Biotic and abiotic factors are discussed when dealing with ecosystems because an ecosystem will take into account both abiotic and biotic factors, while the community level of organization only examines biotic factors. Biotic factors are the living factors within an ecosystem. If a "thing" is classified as a live organism, it is a biotic factor. Plants, animals, bacteria, and protists are all biotic factors found in the ocean. In addition to the creatures themselves, biotic factors also deal with the interactions of those organisms; therefore, things like predation, mutualism, commensalism, and parasitism are also biotic factors. Abiotic factors are nonliving physical or chemical elements within an ecosystem. Sunlight, oxygen levels, water pressure, water temperature, currents, and pH are all abiotic factors that can be found within the ocean.
Abiotic and biotic factors will interact with each other, and their interactions can and do affect the overall health of the the ocean ecosystem. For example, sunlight will warm surface waters. The sunlight also allows for photosynthetic organisms to be found in those warmer surface-level waters. Consequently, a lot of the food available in the oceans can be found in the ocean's top layer. The food webs or chains found in these surface waters are complex, but even small temperature variations can drastically harm or help the health of that ecosystem. If the abiotic factor of temperature causes an increase in the population of one species, all organisms within that food web are affected. The energy available at each trophic level will be impacted. Light is a similarly impactful abiotic factor on ocean health. More light means more photosynthetic organism, which leads to a larger base energy level for the entire ecological pyramid. Ocean currents are another abiotic factor that can stimulate ecosystem health. An upwelling current can bring nutrient-rich ocean water from the bottom to the surface and help build and maintain populations of phytoplankton and seaweed.