Marine ecosystems are influenced by which factor related to light?

• A. Water Temperature
• B. Depth of Sunlight Penetration
• C. Salinity
• D. Water Pressure

Answer: (B)

Light fuels photosynthesis, which forms the base of marine food webs. How far sunlight can penetrate the water determines the depth range where photosynthesis can occur, creating a distinct photic (euphotic) zone at the surface and an aphotic zone below it. This light-driven zone controls primary production, energy flow, and the resulting distribution and productivity of marine organisms. Therefore, the factor tied to light that best shapes marine ecosystems is the depth to which sunlight can reach. While water temperature, salinity, and pressure shape other habitat conditions, they do not define the light-driven limits on photosynthesis and ecosystem structure in the same direct way.