Answer:
Hydras
Explanation:
Algae support hydras because they provide hydras oxygen. Hydras have regenerative ability; they do not appear to die of old age, or to age at all. But sometimes, disease, predators and water contamination kill off hydras before they can achieve "immortality".
Jellyfish need to stay in the water to survive. They get their oxygen from their really thin skin. In some cases, it has been found that jellyfish have an immune system that presents bacterial-specific responses.
In the absence of an adaptive immune system, Hydra polyps employ an elaborate innate immune system to detect and interact with microbes using their two cell layers as efficient defense barriers, making them survive longer or have better defense against the chemicals.
Also take into consideration, what chemicals/acids are being put into the lake and the "age" of the hydra/jellyfish.
