The producers in the food web have the greatest available energy.
Producers are organisms that can make their own food, such as plants, algae, and some bacteria.
They do this by using sunlight or chemicals to convert energy from the environment into food.
In the food web you provided, the producers are the plants and algae.
The other organisms in the food web, such as the rabbits, squirrels, fish, owls, hawks, and ospreys, are consumers.
Consumers are organisms that eat other organisms to get energy.
As energy is passed up the food web from producers to consumers, some of the energy is lost as heat and waste.
This is why the producers have the greatest available energy.
Another way to think about it is that the producers are the first and only organisms in the food web that can capture energy from the environment.
All of the other organisms in the food web rely on the producers for energy.
Therefore, the answer to your question is: The plants and algae in the food web have the greatest available energy.