What are Algae?

The term “algae” covers many different organisms capable of producing oxygen through   photosynthesis.   While they serve as the basis of the aquatic food chain, they can also occur at nuisance levels when aquatic ecosystems are out of balance.

The following summary is from Chapter One of “Diet for a Small Lake”-   Lake Ecology:  Getting Your Feet Wet.

Photo courtesy of Terry Gronwall

Hundreds of species of algae are found in New York State lakes, from little green dots, to bubbling masses,
to stringy filaments that look a lot like weeds. Algae can be classified by growth habitat. Phytoplankton are the free-floating forms (the little green dots).  Periphyton attach to surfaces, such as stones, dock pilings and macrophytes. Periphytons that attach to macrophytes are referred to as epiphytes. In highly productive lakes, stringy masses of filamentous algae attach to boats and submerged objects.  

Within these main categories, there are many different varieties of algae. There is a general progression from one type of algae to another through the seasons. Three major varieties dominate most New York State lakes: diatoms, green algae, and blue-green algae (or cyanobacteria). The rapid growth of algae on the surface of lakes, streams, or ponds, which is generally stimulated by nutrient enrichment, is referred to as an algal bloom.

Lakes that are clear with few algae generally have diatoms, and these are seldom found at nuisance levels in most New York lakes. Diatoms are symmetrical, silica-based, mostly unicellular algae that are literally as fragile as glass, although their cell walls can remain intact in sediments for thousands of years. They form a significant portion of
diatomaceous earth and the “skeletal” base of fossil fuels. Their persistence in sediments can be used to construct a historical record indicating when a lake started suffering excessive algal blooms. In New York State lakes, diatoms tend to be found primarily during the spring, due to their ability to survive somewhat colder conditions, and to extract silica from the water column at a time of the year when it is abundant in higher spring precipitation and runoff. When diatoms lose their competitive advantage, they tend to be replaced by green algae.

Green algae (Chlorophyta) is the most common and abundant form of algae. This group includes plants as well as mobile animals that contain chlorophyll, flagella (whip-like structures used for locomotion) and even eyespots! Green algae thrive where there are elevated nitrogen levels. Excess nitrogen can come from spring runoff due to the import of nitrate-rich water from acid rain and winter field fertilization.  It can come from soils that are naturally nitrogen rich, typical for much of central New York and Long Island. It can also come from long-term use of fertilizers. These algal blooms are occasionally associated with taste and odor problems. The green algae tend to
be replaced by blue-green algae in the late summer or early fall in many lakes, particularly those that have high lake productivity.

Photo courtesy of Ken Belfer

Blue-green algae are more correctly identified as bacteria and given the name Cyanobacteria. Although referred to as blue-green, they are also capable of turning water brown or red. Cyanobacteria are most often the cause of taste and odor problems, as well as nuisance conditions in lakes and ponds. Cyanobacteria maintain a competitive advantage over other algae. They have the ability to extract nitrogen from the atmosphere in a process called nitrogen fixing, allowing them to thrive as phosphorus levels increase in the water. They can avoid predation by producing gas vacuoles to regulate their position in the water.  Some species produce toxins or slimy coats that are unpalatable for zooplankton and zebra mussels (Dreissena polymorpha), and they form masses too large to be ingested. The algae species described above are usually the cause of algal blooms in the lakes and ponds throughout the northeastern United States. In some New York State lakes, however, other algae and microorganisms may also comprise a significant part of the planktonic community.