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Thread: Understanding String Algae

  1. #1
    Daihonmei MikeM's Avatar
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    Understanding String Algae

    First off, this is not a thread about string algae 'problems'. Folks who are seeking advice on their string algae 'problem' are not going to find much here of interest. This thread is about understanding what we call string algae, not about eliminating it. Those seeking advice to solve what they consider a problem would be best served by starting a new thread of their own. {EDIT: Since beginning this thread, I decided to add a review of methods recommended for controlling string algae because that is what most folks are interested in. So, read on and eventually those subjects will be reached.}

    As regulars know, I have an inordinate interest in algae. For years I've tried to develop an understanding of string algae in particular. I have read a great deal about it, but whenever I have thought I'd learned something giving insight, I'll read a study that contradicts what I thought I had learned. In fits and starts, I'll plough through articles that are largely incomprehensible trying to get to the root of what happens in our ponds. I'll grow frustrated, put it all aside as a waste of time and then return to it weeks or months later. Sometimes I think I'll never really grasp the subject. But, the challenge eventually draws me back.

    It would be great to be able to write an article to share real knowledge. I have doubts that I'll ever reach that point. Still, I keep seeing threads on koi and pond forums giving contradictory advice, things being said that are only partially correct or are incomplete, and lots of chatter about folks resorting to all sorts of chemical weapons to combat string algae with little thought about the impacts on the pond eco-system. If I had the time, I'd be spending part of every day replying to the multitude of things people say about string algae. I control myself most of the time, read what people say and move on. But, the superficiality bothers me, even though I have no great insight to reveal. So, I've decided to start this thread with the idea of having an on-going series of posts on different aspects of string algae, each something of a 'mini-chapter', if time and energy permit. As I learn that something I've posted is inaccurate, I hope to go back and edit the original post, or perhaps post an update. It is hard to say how many 'mini-chapters' there will be. The subject really has no limits to the side trails one can wander.

    I do not want to discourage people from posting on this thread, especially about their observations. I encourage you to share them. It is the piling up of individual experiences and observations that provides a better understanding.

    I've now driveled on without saying anything substantive, but I'll start to correct that in the next post, which I'll hopefully compose soon. I do know the subject of the next post... The scientific identity of string algae. Why would that take a separate post? Well, nothing about string algae is simple, as I hope to explain.
    Last edited by MikeM; 06-03-2013 at 01:43 PM. Reason: update;typo

  2. #2
    Daihonmei MikeM's Avatar
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    The Identity Challenge

    Most literature identifies our string algae as being in the genus Cladophora. When a species name is given, it is usually Cladophora glomerata. An identification problem immediately arises because science does not agree on how many species there are. One taxonomist says there are 5 known species, another will say there are a dozen or more. Within each species, there are forms or varieties, and the taxonomists differ on the validity of these differentiations. Adding to the confusion, algae identified in the wild will change form when grown in laboratory conditions. What appeared to be two different species, or two different forms of a single species, may become identical to the eye when grown in identical, controlled conditions. And, there have been instances of what seemed to be a single species in the wild differentiating when grown in identical conditions in the lab, revealing that there were actually two species co-habitating in the wild. However, some forms of a particular species will retain the differentiating traits in most conditions (although perhaps not in all), giving credence to the idea that there truly are different varieties within particular species marked by differing growth habits. Because the growth habit of string algae will vary according to numerous factors, including (but by no means limited to) nutrient availability, current, light intensity, co-habitant influences, temperature, stage of maturity and such, visual determination of a scientific identity can prove erroneous. It really takes an educated eye to be certain.

    DNA analysis to differentiate species and forms has been utilized, resulting in debate as to how different DNA has to be to support a species identification, rather than differentiation between individuals. Some species have such significant DNA differences from other species that there is not much to debate. Some appear to be more gradations of differences, causing a challenging question of where to draw a line, and whether to draw a line, particularly when the differences at the extreme ends of the gradation range seem dramatic at first blush.

    Adding to the complexity, analysis of antibodies produced by string alga (yes, algae produces antibodies), has shown such high immunological distances between certain species as to raise the question of whether all the alga classified as Cladophora rightfully belong in the same genus. One authority on alga taxonomy has described the identification issue as simply 'problematical'. When a scientist who has spent decades of continual taxonomic study so speaks, I am hardly going to venture a guess.

    For the purposes of pondkeepers, we are likely correct if we say our string algae is Cladophora and not bother about species or forms. However, the fact that different species and forms do exist and mimic one another in appearance under certain conditions, is, I think, a major point to keep in mind. When a study finds string algae populations collapse at a temperature of 25C, and another finds them thriving until the temperature reaches 32C, the contradiction may not be a contradiction at all. Both may be accurate observations of different species, or different forms. But, do not jump to the conclusion that all is explained by different forms being involved in apparently inconsistent observations. There are numerous other factors beyond temperature that can play a role in population collapse.

    So, for my first substantive post, I think the practical way to address identification of what is growing in our ponds is to just call it string algae.

    ...which I think well explains why I get frustrated in trying to learn about the stuff. I called it string algae before I spent all those hours reading about it.
    Last edited by MikeM; 06-03-2013 at 01:46 PM. Reason: clarification

  3. #3
    Daihonmei MikeM's Avatar
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    Nutrients

    There are a number of nutrients that have been found crucial to the success of string algae. Nitrogen and phosphate are the ones of most focus, largely because these are waterway pollutants frequently studied. Other nutrients identified as crucial include silicon, boron, iron, zinc and B-vitamins. In particular conditions, there are undoubtedly others that would be limiting factors.

    There is always a lot of comment about nitrate levels in ponds with a bloom of string algae. Studies show that ammonium is the preferred nitrogen source, not nitrate. The string alga are not efficient in using nitrate. However, the utilization of nitrate increases with higher levels of phosphate. Numerous studies indicate that phosphate is the nutrient most critical to a sudden bloom of string algae in natural waterbodies. Add phosphate and the algae proliferates. Limiting phosphorous, however, does not necessarily result in the die-off of the algae, at least not over a short term period. String algae come well-equipped to deal with phosphorous shortages. They take up a luxury amount of phosphorous when it is available. That is, the algae will store excess phosphorous and use it as ambient phosphorous levels in the water decline below what is needed for growth. String algae also possess an enzyme, phosphatase, which is thought to allow it to maximize the use of organic phosphorous available in the water. It would seem apparent that string algae evolved to take advantage of environments where nutrient availability fluctuated radically.

    String algae did not evolve in isolation from other life forms. It is the host for numerous other organisms. These are referred to as epiphytes, organisms that use the algal filaments as a substrate. Of particular interest are various diatoms that colonize the surface of filaments. Some of these diatoms harbor photosynthetic bacteria (blue-green algae) that have the ability to fix atmospheric nitrogen. Atmospheric nitrogen is abundant in dissolved form in water, but cannot be used by plants to meet their nitrogen needs. I'm sure nearly everyone is familiar with the ability of the peanut plant to enrich the soil in which it is grown by adding organic nitrogen. This occurs in root nodules which house bacteria that produce nitrogen in useable form as a by-product of their metabolism. The diatoms colonizing the surface of algal filaments have this ability. A thriving epiphytic colony of diatoms bathes each algal filament with useable nitrogen. The water may have a very low level of available nitrogen, while the concentration at the molecular surface of the algal filament is quite high. The author of one study of a northern California river suggested that the production of useable nitrogen by the epiphytes borne by Cladophora made a greater contribution to the health and vitality of the aquatic plant communities of the river system than any other nitrogen source. Whether that was a bit of over-exuberance or not, it highlights an important point. String algae hosts organisms capable of supplying its nitrogen needs.

    It seems logical that if one eliminates nitrogenous wastes from a pond the algae will die. But, I'm sure those who have borne with me this far have read of experiences where string algae was thriving despite very low levels of detectable nitrate and no detectable ammonia or nitrite. We cannot know the reasons in any particular instance. One possibility is that the string algae community of organisms is simply producing all the nitrogen it needs to supplement the undetectable traces of ammonium continuously produced by the fish in the pond. Every time food is added, phosphorous is added, and the string algae take in all they can to use and store for future use. The two nutrients most examined are both ones that string algae has evolved to take care of for itself, at least to a sufficient degree that survival chances in low nutrient environments are rather good.

    The adaptations of string algae to the low nutrient environment of natural streams make the abundant nutrient environment of the koi pond heavenly. So, why doesn't it exhibit overgrowth all year round in every pond? Once again, nothing about string algae is simple.

  4. #4
    Oyagoi RayJordan's Avatar
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    Nothing about string algae is simple unless it is! Mike I applaud you for taking on this significant topic. I know koi hobbyists that appear to be doing everything correctly that have serious issues with string algae conversely there are other koi hobbyists that break most of the conventional thoughts about preventing string algae and seem to never have a issue. I have also know a number of hobbyists that have killed most of their koi using what were claimed to be fish safe treatments for string algae.

    My current koi pond is 13 years old and during the past 5 years beginning with the typical 8 week winter fast I have seen a significant string algae problem emerge without any known change in environment, filtration, or maintenance. The string algae problem seems to persist for a few months then fades away as water temperature and light level rise along with light feeding schedule resumption. Why has this happened now vs the first 9 years this pond was operating without a significant string algae problem is not yet known? I added a water softener for water changes four years ago which has had no affect on my ponds string algae issues that I can see. One issue I have been trying to address is a reduced flow/turnover rate through my gravity fed bottom drains. Perhaps once that issue is fixed and the string algae fails to reappear the next several winters I will be able to believe I have a answer for my pond but I doubt it will be the universal answer for other ponds with string algae issues.

    I will follow this thread with high interest.
    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.

  5. #5
    Tategoi powerman's Avatar
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    I'm glad you are writing about the difficult topic of string algae. You have already pointed out some really important facts.
    There are several kinds of string algae. They don't all act the same. String algae harbors organisms that allow it to utilize nitrogen from the air. It can utilize and store the phosphorus from the food we feed.

    I have been saying for years that I thought that string algae could get nitrogen from the air without having to have excess nutrients in the pond water much like spanish moss that hangs from the trees existing in the air in environments that have the right mix of temperature, moisture and sun/shade ratio. No fish food feeding it, no high nutrients.. just air, sunlight, rain and humidity in just the right combination...

    I've seen string algae thrive in my pond when I have 0 detectable ammonia, nitrite and even nitrate.. I also had another pond in the same yard, same source water, similar filtration and stocking level.. smaller pond though and in the shade and never had string algae in that pond...I put up a shade screen last year on the main pond, but the string algae had already gotten established... this year, I'm doing a salt treatment for a few weeks at .10% to see if I can stop it before it gets too carried away (I'll do the shade screen again,too) I've got lots of bio filtration and trickle water at almost a semi-flow through rate.. I just think I have the ideal environment for a particular strain of string algae... That's my story and I'm sticking to it...

    Anyway, not hijacking the thread by looking for string algae solutions for my particular situation, just looking forward to the information on this thread and sharing my experience for what it's worth.

  6. #6
    Daihonmei MikeM's Avatar
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    Reproduction

    String algae has a complex reproductive strategy. The simplest means of reproduction has been observed by every pondkeeper. Filaments that break off will become lodged on any rough surface or obstruction and continue growing. The rhizoid-like holdfasts that anchor it to a surface are not necessary for growth. Pinch some off the wall of your pond and you likely have hundreds of filaments in your fingers, each capable of colonizing new territory. Have you ever thought about how many filaments there must in your pond during a bloom? Millions? Trillions? It really is beyond comprehension. However, as numerous as all those filaments may be for successful vegetative reproduction, it is nothing compared to the other weapons in string algae's arsenal.

    Cladophora has a type of sexual reproductive strategy similar to mosses. It is diplohaplontic, meaning that it follows a two-stage process. The mature plant produces spores. The spores become gametophytes, a stage of growth capable of producing gametes, cells with only half of the chromasomes necessary for a complete organism. You might think of these as eggs and sperm, but they are not really either. Two gametes will merge, forming a new plant. The new plant may arise from the gametes of two different parents or the gametes of the same parent. In mosses, the gametophyte stage of growth is physically different than the appearance of the mature moss plant. In Cladophora, the gametophyte state looks the same, or at least enough so that pondkeepers are not going to tell the difference. Not every species has been studied enough to confirm that all are diplohaplontic, but none that have been studied have been found not to be. Each filament is capable of producing an uncountable number of spores.

    String algae also produces zoospores, which you can think of as living baby plants. (This a misnomer, but helpful to understanding, even if not really accurate.) It is this means of reproduction that hobbyists observe all the time without realizing it. As filaments mature, zoospores form within the cells. When mature, the growing zoospores cause the cell wall to rupture, releasing numerous zoospores into the water. The zoospores of Cladophora have flagellae which are used to swim through the water at what is a rapid speed for the little organisms. (Scientists refer to them as protoplasts, rather than organisms.) Within a short time, probably not more than a couple of hours, the zoospores come to rest on the surface of some object in the waterbody, such as the pond wall. There they secrete cellulose, forming a tough outer cell wall and begin developing holdfasts, effectively cementing themselves to the surface each has claimed as a new home. They then begin growing the long filaments we think of as string algae. When the zoospores cause the parent plant's cell wall to rupture, the damage is permanent. The rupture releases cell matter into the water and allows bacterial invaders to begin the decomposition process. This is what we see occurring when we observe a die-off of string algae. Since much of the algae matures at the same time, the die-back can be dramatic over the course of a few days or weeks. It is a common observation that as a die-back occurs, the strands of algae clump, an effect of the gelatinous cell matter of innumerable ruptured cells sticking together; and the water takes on that algae smell we all so dislike. We may be pleased that the trillions of filaments are in dramatic decline, but we do not notice that every filament in decline has released thousands of replicates to colonize all available surfaces.

    These means of reproduction seem sufficient to maintain the species, but string algae has an additional strategy. It also forms akinetes, or cysts. These are microscopic versions of itself which are encapsulated in a hard outer cell wall and can be carried by the currents for long distances. These akinetes seem to form when growth conditions become unfavorable, such as in very cold water or when nutrient is unavailable. In one experiment, akinete formation was triggered by raising Cladophora in distilled water. These cysts can endure for long periods of time. How long does not seem to have been determined. It seems that decades are possible. Obviously, if they can endure for centuries, it will take centuries of study to find out.

    Pull out just a single filament of string algae some time. Look at how thin it is, and how strong. Within it, there are three known means of reproduction potentially occurring, and that single filament is itself ready to grow if you just give it a spot of its own.

  7. #7
    Daihonmei MikeM's Avatar
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    Ray & Powerman: I'm glad someone is reading all of this, and that you've posted your experiences. Trying to make sense of the mysteries is what first got me reading up on the subject. I have no answers, but having more mysteries helps understanding that there are few general truths about string algae.

  8. #8
    Jumbo Appliance Guy's Avatar
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    I'm here too Mike. Had written post requesting taxonomy and nomeclature status but didnt post cuz i didn't know if you wanted posts. Your next post was taxonomy so we are on the same page.

    Good read. Shaping up to be THE thread on string algaes.

  9. #9
    MCA
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    Honmei MCA's Avatar
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    Interesting to correlate the incidence of string algae to water perimeters like, nitrates, TDS, ORP, GH...etc.

    also with water parameters being equal, what about pond design. Such as deep with higher currents with no stream vs. slower moving pond with stream

  10. #10
    Sansai almostgeorgia's Avatar
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    Quote Originally Posted by MCA View Post
    Interesting to correlate the incidence of string algae to water perimeters like, nitrates, TDS, ORP, GH...etc.

    also with water parameters being equal, what about pond design. Such as deep with higher currents with no stream vs. slower moving pond with stream
    Interesting thread, Mike, and thanks for kicking it off. I, too, have been a keen observer of what I assume to be several different species of algae that inhabit my pond, and those of several fellow koi keepers. And I think MCA might be on to some additional 'parameters' that drive the rise and fall, or occurrence of certain algae in our ponds. We often observe string algae in fairly fast moving water, especially over rocky stream beds and waterfalls. Is that because it thrives in a more oxygen enriched environment these features in our ponds are providing? Or is it because the movement of these long strands of algae simply catch our eye at these locations? Does rapid TPR action create a better environment for these several species of algae is well? I know, lots more questions than answers.

    What I have observed in my own particular pond is more of a small, clumping, but free floating form of algae in Ray's aforementioned post-Winter fasting period. Thousands of small, loose 'blobs' with each piece being no larger than a pea to a nickel in size. While not long and 'filamentous' in appearance, I consider it a variant of string algae, and an experienced pond owner tells me this is the 'pre-cursor' form his string algae takes before it starts attaching itself to anything and everything in long strands. Curiously, mine never gets to that stage. But it does grow into a bit of an annoyance, with it's super slick, almost oily black masses clogging filters, skimmer baskets, etc., and increasing my maintenance intervals somewhat.

    I have noticed is it's appearance in the late Winter, early Spring here in north Florida seems to be temperature/sunlight levels related, and drops off dramatically as the water temps rise to 65 degrees or so. A heavy leaf, pollen and 'catkins' (oak tree flowers) load also hits my pond about this same time and a complete, 100% control of this litter is impossible. I have often wondered if this jump in decomposing organic matter might be feeding this algae outburst as well. I have examined this 'glarf' under a microscope and it in no way resembles my pond-wall algae, so I had eliminated slough-off as the source for this algae outburst. Then again, your thread here, Mike, as me now cautious about the many manifestations the same species of algae can take. And I'm quite sure that most of us have virtual 'rain forest' of different species of algae covering our pond sides, but with perhaps only one or two dominant species. The best news about my particular algae invasion is it disappears --- completely, almost as fast as it arrives. Rather disturbing to read that even very low levels of nutrient in a pond will not necessarily affect this algae bloom given its symbiotic relationship to colonies of nitrogen and phosphorus fixing bacteria!

    One other thought on the reproductive processes of algae. As I understand it, virtually all natural bodies of water exposed to the atmosphere will contain small, undetectable traces of algae if that water is not toxic in some manner. it is quite obvious many if not all species of algae must also therefore have a wind-borne form of 'cyst' or dried single-cell form that permits the spread of it's species by air from one body of water to another.

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