Types of algae
There are several thousand known species of algae in the world and they occur in many different colours and forms. Algae can for instance be green, blue-green, brown, red or black.
Some types of algae will drift around in the water, while others grow attached to a surface, e.g. a rock, coral or plant leaf. There are also types of algae that float on the surface since this is the place where they can receive the most light.
In everyday speech, algae are commonly divided into three main groups based on appearance: microscopic algae, filamentous algae and attached-erect algae.
Microscopic algae waft along freely in the water. They form the autotrophic part of the plankton, the diverse group of drifting organisms that inhabits the pelagic zone of everything from oceans to small bodies of water. The name plankton is derived from the Greek word πλαγκτος ("planktos") which means "wanderer" or "drifter". Microscopic algae are commonly referred to as phytoplankton. Distinguishing the individual alga with a naked eye is generally not possible, but large groups of algae can be detected since the chlorophyll inside them turns the water greenish. Some types of microscopic plankton will give the water another colour than green, since they contain accessory pigments.
In filamentous algae the individual algal cells will stick to each other and form long, hair-like strands. The strands can form entangled clumps in the water and pieces can break off to float on the water's surface. Several species of filamentous algae are known to be cold tolerant and an algae bloom can therefore occur even during early spring when the water is relatively cold in temperate parts of the world. The bloom will typically start in shallow parts where the light reaches all the way down to the bottom. Clear water will further enhance the lights ability to reach far down.
Just as the name suggests, attached-erect algae grows attached to a surface, such as a rock, and will grow more or less straight up from the bottom. Many species of attached-erect algae can grow really tall and be very similar to land plants. When studied more closely, there are however significant differences between this type of algae and land living higher plants. Since attached-erect algae can be so similar to higher plants, pond owners sometimes mistake them for each other and try in vain to combat the algae with methods developed for ridding ponds of higher plants, e.g. lotus flowers. Many anglers dislike attached-erect algae since it can ensnare fishing equipment.
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