# If light triggers algae...



## Tom (29 Sep 2010)

... how relevant are the other associated "causes" like low CO2, ammonia etc, and when do they come into play to determine the type of algae that develops? Or is it the combination of light and said "cause" that determines the algae type?

Tom


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## ceg4048 (29 Sep 2010)

Hi Tom,
           Well one really has to look at the components of the system in order to determine cause and effect. If the tank is highly lit and there is a plant in it with a high CO2 compensation point (i.e. the plant requires high levels of CO2 just to get by) then the physiological changes that occur to the plant as a result of acute CO2 starvation have an impact on which algal species are quickest to take advantage of the damage caused by this particular combination of environmental conditions. So lets say HC is on the left and Fern is on the right. The high CO2 compensation point of the HC means that a certain type of damage is caused on that plant whereas the Fern may not incur that type of tissue damage. Spirogyra or filamentous algae spores siting on the surface of both plants may then react to the distress of the HC but not to the Fern. Lets take the plants out of that same tank and raise the lighting some more. Green water algae spores might respond to a lighting threshold and bloom. At a lower lighting level, if there were an ammonia transient, the combination of that lower lighting level and the ammonia transient could trigger the green water algal bloom.

Some plants are less capable of gathering other macronutrients, so under high lighting their physiological responses may be more easily read by other algal spore types which would cause that species to bloom instead of a species which looks for signs of CO2 distress. Anubias for example is typically susceptible to GSA which seems to be able to read both CO2 and PO4 distress signals.

While the nutrient haters focus on the theory that nutrients in the water column trigger algal blooms, the reality has more to do with the fact that plants in the water column interact with the spores. So we get algae in a planted tank in part because there are plants in the tank, not because there are nutrients in the tank. 

There is a dynamic occurring between light-plant, light-algae and plant-algae. In our tank system algae is a more of a predator. The predator reads the signs of weakness and attacks when the symptoms of weakness are detected. Weakness can be caused by poor water conditions which blocks feeding, or it can be cause by other environmental stresses such as too much light and not enough uptake of the required nutrients to support the commanded growth rate. Green water and diatomic forms are typical free agents which respond independently to light and which don't seem to care whether there are plants or nutrients in the water. The different species have their own trigger mechanisms and criteria, however the lighting is the predominant trigger. Unplanted tanks that get blooms have only the lighting to play with as a control unless algaecides are called in.

Cheers,


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## Tom (29 Sep 2010)

Thanks again Clive, I was hoping you might latch onto this one! 

So generally light is the main trigger of algae. Different algae types are able to read different deficiencies of the plants, and then latch on and grow (that's my understanding now). 

In a tank with high lighting levels, will still algae be "triggered" but just not able to grow as long as plants are healthy?

I have 2 stem species (M.micranthemoides and R. rotundifolia) along with Willow and Xmas moss in one tank. The xmas moss has various types of hair algae, whereas the stems and willow moss are totally clean. Working on the theory that hair algae latches onto plants with CO2 deficiency once triggered, does this indicate that xmas moss needs more CO2 than the stems and willow moss, and is struggling due to lack of CO2? Would I then be right in thinking this might be due to the Xmas moss growing mainly above water where CO2 is more abundant, and the others are generally below water?

How does this relate to algae (diatoms/hair/bba) on hardscape or glass, where plants appear OK? Surely the hardscape isn't struggling from a deficiency?

Sorry for going over everything so repeatedly, but I'm gradually getting there! Each thing I find out throws up more questions.

Tom


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## ceg4048 (30 Sep 2010)

Tom said:
			
		

> In a tank with high lighting levels, will still algae be "triggered" but just not able to grow as long as plants are healthy?


Hi mate,
     People get wrapped around the axle with the concept of trigger. That's because they forget that algae have two modes; the spore (analogous to a seed) and flagellate or vegetative, which is the bloom. Spores seemingly have an indefinite "shelf life" and they can hang around in the sediment, on the leaf surface or wherever. The water can dry up and the spores can survive and be blown on the wind to other locations. We assume that the spore sample the environment waiting for an opportunity to bloom into a fully fledged organism, but there is little point in blooming if the environmental conditions are adverse to existence and procreation, right? So they wait and sample

So it's likely the spores have a set of genetic instructions which might be similar to a "logic flow diagram". This diagram would have survival as a prime directive, so perhaps over billions of years they've "figured out" what set of conditions are conducive to their survival. Naturally, moisture content would be in that "should I bloom?" equation.

Conditions that are hostile to plants are usually the most favorable to algae and conversely, conditions that are favorable for higher plants are not so good for algae. Think about a pond of water lilies for example. Broad leaves which cover the surface and block out the light. So if the plants are healthy, they won't break down, will not present a decaying substrate for algae to colonize and will block light thereby suppressing algal growth. So when plants are healthy and growing the spores, sampling the environment would detect low or otherwise stable ammonia levels, adequate CO2 and O2 levels, or perhaps would not sense an ammonia gradient across a plant leaf, or, it might even be that the combination of organic products leaching from the plant may have a certain characteristic identifiable as healthy export. Healthy plants would likely block the light, so the spores would detect lower light. The combination of data gathered by sensors would be fed into this logic tree and the transition from spore to bloom would not be triggered. 

Now, I wouldn't want to presume that water column nutrient content is absolutely not in that equation, only that it isn't really necessary because algae don't need nearly as much nutrients to prosper as plants do. This is by a factor of thousands or even hundreds of thousands. If that's the case then the nutrient concentration wouldn't be all that significant in deciding whether to bloom or not, especially since decaying  plants would automatically release nutrients for them to feed on. The logic is more about;
"Are the plants sick and is there enough light to take advantage?" If yes, then bloom. If no, then don't bloom. 
It can also be "Is the environment itself unhealthy, and is there enough light to take advantage?" 

Check out the 3rd page of this thread => RO water please advice - brown algea-diatoma  where I posted images of spore versus bloom. This is similar to caterpillar-to-moth.

The problem with us though is that we just don't have sufficient control of the tank, so we continually stimulate algae by messing up one or more of the spore measured parameters which affect the decision making of the logic tree. And because there are multiple variables there are multiple ways of totally screwing up either the plants or the environment itself.


			
				Tom said:
			
		

> I have 2 stem species (M.micranthemoides and R. rotundifolia) along with Willow and Xmas moss in one tank. The xmas moss has various types of hair algae, whereas the stems and willow moss are totally clean. Working on the theory that hair algae latches onto plants with CO2 deficiency once triggered, does this indicate that xmas moss needs more CO2 than the stems and willow moss, and is struggling due to lack of CO2? Would I then be right in thinking this might be due to the Xmas moss growing mainly above water where CO2 is more abundant, and the others are generally below water?


It could easily be that one species has a higher CO2 compensation point than another. I'm afraid I don't know what they are for these species. However, it could also be that due to geometric and density differences with the moss beds, flow is less well distributed within the Xmas moss bed than in Rotala bed. Poor flow within the bed will distribute less CO2 to the leaf so that this could be the issue. Barr's data indicated that CO2 concentration levels in the free water column can be as much as 10X higher than the concentration level within the plant beds. Whatever the reason, you may simply need to do either a better job of flow distribution within a moss bed, or you may need to reduce the light intensity contacting the moss bed so that the CO2 demand is lowered in the moss. Thinning or combing the moss bed, shaking it more vigorously to dislodge detritus (which contributes to blocked flow) are also possibilities.



			
				Tom said:
			
		

> How does this relate to algae (diatoms/hair/bba) on hardscape or glass, where plants appear OK? Surely the hardscape isn't struggling from a deficiency?


No, you're right, but again, remember that algae on hardscape is a bit different because one of the sensor inputs that determines plant health is also whether the plant surface is growing and at what rate. Surfaces that grow quickly equate to health, but surfaces that do not grow indicate weakness. GSA is another that attacks hardscape. Anubias, although easy  to care for grows slowly and seemingly always get hit with GSA. One of the tricks? Move them to the more shaded area or lower the light. So on hardscape the light is still part of the equation and spores in those areas may in fact actually measure low or unstable CO2 levels at those specific points. Again, different things feed into the spores calculator but high light tanks operate at a major disadvantage simply because of the high photonic energy levels which tend to override everything else.

Have a look at Saintly (Mark Evans) tanks and you'll see that he has mastered the art of keeping algae off of hardscape simply by judicious use of PAR control, i.e. raising the halide bulbs high enough from the surface to lower their effective energy.



			
				Tom said:
			
		

> Each thing I find out throws up more questions.


This is the nature of The Universe. Each time we solve one mystery we then find ourselves asking "What causes that?" which leads to 10 more mysteries. Imagine what we'll "know" tomorrow...

Cheers,


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