1. Smothering: Didymo can form dense mats on the streambed, covering rocks, gravel, and other substrates that trout use for spawning and feeding. This can smother trout eggs and alevin (newly hatched trout), reducing their survival rates.
2. Reduced feeding efficiency: Didymo mats can also interfere with trout's ability to feed. Trout rely on their eyesight to locate prey, and the thick layer of algae can make it difficult for them to see and capture food. As a result, trout may have to expend more energy searching for food, leading to reduced growth and weight loss.
3. Habitat degradation: Didymo mats can alter the physical and chemical properties of the stream environment. They can reduce water flow, increase water temperature, and decrease oxygen levels. These changes can degrade the overall habitat quality for trout and other aquatic organisms, making it less suitable for their survival.
4. Stress and disease: The presence of didymo can cause stress in trout, which can make them more susceptible to diseases and parasites. Stressed trout may exhibit decreased immune responses, making them more vulnerable to infections and illnesses.
5. Competition for resources: Didymo mats can compete with trout for food and space. The algae can absorb nutrients that would otherwise be available to trout, and its growth can crowd out other aquatic plants that provide food and shelter for trout.
6. Impact on food sources: Didymo can also affect the availability of food sources for trout. The mats can cover and smother aquatic insects and other invertebrates that trout prey upon, reducing the amount of food available to them.
Overall, didymo can have significant detrimental effects on trout and other aquatic organisms, leading to reduced survival, growth, and overall health. It can alter the stream ecosystem and disrupt the ecological balance, making it more challenging for trout to thrive and sustain healthy populations.