Phytoplankton Monitoring Program  

PHYTO MONITORING PROGRAM ONLINE DRAFT 3 (2)
at Morgan State University Estuarine Research Center

Almost every year, parts of the Chesapeake Bay turn dark red. Area residents often call this phenomenon a mahogany tide. The discoloration is the most visible sign of an excessive growth of microscopic plants called phytoplankton, but not the most troubling.

When the phytoplankton experiences a population explosion because of an excess of nutrients and other factors, these tiny plants produce algae blooms. Many blooms accumulate at the very surface of the water and cause dramatic discoloration, such as the mahogany tide. But scientists at the Morgan State University Estuarine Research Center (MSUERC) know that a bloom that you can’t see isn’t the one that can have the most devastating effect on the overall health of the bay. Blooms can result in the loss of aquatic life because they can reduce the amount of oxygen in the water and they prevent sunlight from reaching plants in the bay.

MSUERC biologists have developed a groundbreaking index for monitoring trends in phytoplankton growth. MSUERC (formerly the Academy of Natural Sciences Estuarine Research Center) has been tracking phytoplankton in the Maryland portion of the Chesapeake Bay, the Potomac, Patuxent and Choptank Rivers and Baltimore Harbor since 1984. The center’s Phytoplankton Monitoring Program measures the plant’s types, densities and photosynthetic production.

The center collects samples 13 times each year at 16 sites. Over time, the phytoplankton program has focused on investigating how changes in phytoplankton communities are related to shifts in chemical and physical characteristics of the estuary. Excessive loads of nutrients from sewage treatment plants, agricultural and industrial runoff and from atmospheric deposition cause the proliferation of phytoplankton. This overabundance of nutrients and hence phytoplankton gives rise to a condition known as eutrophication. The monitoring of nutrient concentrations and the populations of the microscopic plants and animals is crucial in the assessment of water quality conditions and habitat further up the food chain. The MSUERC system shows that progress in reducing blooms will take time, relying in part on increased efforts to control pollutants in the bay.

Part of a Comprehensive Effort

In 1983, the United States Environmental Protection Agency (EPA) published the results of a 7-year study of the Chesapeake Bay’s health that concluded that the state of the ecosystem was in decline. Trends included increasing levels of nutrients, blooms, increasing areas of low dissolved oxygen during the summer, the disappearance of submerged aquatic vegetation beds and the decline in stocks of valuable commercial resources such as oysters, shad, striped bass and several other species of finfish.

The following year, the state governments of Maryland, Virginia, Pennsylvania and the governing body of the District of Columbia launched, with the financial assistance of the federal government, a multifaceted bay restoration and protection program. One arm of this project, the Chesapeake Bay Water Quality Monitoring Program, monitors the vital signs of the ecosystem to ascertain long-term trends and to make recommendations to policymakers for the development of best management practices.

The Chesapeake Bay Water Quality Monitoring Program has evolved into a state-of-the art design targeting many of the problems identified in the EPA study. The program includes components to study pollutants, chemical and physical properties and many other aspects of bay water quality, including the MSUERC’s phytoplankton monitoring effort.

The bay’s phytoplankton populations show distinct patterns in their quantity and quality over space and time. Changes in the amount of freshwater that enters the ecosystem from year to year, along with variations in water temperature, salinity and of course, nutrients, affect these patterns. The primary factor man can alter: the amount of nutrient

Three Prominent Blooms

The largest and ecologically most prominent bloom in Chesapeake Bay is the spring diatom bloom. Diatoms are

microscopic plants that live in glass houses or frustules composed mostly of silica. Unlike most other algal blooms, this bloom doesn’t discolor the water. The spring diatom bloom is largely composed of two or three species that occur in vast numbers both vertically and laterally in the water. The surplus of diatoms fuels the creation of harmful low dissolved oxygen conditions in the bottom waters of the bay, known as anoxia or dead zones.


Two other prominent features occur in the Chesapeake Bay estuary annual phytoplankton cycle – dinoflagellate blooms in the brackish and saltier regions and cyanobacteria blooms in the fresh water areas.

The MSUERC phytoplankton group participated in the intensive study of the fish-killing dinoflagellate Pfiesteria piscicida which caused ecological and health problems on Maryland’s Eastern Shore from 1999 to 2003. Dinoflagellates, single-celled plants, live within a stout cell wall. Dinoflagellates are an interesting group of plants partially because they get their nutrients in a wide variety of ways. Some dinoflagellates are autotrophic, meaning that they produce their own food via photosynthesis; others are heterotrophic which indicates that they ingest food (yes, that’s right, a plant that eats other organisms for food!) and finally some are mixotrophic which means that they can switch from autotrophs to heterotrophs, depending upon environmental and biotic conditions. These are the blooms that are often called red, brown or mahogany tides.

Cyanobacteria blooms occur during the warm summer months in some of the freshwater areas of the estuary (the upper parts of the rivers). Cyanobacteria, once called blue-green algae, are an ancient group of plants (more than 2 billion years old) which in many ways are closely aligned to bacteria. Some forms of cyanobacteria have the unique ability to fix molecular nitrogen and therefore don’t have to use either inorganic nitrogen salts or organic forms of nitrogen compounds as one of their primary nutrients. Most blooms of cyanobacteria occur in the surface layer of the water (see Figure 5). This group is generally a poor food source for other aquatic life. The major cyanobacteria bloom-forming species in Chesapeake Bay is a colonial form, Microcystis aeruginosa, which forms dramatic green surface scums and white foam after the alga dies.


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