In the spring, after the river flooded, a small reservoir was formed. The following organisms were found in it: shchiten

In the spring, after the river flooded, a small reservoir was formed. The following organisms were found in it: shchiten, hydras, white planarians, cyclops and daphnia, small pond snail. Explain if this body of water can be considered an ecosystem. Please provide at least three pieces of evidence.

This body of water cannot be called an ecosystem, since it contains:
1) there are no producers;
2) there are no reducers;
3) there is no closed circulation of substances, since the food circuits are broken.