Most marine mollusks have a pelagic larval phase, and they need to undergo metamorphosis to develop into adults. Metamorphosis is affected by many factors, including abiotic factors such as temperature, salinity and illumination as well as biological factors such as food and microorganisms. In our previous study, we found that the metamorphosis of Rapana venosa requires induction by juvenile oysters, which are the food source of R. venosa. However, the regulatory mechanism of this induction is largely unknown. In the present study, we evaluated the impacts of induction by juvenile oysters on competent larvae of R. venosa. Competent larvae were experimentally divided into two pools, and scallop shells without juvenile oysters and scallop shells with juvenile oysters were added for 2 h and 12 h to monitor alterations in critical gene expression, symbiotic microbiota and metabolomic responses. The carboxypeptidase gene was increased while the cellulase gene was decreased, which may mean that the food habit transition was induced by juvenile oysters. Meanwhile, critical genes in the neuroendocrine system were also significantly altered in juvenile oysters. Furthermore, dramatic changes in the symbiotic microbiota and metabolism profiles were observed, with many of them associated with the digestive system and neuroendocrine system. In conclusion, juveniles as food resources may induce metamorphosis in R. venosa by regulating the neuroendocrine system and promoting the development of the digestive system and changes in digestive enzymes. This study may provide evidence that induction by juvenile oysters can promote food habit transition and metamorphosis in R. venosa by regulating the metabolome and microbiome and further altering the digestive and neuroendocrine systems of R. venosa, which expands our understanding of the regulatory mechanism of metamorphosis in R. venosa. However, further studies are needed to explore the specific substance inducing metamorphosis released by juvenile oysters.

Polychaetes (such as Sternaspis sculata) can biotransform polycyclic aromatic hydrocarbons (PAHs) in the environment, and the cytochrome P450 (CYP) enzyme is the key substance in this process. Here, a novel CYP gene was identified from S. sculata, a marine polychaete that is abundantly distributed along marine coasts worldwide. The full-length cDNA of the new CYP is a 1829 bp, encoding a protein of 509 amino acids. The deduced amino acid sequence of the CYP gene contains the conserved motifs of the P450 family (FxxGxxxCxG) and the characteristic sequences of the CYP4 family (EVDTFMFEGHDTT), showing high similarity to CYP4V from marine polychaetes. Therefore, the cDNA sequence might belong to the subfamily of CYP4V, tentatively named SsCYP4V. The expression levels of SsCYP4V in the field were detected in S. sculata sampled from six sites along the coasts of the Liaodong Peninsula. The results showed that the relative expression levels of SsCYP4V in S. sculata were significantly different among the sampling sites; however, no positive relationship was found between SsCYP4V expression levels and PAHs concentrations in the sediments. These findings suggested a complexity of CYP gene expression in the field, and SsCYP4V cannot be used as a biomarker for the field monitoring of PAH pollution.

Juvenile Rapana venosa are vulnerable immediately after metamorphosis. The high mortality rate of juveniles seriously limits the development of the aquaculture industry. A number of gastropods use burrowing as an environmental adaptation. R. venosa is a widespread gastropod species, but little is known about its ecology, especially its burrowing behaviour. Here, we studied the obvious burrowing behaviour of juvenile R. venosa. Our results showed that the size of the juvenile snail, grain size of the sediment, dissolved oxygen and water temperature significantly affect the burrowing behaviour of juveniles. Large juveniles have a strong burrowing capacity. The shortest burrowing time occurred in sediment of small grain size. When dissolved oxygen was high (8 mg/L), juveniles displayed obvious burrowing behaviour, and as the dissolved oxygen decreased, the juveniles reduced their burrowing behaviour. Low or high temperatures (≤15 or 30°C, respectively) significantly increased the burrowing rate and depth. Moreover, small snails (shell height <2.5 cm) exhibited obvious shell and tissue detachment (an abnormal phenomenon) when the water temperature was low (5°C). Small snails could reduce shell and tissue detachment and mortality rate by submerging themselves in sand (diameter: 0.50–1.00 mm), indicating that burrowing was a kind of protective behaviour that enables juvenile R. venosa to adapt to the environment. Our results add to the body of knowledge on snail responses to particular environmental factors and allow a better understanding of the species’ needs in its natural environment and can be used to improve commercial breeding strategies for R. venosa.

Population growth, rising energy demand, and global climate change are increasing the need for both food and renewable energy, particularly seafood and solar power. Aquavoltaics – the combination of solar photovoltaic systems with aquaculture – presents a viable approach to addressing land competition between food and energy production. Sea cucumbers, especially Apostichopus japonicus, are economically crucial in aquaculture, particularly in China, where extreme temperatures and harmful algal blooms have caused significant mortality and economic losses. Integrating sea cucumber aquaculture with photovoltaic power generation offers a promising solution to large-scale sea cucumber die-offs while delivering dual benefits in aquaculture and energy production. This article examines the development of aquavoltaics and its impacts on physicochemical parameters in aquaculture environments, as well as biological aspects. It identifies key causes of sea cucumber mortality in pond farming and proposes practical approaches for combining sea cucumber aquaculture with photovoltaics. Furthermore, innovative models and future research directions are suggested to enhance the synergy between sea cucumber cultivation and solar energy development, thereby promoting sustainability in both sectors.