Final answer:
Primary productivity in the ocean is mainly achieved through photosynthesis, with phytoplankton being the most significant contributors. The two main factors influencing it are nutrient availability and light penetration, with nutrient availability playing a critical role in areas of ocean upwelling.
Step-by-step explanation:
The methods by which primary productivity is accomplished in the ocean are predominantly through photosynthesis and chemosynthesis. Of these, photosynthesis is the most significant as it is responsible for the majority of the oxygen production in the marine environment. Phytoplankton, including photosynthetic bacteria and larger algae, are the main contributors to this process. They in turn serve as a primary food source for zooplankton and smaller fishes, which are crucial for maintaining marine biodiversity and supporting the world's fisheries, especially in the neritic zone.
The two main factors that influence primary productivity in the ocean are nutrient availability and light penetration. Nutrient availability is affected by factors like ocean upwelling, which brings nutrient-rich deep waters to the surface. Light penetration influences the depths at which photosynthesis can occur and is dictated by factors such as water clarity and depth.