Nutrient loading impacts on culturable E. coli and other heterotrophic bacteria fate in simulated stream mesocosms.

Understanding fecal indicator bacteria persistence in aquatic environments is important when making management decisions to improve instream water quality. Routinely, bacteria fate and transport models that rely on published kinetic decay constants are used to inform such decision making but may not adequately represent instream conditions. The objective of this work was to evaluate bacterial responses to applied nutrient amendments and provide additional information regarding bacterial response to applied changes that can be incorporated into future modeling efforts. Re-created stream mesocosms were established in laboratory-based, repurposed algae raceways filled with water and sediment from a small, 3rd order Southeast Texas stream. Mesocosm treatments consisted of low (10x) or high (50x) nutrient doses above ambient water concentrations operated at low (0.032 m/s) or high (0.141 m/s) flow rates. Escherichia coli and heterotrophic bacterial concentrations were quantified in water and sediment over 22 days. No significant differences in kinetic constants were observed among E. coli in water or sediment, and only E. coli in sediment showed any growth response. Heterotrophic plate counts revealed a pronounced growth response in water and sediment within 24 h of nutrient addition but did not differ significantly from control mesocosms. Significant kinetic constant differences between E. coli and heterotrophic bacteria in water were identified (p < 0.01) but did not differ significantly in sediment (p > 0.48). Results indicate that nutrient addition does affect microbial numbers instream, but competition from heterotrophic bacteria may prevent an E. coli growth response.

Stress responses and sexing of wild Kemp's ridley sea turtles (Lepidochelys kempii) in the northeastern Gulf of Mexico.

Plasma corticosterone, glucose, and testosterone concentrations were measured in wild, immature specimens of the highly endangered Kemp's ridley sea turtle (Lepidochelys kempii) to determine effects of acute handling stress. Thirty-nine free-ranging turtles were captured by entanglement net near the Cedar Keys, Florida. Blood samples were collected immediately after retrieval from the net, and at 30 min (n = 15) and at 60 min (n = 29) thereafter. Mean plasma corticosterone and glucose concentrations increased significantly with time. No significant difference was observed over time for mean testosterone concentrations. Approximately half of the turtles demonstrated an increase in plasma testosterone after 60 min of captivity while the others demonstrated a decrease. Initial testosterone concentrations were used to determine the sex of individual turtles. Fifty-nine percent of turtles were classified as female, 33% as male, and 8% as indeterminant. The results of this study demonstrate a responsive hypothalamic-pituitary-adrenal axis and hyperglycemia in immature Kemp's ridley turtles during acute handling stress.

Plasma corticosterone concentrations associated with acute captivity stress in wild loggerhead sea turtles (Caretta caretta).

Plasma corticosterone concentrations were measured in wild loggerhead sea turtles (Caretta caretta) in response to acute captivity (capture, serial bleeding, and restraint up to 6 hr). In general, concentrations of corticosterone dramatically increased 1 hr after capture, peaked at 3 hr, and decreased by 6 hr. Initial corticosterone concentrations were significantly lower in animals captured by tangle net than in those captured by trawl and were thought to more closely represent baseline levels. Significant effects of season and size class on corticosterone concentrations were found for turtles captured by trawl. Corticosterone concentrations of small turtles captured in summer were higher than those of large turtles captured in the same season and of all turtles captured during winter. In winter, corticosterone concentrations for small turtles were higher than those for large turtles at 3 hr after capture. Large turtles captured during winter experienced the slowest rate of increase in plasma corticosterone and a decline at 3 hr after capture. Although cloacal temperatures were significantly higher in summer samples, corticosterone concentrations of large turtles did not differ between seasons until 1 hr after capture. In addition, several large turtles during summer did not experience an increase in corticosterone concentrations 1 hr after capture. It is possible that the lower corticosterone response of large turtles captured during summer may be associated with reproductive condition.