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RED ALGAE, continued
DENSITY OF P. RUBESCENS DURING STRATIFICATION
This graph shows three variables (temperature, light, and P. rubescens) as they relate to lake depth. The top and bottom of the graph represent the surface and bottom of the lake, respectively.
The topmost arrow is at the Secchi depth, 12 feet. About 20% of the sun’s light penetrates to this depth. The temperature is the same as at the surface (about 74°F), and there is no red algae present.
At 36 feet (the second arrow), there is no sunlight, the temperature is much cooler (about 40°F) and the density of P. rubescens is the highest. This depth marks the bottom of the metalimnion, where there is likely access to a supply of dissolved phosphorus from the nutrient-rich hypolimnion. |
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P. rubescens has adapted to life in the summer metalimnion by tolerating cool temperatures and low light. The cool, dark and deep water of the hypolimnion tends to have more nutrients, thanks to settling particulates and the release of nutrients from the sediment (see “Phosphorus From Within” Fall 2006 Water Line). While in or near the hypolimnion, P. rubescens takes advantage of the higher nutrient levels by stocking up. Thanks to its tolerance of low-light conditions, P. rubescens has an advantage over the algae that are restricted to the epilimnion where nutrient concentrations are lower and competition is higher. Even during turnover, when the water column is mixed, this blue-green competes well under low-nutrient conditions. As a result, its presence in lakes with low nutrient concentrations can be prolonged, highlighting the contrast between the clear water state before turnover and the sudden, startling appearance of the red bloom.
P. rubescens is capable of producing two kinds of toxins; a neurotoxin (which affects the nervous system) and a hepatotoxin (which affects the liver). However, P. rubescens does not produce these toxins at all times. It is not well understood why P rubescens or and other blue-green algae sometimes produce toxins. To be safe, avoid swimming during any algae bloom, red or green.
Blue-green algae are not technically algae at all, but rather bacteria that contain chlorophyll and have the ability to photosynthesize. Like all bacteria, blue-green algae (a.k.a. cyanobacteria) are prokaryotes and have no nucleus. Green algae are eukaryotes, with a nucleus and other organelles within their cell membranes. In photosynthesizing eukaryotes, the chlorophyll resides within organelles called chloroplasts.
Chloroplasts are interesting because they have their own DNA and replicate independently from the rest of the cell. It is believed that chloroplasts (and mitochondria) originated as cyanobacteria. Long ago, one cell enveloped another and rather than consuming it, assimilated it. The two cells mutually benefited in a process known as endosymbiosis, setting the stage for the myriad of life forms that would follow. |
P. rubescens can create red "flower" patterns by seeping through fissures in ice-covered lakes.
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