Abundance of Benthic Macroinvertebrates in Natural and 
Altered Estuarine Areas! 
GIL GILMORE? and LEE TRENT? 
ABSTRACT 
The abundance of benthic macroinvertebrates during March-October 1969 in West Bay, Texas, was 
compared between 1) a natural marsh area, 2) an adjacent marsh area altered by channelization, bulk- 
heading, and filling, and 3) an open bay area. Animals representing four phyla were caught. Abundance 
indices (areas combined) of the four groups in terms of numbers were 66.4% polychaetes, 29.6% crusta- 
ceans, 2.5% pelecypods, and 1.5% nemerteans; volumes were 44.0% polychaetes, 40.8% pelecypods, 
10.7% nemerteans, and 4.4% crustaceans. 
When all organisms were combined, they were slightly more abundant numerically and over twice as 
abundant volumetrically in the marsh than in the canals and were least abundant in the bay. Polychaetes 
were most abundant in the canals and least abundant in the bay; abundance was highest at stations with 
low to intermediate amounts of silt and clay or where vegetative matter was composed mostly of live sea 
grasses or detritus. Crustaceans were more abundant in the natural marsh than in the other two areas and 
showed a definite preference for sandy substrate in marsh areas. Pelecypods were numerically most 
abundant in the bay but volumetrically the marsh had the highest standing crop. Nemerteans were most 
abundant in the marsh and least abundant in the bay. 
In general, the seasonal abundance of polychaetes and nemerteans varied little during the study, 
whereas crustaceans and pelecypods were abundant only during the spring and early summer. An 
exception to this seasonal abundance pattern was the reduction in numbers of polychaetes at the upper- 
most canal station where the habitat was apparently unsuitable due to low oxygen levels during the 
summer and early fall. 
INTRODUCTION 
Development of bayshore property into housing 
sites by dredging, bulkheading, and filling is occurring 
in many estuaries. When this property is developed, 
shallow bay and tidal marsh areas are dredged out or 
filled with spoil, thus changing the environment for 
marine organisms. The effects of the resulting en- 
vironmental changes on the abundance of benthic or- 
ganisms are poorly understood. 
Some studies on the succession and abundance of 
benthic marine animals in canals following excavation 
indicate that succession may occur rapidly and that 
climax communities may be established within 2 yr 
(Brandt, 1897; Reish, 1956, 1957). For example, peaks 
in the number of species and specimens of benthic 
invertebrates were reached about 2 yr after seawater 
entered a newly constructed boat harbor in California, 
and the abundance and species diversity in the harbor 
* Contribution No. 335, Galveston Laboratory, Gulf Coastal 
Fisheries Center, National Marine Fisheries Service, Galveston, 
Texas. 
* Marine Laboratory, Texas A&M University, Galveston, TX 
77550. 
® Panama City Laboratory, Gulf Coastal Fisheries Center, Na- 
tional Marine Fisheries Service, NOAA, Panama City, FL 32401. 
2 yr after opening were comparable to those in adja- 
cent natural areas (Reish, 1961). 
In other cases, however, climax communities may 
be altered or natural succession may not occur. Reish 
(1961) found that the benthic population in a boat har- 
bor in California decreased markedly during the third 
year, probably because of low dissolved oxygen. 
Taylor and Saloman (1968) concluded that soft de- 
posits in the canals of a Boca Ciega Bay housing de- 
velopment in Florida were in some way unsuitable for 
most benthic invertebrates that were found in the 
natural areas of the same bay. After 10 yr, recoloniza- 
tion of canal sediments by benthic organisms was neg- 
ligible, and it appeared doubtful that soft sediments of 
the canals would ever support a rich or diverse in- 
fauna. The habitat in Boca Ciega Bay was, however. 
changed drastically by channelization of the natural 
bay area which was sandy and shallow, and had con- 
tained numerous turtle grass (Thalassia testudinum) 
beds and oyster reefs. 
The objectives of our study were 1) to determine the 
relative abundance of benthic macroinvertebrates in 
three habitats: a natural marsh characterized by cord 
grass (Spartina alterniflora) and by sparse, submerged 
vegetation; a previously similar area altered by dredg- 
ing, bulkheading, and filling; and an open bay area; 
and 2) to relate invertebrate abundance within each 
