first overview of molecular ecology to assess the impacts of artificial reefs on the bacteria community.

Organotins, especially tributyltin (TBT) and triphenyltin (TPT), are of particular concern due to their ubiquity in the aquatic environment and theirtoxicityto aquatic organisms. This study reports field studies on trophic magnification factors (TMF) of TBT and TPT in a marine food web. TBT, TPT, and their metabolites in plankton, five benthic invertebrate species, and six fish species collected from Bohai Bay, North China were determined, and it was found that the concentrations of TPT in marine fish were unexpectedly higherthan those of TBT. A positive relationship was found between trophic levels and concentrations of TPT, indicating trophic magnification of TPT in this food web. The TMF of TPT was calculated to be 3.70. On the other hand, concentrations of TBT, dibutyltin (DBT) and monobutyltin (MBT) did not exhibit statistically significant trends with trophic levels, and the TMF of TBT was 0.59. Analysis of organotins in the water and surface sediment from Bohai Bay revealed low inputs of TPT to the environment, which indicated that the high concentrations of TPT found in fish from Bohai Bay were due to the food web magnification of TPT.

Aquaculture farms are known to attract wild organisms from nearby areas. Sea cucumber Apostichopus japonicus aquaculture farms in Bohai Bay, the Bohai Sea, China, might provide spawning and nursery grounds for wild black rockfish Sebastes schlegelii populations. To identify the above, we studied the variation in the numbers of S. schlegelii larvae (and length-categories as a percentage of the natural population) via ichthyoplankton surveys by months from January to October 2020, and assessed the food web structure and energy flow distribution of the farm and trophic links of S. schlegelii natural stock by using Ecopath modeling in July 2016 to August 2017. Larvae with a length between 3.90-5.80 mm were observed in the farm in May 2020, the juveniles with an estimated trophic level of 4.31. Juveniles used the farms as first-year nursery ground, and then they swam into deeper waters in August of the following year. MTI analysis showed increasing biomass of S. schlegelii might result in a decrease in the biomass of crustacea, and had positive and negative impacts on mollusk and Hexagrammos otakii biomass. We argued that aquacultural infrastructures constructed by artificial reefs could be used as a fisheries management tool to enhance S. schlegelii stocks and that monitoring of other marine organisms, such as oysters, Rapana venosa, Charybdis japonica, and Asterias spp. etc., was necessary to maintain sustainable exploitations of aquacultural farm ecosystems. A paucity of knowledge surrounding the interactions between aquaculture farms and wild organisms needs furthermore researches.

An observational study on the impact of sea-land breeze and low-level jet on air pollutant transport in the Bohai Bay

Determination of trophic relationships within a Bohai Bay food web using stable δ15N and δ13C analysis

IntroductionShellfish play an important role in ecological restoration and as carbon (C) sinks, but studies on their ecological carrying capacity (ECC) and C sequestration potential are sparse.MethodsIn this study, we selected a 57-hectare artificial oyster reef in a typical marine ranching in Bohai Bay, China, to evaluate the ECC and their C sequestration potential of bivalve shellfish, and projecting their impact on functional groups in the system, with an Ecopath with Ecosim (EwE) food web model. We conducted four biological surveys to obtain the biomass measurements, with one conducted in each of the summer, autumn, and winter of 2019 and one in the spring of 2020; and the functional groups included in the surveys comprised fish, cephalopods, crustaceans, snails, bivalve shellfish, annelids, other macrobenthos, meiobenthos, starfish, sea cucumbers, zooplankton, phytoplankton, and detritus.Results and DiscussionThe EwE model prediction results showed that the ECC of bivalve shellfish was established to be 282.66 t/km2, far more than the existing quantity of 187.76 t/km2. Therefore, at present, the ecosystem of the study marine ranching is not yet mature. Moreover, our ecological network analysis parameters indicated that the marine ranching ecosystem will be mature and stable when the bivalve shellfish population reaches its ECC. However, the increase in bivalve shellfish biomass will result in a decrease in the population sizes of species competing for food resources with bivalve shellfish, mainly gobiid fish such as Tridentiger bifasciatus, Tridentiger trigonocephalus, Tridentiger barbatus. Simultaneously, when the bivalve shellfish reach their ECC, 29.23 t of CO2 can be sequestrated by bivalve shellfish, comprising 14.32 t being removed from the ecosystem as prey and 14.91 t being stored on the seafloor through biodeposition.ConclusionTherefore, the research demonstrated that, within the scope of ECC, the increasing bivalve shellfish can improve the C sequestration capacity of the marine ranch ecosystem, and effective management of bivalve shellfish in marine ranching can improve the economic benefits and C sink service functions of marine ranching.

4-Nonylphenol (4-NP) is of particular concern because of its ubiquity in aquatic environment and its endocrine-disrupting effects in aquatic organisms. On the basis of its octanol-water partition coefficient (104.6), it has a potential to bioaccumulate in aquatic food webs. However, there are no reported field studies on the trophodynamics of 4-NP and its precursor, nonylphenol polyethoxylate (NPEOs) surfactants, in aquatic food webs. This study reports the trophodynamics of 4-NP and NPEOs (4 < s < 16) in a marine aquatic food web from Bohai Bay, North China. 4-NP and NPEOs (4 < s < 16) were determined in 14 marine species including plankton, benthic invertebrates, fish, and marine birds. This paper provides the first report on the occurrence of NPEOs with s > 5 in marine biota. Co-analysis of DDTs in all samples allowed a direct comparison of the bioaccumulation behavior of DDTs with that of NP and NPEOs. The lipid equivalent concentration of DDE and 2,2-bis(chlorophenyl)-1-chloroethylene (DDMU) increased with increasing trophic level, and the trophic level was determined by stable isotope ratios. The trophic magnification factors (TMFs) of DDE and DDMU were 3.26 and 3.7, respectively. Lipid equivalent concentrations of 4-NP and of all NPEOs did not exhibit a statistically significant correlation with trophic levels in the food web, and the TMF of NP was 0.83, which was similar to those of all NPEOs (0.45-1.22). These results show that in the studied aquatic food web, there was no trophic magnification for 4-NP and NPEOs, whereas DDE and DDMU biomagnified.

Tracing the influence of seasonal variation on bioaccumulation and trophodynamics of phthalate esters (PAEs) in marine food web: A case study in Bohai Bay, North China.

Polybrominated diphenyl ethers (PBDEs) are of great environmental concern due to the exponential increase of the concentrations in the environment, especially in high trophic level organisms, and the trophodynamics of these chemicals in aquatic food webs is an important criterion for assessing their ecological risk. This study analyzed 13 PBDEs in the zooplankton, five invertebrate species, six fish species, and one marine bird species collected from Bohai Bay. PBDE concentrations in organisms from Bohai Bay (sigmaPBDEs: 0.15-32.8 ng/g lipid weight) were low compared with other marine organisms worldwide, and BDE-47 wasthe predominant compound in most samples,followed by BDE-28, BDE-99/BDE-100, and BDE-119. Correlation between lipid-normalized concentrations of PBDEs, and trophic levels determined by stable nitrogen isotope technologies confirmed that PBDEs were biomagnified in the marine food web. Significantly positive relationships were found fortotal PBDEs and four PBDE compounds (BDE-28, BDE-47, BDE-100, and BDE-119), and their trophic magnification factors (TMFs) were 3.53, 3.57, 7.24, 3.23, and 2.60, respectively. The concentration ratios between congeners (BDE-99/BDE-100 and BDE-99/BDE-47) were found to decrease with increasing trophic levels, suggesting that trophic-level-dependent concentrations ratios between BDE-99 and BDE-100 would be contributed by trophic level-dependent biotransformation between BDE-99 and BDE-47, and therefore resulting in the dominance of BDE-100 compared with BDE-99 and the relatively high trophic magnification of BDE-47 in the marine food web.

Trophic transfer of polycyclic aromatic hydrocarbons (PAHs) in aquatic ecosystems is an important criterion for assessing their ecological risk. This study analyzed 18 PAHs in phytoplankton/seston, zooplankton, five invertebrate species, five fish species, and one seabird species collected from Bohai Bay, and trophic transfer of the PAHs was determined in the food web, of which the length was approximately 4 on the basis of stable nitrogen isotope values. The concentrations of PAHs (2-64.5 ng/g wet weight) in the marine ecosystem were moderate compared with other marine organisms worldwide, and the PAH compositions exhibited species-specific profiles that were related to trophic levels in some organisms. Significant negative relationships were also found between trophic levels and lipid-normalized concentrations for 10 PAH compounds (acenaphthylene, anthracene, fluoranthene, pyrene, chrysene, benz[a]anthracene, benzo[b]fluoranthene + benzo[k]fluoranthene, benzo[e]pyrene, benzo[a]pyrene, and perylene), and their trophic magnification factors (TMFs) ranged from 0.11 for fluoranthene to 0.45 for acenaphthylene. These results confirm that PAHs undergo trophic dilution in the marine food web, which is likely to be the combined results of low assimilation efficiencies and efficient metabolic transformation at higher trophic levels.

Occurrence, bioaccumulation and trophic transfer of organophosphate esters in marine food webs: Evidence from three bays in Bohai Sea, China

In order to study the stability of the square perforated cubic artificial reef deployed in Bohai Bay, the flow field and the pressure field around the reef were simulated on Fluent, then the flow force on the reef was calculated, and the coefficients of anti-slide and anti-rolling were calculated further. The results show that the flow force is not strong compared with the static force of friction. The coefficients of anti-slide and anti-rolling are large enough to ensure the stability of the reef.

Model description of trophodynamic behavior of methylmercury in a marine aquatic system

Probabilistic ecological risk assessment of DDTs in the Bohai Bay based on a food web bioaccumulation model

Many investigations have highlighted the bioaccumulation of dioxins in animals, but little is known about the trophodynamics of dioxins in the food web. In this study, the trophic transfer of nine dibenzo-p-dioxin (PCDD) congeners, eleven dibenzofuran (PCDF) congeners, and twelve non-, mono-ortho polychlorinated biphenyl (non- and mono-ortho PCBs) congeners in a marine food web were determined. The concentrations of PCDDs, PCDFs, non- and mono-ortho PCBs were analyzed in phytoplankton/ seston, zooplankton, three invertebrate species, six fish species, and one seabirds species collected from Bohai Bay, representing approximately 4 trophic levels based on stable nitrogen isotope values. Positive relationships were found between trophic levels and lipid equivalent concentrations of non- and mono-ortho PCBs except for PCB-77, PCB-81, PCB-126, PCB-156, and PCB-167, indicating bioaccumulation of these compounds in this food web. But lipid equivalent concentrations of low chlorinated 2,3,7,8-substituted-PCDD/Fs did not exhibit statistically significant trends with trophic levels. And lipid equivalent concentrations of high chlorinated 2,3,7,8-substituted-PCDD/Fs and three non-2,3,7,8-substituted-PCDD/Fs declined significantly with increasing trophic levels providing that these isomers undergo trophic dilution. The similarity in log Kow values for non-, mono-ortho PCBs, non-2,3,7,8-substituted-PCDD/Fs, and some 2,3,7,8-substituted-PCDD/Fs suggests that the difference of trophic transfer is mainly due to their different metabolic transformation rates.