Cocconeis pinnata is a marine and brackish-water diatom in the family Cocconeidaceae, distinguished within the genus by the pinnate (feather-like) arrangement of its striae and the specific valve morphology of its silica frustule. As an adnate epiphyte, C. pinnata attaches to a wide variety of substrates in coastal and estuarine environments, including seagrass blades, macroalgal surfaces, sandy sediments, and biogenic hard substrates such as shells and coral rubble. The species has been documented from tropical and subtropical marine habitats across the Indo-Pacific and Atlantic, with records from South American coastal waters as well as other warm marine regions. Cocconeis pinnata plays a significant ecological role in seagrass ecosystems, where epiphytic diatom communities including this species form a productive biofilm layer on leaf surfaces that serves as food for grazing invertebrates, sea urchins, and small fish. In areas of excessive nutrient loading, however, proliferation of epiphytic algae including diatoms can shade out the underlying seagrass, contributing to meadow decline. The production and dissolution of silica frustules by marine benthic diatoms contributes to the benthic silica cycle, linking biological productivity with the geochemistry of shallow coastal sediments. Species-level identification of Cocconeis taxa requires electron microscopy due to subtle morphological differences. Conservation status has not been formally assessed.