Diatoms
Overview
Diatoms are a major group of algae, and are among the most common types of phytoplankton. They are unicellular organisms that exist as solitary cells or in connected chains or groups, depending on the species. Diatoms are producers within the food chain, and contribute significantly to the primary productivity of the world's oceans.
Biology
Diatoms are unique among phytoplankton in having a glass-like exterior made of silica. This silica shell, or frustule, is composed of two halves, and its intricate and delicate design is characteristic of each species. The frustule provides protection and contributes to the buoyancy of the diatoms.
Diatoms reproduce both sexually and asexually, with the asexual reproduction being the most common. During asexual reproduction, each diatom cell divides, producing two new cells, each with one half of the parent cell's silica shell. The new cells then produce a smaller shell within the old one. Over time, this results in a decrease in size among the population, which is counteracted by sexual reproduction leading to the formation of larger cells.
Ecology
Diatoms are found in all aquatic environments, both marine and freshwater. They form the base of many aquatic food chains, and are primary producers, converting sunlight into energy through photosynthesis. Diatoms are responsible for about 20% of the world's primary productivity, which is comparable to the amount of oxygen produced by all the world's tropical rainforests.
Diatoms also play a crucial role in the biogeochemical cycles of several key elements, including carbon, nitrogen, and silicon. When diatoms die, their silica shells sink to the ocean floor, where they form a layer of sediment known as diatomaceous earth. This process, known as the biological pump, is an important part of the carbon cycle, as it helps to sequester carbon in the deep ocean.
Applications
Diatoms have a wide range of applications, from their use in scientific research to their commercial exploitation. In scientific research, diatoms are used as indicators of environmental conditions, both past and present. They are used in studies of climate change, water quality, and other environmental issues.
Commercially, diatoms are used in a variety of products and processes. Diatomaceous earth, composed of the silica shells of dead diatoms, is used as a filtering agent, a mild abrasive, and as a soil conditioner. Diatoms are also being investigated for their potential in biofuel production, due to their high lipid content and rapid growth rate.