| Benthic macroinvertebrates at 5 stations in the Galveston estuary were sampled quarterly for 8 years to evaluate relationships with water quality variables (salinity, temperature, nutrients, dissolved oxygen (DO), suspended solids, and water clarity), long-term trends, and the effects of wet years and dry years on the benthos. The stations were located along the estuarine gradient, and mean salinities ranged from 9.6 ppt at the site in Trinity Bay to 23 ppt at the station in West Bay. Benthic abundance and number of taxa were reduced in wet years compared with dry years throughout the bay; the effect was stronger at the stations with higher mean salinities. At the station in West Bay, abundance declined over the 8 year period (−615 organisms/m 2/yr), while the benthic community remained relatively stable at the other stations. The relationships between the benthic community and the water quality variables were examined using canonical correspondence analysis. Overall, the benthic communities were strongly affected by salinity (this variable explained 29% of the variance among all the samples), but most of the water quality variables were also significant. At the individual stations, however, different processes were apparent in different parts of the bay. At the 2 lower salinity stations in Trinity Bay and Upper Galveston Bay, salinity explained 19% and 24% of the variance, although nutrients and water clarity were also important. At the 2 stations in the middle and lower bay, temperature, salinity, ammonia, and DO were the most significant variables in the model. At the station in West Bay, temperature, ammonia and DO were the only significant variables in the model, and together they explained just 15% of the variance. The significant water quality variables at the other 4 stations explained between 47% and 80% of the variance. The benthic community at the stations in the upper part of the estuary may be more disturbed or more affected by the highly variable water quality conditions. There is a gradually more stable community along the estuarine gradient towards West Bay, which has less variable water quality conditions, and the benthic community in West Bay is probably controlled by other factors, either biological or physical. |
