The Effect of Mono-Species Bacterial Biofilms Formed on the Surface of Artificial Reef on Settlement of Plantigrades in Mytilus coruscus

Abstract

Aquaculture is the fastest growing food production industry. The Chinese mariculture industry has made great progress in the past 40 years to become the dominant producer of aquaculture. However, the current deterioration of the water environment and the aggravation of farming diseases poses challenges for the traditional culture model to meet the new requirements of healthy development in marine fishery resources. This problem was addressed using marine ranching. This is a new mariculture model that includes two approaches (artificial reefs and stocking) with the goal of achieving environmental and ecological harmony. Artificial reefs are an important component of this marine ranching model since they can help improve the water environment around the reefs, promote nutrient circulation, provide a suitable habitat for marine organisms, and encourage colonization of the reef surface by sessile organisms. The placement of artificial reefs into seawater may serve as a substrate for bacteria to form a biofilm on the surface. Biofilms play a crucial role in the settlement of many marine invertebrate species. However, limited research was conducted into the relationship between bacteria on the surface of artificial reefs, biofilm formation, and the settlement behavior of Mytilus coruscus.This study placed white acrylic plates and tetrahedral structured artificial reefs in Gouqi Island, Zhoushan City, Zhejiang Province, China (122°46′ E; 30°43′ N). Nine strains of bacteria isolated from the surface of the artificial reefs were used to construct mono-species bacterial biofilms and induce plantigrade settlement of M. coruscus. The aim of the study was to investigate the interactions between marine bacteria and the settlement of M. coruscus on the surface of artificial reefs. The marine biofilms impacted the settlement process of M. coruscus. The bacterial species from the marine biofilm were screened for high and low inducing activity and analyzed for bacterial density, protein, and polysaccharide content to further explore the relationship between different bacterial biofilms and M. coruscus settlement.There were significant differences in the induction activity of biofilms formed by the nine strains of artificial reef bacteria on the settlement of M. coruscus: Mesoflavibacter sp.2 and Phaeobacter sp.2 showed the highest and lowest induction activity, respectively. Bacteria within the same genus exhibited differences in induction activity. This indicated that the induction activity of bacterial biofilms on mussel settlement was independent of bacterial species. Phylogenetic analysis showed that genetically similar strains (such as Pseudoalteromonas sp.31 and Pseudoalteromonas sp.32) and genetically distant strains (such as Mesoflavibacter sp.2 and Jeotgalibacillus sp.1) showed significant differences in the induction activity of M. coruscus settlement. Only four of the nine bacterial strains showed significant correlation between biofilm density and the settlement rate. Sutcliffiella sp.1 and Jeotgalibacillus sp.1 exhibited a positive correlation between bacterial density and induction activity. This indicated that bacterial density may play a role in M. coruscus settlement, although it may be strain specific. Additionally, the trend of induction activity of mussel larvae attachment varied with increasing initial bacterial density. The optimal density for settlement is strain specific. Further analysis of biofilm active substance content in Mesoflavibacter sp.2 and Phaeobacter sp.2 revealed that polysaccharide content negatively correlated with induction activity of M. coruscus and positively correlated with protein content. This suggests that bacterial species may not directly affect M. coruscus settlement, although bacteria may indirectly influence settlement by affecting the secretion of extracellular products.This study showed that nine bacterial strains had significant differences in their ability to induce mussel settlement on the surface of artificial reefs. Interestingly, these differences did not necessarily correlate with the genetic distance between the marine bacteria. Further investigations were conducted on two selected strains of bacteria (Mesoflavibacter sp.2 and Phaeobacter sp.) that exhibited different levels of inductive activity on M. coruscus. The polysaccharide content and protein content negatively and positively correlated with the induction activity of M. coruscus, respectively. This suggests that the presence of specific polysaccharides may negatively affect the settlement of M. coruscus according to cellulose content measurements.This is the first study investigating the effect of bacteria on M. coruscus settlement on the surface of artificial reefs. This has significant theoretical implications for further research on the interactions between biofilms and marine invertebrates on the surface of artificial reefs in natural marine environments. Understanding the settlement mechanisms of marine benthic organisms on artificial reefs is crucial to manage and conserve marine resources since artificial reefs are widely used to enhance marine habitat and biodiversity. The findings of this study have practical implications for the design and construction of artificial reefs. Understanding the role of bacteria in mussel settlement facilitates the optimization of artificial reef structures to promote or inhibit the settlement of target species. This knowledge can help develop effective strategies to manage biofouling on artificial reefs. This can impact the performance and longevity of these structures. Further research in this field will deepen our understanding of the underlying mechanisms and enable development of management strategies for artificial reefs and marine conservation efforts.

Keywords

• artificial reef
• mytilus coruscus
• mussel juvenile
• settlement
• biofilm