Which of the following best describes a characteristic of phytoplankton?

Phytoplankton are a crucial component of aquatic ecosystems, serving as primary producers. These microscopic organisms utilize sunlight to perform photosynthesis, converting light energy into chemical energy and producing organic compounds that serve as food for a variety of marine organisms. This process is fundamental to the energy flow in aquatic environments, making phytoplankton essential to the base of the food web.

Since they are primary producers, phytoplankton form the foundation of the aquatic food chain, supporting various levels of consumers, including zooplankton and larger fish species. Their abundance and diversity play a significant role in regulating ecosystems' productivity and can also influence global carbon cycles through carbon dioxide absorption during photosynthesis.

The other options present characteristics that do not align with the biological and ecological role of phytoplankton. For instance, they are not typically larger than zooplankton; instead, phytoplankton are generally much smaller. Additionally, they are not incapable of photosynthesis, as photosynthesis is a defining trait of phytoplankton. Lastly, while some species may inhabit different depths of ocean waters, phytoplankton are primarily found in the photic zone, where sunlight penetrates, rather than deep ocean waters where light is scarce.