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Thread: Understanding String Algae

  1. #31
    Daihonmei MikeM's Avatar
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    Allelopathy

    For those not familiar with allelopathy, it refers to how plants emit various chemicals harmful to other plants. It is the same sort of thing as occurs with molds and fungi releasing chemicals that kill bacteria, such as the chemical we turned into penicillin. Some desert plants release very strong chemicals that create dead zones around them, thereby monopolizing all water and nutrient in their square meter of the earth. In aquatic environments, far less dramatic examples of allelopathy are all around. Or, should I say, equally dramatic if you think about it? Healthy underwater vegetation would seem to be a great substrate for algae of all sorts. Why aren't all submerged aquatic plants totally covered with algae to the point of being killed by it? A major reason is that these plants release substances that make their surfaces repellant to most algae. Allelopathy studies concerning aquatic plants have focused on how plants combat algae and other plant species, not on the chemical weapons used by algae. However, one study I came across a couple of years ago is very interesting.

    Scientists in Uruguay performed a series of experiments studying the effects of filamentous green algae (they used both Cladophora and Spirogyra species) on greenwater algae in small experimental ponds. Their lab work was supplemented by field observations of natural waterbodies, and they followed-up with use of algae filtrates as additives to greenwater. Their findings were that the filamentous green algae suppressed the growth of greenwater algae without regard to nutrient levels or nutrient additions or other conditions. Without regard to the initial concentration of greenwater algae, the presence of the filamentous green algae had a strong suppression effect. To confirm that allelopathy was involved, filamentous algae filtrates were added to greenwater. The result was suppressed growth in the greenwater algae exposed to the filtrates. The suppression observed in cohabitation was greater when water was warmed to optimal ranges for filamentous green algae growth. The particular allelochemicals responsible for the impact now need to be identified. It should be noted that alellochemicals studied in regard to various plants have been found to breakdown over rather short time periods (hours and days, not weeks or months) and are typically in a lethal concentration only at the leaf surface. The algal filtrates used in the experiments would have been highly concentrated.

    Once one accepts the fact that plants release chemicals necessary to combat plant competitors, it is logical that filamentous algae would benefit from combating the light-blocking unicellular algae. However, the amount of chemical needed to be effective in a natural waterbody would seem to me to be far too great, unless it was quite persistent in the environment, which allelochemicals typically are not. In the closed confines of an aquarium or pond, I can more readily accept the notion of allelopathic impacts. I think there will be a good deal more knowledge gained in the field of allelopathy over the next decade. I expect what is already a complexity of interactions will prove to be even more complicated.

  2. #32
    Jumbo RobF's Avatar
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    Instead of brushes and pads in black boxes just use string algae and blanket weed in bright boxes.
    Attached Thumbnails Attached Thumbnails Understanding String Algae-algae-filtration-bright-box.jpg  

  3. #33
    Honmei ricshaw's Avatar
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    Quote Originally Posted by MikeM View Post
    For those not familiar with allelopathy, it refers to how plants emit various chemicals harmful to other plants. It is the same sort of thing as occurs with molds and fungi releasing chemicals that kill bacteria, such as the chemical we turned into penicillin. Some desert plants release very strong chemicals that create dead zones around them, thereby monopolizing all water and nutrient in their square meter of the earth. In aquatic environments, far less dramatic examples of allelopathy are all around. Or, should I say, equally dramatic if you think about it? Healthy underwater vegetation would seem to be a great substrate for algae of all sorts. Why aren't all submerged aquatic plants totally covered with algae to the point of being killed by it? A major reason is that these plants release substances that make their surfaces repellant to most algae. Allelopathy studies concerning aquatic plants have focused on how plants combat algae and other plant species, not on the chemical weapons used by algae. However, one study I came across a couple of years ago is very interesting.

    Scientists in Uruguay performed a series of experiments studying the effects of filamentous green algae (they used both Cladophora and Spirogyra species) on greenwater algae in small experimental ponds. Their lab work was supplemented by field observations of natural waterbodies, and they followed-up with use of algae filtrates as additives to greenwater. Their findings were that the filamentous green algae suppressed the growth of greenwater algae without regard to nutrient levels or nutrient additions or other conditions. Without regard to the initial concentration of greenwater algae, the presence of the filamentous green algae had a strong suppression effect. To confirm that allelopathy was involved, filamentous algae filtrates were added to greenwater. The result was suppressed growth in the greenwater algae exposed to the filtrates. The suppression observed in cohabitation was greater when water was warmed to optimal ranges for filamentous green algae growth. The particular allelochemicals responsible for the impact now need to be identified. It should be noted that alellochemicals studied in regard to various plants have been found to breakdown over rather short time periods (hours and days, not weeks or months) and are typically in a lethal concentration only at the leaf surface. The algal filtrates used in the experiments would have been highly concentrated.

    Once one accepts the fact that plants release chemicals necessary to combat plant competitors, it is logical that filamentous algae would benefit from combating the light-blocking unicellular algae. However, the amount of chemical needed to be effective in a natural waterbody would seem to me to be far too great, unless it was quite persistent in the environment, which allelochemicals typically are not. In the closed confines of an aquarium or pond, I can more readily accept the notion of allelopathic impacts. I think there will be a good deal more knowledge gained in the field of allelopathy over the next decade. I expect what is already a complexity of interactions will prove to be even more complicated.
    Could "barley straw" have any connection to above?

  4. #34
    Daihonmei MikeM's Avatar
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    Quote Originally Posted by ricshaw View Post
    Could "barley straw" have any connection to above?
    A different, but related subject. Barley straw's impact on unicellular algae comes from the breakdown of cellulose, particularly in the presence of sunlight. Once decomposition becomes advanced, there is no longer an impact.

  5. #35
    Daihonmei MikeM's Avatar
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    Diseases

    There are a number of investigatory studies seeking to learn what diseases algae can suffer. The ones I have seen are mostly about marine species. When it comes to freshwater Cladophora species, there does not seem there is much of anything known. At least, I have not come across much. There is a fungus mold that has been shown to have substantial negative impact on string algae. This mold, Acremonium kiliense, inhibits growth and can cause chlorotic appearance. This is a common mold. Why it affects string algae when other funguses do not is something I've not seen in studies. As far as I am aware, it has not been established under what conditions the mold will infect string algae. Studies have shown that warm water coincides with the most significant negative effects, and it seems to have a greater impact during summer months than in other seasons. It is not clear to me whether the mold infections begin with healthy string algae, or are taking advantage of algae going into decline, as it often does in summer when water temperatures rise.

    Bacterial diseases do not appear to bother string algae. It does produce antibiotic chemicals, which are a subject for medical study. Of course, all sorts of bacteria come into play when the algae dies. I have personally observed that clumps of the stuff removed from my pond and tossed in the garden take a long time to breakdown into soil. Whether that is due to residual antibiotic effects of algal chemistry or the percentage of cellulose I do not know. That's a subject on my 'curious about it' list.

    There is also an unwritten 'get around to it some day' list. Finding studies concerning string algae diseases is on it.

  6. #36
    Daihonmei MikeM's Avatar
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    Residents

    A lot of creatures call string algae home. I previously mentioned the epiphytic diatoms with nitrogen-fixing capabilities. There are several species of diatoms that take up residence on the filaments. Joining them are various cyanobacteria species. These epiphytes can become quite thick, leading to some scientific speculation that as a clump of string algae matures, the epiphytes would block light from reaching chlorophyll within the filaments. When filaments are relatively free of epiphytes, the color is a bright green. As the epiphyte community reproduces, the color becomes darker. With a heavy presence of diatoms, there can be a brownish cast. With heavy growth of cyanobacteria, the color takes on a dark, bluish-green cast. Although a number of articles refer to the potential of epiphytes to cause a material loss in photosynthetic capacity, I have not come across studies specifically addressing the impact of the epiphytes. I've also not made a particular effort to locate such studies. That is on my unwritten 'get around to it some day' list. What has been consistently observed is that as the epiphytic community increases, the hydro-dynamics of string algae streamers change. There is more drag, and the streamers lose buoyancy. (Sediments captured in the filaments contribute to this as well.) The rate of current flow within a streamer declines, reducing the availability of nutrient to filaments in the center of the streamer. These effects have negative impacts on growth.

    String algae also serves as a habitat for numerous insect species' larvae, with midge larva often being found in residence. There are a number of nematode species (round worms) and isopods (little crustaceans) that take up residence. In many instances these critters graze on the detritus captured in the filaments. Studies of the gut contents of these creatures show that many consume at least some of the string algae itself. Some insect larva have been found to have as much as 20% of the gut contents composed of string algae. Most of the time, however, the percentage is quite small, say around 2-5%. Whether the algae was consumed purposefully, or came along with detritus being consumed, I cannot say. Various freshwater shrimp seem to like living in the streamers. Some of these are filter feeders, which like to be where currents will bring their food to them. Some are grazers, which appear to clean the filaments of detritus and epiphytes. It is unclear to me to what extent freshwater shrimp will consume string algae. Some small percentage of gut contents being composed of string algae would be consistent with unintentional consumption. The Malaysian Prawn (a/k/a Giant Freshwater Prawn) can be commercially raised using string algae as a major food. Otherwise, the only reports I have come across referring to freshwater shrimp consuming string algae are in the plant aquarium hobby, where many report that the so-called Amano Shrimp will keep string algae from proliferating, but appear to be of little use in ridding an established bloom. Perhaps they only like the young growth tips, which may not contain much of the chemicals that make string algae unpalatable. I have not come across reports of significant damage being done to string algae by grazing shrimp. It has been observed that mayfly nymphs graze selectively on the apical tips of filaments, but not the mature portions of filaments.

    Bacterial inhabitants vary considerably from place to place. Of major concern in several studies is the presence of bacteria harmful to human health, such as E. coli. String algae growing in the vicinity of sewage plants is often loaded with it, and it proliferates in rotting masses that come ashore at lakes. Since our koi ponds contain quite large amounts of macro digestive waste, I think we can (and should for safety purposes) assume that E. coli is in residence in substantial quantities. Whether or not the particular strains are comparatively virulent, none should be assumed to be innocuous.

    And, of course, in nature string algae provides protection for fish fry, tadpoles and innumerable other creatures. It is also a trap for some creatures. Daphnia and various rotifers become entangled in it, and then become subjects of predation by creatures inhabiting the algae. Where daphnia are numerous, there are certain flatworms that take up residence, with the daphnia becoming their main food sourceā€¦ one they could never capture but for the entrapment by all those filaments.

    So, as with so much that occurs in the bio-system of the koi pond, string algae is not just algae. There is a community of organisms, some consuming the string algae and many calling it home.

  7. #37
    Daihonmei MikeM's Avatar
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    Food For Koi??

    We have all seen our koi grazing on algae. Mine appear to nibble on it every day, mouthing the pond walls. However, I do not find much algae in the waste stools other than when the fish are being fasted. I figure they like the taste of all the creatures inhabiting the algae on the pond walls, but not so much the algae. Still, they do consume quite a bit when a fast is imposed on them. But, I've never seen them try to eat any string algae streamers. There are studies finding string algae among the gut contents of various carp species, as well as tilapia and other fish. Various percentages are calculated. Thus far, I have not seen a report on stomach contents where string algae content was much more than around 20%.

    There is good reason for our omnivorous koi not eating string algae. First, string algae has a low ratio content of amino acids, relatively high cellulose content and comparatively high amounts of capric, lauric, myristic and palmitoleic fatty acids. These are fatty acids which are considered toxic when concentrated. Some have been used as insecticides. The result is that string algae is not a very good source of nutrition, it is hard to digest and it tastes bad.

    However, all the insect larvae, diatoms, isopods, and other critters living in and on the string algae are very nutritious. It is not surprising that grazing occurs on algae growing on pond walls where the fish can suck in the resident critters. To get the ones growing on streaming filaments, the koi would have to consume the full filament. Obviously, they do not care to do so.

    There are other algae species that are regularly consumed in quantity by fish; but, not string algae.

  8. #38
    Daihonmei MikeM's Avatar
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    Break Time

    I think it is time to take a break from all this talk about algae. I had not intended to get into posting something about string algae every day. But, once I got started I found it energized me to summarize what I've read over the years. Now that I've gone through a lot of 'the basics', I'm getting tired of the subject. There are lots of rabbit trails that can be covered, and there are various theories that stay in mind, but they will all still be there to chat about another time. So, I'll take a break. If I had realized years back how much time I would end up spending reading stuff about algae, I would never have started. But, it has become something like those addictive video games that never end, you just move to different levels and down different trails, sometimes lost in a maze and sometimes coming out where you began, and almost always not really knowing anything useful in the end.

  9. #39
    Tategoi powerman's Avatar
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    Thanks for posting what you have so far... enjoy your break... interesting subject

  10. #40
    Oyagoi RayJordan's Avatar
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    Hi Mike,

    I have really enjoyed reading your daily posts about string algae. You have taught me quite a lot of information that is new to me. One of my take away's is that once string algae starts appearing in significant blooms it is likely to reappear annually. Any potential treatments are likely worse that waiting for the string algae to complete it's cycle and fade away on it's own. I am not sure if a winter fast contributes to these cycles but I suspect it does. But I still feel it is more beneficial to fast my female adult koi regardless of any causative effect on string algae.

    I would enjoy reading your summary of the information and thoughts about minimizing the annoying and sometimes even exhausting annual outbreaks.
    Disclosure:These opinions are based on my experience and conversations with persons I consider accomplished koi keepers and do not reflect the viewpoint of any organization.

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