THE ROLES OF BLUE-GREEN ALGAE 
by 
Dr. Lawrence W. Haas 
Virginia Institute of Marine Sciences 
and 
Dr. Hans W. Paerl 
University of North Carolina 
When you mentioned the word cyanobacteria to a plankton 
ecologist or water quality manager in the Chesapeake Bay Region, 
more likely than not, their thoughts turn to a surface scum of 
cyanobacteria in the tidal freshwater section of the Potomac 
River. For many, these blooms have come to epitomize the un¬ 
desirable effects of eutrophication in the Chesapeake Bay Re¬ 
gion . 
What are cyanobacteria? Why do they appear in such high 
concentrations in the certain parts of the estuary at certain 
times of the year? Can we expect similar occurrences in the 
future in saline portions of the Chesapeake Bay? Are there cya¬ 
nobacteria in the more saline portions of the Bay and, if so, 
what role do they play in the plankton community? These are 
some of the questions I hope to answer. 
Cyanobacteria are photosynthetic organisms which occur in a 
variety of morphological types including single cells measuring 
only a micrometer in diameter, chains of single cells, colonies 
of single cells held together by a mucoid-like substance, fila¬ 
ments composed of many cells, and aggregates of filaments rang¬ 
ing in size from loosely aggregated tufts barely visible to the 
naked eye, to "mats" of filaments measuring several centimeters 
thick. Cyanobacteria are widely distributed in both marine and 
freshwater habitats. My comments today will address only plank¬ 
tonic cyanobacteria, those forms which spend all of most of 
their life cycle suspended in the water column. I will ignore 
the variety of cyanobacteria found, often in abundance, on es¬ 
tuarine and salt pond sediments, and attached to salt marsh 
plants, submerged aquatic vegetation, shells, pilings, or almost 
any solid substrate in the marine environment. 
Some of the pertinent physiological, morphological charac¬ 
teristics of cyanobacteria are listed in Table I and include: 
1. A cellular structure fundamentally similar to that of 
bacteria which places them with bacteria in the group of organ¬ 
isms known as prokaryotes. It is this characteristic which ac¬ 
counts for the commonly used term cyanobacteria. 
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