Changes in infaunal assemblage structure influence nutrient fluxes in sediment enriched by mussel biodeposition

Intensive oyster farming alters the microbial-regulated blue carbon storage in sediment

Intensive oyster farming enhances the organic matter coupling from water to sediment through biodeposition, potentially contributing to carbon storage. Microbes play a key role in regulating biogeochemical cycling in the coastal sediment. However, their specific contributions to carbon storage under oyster farming remain poorly understood. This study investigates microbial necromass and associated biogeochemical processes in sediments from an intensive oyster farm in Sanggou Bay, China, and compares these indicators with adjacent seagrass beds and bare zones. Additionally, carbon use efficiency (CUE) was employed to indicate microbial-regulated carbon cycling and storage in sediment. The results demonstrate that oyster farming promotes organic carbon accumulation in surface sediments but reduces its stability. Microbial necromass was identified as a critical driver of sedimentary organic carbon in oyster farm sediments, supported by enhanced nitrogen and sulfur cycling pathways. Notably, contrasting relationships between CUE and organic carbon were observed between the seagrass bed and the oyster farm. Functional metagenomic analysis further revealed distinct microbial metabolic pathways across habitats, highlighting the role of biodeposition in shaping microbial functions. These findings enhance our understanding of microbial contributions to blue carbon storage in aquaculture systems and provide new insights into coastal carbon storage beyond vegetated ecosystems.

Assessing shellfish farming-mediated benthic impacts based on organic carbon flux simulation and composition of macrofaunal community

Marine benthic environments serve as the ultimate sink for sediment organic matter (SOM), but shellfish farming can potentially disturb the natural sink of seston, altering ecosystem functioning. Understanding the potential disturbance of a shellfish farm and its ecological effects is therefore important for a responsible management of shellfish-mediated marine ecosystem. In this study, the variations in benthic organic carbon flux of a bottom-based Manila clam (Ruditapes philippinarum) farm in Laizhou Bay, China were estimated by using a carbon flux model coupled with hydrodynamic and individual growth models. SOM and macrofaunal community were monitored for 3 years to investigate their changes to the carbon fluxes. Model simulations illustrated that the carbon flux in an area of 247 km² was altered due to seston depletion and biodeposition, which caused decrease and increase in SOM in different areas, respectively. Cluster analysis based on taxonomic composition of macrofaunal community divided the sites into four groups, which corresponded with predicted changes of carbon flux. Increased carbon flux caused higher disturbance level (indicated by AMBI) to the macrofaunal community but increased species richness, abundance, and Shannon-Wiener index, suggesting the community was both disturbed and benefited from clam farming. This study confirmed that the benthic organic carbon flux is a key factor causing differences in SOM and macrofaunal community outside the farm, and thus can be used as an efficient method for estimating the benthic impacts of shellfish farming both in and outside the farming area.

Symbiont-induced intraspecific phenotypic variation enhances plastic trapping and ingestion in biogenic habitats

Plastic contamination has major effects on biodiversity, enhancing the consequences of other forms of global anthropogenic disturbance such as climate change and habitat fragmentation. Despite this and the recognised importance of intraspecific diversity, we still know relatively little about how plastic pollution affects diversity below the species level. Here, we assessed the effects of intraspecific variation in a habitat forming species (the Mediterranean mussel Mytilus galloprovincialis) on the trapping and ingestion of microplastics. We focused on symbiont-induced phenotypic variation in mussel beds. Using fractal analysis, we measured an increase in the complexity of mussel bed surfaces by ca. 15% caused by phototropic shell-degrading endoliths. By simulating high tide flow conditions and incoming waves, we found that symbionts significantly increased microplastic accumulation in mussel beds. This likely reflects deceleration of near-bed flow velocities, creation of turbulence in the bottom boundary layer and consequently increased particle retention. This effect was not constant at high tide, with no effect of infestation on retention at the base of the mussel bed under mid and high flow conditions and reduced microplastic trapping on the surface of mussel shells. Nevertheless, under natural conditions, the ingestion and trapping of microplastic were higher by the mussels comprising beds with symbionts than those in beds without symbionts. Given the dependency of many species on mussel biogenic habitats, there is an increased risk of plastics moving up the food chain in mussel beds infested by symbiotic endoliths. Our results highlight how the effects of within-species phenotypic diversity may influence the consequences of rising levels of plastic pollution.

Biomonitoring of the Application of Monoculture and Integrated Multi-Trophic Aquaculture (IMTA) Using Macrobenthic Structures at Tembelas Island, Kepulauan Riau Province, Indonesia

Sustainable aquaculture needs to be considered when it comes to the utilization of water resources. The aim of this study was to apply biomonitoring using macrobenthic structures on both spatial and temporal applications of monoculture and integrated multi-trophic aquaculture (IMTA) at Tembelas Island, Kepulauan Riau Province, Indonesia. Samples of sediment were taken from three fish farm locations, namely from an IMTA site, a monoculture site, and a reference site. Macrobenthic organisms obtained through rinsing, sieving, and sorting were then identified under a stereo-microscope. Diversity of the macrobenthic assemblages was analyzed with a Shannon-Wiener index (H’). Equitability was expressed through Pielou’s evenness index. Finally, Bray-Curtis’ non-metric multi-dimensional scaling (NMDS) was used for similarities derived from log (X+1) transformed macrobenthic abundance to provide a visual representation of differences in their structure between sites over time. Results showed polychaetes exhibited differences in both variation and abundance of genera between the farm and reference site. The assemblage of macrobenthos at the IMTA site consisted of 9 genera of gastropods, 3 genera of bivalves, 5 genera of polychaetes, and 2 genera of crustaceans. At the monoculture site, 12 genera of gastropods, 4 genera of bivalves, 8 genera of polychaetes, 1 genera of crustaceans, and 1 genera of ophiuroid were observed. A relatively high abundance was observed at the reference site, with 27 genera of gastropods, 11 genera of bivalves, 3 genera of polychaetes, and 1 genera of crustacean. The favorable water conditions and possible absence of waste input from aquaculture resulting in a more suitable habitat for macrobenthic life may explain this relative abundance. Some of them were recognised as opportunistic taxa, i.e., Capitella sp., Heteromastus sp., and Lumbrinereis sp. Based on the diversity and evenness indices and the MNDS ordination, it can be concluded that the application of IMTA systems results in a suppressed or reduced potential impact on environmental disturbance due to aquacultural activities.