Table 4.5. Species Richness of Benthic Macroinvertebrate Assemblages. 
Location 
Mollusks 
Number of Species 
Polychaetes 
Crustaceans 
West Bay 
42 
48 
40 
Galveston Bay 
32 
41 
29 
East Bay 
9 
20 
14 
Trinity Bay 
7 
7 
3 
Clear Lake 
Houston Ship Channel 
1 
4 
2 
San Jacinto River 
Source: 1. 
Table 4.6. Galveston Bay Wetland Habitat Changes, 1956-1979. 
Change 
Acres Percent 
Wetland Habitat Type 
Estuarine Marsh 
Freshwater Marsh 
Estuarine Open Water 
Freshwater Open Water 
Wooded 
Streams 
Beach 
1956 
1979 
Acres 
Acres 
154,588 
130,139 
51,496 
39,119 
363,213 
388,397 
19,648 
21,939 
1,873 
6,267 
3,499 
3,835 
3,015 
1,413 
-24,449 
-15.8 
-12,377 
-24.0 
+25,184 
+6.9 
+2,291 
+11.7 
+4,394 
+234.6 
+336 
+9.6 
-1,602 
-53.1 
understanding of sediment dynamics becomes an important issue. The quantity of sediment 
contributed by streams, and where it is ultimately deposited, is inadequately known. We do not 
know where the sediments of eroded shorelines go or how they get there. Sediments are resuspended 
by waves but the details of the processes are not well known. Sediment is transported from the bay 
to the gulf and some is returned but the mass balance is not known. 
Subsidence, shoreline erosion and changes in riverine suspended sediments have all contributed 
to a general loss of wetlands. It can occur as small nibbles or the loss of large tracts, indirectly or by 
deliberate land-use conversion. Estuarine marshes provide shoreline stabilization, maintenance of 
water quality by filtration of upland runoff and tidal waters, nursery habitats for economically 
important estuarine-dependent fisheries, and detrital materials to the bay food web. The U.S. Fish 
and Wildlife Service classified and quantified the wetlands surrounding Galveston Bay in 1956 and 
again in 1979, using aerial photo interpretation techniques. Habitat changes detectable in this manner 
are shown in Table 4.6. Substantial areas of brackish and freshwater wetlands were lost during the 
23-year interval between surveys. 
Seagrasses, never prominent, have also suffered major declines in recent years. The exact causes 
for this precipitous decline in seagrass habitats, from 5,200 acres in 1956 to 250 acres by 1979, will 
never be fully understood. The rapid industrial and residential growth of the Houston-Galveston 
metropolitan area is the likely cause. Increases in turbidity, pollutant runoff, vessel and boat activity, 
and coastal development are all suspected factors. The northern widgeon grass beds in Trinity Bay 
declined after construction of a power plant. The Clear Lake-Kemah-Seabrook area has become 
heavily urbanized. The Gulf Intracoastal Waterway and its dredged material disposal sites run 
adjacent to former seagrass beds on the northern short of West Bay. At least six major housing 
developments along the northern shore of Galveston Island were built adjacent to once-thick 
74 
