1. Dr. Weston Nowlin Parvathi Nair Dr. Benjamin Schwartz
Evaluation of long-term temperature and low dissolved oxygen tolerances of the Comal Springs riffle beetle
Dr. Weston Nowlin
Parvathi Nair
Dr. Benjamin Schwartz

2. Habitat Associations and Spring Openings

3. Habitat Associations and Spring Openings

4. Habitat Associations and Spring Openings
“Adapted” for spring conditions
Physiochemical consistency
Changes in physicochemistry related to changes in flow regimes

5. CSRB and Spring Flows

6. CSRB and Spring Flows O2

7. CSRB and Spring Flows
Temperature

8. CSRB and Spring Flows
O2 demand
Temperature

9. CSRB and Spring Flows
O2 demand
Temperature O2

10. Study Objectives
Examine the effects of relatively long-term increases temperatures and declines in DO concentrations on performance and survival of CSRB
Compare long-term temperature and DO response among elmid species that differ slightly in habitat associations and/or trophic ecology
Explore use of non-listed surrogate species

11. H. glabra
H. vulnerata
H. comalensis
M. pusillus

12. First Set of Experiments
Examine responses of H. comalensis to increasing temperature or declining DO
1oC or 1 mg/L per day
Start at 23oC or 5 mg/L
12 individual beetles
Utilize same methods as study conducted on H. glabra
Compare results to those of H. glabra
Examined the “limits of acclimation”
Loss of response (LOR) is the response variable
Onset of rapid movement

13. Critical Threshold Methodology

14. Critical Threshold Experiments

15. H. comalensis exhibits onset of rapid movement ~33oC
Lower onset than H. glabra (~34oC)

16. H. comalensis exhibits LOR ~36oC
Not different from H. glabra

17. H. comalensis exhibits LOR at ~1.1 mg/L
Different from H. glabra (~0.5 mg/L)

18. Limits of Acclimation Summary
Temperature
Onset of rapid movement
32.4oC
LOR
35.97oC
Similar to H. glabra
Dissolved oxygen
1.14 mg/L
Lower than H. glabra

19. Second Set of Experiments Persistent Temperatures Conditions
How survival and performance is affected by persistent high temperatures
Compare to several other species of riffle beetles
H. comalensis, H. vulnerata, M. pusillus (H. glabra)
Acclimate to a temperature and hold at conditions for ~2 month period
23, 26, 29, 31oC
5 groups of 3 individuals per temperature
% Survival
Metabolic rate (Q-bit system) at each temperature (day 21)
Oxygen consumption rate
Q10 calculated – change in metabolic rate across a 10oC change

20. Long-Term Survival and Stress at Various Temperatures

21. H. comalensis
Beetles exposed to temperatures exhibited higher mortality
No beetles survived in 29, 31oC
Substantial mortality difference at 26oC

22. H. vulnerata
Mortality much more variable
Temperature effect was not significant

23. M. pusillus
Beetles exposed to temperatures exhibited higher mortality
Survivors in all treatments at the end of 60 days

24. Metabolic Responses

25. Metabolic Responses Q10 (23oC – 31oC)
M. pusillus = 8.1
H. vulnerata = 2.5

26. Metabolic Responses Q10 (23oC – 31oC)
H. comalensis = 27.8
H. glabra = 20.8

27. Second Set of Experiments Persistent DO Conditions
Survival affected by persistent low DO
Compare to H. glabra
Acclimate to a temperature and hold at conditions for 14 day period
5, 3, 2, and 1 mg/L
15 beetles at each DO held individually
Time to death, Survival at 14 d

29. Persistent Conditions Summary
Temperature
Significant increase in mortality at 26oC
Indication of severe metabolic stress >29oC
H. comalensis differed from other species
Dissolved oxygen
Increased mortality and shorter survival times at 3 mg/L
More sensitive than H. glabra

30. Comal Springs Field Data
Review of 11 years of Comal Springs temperature and DO data
Biological Monitoring Program
Spring Runs 1, 3, and 7
Establish observed range in temperatures and DO in the system during different flow conditions
Compare it to Critical Thresholds observed in experiments and the temperature- and DO-survival data obtained in second set of experiments

31. 30oC
26oC
Spring Run 1
Spring Run 3
Spring Run 7

32. Spring Run 1
Spring Run 3
Spring Run 7
1 mg/L

33. Overall Conclusions and Future Directions
H. comalensis appears to be “spring adapted”
“Ecotone specialist”
Small temperature or DO changes affects on survival
Limit of acclimation at 36oC, effect on survival at 26oC
Increased mortality with prolonged exposure to DO <3 mg/L
No acceptable surrogate species for experiments
Field conditions indicate that temperature and DO “thresholds” are rarely crossed
Dewatering is a larger risk (dispersal is not the best)
Low temperatures?
More formal risk assessment is needed