* Water: Marine biologists study the physical and chemical properties of water, such as temperature, salinity, density, and pH. They also study the movement of water, including waves, currents, and tides.

* Sunlight: Marine biologists study how sunlight affects marine organisms. They measure the amount of sunlight that penetrates the water column and how it is absorbed by different organisms. They also study the effects of sunlight on the behavior, physiology, and reproduction of marine organisms.

* Sediment: Marine biologists study the composition and structure of sediment on the ocean floor. They also study how sediment is transported by waves and currents, and how it affects the distribution and abundance of marine organisms.

* Rocks: Marine biologists study the types and distribution of rocks on the ocean floor. They also study how rocks are formed, eroded, and weathered, and how they affect the distribution and abundance of marine organisms.

* Atmosphere: Marine biologists study the interactions between the ocean and the atmosphere. They measure the exchange of heat, gases, and water vapor between the ocean and the atmosphere, and how these exchanges affect the climate.