Red tide control agent
A red tide control agent made from dried sea lettuce with a thickening agent addresses the limitations of current methods by ensuring effective, adjustable, and sustained algal control with rapid distribution and long-term storage.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- 奥西 将之
- Filing Date
- 2022-03-15
- Publication Date
- 2026-05-19
AI Technical Summary
Current methods for controlling red tides, such as symptomatic treatments and physicochemical/biochemical interventions, are costly, time-consuming, or have environmental impacts, and existing red tide control agents lack sustained release properties and effective distribution mechanisms.
A red tide control agent is formulated by molding dried sea lettuce with a thickening agent to achieve controlled sustained release, allowing for adjustable dissolution rates and long-term storage.
The agent effectively kills various red tide-causing plankton species and can be stored for over two years, providing immediate or sustained algal control as needed, with even distribution and rapid action possible through particle formation.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a red tide control agent, and particularly to a red tide control agent having sustained release properties.
Background Art
[0002] Red tides cause the death of fishery animals and are particularly a major problem in the aquaculture industry.
[0003] When a red tide occurs, symptomatic treatments such as blocking food to minimize damage or moving the aquaculture cages from the red tide area to an area where no red tide has occurred are taken. This treatment requires excessive labor and high costs.
[0004] Regarding the generated red tides, physicochemical methods such as UV irradiation, chemical agent spraying, and clay spraying, and biochemical treatments using algicidal bacteria and viruses have been attempted, but few have been put into practical use due to the implementation scale, cost, and environmental impact.
[0005] On the other hand, seaweeds generally contain chemical substances that exclude others, which is commonly called allelopathic action. It has been conventionally known that the green seaweeds used in the present invention also exhibit algicidal properties against microalgae.
Prior Art Documents
Patent Documents
[0006] None
Non-Patent Documents
[0007]
Non-Patent Document 1
[0008] As mentioned above, symptomatic treatments such as withholding food or moving the fish farms are currently the most practical and widely adopted methods, but they have the drawback of being extremely costly and time-consuming.
[0009] On the other hand, physicochemical methods such as UV irradiation, as well as biochemical treatments using algaecides and viruses, have hardly been put into practical use due to their scale of implementation, cost, and environmental impact.
[0010] On the other hand, as mentioned above, it is a well-known fact that sea lettuce possesses algal-killing properties. Therefore, it is certainly possible to directly introduce fresh sea lettuce into areas contaminated with red tide, but handling sea lettuce, which contains a large amount of water, requires considerable effort and has the disadvantage of being difficult to store.
[0011] Furthermore, as explained below, dried sea lettuce also has algaecidal properties, but when scattering dried sea lettuce powder in the event of a red tide near a fish farm, a slight breeze can make it difficult to distribute it evenly across the target area.
[0012] Furthermore, even when a red tide occurs and some kind of red tide control agent is used, there are various situations, such as when an emergency response is necessary, or when it is not an emergency but sustained algal action is required. Therefore, the aforementioned red tide control agent needs to have sustained release properties that can be adapted to each situation. However, the current situation has the drawback that it cannot be expected to meet these various requirements.
[0013] This invention was proposed in view of the above-mentioned conventional circumstances, and aims to provide a red tide control agent that is easy to spray, allows for adjustment of its sustained release over a certain period of time, and can withstand long-term storage. [Means for solving the problem]
[0014] This invention relates to a red tide control agent, which is made by molding dried sea lettuce with a thickening agent at a concentration appropriate for its sustained release in the sea.
[0015] The concentration of the thickener is 0-25 w% (excluding 0). After adding enough water to the mixture of dried sea lettuce and thickener to form the product, it is dried at 40-60°C for 6-24 hours to completely remove the moisture. The lower limit of the thickener is the amount of thickener that allows the dried sea lettuce to maintain its shape, and this depends on the type of thickener. There is no particular upper limit, but 25 w% is used to achieve sustained release within 1 hour. [Effects of the Invention]
[0016] With the above configuration, the ease of solubility in seawater (sustained release) can be controlled by controlling the amount of thickener, making it possible to obtain a red tide removal agent that is suitable for the type and occurrence of red tides.
[0017] Also, as described above, by molding and drying, the lower the concentration of the thickener, the faster the dissolution rate in water. When immediate effect is required, it is conceivable not to add the thickener. Also, as a storage period, the algicidal effect can be maintained for about two years.
Brief Description of the Drawings
[0018] [Figure 1] Photograph showing a red tide remover obtained by solidifying dried sea lettuce with starch. [Figure 2] Graph showing the algicidal property of sea lettuce against Heterosigma akashiwo. [Figure 3] Graph showing the algicidal property of sea lettuce against Karemia mikimotoi. [Figure 4] Graph showing the algicidal property of sea lettuce against Chattonella marina. [Figure 5] Graph showing the algicidal property of sea lettuce against Cochlodinium polykrikoides. [Figure 6] Graph showing the algicidal property of sea lettuce against the water-soluble dissolved fraction of sea lettuce. [Figure 7] Graph showing the algicidal property of sea lettuce against the methanol extract fraction of sea lettuce. [Figure 8] Graph showing an application example of the present invention to an actually occurring red tide.
Modes for Carrying Out the Invention
[0019] <Preparation of Samples> Natural anae sea lettuce growing in Nagashima, Kagoshima Prefecture was collected and washed with filtered seawater.
[0020] Sample (1): 10 g of the above sea lettuce and 300 mL of filtered seawater were put into a mixer and chopped fresh sea lettuce for 5 seconds.
[0021] Sample (2): Dried sea lettuce obtained by drying the above fresh sea lettuce at 50 °C using a heating dryer.
[0022] Sample (3): 10 g of collected Ulva lactuca was freeze-dried, immersed in 90 mL of distilled water, stirred overnight with a stirrer, and the supernatant was freeze-dried again. This dissolved fraction was then dissolved in distilled water to obtain a water-soluble solution.
[0023] Sample (4): Methanol extract fraction obtained by immersing freeze-dried Ulva in methanol, concentrating the supernatant, and then dissolving it again in methanol.
[0024] Sample (5): Dried Ulva (Sample 1) was mixed with starch, dried for a specified time to solidify, and used as a red tide control agent (Figure 1). See Experiment 3 below for details.
[0025] <Experiment> The algal-killing properties of each of the above samples against red tide algae were examined.
[0026] (Experiment 1) Various red tide-causing plankton were cultured together with Ulva purtusa from sample 1 (fresh Ulva) and sample 2 (dried Ulva). The amount added was 0.1 g of fresh Ulva (sample (1)) crushed in the aforementioned mixer per 10 mL of culture solution of red tide-causing plankton. Since the water content of the fresh Ulva is approximately 90%, 0.01 g of dried Ulva (sample (2)) was added.
[0027] Figure 2 shows the algal action against Heterosigma akasiwo.
[0028] In the control group (a) without added sea lettuce, the number of motile cells remained almost unchanged after 24 hours of mixed culture. In contrast, in the group with added fresh sea lettuce (b), the number of motile cells began to decrease after 3 hours, and after 12 hours, almost no motile cells were observed. This trend was even more pronounced in the group with added dried sea lettuce (c), where the number of motile cells was about 15% of the pre-addition level after 3 hours, and nearly zero after 6 hours.
[0029] Figure 3 shows the algal action against Karenia mikimotoi.
[0030] In the control group (a) without added sea lettuce, the number of motile cells remained almost unchanged after 24 hours of mixed culture, similar to Heterosigma akasiwo. In contrast, the group with added fresh sea lettuce (b) showed a gradual decrease over time. In the group with added dried sea lettuce (c), the number of motile cells was about 10% of the pre-addition level after 3 hours, and nearly zero after 6 hours.
[0031] Figure 4 shows the algal action against Chatonella marina.
[0032] In both the fresh sea lettuce supplementation group (b) and the dried sea lettuce supplementation group (c), it can be seen that the number of motile cells gradually decreased, reaching about half of the initial number after 24 hours.
[0033] Figure 5 shows the algal action against Cohlodinium polykrikoides.
[0034] In the fresh sea lettuce supplementation group (b), a gradual decrease in the number of motile cells was observed over time. After 3 hours, the number of motile cells was 65% of the initial level, after 6 hours it was approximately 40%, and after 24 hours it was about 10%. In the dried sea lettuce supplementation group (c), after 1 hour the number of motile cells was about 16% of the initial level, and after 12 hours it was almost zero.
[0035] From the above, it can be understood that dried Ulva (sample 2) exhibits algalicidal activity against various types of red tide-causing plankton, regardless of their species.
[0036] (Experiment 2) The algal action of the Ulva extract against red tide algae was investigated using Sample 3 (water-soluble solubility fraction) and Sample 4 (methanol-extracted fraction).
[0037] Figure 6 shows the ratio of the number of motile cells to the number before addition when the water-soluble fraction of sample 3 was added to various red tide algae and cultured, counted 6 hours after addition.
[0038] The amount added was 0.1 ml for both sample 3 and sample 4 per 10 ml of red tide-causing plankton.
[0039] The effects were observed in the order of Cohlodinium polykrikoides > karenia mikimotoi > Chatonella marina, but almost no effect was observed for Heterosigma akasiwo.
[0040] On the other hand, Figure 7 shows the number of motile cells after 6 hours of culture when the methanol extract fraction of sample 4 was added to various red tide algae, expressed as a percentage of the number of cells before addition. It can be seen that a much greater effect is obtained than with the water-soluble lysis fraction. From the above, it can be understood that the methanol extract fraction of Ulva is effective in controlling various types of red tide algae.
[0041] (Experiment 3) By the way, if we consider the case where dried sea lettuce is used as a red tide control agent when a red tide occurs near a fish farm, the sea lettuce would be added in powder form. In this case, even a slight breeze would make it difficult to distribute it evenly to the target area. To solve this problem, it is preferable to process the dried sea lettuce into a solid state.
[0042] In this case, it is preferable to form the control agent into particles of a predetermined size and in a shape that is easy to handle. Therefore, sample 2 (dried sea lettuce) was solidified into particles of a predetermined size with 10 wt% starch and dried for 7 hours to control red tide (Figure 1). Figure 7 shows the results of adding this red tide control agent to the culture solution of various red tide-causing plankton at a concentration of 1 wt%.
[0043] With the exception of H. akashio, all other species lost almost all of their motility within one hour, and even H. akashio had almost completely lost its motility after three hours.
[0044] (Experiment 4) The red tide control agent using Ulva, as described above, primarily demonstrated effectiveness against cultured microalgae that cause red tides, but its effectiveness against red tides (Chatonella antica) that actually occurred in coastal waters was also confirmed.
[0045] In July 2021, a red tide caused by Chatonella antica occurred in the Yatsushiro Sea. On July 12, it was observed over a wide area of the Yatsushiro Sea, with a maximum density of 308 cells / mL in Kusunoura Bay, Kumamoto Prefecture. Subsequently, on July 15, the area expanded further, and the highest density reached 1,889 cells / mL in the northern part of Otsukishima Island, Kumamoto Prefecture.
[0046] Therefore, on July 18, surface water was collected at the location where a red tide was confirmed off Hishima Island, and 200 liters were placed in a 500 liter capacity panlight tank (confirmed on board the ship). A red tide control agent made from dried sea lettuce was added to this water at a concentration of 1% by weight of the seawater, and the number of Chatonella antica cells was counted at 5, 30, and 60 minutes. Similarly, the change in cell count over time when a red tide control agent was added at a concentration of 0.1% was also investigated.
[0047] The red tide control agent used here was made by solidifying dried sea lettuce with 5% by weight of starch.
[0048] The cell density of Chatonella antica in the collected seawater was 3,650 cells / mL. As shown in Figure 8, the cell density was 400 cells / mL 5 minutes after the addition of the control agent, and 50 and 100 cells / mL after 30 and 60 minutes, respectively.
[0049] In other words, the study showed that adding a 1% concentration of the Ulva red tide control agent killed 97.9% of the red tide algae within 60 minutes. On the other hand, the control group, which did not receive the red tide control agent, showed almost no change in cell density, from 1,200 cells / mL before the experiment to 1,257 cells / mL after 60 minutes.
[0050] In the test plots where a red tide control agent was added at a concentration of 0.1% relative to the weight of seawater, the cell density before addition was 1,156 cells / mL, and the cell densities after 5 minutes, 30 minutes, and 60 minutes were 1,400, 1,150, and 956 cells / mL, respectively. This indicates that 60.3% of the cells died after 60 minutes.
[0051] Thus, it became clear that while the time it takes for the effect to manifest decreases as the concentration of the additive decreases, it is still sufficiently effective against red tides that actually occur.
[0052] (Experiment 6) While starch has been given as an example of a thickening agent applicable to the present invention, the following examples of thickening agents can also be used. However, these are merely examples and do not preclude the use of other types of thickening agents.
[0053] Red tide control agents were prepared by varying the type of thickener used with dried sea lettuce, and the time it took for the sea lettuce to break apart in the beaker (corresponding to sustained release) was measured. The results when the amount of thickener was 5% by weight relative to the dried sea lettuce are shown in Table 1.
[0054] [Table 1]
[0055] Of course, if only one type of thickening agent is used, the time it takes for the material to break apart (sustained release) will vary depending on the amount added. If immediate action is required, a red tide control agent should be used with a thickening agent added in an amount close to zero, within the range that allows the dried sea lettuce to solidify.
[0056] The dried sea lettuce, individualized with the thickening agent described above, can be stored in granular form and was confirmed to exhibit the same algaecidal properties even after being stored for more than two years. While there is no particular upper limit, to achieve sustained release within one hour, the amount is approximately 25 w% depending on the type of thickening agent. [Industrial applicability]
[0057] As described above, the present invention exhibits algal action against various types of red tide-causing plankton and can also be stored, making it extremely useful for the aquaculture industry. [Explanation of symbols]
[0058] (a) Without sea lettuce (b) Fresh sea lettuce (c) Dried sea lettuce
Claims
[Claim 1] A red tide control agent characterized by adding a thickening agent, one of the following: starch, tapioca starch, xanthan gum, guar gum, or collagen, to dried sea lettuce in a concentration of 0 to 25% wt (excluding 0), and then molding and heat-drying the mixture.