Investigating Rangia cuneata Clams as Ecological Response Bioindicators to Three Decades of Variable Freshwater Inflows

Freshwater inflow management (quality and quantity) is critical for both environmental and human demands. Inflows needed to maintain ecosystem functionality can be assessed by observing how organisms sensitive to environmental change (bioindicators) respond to varying flow conditions. In Galveston Bay (Texas, U.S.A.), Rangia cuneata clams were proposed as bioindicators of ecological response to freshwater inflows. Rangia cuneata abundance has decreased and their distribution has retracted proximal to freshwater sources from 1983 to 2010. From 2010 to 2014, the highest mean shell lengths (Trinity River delta, 48.0 +/- 0.4 mm) and meat indexes (Clear Lake, 13.3% +/- 0.3%) of R. cuneata were observed in areas most influenced by freshwater inputs. In the Trinity River delta, clam biomass and density averaged 3.4 (+/- 0.3) kg m (3) and 25.6 (+/- 3.5) clams m (2), respectively. A general decreasing trend was observed in biomass and density between like seasons after the drought of 2011, which persisted throughout most of 2014. Sex ratios (62.8% +/- 2.4% male) and juvenile abundance (highest in winters and summers after spawning) were consistent with life-history observations. Life-cycle observations were not available before 2010 and are important to consider in future studies. Without them, long-term decadal declines in R. cuneata clams are difficult to explain when limited to terms of natural and anthropogenic stressors. Rangia cuneata's utility as bioindicators of the ecological functionality of an estuary affected by changing freshwater inflows requires further investigation for resource management.