useful and harmful effects of algae-FOB-btechbiotechnology-introduction to microorganisms-1st chapter

Algae are a natural and critical part of our Chesapeake and Coastal Bays ecosystems. Algae, like land plants, capture the sun’s energy and support the food web that leads to fish and shellfish. They occur in a size range from tiny microscopic cells floating in the water column (phytoplankton) to large mats of visible “macroalgae” that grow on bottom sediments.

Algae may become harmful if they occur in an unnaturally high abundance or if they produce a toxin. A high abundance of algae can block sunlight to underwater bay grasses, consume oxygen in the water leading to fish kills, produce surface scum and odors, and interfere with the feeding of shellfish and other organisms that filter water to obtain their food. Some algal species can also produce chemicals that are toxic to humans and aquatic life. Fortunately, of the more than 700 species of algae in Chesapeake Bay, less than 2% of them are believed to have the ability to produce toxic substances.
The blue-green algae Microcystis aeruginosa also had significant blooms in the summer of 2000 in Chesapeake Bay. Algal bloom samples tested toxic and resulted in temporary, precautionary beach closures in the upper Bay. A bloom of Dinophysis acuminata was detected in the Potomac River during the winter 2001 and resulted in a temporary closure of shellfish waters. The shellfish waters were reopened as toxin levels in oysters were found to be below threshold levels by the U.S. Food and Drug Administration. The Coastal Bays experienced macroalgae blooms that concerned citizens about their effects on boating, Pfiesteria and Brown tide blooms occurred, and potentially toxic species of Chattonella, Fibrocapsa and Heterosigma were identified in the region for the first time between 2000 and 2002.
Declines in coral cover are generally associated with increases in the abundance of fleshy algae. In many cases, it remains unclear whether algae are responsible, directly or indirectly, for coral death or whether they simply settle on dead coral surfaces. Here, we show that algae can indirectly cause coral mortality by enhancing microbial activity via the release of dissolved compounds. When coral and algae were placed in chambers together but separated by a 0.02 μm filter, corals suffered 100% mortality. With the addition of the broad-spectrum antibiotic ampicillin, mortality was completely prevented. Physiological measurements showed complementary patterns of increasing coral stress with proximity to algae. Our results suggest that as human impacts increase and algae become more abundant on reefs a positive feedback loop may be created whereby compounds released by algae enhance microbial activity on live coral surfaces causing mortality of corals and further algal growth.
usefule effects

Freshwater algal blooms

Freshwater algal blooms are the result of an excess of nutrients, particularly phosphorus.[1] The excess of nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes, these nutrients can then enter watersheds through water runoff.[2] Excess carbon and nitrogen have also been suspected as causes.

When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. Algae tend to grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter which starts to decay. The decay process consumes dissolved oxygen in the water, resulting in hypoxic conditions. Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers.

Blooms may be observed in freshwater aquariums when fish are overfed and excess nutrients are not absorbed by plants. These are not generally harmful for fish, and the situation can be corrected by changing the water in the tank and then reducing the amount of food given.
# Cyanobacteria
Cyanobacteria are single-celled organisms that live in fresh, brackish, and marine water and can use up the oxygen and block the sunlight that other organisms need to live and can produce powerful toxins that affect the brain and liver of animals and humans ...more
# Harmful Marine Algae

* Ciguatera
Ciguatera fish poisoning is an illness caused by eating fish that contain toxins produced by a marine microalgae ...more
* Red Tide
Overgrowth of the microscopic marine algae called Karenia brevis can create blooms that can make the ocean appear red or brown. People often call these blooms “red tide” ...more

# Pfiesteria piscicida
Pfiesteria piscicida is a microscopic alga that lives in estuaries—where freshwater streams or rivers mix with salt water—along the Atlantic and Gulf coasts