Question

Why is algae placed in the first place of the food chain?

Answer 1

Hint: Depending on their feeding relationship with other organisms, organisms have a place in the environment or community in which they dwell. The position or location inhabited by an organism is known as their trophic level, and it is determined by the source of sustenance.
Producers, such as plants, are organisms that make their own food through the process of photosynthesis. Primary consumers, such as herbivores, are species that feed on these producers. Secondary consumers, such as carnivores, are organisms that feed on herbivores.

Complete answer:
Algae are primary producers, capturing solar energy and converting it to chemical energy that passes through the ecosystem. All photosynthetic organisms are positioned as producers at the top of the food chain.
Producers, multiple tiers of consumers, and decomposers make up any food chain. Phytoplankton and algae, which are part of the first trophic level, are the producers in an aquatic food chain. Producers are so named because they make their own food. As we progress through the trophic levels, we come across primary, secondary, and even tertiary consumers, all of whom grow in size.
Primary consumers are classified as predators because they kill and eat other animals, whereas secondary and tertiary consumers feed directly on the producers. The decomposers arrive at the very end.
Decomposers are in charge of breaking down any residual biological material into nutrients that may then be used by the producers.

Note:
The flow of energy is unidirectional from one trophic level to the next until all energy is lost to the environment. Only $10\% $ of the energy of a trophic level's organism is passed onto the next trophic level. Except for deep-sea hydrothermal habitats, all ecosystems get their energy from the sun.