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

Habitat Associations and Spring Openings

Habitat Associations and Spring Openings

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

CSRB and Spring Flows

CSRB and Spring Flows O2

CSRB and Spring Flows Temperature

CSRB and Spring Flows O2 demand Temperature

CSRB and Spring Flows O2 demand Temperature O2

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

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

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

Critical Threshold Methodology

Critical Threshold Experiments

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

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

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

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

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

Long-Term Survival and Stress at Various Temperatures

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

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

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

Metabolic Responses

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

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

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

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

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

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

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

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