Experimental Studies On The Attractive Effects Of Sea Cucumber Artificial Reefs On Apostichopus Japonicus

The intensive exploitation of biological resources in the ocean leads to the problem of overfishing, which becomes more and more obvious in recent years. Meanwhile, with the rapid development of industrialization, environment pollution tends to be more serious than decades ago, and marine ecological environment, especially inshore environment, is deteriorating. Both problems above result in the rapid decline of sea cucumber resources around the world.In order to relieve the fishing pressure and recover sea cucumber resources, the development of sea cucumber artificial reefs has sprung up vigorously. Artificial reefs not only provide shelter for sea cucumbers but also improve aquatic environment, which helps to protect and enhance sea cucumber stocks. The construction of sea cucumber artificial reefs is crucially important in sea cucumber aquaculture and stock enhancement. Considering the above functions of artificial reefs, it is very necessary to study the attractive effects and mechanisms of sea cucumber artificial reefs. However, few studies have been conducted in this aspect. Considering the situation of lacking scientific experiment data, researches on artificial reefs are vitally important. This thesis mainly researches the attractive effects of artificial reefs on Apostichopus japonicus, and further explores the mechanisms of the attractive effects, which may offer some scientific information for the development of sea cucumber artificial reefs in the future. The structure of this thesis is as follows.The first chapter will give a detailed introduction of the biological traits, distribution and resource status of sea cucumbers, then studies the aquaculture and stock enhancement of sea cucumbers from the aspects of international trade, seed breeding, production and area of aquaculture and stock enhancement. This chapter may offer some valuable information about the techniques and studies of sea cucumber aquaculture and stock enhancement.The second chapter introduces the status quo of sea cucumber artificial reefs construction to offer references and ideas for studies on the attractive effects of sea cucumber artificial reefs. This chapter reviews the status and development of the studies on the attractive effects of artificial reefs on sea cucumbers, and focuses on discussing the problems in recent studies of sea cucumber artificial reefs.By analyzing the experimental phenomenon and results of the attractive effects of artificial reefs on sea cucumbers, the third chapter explores the mechanisms of artificial reefs when attracting sea cucumbers. Combining the behaviorism of sea cucumbers, this chapter concludes that the point of artificial reefs when attracting sea cucumbers is that they can relieve their survival pressure. The functioning mechanisms of sea cucumber artificial reefs are mainly related with environment effect, which includes feed effect, defense effect, shadow effect and water flow effect. This chapter may offer some theoretical evidences for further studies of sea cucumber artificial reefs.In the fourth chapter, based on the experimental methodologies of behavior study, the behaviors of Apostichopus japonicus under natural light in the experiment water tank with and without the artificial reef models (the control group) were observed. The body lengths of Apostichopus japonicus were 2~7 cm and body weights were 2~30 g. In the experiment, the bottom of water tank was divided into 15 areas and artificial reef models varied in shape, material and distance to the tank bottom. Mean distribution rates (MDR) of Apostichopus japonicus were recorded; the artificial reefs' mean attractive rates (MAR) were analyzed and compared. The experiment demonstrated that Apostichopus japonicus inclined to climb the tank wall and searched for shadows or narrow inter-space; meanwhile, in PVC reefs, Apostichopus japonicus passed through them but seldom stayed. MAR of the triangular prism reef model without bottom and space was very significantly different from that of the control group (P<0.01), and was much higher than that of the triangular prism reef model with bottom and space as well as model with bottom and without space (P<0.05). MAR of clay reef model was much higher than that of cement and PVC models (P<0.05). MAR of the tile reef model with a 3.4 cm distance from the tank bottom was very significantly different from that of the control group (P<0.01), and was much higher than that of the tile reef with a 0.8 cm distance from the tank bottom (P<0.05). The experiment results showed that: 1) artificial reefs had good attractive effects on Apostichopus japonicus; 2) preference for reef shapes was related to inter-space and brightness of shadows; 3) preference for reef materials was related to roughness of reef surface; 4) In a nutshell, between material and shape of artificial reefs, Apostichopus japonicus gave the latter a top priority.The last chapter describes the aspects in further studies. Experiments should be conducted to study whether the response of Apostichopus japonicus towards light and water flow is taxis or not; the construction of sea cucumber artificial reefs should be further improved to increase their attractive rates on sea cucumbers; design of sea cucumber fishing gears also needs to be studied.