Abstract
Sometimes the waters of seas, rivers, or lakes turn an odd color, becoming brown, red, or green. These colors are actually those of tiny algae that are invisible to the naked eye—but those algae are reproducing so fast that they stain the water. These events are called algal blooms, and they can be harmful because they produce toxins that kill aquatic animals and can cause poisoning in humans. Our group investigated the harmful algal blooms that have been occurring regularly in Lampung Bay, Indonesia, since 2012. We tracked down the algal species responsible for these blooms by analyzing seawater and the seabed sediments of the bay. We identified one species of algae, a dinoflagellate called Margalefidinium polykrikoides , as the culprit. This species can take on multiple shapes, which makes its identification particularly difficult. Improving our knowledge about this algal species will eventually help us understand what triggers harmful algal blooms and how to prevent them.