Ecosystems are controlled by a multitude of factors, each influencing the other. Almost all living organisms rely on the energy from the sun. Organisms at the base of the food chain, such as phytoplankton and plants, use the sun’s energy directly. Organisms higher on the food chain receive energy from the sun indirectly. The only organisms on the planet capable of producing energy without the sun are microorganisms called chemoautotrophs that often live near deep sea vents and synthesize energy through a chemical process. Within an ecosystem there are trophic levels based on feeding relationships including producers, primary consumers, secondary consumers, tertiary consumers, and decomposers. Many organisms consume both plants and animals (omnivores) and prey on a variety of species to avoid starvation in case their primary prey becomes scarce; therefore they are sometimes categorized into more than one trophic level depending on the circumstances. Abiotic factors like temperature, light, nutrients, and salinity play a large part in the control of growth, location, and abundance of marine populations. Lastly, species within a population are also regulated by competition, predation, parasitism and disease. Every part of the complex web of biotic and abiotic factors fits together to make a system that is balanced and capable of withstanding most changes.
There are thousands of species of primary producers in the ocean that convert inorganic carbon into organic compounds. Phytoplankton are responsible for 95% of all primary production and use energy from the sun directly. These primary producers absorb energy from the sun through pigments inside the chloroplasts or through membranes in the cytoplasm of bacterial cells. Other organisms capable of transforming inorganic material into a food source in the food chain include bottom-dwelling benthic algae, macroalgae and seaweeds, symbiotic producers like corals, and more complex plants like seagrasses. Because the ocean covers 71% of this planet, phytoplankton are widely viewed as the most crucial component of the food web.