Biological Components 
of Galveston Bay 
Peter F. Sheridan, R. Douglas Slack, Sammy M. Ray, Larry W. McKinney, 
Edward F. Klima, Thomas R. Calnan 1 
Distribution and Abundance 
Estuarine Vegetation 
PETER F. SHERIDAN—The plant life of Galveston Bay includes phytoplankton in the water 
column, benthic microflora, macroalgae, submerged aquatic vegetation and emergent vascular 
plants. Some groups are so dense that they are major sources of physical structure for other estuarine 
organisms, while some groups are major producers of organic materials for assimilation by 
consumers. Other functions of vegetation include refuge from predators, maintenance of water 
quality by filtering runoff and tidal inputs, and shoreline stabilization. 
Phytoplankton—The phytoplankton of upper Galveston and Trinity Bays is composed of at least 
132 species, including diatoms (54 taxa), green algae (45 taxa), blue-green algae (14 taxa), dinoflagel- 
lates (9 taxa), euglenoids (7 taxa), cryptophy tes (2 taxa), and golden-brown algae (1 taxon) (1). Many 
of these species, particularly the green algae, are freshwater forms entering via river discharge. Over 
an annual cycle (September 1975-August 1976), the mean percentage of the standing crop for each 
division was found to be diatoms (41.6 percent), green algae (24.2 percent), blue-green algae (23.0 
percent), dinoflagella tes (5.9 percent), euglenoids (2.6 percent), and others (2.7 percent). Major peaks 
in phytoplankton density occurred in late winter and mid-summer. The winter peak was due to the 
diatoms Skeletonema costatumand Cyclotellamenenghiniana, while the summer peak in densities 
was due to a bloom of the blue-green Oscillatoria sp. As a group, diatoms were the dominant 
phytoplankters in November, December and February-June (Skeletonema and Cyclotella in cold 
months, Nitzschia closterium, Navicula abunda and Thalassionema nitzschoides in warmer 
months). Green algae were a consistent 20 to 30 percent of the monthly standing crops, and 
Ankistrodesmus sp. bloomed in September-October. Blue-green algae were relatively abundant 
July to October, and a bloom of Oscillatoria in July represented 70 percent of the standing crop. The 
dinoflagellate Prorocentrum sp. comprised 45 percent of the total density in January. Euglenoids 
such as Euglena spp. and Eutreptia spp. were relatively abundant in May and August. Lower salinity 
stations were dominated by blue-green and green algae while high salinity sites were dominated by 
diatoms. 
Similar studies on phytoplankton distribution and abundance have not been conducted in lower 
Galveston, East or West Bays. 
Benthic Micro flora—Components of the benthic microflora have been examined in a descriptive 
sense (2-4), but little information on temporal or spatial distribution is available. Thirty-three genera 
’Peter F. Sheridan and Edward F. Klima represent the National Marine Fisheries Service; R. Douglas Slack, 
Texas A&M University; Sammy M. Ray, Texas A&M University at Galveston; Larry D. McKinney, Texas Parks 
and Wildlife Department; Thomas R. Calnan, Bureau of Economic Geology, The University of Texas at Austin. 
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