Spat collection bed for juvenile bivalves that burrow in sand, and method for collecting juvenile bivalves therefrom.

Abstract

To provide a seedling collection bed for juvenile burrowing bivalves that can be easily mounted on a beach or the like and can smoothly discharge suspended mud in seawater, bivalve feces and the like by following the flow of seawater caused by tidal ebb and flow, and a method for collecting juvenile bivalves therefor.SOLUTION: The seedling collection bed includes: an enclosure frame 2 which is formed by a perforated pipe 3 having a rod-like elongated shape with a mesh-like peripheral surface, the perforated pipe being filled with pebbles 4; a substrate layer 5 in which crushed stones 51 are spread and filled within the enclosure frame mounted on a ground surface GL where seawater flows due to tidal ebb and flow; a mesh member 6 which covers an upper opening 20 of the enclosure frame and whose peripheral portion 61 is locked to the enclosure frame 2 or locked to the ground surface; a spacer 7 which is placed on an upper surface 5a of the substrate layer while securing a gap space S between the upper surface of the substrate layer and the mesh member 6; and a stopper 8 which locks the enclosure frame to the ground surface. The seedling collection bed allows floating larvae to settle and be grown into juvenile bivalves.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a juvenile seedling bed for infaunal bivalves such as Japanese littleneck clams, which allows the floating larvae of infaunal bivalves to settle to the bottom and grow into juveniles, and a method for cultivating juvenile seedlings of infaunal bivalves using the same.

Background Art

[0002] Infaunal bivalves such as Japanese littleneck clams have long occupied an important position as food in Japan. However, due to recent environmental degradation and nutrient deficiency in the sea, the production volume of Japanese littleneck clams in Japan has decreased to about 1 / 5 compared to the 1970s and 1980s. In view of such a situation, the present inventor has proposed inventions related to a method for cultivating infaunal bivalves and a cultivation structure for the same, aiming to recover the domestic production volume of shellfish (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Document 1, in "a cultivation structure for infaunal bivalves that is installed in a place where water flows due to the ebb and flow of the tide, allows the floating larvae of infaunal bivalves to settle to the bottom and grow into juveniles or adult shellfish, and has a container, a perforated pipe attached to the container, and a granular material filled in the container, and discharges excrement and the like of infaunal bivalves from the perforated pipe to the outside of the container by using the tidal flow during ebb and flow", the perforated pipe was an essential component. The outer periphery for supporting the filled granular material was a shielding structure whether it was a fence or a container, and the excrement of infaunal bivalves could only be discharged from inside the fence or the container to the outside through the perforated pipe.

[0005] Furthermore, the invention of an aquaculture structure in which perforated pipes laid inside an enclosure or container are filled with large-particle granular material, a separation net is placed on the surface, and then small-particle granular material is filled in, required the adoption of at least a two-layer structure, resulting in a complex structure. Furthermore, even when the aquaculture structure shown in Figure 5 of Patent Document 1 was manufactured and could be easily placed in a designated location on the tidal flat without taking much time, transporting it to the installation site was difficult. The container was three-dimensional and large, requiring considerable effort to transport to the designated location on the tidal flat. In addition, even if it could be placed in a short time after arriving at the designated location, it was heavy, and in some cases cranes or other equipment had to be used.

[0006] The present invention aims to solve the above problems by providing a seedbed for collecting juvenile bivalves that burrow into the sand, which does not require perforated pipes, is easy to transport and install on beaches, etc., and can smoothly discharge seawater sediment, shellfish feces, etc., in accordance with the flow of seawater due to the ebb and flow of the tides, and a method for collecting juvenile bivalves therefrom. [Means for solving the problem]

[0007] To achieve the above objective, a first aspect of the present invention provides a spat collection bed for juvenile bivalves that burrow into the seabed, characterized by allowing planktonic larvae to settle and grow into juvenile shellfish, comprising: an enclosure frame formed by long, rod-shaped perforated tubes with a mesh-like circumferential surface, the perforated tubes being filled with pebbles; a substrate layer in which crushed stone is laid within the enclosure frame and installed on the ground where seawater flows with the ebb and flow of the tide; a mesh-like member that covers the upper opening of the enclosure frame and whose peripheral edge is locked to the enclosure frame or to the ground; a spacer placed on the upper surface of the substrate layer, ensuring a gap space between the mesh-like member and the upper surface of the substrate layer; and a stopper that locks the enclosure frame to the ground. A second aspect of the present invention is the first aspect, characterized in that the spacer is made of a perforated tube. A third aspect of the present invention is the first or second aspect, characterized in that the holes in the perforated tube are formed as mesh-like through-holes that do not allow the pebbles to pass through, and further, the perforated tube and the perforated tube are made of a mesh-shaped resin member. A fourth aspect of the present invention is the third aspect, characterized in that the substrate layer comprises the crushed stone and granular neutralizing solids that dissolve in water and exhibit a weakly alkaline state, and the neutralizing solids neutralize the seawater in which the planktonic larvae of intertidal sand-burrowing bivalves drift, causing the planktonic larvae to settle and grow into juvenile shellfish. A fifth aspect of the present invention is the fourth aspect, characterized in that a rod-shaped reinforcing bar is formed into a U-shape as the stopper, and the end portions of the U-shaped legs that straddle the perforated tube from above are thrust into the ground to secure the enclosure frame to the ground. A fifth aspect of the present invention is a method for collecting juvenile bivalve spat, characterized by the following steps: filling the inside of a long, rod-shaped perforated resin tube with a mesh-like circumferential surface with pebbles to form an enclosure frame, which is then placed on the ground where seawater flows due to the ebb and flow of the tide, and then fixing the enclosure frame to the ground with a stopper; next, providing a substrate layer by laying crushed stone up to near the upper edge of the enclosure frame; then, placing a plurality of spacers made of small perforated resin tubes with a diameter smaller than the diameter of the perforated tube at intervals from each other on the upper surface of the substrate layer; and then covering the upper opening of the enclosure frame from above the spacers and the upper surface of the layer with a mesh-like member to complete a juvenile bivalve spat collection bed for the juvenile bivalve, which has a gap space between the upper surface of the substrate layer and the mesh-like member; and then allowing the planktonic larvae to settle and grow into juveniles. [Effects of the Invention]

[0008] The present invention provides a seedbed for collecting juvenile bivalves that burrow in the sand, and a method for collecting juvenile bivalves. The seedbed is easy to transport and install on beaches, and it follows the flow of seawater due to the ebb and flow of the tides well. It also allows for the smooth drainage of floating larvae and shellfish waste from the enclosed frame, enabling efficient collection of juvenile bivalves by allowing planktonic larvae to settle on the bottom. Furthermore, it accelerates the growth of the bivalves, making it possible to collect adult bivalves as well, thus offering numerous advantages. [Brief explanation of the drawing]

[0009] [Figure 1] This is one embodiment of the juvenile shellfish seedling bed and juvenile shellfish seedling method according to Embodiment 1, where (a) is a cross-sectional view of a perforated tube and (b) is a perspective view showing a portion thereof in the longitudinal direction. [Figure 2] (a) is a cross-sectional view of the perforated pipe that replaces Figure 1, and (b) is a front view showing a portion of it in the longitudinal direction. [Figure 3] This is a cross-sectional view of a perforated pipe in an alternative embodiment to that shown in Figure 1(a). [Figure 4] This is a plan view of the enclosure frame installed on the ground. [Figure 5] This is a view along the VV line in Figure 4. [Figure 6] This is a plan view showing the area within the enclosure shown in Figure 4, with spacers placed on a substrate layer made of crushed stone. [Figure 7] This is a view along the line VII-VII in Figure 6. [Figure 8] This is a plan view of the mesh-like member. [Figure 9] This is a partially broken cross-sectional view showing the upper opening of the enclosure frame in Figure 7 covered with a mesh member. [Figure 10] This is a partially broken cross-sectional view corresponding to Figure 9 in Embodiment 2. [Figure 11] This is a partial cross-sectional perspective image of Embodiment 3, in which a strip-shaped spat collection bed for burrowing bivalves is installed along the shoreline where seawater flows due to the ebb and flow of the tide. [Figure 12] This is another diagram of Embodiment 3, and is a cross-sectional view corresponding to Figure 10. [Modes for carrying out the invention]

[0010] The following describes in detail the juvenile bivalve spat collection bed (hereinafter also simply referred to as "juvenile spat collection bed") and the method for collecting juvenile bivalves according to the present invention. Figures 1 to 9 show one form of the juvenile spat collection bed and method for collecting juvenile bivalves according to Embodiment 1. In Figure 1, (a) is a cross-sectional view of a perforated tube and (b) is a perspective view thereof. In Figure 2, (a) is a cross-sectional view of a perforated tube replacing that in Figure 1 and (b) is a front view thereof. In Figure 3, a cross-sectional view of a perforated tube in another form replacing that in Figure 1(a). Figure 4 is a plan view of an enclosure frame installed on the ground. Figure 5 is a view taken along the line VV in Figure 4. Figure 6 is a plan view of the enclosure frame in Figure 4 with spacers placed on a substrate layer of crushed stone. Figure 7 is a view taken along the line VII-VII in Figure 6. Figure 8 is a plan view of a mesh member. Figure 9 is a cross-sectional view of the enclosure frame in Figure 7 with the top opening covered by the mesh member. Figure 10 is a cross-sectional view of Embodiment 2, corresponding to Figure 9; Figure 11 is a partial cross-sectional perspective view of Embodiment 3, showing a strip-shaped juvenile shellfish seedling bed installed along the shoreline; and Figure 12 is a cross-sectional view corresponding to Figure 10. Note that each figure has been simplified and the essential parts of the invention have been emphasized for clarity. Parts not directly related to the present invention have been omitted.

[0011] (1) Embodiment 1 (1a) Spat collection bed for juvenile sand-burrowing bivalves 1 The spat collection bed 1 for burrowing bivalves comprises an enclosure frame 2, a substrate layer 5, a mesh member 6, a spacer 7, and a stopper 8 (Figures 5, 7, and 9). The enclosure frame 2 is a frame formed by a porous mesh-like perforated tube 3 in which pebbles 4 are packed inside the tube and the circumferential surface of the tube is made up of long, rod-shaped perforated tubes 3, and the frame is formed to surround the substrate layer 5 so that it can be held in place. The perforated tube 3 that forms the frame is packed with pebbles 4. In plan view, it is a rectangular, specifically almost square, enclosure frame 2 as shown in Fig. 4, but it may also be a rectangular enclosure frame 2 with a vertically long long side, or further a rectangular enclosure frame 2 in plan view with a long side that is long and strip-shaped. The outer diameter D of the perforated pipe 3 is equal to the height h for securing the spat collection bed 1. Here, the outer diameter D of the perforated pipe 3 is 130 mmφ. An outer diameter D of the perforated pipe 3 of 80 mmφ to 200 mmφ is a preferable height for the spat collection bed 1. If the outer diameter D is less than 80 mmφ, it becomes insufficient to secure the space gap by the spacer 7 and the effect of the spat collection bed 1 for allowing larvae to settle on the bottom and become spat is insufficient. Also, if the outer diameter D exceeds 200 mmφ, the collection effect of the spat does not increase much and remains unchanged.

[0012] The perforated pipe 3 of the present embodiment is a mesh-like resin member having a mesh that does not allow the small stones 4 to pass through. For example, the perforated pipe 3 having a mesh structure with mesh-shaped through holes 39 formed by vertical threads 31 and horizontal threads 32 as shown in Fig. 1 penetrates from the pipe surface to the pipe inner surface. Specifically, a tri-cal pipe (registered trademark) manufactured by Takiron Shiaisin Building Co., Ltd. is used. The mesh-like pipe structure of the mesh-like framework is formed of a resin molding member of polyethylene or polypropylene by the vertical threads 31 and the horizontal threads 32 as shown in Fig. 1. In the figure, the symbol 31pt indicates the vertical thread pitch, and the symbol 32pt indicates the horizontal thread pitch. Not only the perforated pipe 3 having a mesh formed by the vertical threads 31 and the horizontal threads 32 in Fig. 1, but also a perforated pipe 3 having a mesh formed by diagonal threads 33 as shown in Fig. 2 may be formed. Also, as shown in Fig. 3(A), a perforated pipe 3 having outer fins 34 with a part of the vertical threads 31 protruding can be formed. The outer fins 34 can pierce the ground GL and stably fix the enclosure frame 2. Further, instead of the perforated pipe 3 having a circular cross-section in Figs. 1 to 3(A), a perforated pipe 3 having a rectangular cross-section as shown in Fig. 3(B) can also be used.

[0013] Here, perforated pipes 3 with an outer diameter of 130 mmφ and a rod-shaped length of 4 m are used, with the warp threads 31 and weft threads 32 in Figure 1 forming mesh perforations 39. Small pebbles 4 of No. 3 crushed stone 41, ranging in size from 30 mm to 40 mm, are packed into these perforated pipes 3. The perforated pipes 3, which are framed and installed on the ground GL where seawater flows, become immobile by being packed with pebbles 4, thus preventing them from moving in accordance with the seawater flow. The opening 30 of the perforated pipes 3, after being packed with pebbles 4, is closed with a cap (not shown). Using four of these pebble-filled perforated pipes 3, a rectangular enclosure frame 2 is formed as shown in Figures 4 and 5. The upper surface of the pebble layer 4 inside the perforated pipes 3 forming the enclosure frame 2 is approximately the same as the upper surface 5a of the matrix layer 5 described below in cross-sectional view (Figure 7). The way the pebbles 4 are packed into the perforated tube 3 is such that when the enclosure frame 2 is formed, a gap ε is created between the upper surface of the pebbles 4 layer and the upper inner surface of the perforated tube 3. This gap ε prevents the pebbles 4 from obstructing seawater flowing into the upper surface 5a of the substrate layer inside the enclosure frame 2 through the perforations 39 of the perforated tube 3, or when seawater on the upper surface 5a of the substrate layer flows out of the enclosure frame 2. A substrate layer 5, which will be the main part of the juvenile shellfish seedling bed 1, is provided within the enclosure frame 2.

[0014] The substrate layer 5 is the seeding body of the juvenile shellfish seeding bed 1 formed by spreading crushed stones 51 within an enclosure frame 2 installed on the ground GL where seawater flows due to the ebb and flow of the tide. Here, the outer diameter of the pipe of the perforated pipe 3, which is 130 mm φ, becomes the height h of the enclosure frame 2 and is installed on the ground GL. Within the enclosure frame 2, the crushed stones 51 are spread until the layer thickness 5t of the substrate layer 5 reaches approximately 80 mm (Figure 7). The layer thickness 5t of the substrate layer 5 is based on 80 mm, but the layer thickness 5t is appropriately adjusted at the laying location of the juvenile shellfish seeding bed 1 or where the sand movement is intense. The crushed stones 51 are spread until the height reaches the height obtained by subtracting the height of the spacer 7 from the height h of the enclosure frame 2. In Figure 7, the value obtained by subtracting the layer thickness 5t from the height h of the enclosure frame 2 is the height α of the gap space S, and the spacer 7 (details will be described later) with this height α is selected. The crushed stones 51 spread within the enclosure frame 2 are, for example, No. 6 crushed stones 51 with a granular feeling having a particle size of about 5 mm to 13 mm and No. 7 crushed stones 51 with a fine particle size of 2.5 to 5 mm, which are mixed and used. Specifically, the No. 6 crushed stones 51 and the No. 7 crushed stones 51 are mixed at 50% by weight and 50% by weight, respectively, and used. When mixing, 20 to 30 parts by weight of the neutral solid matter 52 described below is further mixed with respect to 100 parts by weight of the crushed stones 51. Incidentally, the crushed stones 51 referred to in the present invention include small round stones of the same size.

[0015] In this embodiment, the substrate layer 5 includes, in addition to the crushed stones 51, a granular neutral solid matter 52 that dissolves in water and exhibits weak alkalinity. The neutral solid matter 52 neutralizes the seawater in which the floating larvae of intertidal buried bivalves drift, causing the floating larvae to settle to the bottom and grow into juvenile shellfish. The neutral solid matter 52 is the granular hardened body neutral solid matter 52 disclosed in Patent No. 6864417. Specifically, it includes oyster shell powder, an alkaline binder whose main component is an inorganic magnesium compound, and a pH increase inhibitor whose main component is calcium sulfate or / and sodium hydrogen carbonate. The granular molded body formed by kneading and solidifying with water is hardened by being stored in a carbon dioxide gas atmosphere filled with carbon dioxide gas, which is the granular hardened body neutral solid matter 52.

[0016] The neutralizing solid 52 exhibits weak alkalinity when dissolved in seawater, neutralizing acidic substances in the acidic seawater. When the neutralizing solid 52 dissolves in the intertidal seawater where the bottom sediment that serves as the habitat for clams is becoming acidic, unlike the strongly alkaline nutrient supplement disclosed in Japanese Patent Application Publication No. 2004-33133, it does not cause a rapid increase in the alkalinity of the surrounding seawater, but rather dissolves gradually into the seawater, which becomes more acidic over time. Therefore, it does not put a load on the planktonic larvae of sand-burrowing bivalves that drift in the seawater. The pH environment of the seawater for the organisms living there can be sustainably improved for a long period of more than one month. By adjusting the pH environment of the seawater, which was on the acidic side where shellfish larvae float, to a pH environment where the larvae can easily settle, it is possible to allow the larvae to settle and then collect the grown juvenile clams at high density. Incidentally, clam larvae do not settle on the neutralized solids 52, but on the crushed stone 51. Therefore, in this embodiment, the crushed stone 51, which is used to settle the planktonic larvae of sand-burrowing bivalves such as clams, is mixed with the neutralized solids 52 in a range of 20 to 30 parts by weight, so that they are dispersed almost evenly. The crushed stone 51 containing the neutralized solids 52 is then laid out in the enclosure frame 2 as shown in Figures 6 and 7 to form the substrate layer 5.

[0017] The mesh member 6 is a net material that covers the upper opening 20 of the enclosure frame 2 and has its peripheral edge 61 secured to the enclosure frame 2 or to the ground GL (Figures 8 and 9). The mesh member 6 covers the upper opening 20 of the enclosure frame 2 and has its peripheral edge 61 secured to the enclosure frame 2, or is secured to the ground GL next to the enclosure frame 2 where seawater flows due to the ebb and flow of the tide. This embodiment provides a mesh member 6 of a Russell net manufactured using a knotless, lace-like knitting method. The mesh member 6 of the Russell net has a mesh size of 3.0 mm to 4.0 mm and prevents juvenile sand-burrowing bivalves that have settled on the crushed stone 51 from being preyed upon by predatory organisms such as black sea bream and moon snails.

[0018] The mesh member 6 is attached and secured to the perforated pipe 3 by fasteners (not shown) made of vinyl cable ties, so as to completely cover the upper opening 20 of the enclosure frame 2. Alternatively, the mesh member 6 can be secured to the perforated pipe 3 of the enclosure frame 2 by weaving the mesh into the perforated pipe 61 of the mesh member 6, or by sewing a tag onto the raschel mesh of the mesh member 6 with a sewing machine, and then passing a fastener 65 with a rope through it. The fastener 65 in Figure 8 has a hook attached to the end of the rope. Instead of the fastener 65, an anchor may be attached to the end of the rope, and the anchor may be driven into the ground GL around the enclosure frame 2 to secure the mesh member 6. Furthermore, the mesh member 6 of this embodiment is fitted with a fastener 62 as shown in Figure 8. When harvesting juvenile shellfish that have grown after the floating larvae have settled on the seed bed, or when harvesting larger adult shellfish, the mesh member 6 can be easily opened with the fastener without having to remove the locking device 65 from the surrounding frame 2, allowing for easy harvesting.

[0019] The spacer 7 is a gap space forming body placed on the upper surface 5a of the substrate layer 5 to secure a gap space S between the upper surface 5a of the substrate layer 5 and the mesh member 6 (Figure 9). The spacer 7 may be, for example, a block with a height α of the gap space S, scattered on the upper surface 5a of the layer. However, in this embodiment, the spacer 7 is a small perforated tube 71 with a diameter smaller than the outer diameter D of the perforated tube 3 (corresponding to the height α of the gap space).

[0020] When the top opening 20 of a 4m x 4m enclosure frame 2 having a substrate layer 5 is covered with a mesh member 6, the mesh member 6, particularly the central part of the net, sags and comes into contact with the top surface 5a of the substrate layer 5. This condition inhibits the settlement of juvenile shellfish and the growth of juvenile shellfish that have settled. Therefore, a spacer 7 is placed between the top surface 5a of the substrate layer 5 and the mesh member 6 to create a gap space S and eliminate the above-mentioned inhibiting factor. In order to ensure a uniform gap space S, perforated tubes 71 are arranged in parallel at intervals of approximately 1.0m as shown in Figure 6. Furthermore, the perforated tubes 71 may be arranged in a cross shape. The perforated tubes 71 that serve as spacers 7 are products of Takiron C.I.S. Building Co., Ltd., with a diameter of approximately 50mmφ, and are resin molded members with a mesh formed by diagonal threads 33 as shown in Figure 2. Even if the perforated pipe 71 is installed, the numerous holes in the perforated pipe do not obstruct the movement of water entering and leaving the enclosure frame 2. In this embodiment, the perforated tubes 71 are separate from the mesh member 6. However, the perforated tubes 71, which are arranged in parallel at 1.0m intervals on the lower surface of the mesh member 6 and on the upper surface opening 20 of the enclosure frame 2, can be attached and fixed to each other in advance using cable ties, for example, to improve the efficiency of the installation work of the juvenile shellfish seedling bed 1.

[0021] The stopper 8 is a locking member that secures the enclosure frame 2 to the ground GL. Here, the stopper 8 is made of a rod-shaped reinforcing bar formed into a U shape (Figures 4 and 5). The stopper is made in an inverted U shape, and the tips 821 of the two U-shaped legs 82 that straddle the perforated pipe 3 from above are thrust into the ground GL next to the enclosure frame 2, which is installed on the ground GL where seawater flows due to the ebb and flow of the tide, thereby playing the role of locking and fixing the enclosure frame 2 to the ground GL.

[0022] The enclosure frame 2, substrate layer 5, mesh member 6, spacer 7, and stopper 8 are provided, and the substrate layer 5 is placed inside the enclosure frame 2 which is locked and fixed to the ground GL by the stopper 8, the spacer 7 is placed on the upper surface 5a of the substrate layer, and the spacer 7 and the upper opening 20 of the enclosure frame 2 are covered with the mesh member 6 to form the juvenile shellfish spat bed 1. By installing the enclosure frame 2 on the ground GL where seawater flows with the ebb and flow of the tide, a desired juvenile shellfish spat bed 1 for burrowing bivalves is created in which planktonic larvae in seawater can settle and grow into juvenile shellfish.

[0023] (1b) Method for collecting juvenile bivalves that burrow in the sand Next, we will describe an example of a method for collecting juvenile bivalve spat of sand-burrowing mollusks, using the aforementioned enclosure frame 2, which includes a perforated pipe 3 filled with pebbles 4, crushed stone 51, a substrate layer 5, a mesh member 6, a spacer 7, and a stopper 8. First, fill the inside of a long, rod-shaped perforated resin pipe 3 with pebbles 4, which has a mesh-like surface around its circumference. Fill the perforated pipe 3, which has an outer diameter of 130 mmφ and a length of approximately 4 m, with pebbles 4 of No. 3 crushed stone 41. After filling the inside of the pipe with pebbles 4, seal the pipe opening 30 with a polyvinyl chloride cap (not shown) to form four perforated pipes 3 filled with pebbles 4. Note that this work may be done before driving to the beach or other location.

[0024] Next, an enclosure frame 2 is installed on the ground level (GL) where seawater flows due to the ebb and flow of the tide. This enclosure frame 2 is formed using four perforated pipes 3 containing pebbles 4, as shown in Figure 4. The enclosure frame 2 is then fixed to the ground level (GL) with stoppers 8. The U-shaped stoppers 8 are positioned in an inverted U shape, and the tips 821 of the U-shaped legs 82 that straddle the perforated pipes 3 are thrust into the ground level (GL) from above, thereby locking and fixing the enclosure frame 2 to the ground level (GL) (Figure 5). The mounting pitch of the stoppers 8 to the enclosure frame 2 is approximately 1.0 m. The tips 821 of the legs 82 of the stoppers are buried to a depth of about 60 cm in the ground level (GL) where seawater flows.

[0025] Subsequently, the crushed stone 51 containing the neutralized solids 52 is laid within the enclosure frame 2, which is fixed to the ground level (GL) so as not to move, up to near the upper edge of the enclosure frame 2, to form a substrate layer 5. The crushed stone 51 containing the neutralized solids 52 is prepared by mixing 20 to 30 parts by weight of the neutralized solids 52 with 100 parts by weight of the crushed stone 51. In this embodiment, in order to ensure a substrate layer thickness of 5t for a frame height h of 130mm, crushed stone No. 6 51 and / or crushed stone No. 7 51 are laid inside the frame to a height of approximately 80mm from the ground level (GL) inside the frame. Gaps are left between the crushed stones 51.

[0026] Next, multiple spacers 7, each consisting of a resin perforated tube 71 with a diameter smaller than that of the perforated tube 3, are placed on the upper surface 5a of the substrate layer 5, spaced apart from each other. Here, resin perforated tubes 71 with an outer diameter of 50 mmφ and a length of approximately 4 m are arranged in parallel on the upper surface 5a of the substrate layer 5 within the enclosure frame 2 at a pitch of approximately 1.0 m (Figure 6). Both ends of the perforated tubes 71 are locked and fixed to the enclosure frame 2.

[0027] Subsequently, the upper opening 20 of the enclosure frame 2 is covered with the mesh member 6 from above the spacer 7 and the upper surface 5a of the layer, thereby completing the juvenile bivalve spat collection bed 1 for burrowing sand mollusks, with a gap space S secured between the upper surface 5a of the substrate layer 5 and the mesh member 6. The mesh member 6 is secured to the enclosure frame 2 with a fastener 65 having a rope woven into the peripheral edge 61 of the mesh member 6, thereby maintaining the state in which the top opening 20 is covered. The fastener 65 may be replaced with a vinyl cable tie. One block of juvenile oyster spat collection bed 1 measuring approximately 4m x 4m in plan view is completed, and multiple juvenile oyster spat collection beds 1 are completed by placing them close together according to the above procedure. In addition, the enclosure frame 2 for the juvenile oyster spat collection bed 1, which measures approximately 4m x 4m in plan view, can also be changed to a vertically elongated juvenile oyster spat collection bed 1 measuring approximately 4m x 8m or 4m x 12m in plan view by connecting perforated pipes 3 with a basic length of 4m vertically. Subsequently, the ebb and flow of seawater due to the tides causes the floating larvae to settle on the completed juvenile shellfish seedling bed 1 and grow into juvenile shellfish, thus becoming a method for collecting juvenile shellfish of the desired sand-burrowing bivalve species.

[0028] (2) Embodiment 2 In this embodiment, the juvenile clam spat collection bed 1 has a substrate layer 5 formed of crushed stone 51 that does not contain the neutralizing solids 52 of Embodiment 1 (Figure 10). A juvenile clam spat collection bed 1 in which crushed stone 51 without neutralizing solids 52 is laid in an enclosure frame 2 installed on the ground GL where seawater flows due to the ebb and flow of the tide, can also allow planktonic larvae in seawater to settle on the bottom and grow into juvenile clams such as Manila clams, which can then be harvested. Furthermore, in the case of the juvenile clam seedling bed 1 of Embodiment 1, in which the crushed stone 51 is mixed with neutralized solid matter 52, not only can juvenile clams such as Manila clams be collected, but the growth of the clams is accelerated, so adult clams with a shell length of 25-30 mm can also be collected. Other components are the same as in Embodiment 1, and their description is omitted. The same reference numerals as in Embodiment 1 indicate the same or corresponding parts.

[0029] (3) Embodiment 3 This embodiment is a juvenile shellfish seedling bed 1 as shown in Figure 11, which is a rectangular enclosure frame 2 in plan view with its long side elongated in a strip shape. The perforated pipes 3 here are made of mesh-shaped polyvinyl chloride molded members (PVC mesh pipes). For example, the enclosure frame 2 is formed by connecting perforated pipes with a unit length of 4 m in a strip direction. In Figure 11, perforated small pipes 71 are arranged in the longitudinal direction at the passage points of a pair of long-side perforated pipes 3 so as to be approximately parallel to the long-side perforated pipes 3. In the figure, the dashed lines indicating breaks in the perforated small pipes 71 represent the holes. Here, if the width of the enclosure frame 2 is narrowed to approximately 0.5m to 1.5m, the perforated tubes 71 may be arranged at regular intervals so as to cross the long-side perforated tubes 3 that run in the longitudinal direction, and both ends of the perforated tubes 71 may be secured to a pair of the long-side perforated tubes 3. Like a ladder, the perforated tubes 71 that serve as footholds are arranged at a predetermined pitch between the two long perforated tubes 3. By providing the perforated tubes 71 at a predetermined pitch in the longitudinal direction of the enclosure frame 2, the mesh member 6 is prevented from sagging and coming into contact with the upper surface 5a of the substrate layer.

[0030] Furthermore, the juvenile shellfish seedling bed 1 is equipped with a surrounding frame 2, a substrate layer 5, a mesh member 6, a spacer 7, a stopper 8, and a rope 9. The spacer 7 is placed on the upper surface 5a of the substrate layer 5, and the mesh member 6, which covers the upper opening 20 of the enclosure frame 2, is placed above the upper surface 5a of the layer. The rope 9 is then placed over it from above, and the enclosure frame 2 and the mesh member 6 are tied and fixed together in a zigzag pattern as shown in the figure. Specifically, at the point where the rope 9 bends in a zigzag pattern toward the longitudinal direction of the long-side perforated pipe 3 of the enclosure frame 2, an anchor (not shown) engaged with the bend is driven into the ground GL near the outer edge of the strip-shaped enclosure frame 2, thereby firmly locking and fixing the enclosure frame 2 and the mesh member 6 with the rope 9.

[0031] Incidentally, as shown in Figure 11, if a rectangular enclosure frame 2, whose longer side is elongated in a band-like manner, is placed along the shoreline where seawater flows due to the ebb and flow of the tide, the longer the frame, the greater the influence it will receive from the incoming waves. It will be difficult to maintain the initial plan view shape as shown in Figure 11 when the enclosure frame 2 is installed, and there is a risk that it will meander or bend significantly. The rope 9 plays the role of maintaining the initial plan view shape of the enclosure frame 2 (juvenile shellfish seedling bed 1) installed along the shoreline. Furthermore, Figure 11 shows that the internal space of the perforated pipe 3 is filled with small stones 4 of crushed stone No. 3 41, without leaving an empty space ε as shown in Figure 5.

[0032] Figure 12 is a cross-sectional view corresponding to Figure 10, showing another embodiment where the width of the enclosure frame 2 for the juvenile shellfish seedling bed 1 in Figure 11 is approximately 2 m. When the width of the enclosure frame 2 is narrower to approximately 2 m compared to Embodiment 1, a long perforated tube 71 is placed approximately in the middle of the pair of long-side perforated tubes 3 related to the enclosure frame 2, parallel to the long-side perforated tubes 3 and extending in the longitudinal direction. By placing the perforated tube 71 approximately in the middle of the pair of long-side perforated tubes 3, the mesh member 6 is prevented from sagging in the width direction and coming into contact with the upper surface 5a of the substrate layer. Of course, instead of the perforated tube 71, perforated tubes 71 as described in Figure 11, which act as ladder crossbars, may be provided with a narrower spacing between them. In addition, in Figure 12, a void portion ε similar to that in Figure 5 is provided inside the perforated tube 3 and filled with pebbles 4. Other components are the same as in Embodiments 1 and 2, and their description is omitted. The same reference numerals as in Embodiments 1 and 2 indicate the same or corresponding parts.

[0033] (4) Effects According to the above-described seed collection bed and seed collection method for burrowing bivalves, the enclosure frame 2 is formed using long, rod-shaped perforated tubes 3 with a mesh-like surface around the tubes. As seawater flows, hydrogen sulfide from the seawater, including sediment and clam feces, that enters the enclosure frame 2 can flow out of the enclosure frame 2 through the perforations 39 of the perforated tubes 3 and the gaps between the pebbles 4. There is no need to provide the perforated tubes described in Patent Document 1. The present invention eliminates the need for heavy, large-particle-grained powders used to fill perforated pipes, as described in Patent Document 1, thus significantly contributing to weight reduction.

[0034] Patent Document 1 describes a method in which perforated pipes are filled with large stones up to approximately the middle height of the enclosure, a mesh separation net is laid on top of it, and a substrate layer 5 is provided on top of it, so that hydrogen sulfide from seawater silt and clam feces can flow out of the enclosure frame 2 through the perforated pipes. However, in the present invention, the enclosure frame 2 is formed of perforated pipes 3, so such perforated pipes, large stones, mesh separation nets, etc. become unnecessary. This invention allows for the completion of a juvenile shellfish seedling bed 1 simply by providing an enclosure frame 2, a substrate layer 5, a mesh member 6, a spacer 7, and a stopper 8, resulting in a simple structure and low equipment costs.

[0035] Furthermore, although pebbles 4 are packed inside the perforated tube 3, there are gaps between the pebbles 4, allowing the floating sediment and clam feces from the seawater that has entered the enclosure frame 2 to flow out. Moreover, if a gap portion ε is provided between the upper surface of the layer of pebbles 4 and the upper inner surface of the perforated tube 3 as shown in Figure 5, the pebbles 4 can flow out smoothly without obstruction. As shown in Figure 9, when the pebbles 4 are used as the enclosure frame 2, if the top surface of the packed pebbles 4 is aligned with the upper surface 5a of the substrate layer, the pebbles 4 do not obstruct the movement of seawater flowing over the upper surface 5a of the substrate layer. Unlike conventional barriers made of concrete blocks used in Patent Document 1, etc., seawater enters through the perforations 39 in accordance with the ebb and flow of the tide. Furthermore, the seawater that enters the enclosure frame 2 can effectively follow the flow of seawater caused by the ebb and flow of the tide and flow out. Thus, since the planktonic larvae of natural clams and other shellfish naturally settle on the crushed stone 51 of the seed bed, there is no need to purchase juvenile clams.

[0036] Furthermore, the method for collecting juvenile bivalve spat is designed with a relatively simple structure in which the spat collection bed 1 consists of an enclosure frame 2, a substrate layer 5, a mesh member 6, a spacer 7, and a stopper 8, and each component part can be separated. This allows for compact storage, saving space and facilitating transportation to beaches and other locations. Assembly and installation of the spat collection bed 1 is also easy due to its structure. It can be assembled and installed manually without the use of large machinery. For example, after creating a perforated pipe 3 filled with pebbles 4, an enclosure frame 2 is formed on the ground level (GL) of a sandy beach or other location where it will be installed, and the enclosure frame 2 is fixed with a stopper 8. Next, crushed stone 51 is laid inside the opening frame to form a substrate layer 5, spacers 7 are placed on the upper surface 5a of the substrate layer, and then the spacers 7 and the upper opening 20 of the enclosure frame 2 are covered with a mesh member 6, and the mesh member 6 is fixed to the enclosure frame 2 or the ground level (GL), thereby completing the juvenile shellfish seedling bed 1. Labor burden is also reduced. Working time can be shortened, and installation can be done during low tide. After that, seawater flowing with the ebb and flow of the tide enters the enclosure frame 2, and the floating larvae settle on the crushed stone 51 and grow into juvenile shellfish.

[0037] Furthermore, by creating a substrate layer 5 by spreading a mixture of crushed stone 51 and granular neutralized solids 52 within the enclosure frame 2, not only can juvenile shellfish be collected, but the growth of the shellfish is accelerated, making it possible to collect adult shellfish with a shell length of 25-30 mm.

[0038] Furthermore, if the perforated tube 3 and the perforated small tube 71 are made of a mesh-shaped resin molded member, the weight can be reduced due to the resin material, the burden of installing the enclosure frame 2 can be further reduced, and the assembly time of the juvenile shellfish seedling bed 1 can be shortened. Furthermore, it is possible to prepare perforated tubes 3 with pebbles 4 in advance on land, and by preparing in this way on land, the assembly time for the juvenile shellfish seedling bed 1 on the sandy beach where the enclosure frame 2 is installed can be further reduced.

[0039] Furthermore, if the stopper 8 is formed in a U-shape, and is also made in an inverted U-shape, the tips 821 of its legs 82 that straddle the perforated pipe 3 from above are thrust into the ground GL, the arc-shaped head 81 of the U-shaped stopper 8 can be aligned with the arc-shaped cross-section of the perforated pipe 3, thereby increasing the degree of contact between the two and securely locking the enclosure frame 2 to the ground GL.

[0040] Furthermore, the present invention is not limited to those shown in the embodiments described above, and can be modified in various ways within the scope of the present invention depending on the purpose and application. The shape, size, number, material, etc. of the juvenile clam seedling bed 1, enclosure frame 2, perforated tube 3, pebbles 4, substrate layer 4, mesh member 6, spacer 7, stopper 8, etc. can be appropriately selected according to the application. The embodiments have mainly described clams in the intertidal zone, but this neutralizing solid 52 is an invention for neutralizing seawater in the intertidal zone and can of course be applied to other organisms that live in the intertidal zone other than clams. The shape of the enclosure frame 2 is based on a 4m x 4m form using a 4m long perforated tube 3, but for example, a juvenile clam seedling bed 1 may be made by forming a 3m x 3m enclosure frame 4 using a 3m long perforated tube 3. [Explanation of Symbols]

[0041] 1 Young shellfish nursery 2 Enclosure Frame 3-hole empty tube 4 pebbles 5 Substrate layer 51 Crushed stone 52 Granular neutralized solids 6 Mesh member 7 Spacers 8 Stoppers

Claims

1. A frame is formed by creating a mesh-like surface around the pipes and using long, rod-shaped perforated pipes, with small stones packed inside the perforated pipes. A substrate layer made of crushed stone is laid within the aforementioned enclosure frame installed on the ground where seawater flows due to the ebb and flow of the tide, A mesh-like member that covers the upper opening of the enclosure frame and whose peripheral edge is secured to the enclosure frame or to the ground, A spacer is placed on the upper surface of the layer, with a gap space secured between the mesh member and the upper surface of the substrate layer, The enclosure frame is equipped with a stopper for securing it to the ground, A spat collection bed for juvenile sand-burrowing bivalves, characterized by allowing planktonic larvae to settle on the seabed and grow into juvenile shellfish.

2. The seedbed for collecting juvenile bivalves that burrow in sand, according to claim 1, wherein the spacer consists of a perforated tube.

3. The spat collection bed for juvenile sand-burrowing bivalves according to claim 1 or 2, wherein the holes in the perforated tube are formed as mesh-like perforations that do not allow the pebbles to pass through, and further, the perforated tube and the perforated tubular parts are made of a mesh-shaped resin material.

4. The substrate layer comprises the crushed stone and granular neutralizing solids that dissolve in water and exhibit a weakly alkaline state, and the neutralizing solids neutralize the seawater in which the planktonic larvae of sand-burrowing bivalves drift in the intertidal zone, thereby causing the planktonic larvae to settle and grow into juvenile shellfish, as described in claim 3.

5. The spat collection bed for juvenile sand-burrowing bivalves according to claim 4, wherein the stopper is formed from a rod-shaped reinforcing bark into a U-shape, and the tip portions of the U-shaped legs, which are in an inverted U-shape and straddle the perforated pipe from above, are thrust into the ground, thereby securing the enclosure frame to the ground.

6. A method for collecting juvenile bivalves of the sand-burrowing bivalve species, characterized by: filling the inside of a long, rod-shaped perforated resin tube with a mesh-like circumferential surface with pebbles to form an enclosure frame, installing the enclosure frame on the ground where seawater flows due to the ebb and flow of the tide, fixing the enclosure frame to the ground with stoppers, then providing a substrate layer by laying crushed stone up to near the upper edge of the enclosure frame, then placing a plurality of spacers made of small perforated resin tubes with a diameter smaller than the diameter of the perforated tube at intervals from each other on the upper surface of the substrate layer, and then covering the upper opening of the enclosure frame from above the spacers and the upper surface of the layer with a mesh-like member to complete a juvenile bivalve spat collection bed for sand-burrowing bivalves, thereby ensuring a gap space between the upper surface of the substrate layer and the mesh-like member, and then allowing the planktonic larvae to settle and grow into juvenile bivalves.

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