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Seaweeds are multicellular algae living in the oceans. A. Seaweeds are limited to areas with enough light for them to survive, with most living on the seafloor and more species inhabiting warm waters than colder waters. B. Some recent evidence shows that the color of any species of seaweed is determined by the amount of chlorophyll a contained in its accessory pigments. C. The greatest diversity of seaweed is found in warm waters, and seaweed cannot survive when the temperature is either too hot or too cold. D. Seaweeds are distributed most evenly over areas of ocean that experience changing tides, strong waves, a dry climate, and high concentrations of salt and minerals. E. The chromatic-adaptation hypothesis was long thought to explain the vertical distribution of seaweed, but current belief is that distribution is better explained by other factors. F. Temperature extremes in tropical and subtropical areas as well as at high latitudes cause seaweeds to abandon the intertidal areas for the subtidal zones of the seafloor.