An aquatic ecosystem is a complex and dynamic network of organisms, physical factors, and chemical interactions that function together in a water-based environment. Aquatic ecosystems include freshwater systems such as rivers, lakes, ponds, and wetlands, as well as marine systems such as oceans, seas, estuaries, and coral reefs. They play a crucial role in maintaining the planet’s ecological balance by supporting biodiversity, regulating climate, purifying water, and providing food and livelihood to countless species including humans. The ecological composition of aquatic ecosystems can be understood by examining the biotic components such as producers, consumers, and decomposers, as well as abiotic components such as water chemistry, light, temperature, and nutrient availability. The dynamics of these ecosystems involve interactions among organisms, energy flow, nutrient cycling, and processes such as succession and adaptation that maintain the overall stability of the system. The biotic components of an aquatic ecosystem can be broadly categorized into producers, consumers, and decomposers. Producers, mainly autotrophic organisms, are the foundation of the aquatic food web. In freshwater and marine systems, the primary producers include phytoplankton, algae, and submerged aquatic plants that carry out photosynthesis. Phytoplankton, microscopic photosynthetic organisms, are particularly significant as they contribute a major share of global primary productivity and release oxygen into the atmosphere. Larger macrophytes, such as seagrasses in marine environments or water lilies in freshwater, also serve as primary producers and provide habitat for a variety of organisms. Consumers form the next trophic level and include herbivores, carnivores, and omnivores. Zooplankton are the primary consumers that feed on phytoplankton and form the base for higher trophic levels such as small fishes, amphibians, crustaceans, and larger predators like aquatic birds, turtles, and mammals. In marine ecosystems, larger consumers such as squids, dolphins, and sharks play a critical role in maintaining population balance. Decomposers such as bacteria and fungi break down dead organic matter, recycling essential nutrients back into the water, thereby sustaining productivity. This constant recycling of matter is vital for ecosystem functioning. The abiotic factors of an aquatic ecosystem strongly influence its ecological composition and productivity. Light penetration is one of the most critical determinants, as photosynthesis can only occur within the photic zone, the upper layer of water where sunlight can penetrate. In deeper zones where light does not reach, organisms rely