FORAMINIFERAL POPULATION RESPONSE TO FLUCTUATING INFLOW INTO NUECES BAY, TEXAS

Freshwater input into Texas estuaries is critical to maintaining habitat, and foraminiferal populations can provide a means for assessing the effects of natural inflow as well as mandated releases. Nueces Bay receives freshwater from the Nueces River, which enters at the south shore. From 1998 to 2007 foraminifers were sampled on a mid-bay, north-south transect at five different stations. The populations were sampled during periods of low inflow (mean monthly discharge of .47-2564 ft³/s, 1998-2002), high inflow (mean monthly discharge of 19.69-16,170 ft³/s, 2002-2003), and relatively moderate inflow (mean monthly discharge of 7.12-196.83 ft³/s, 2006-2007). During the low inflow period, the Central Power and Lighting Plant (CPL) was in operation at the south shore, pumping heated, more saline coolant water into the bay. Salinities were nearly constant, ranging from 23-27 ppt at the stations. Results from the 1998-2002 sampling showed statistical differences in total populations and community structure between the north and south shores, as well as a high incidence of shell dissolution. In the 2003 samples, taken after the CPL closed and the area received abundant precipitation, salinities varied from 12 ppt at the south shore to 21 ppt at the north shore. Foraminiferal abundance was from 6-98 times greater, there were no differences in total populations or community structure, and there was a low percentage of shell dissolution. To see how populations respond during more moderate inflow, a final set of samples was taken in 2007. Salinity at the southernmost station was 21 ppt, and at the northernmost it was 30 ppt. Data thus far show that total densities are intermediate between those recorded during low and high discharge conditions, and that there is again an increased occurrence of shell dissolution. This project establishes the receptivity of foraminifers to short-term fluctuations in freshwater inflow, and highlights their value for monitoring discharge into Texas estuaries. The ability of foraminifers to respond to changing environmental circumstances may be a characteristic that imparts species resilience through time.