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Limitations of Comal Springs Riffle Beetle Plastron Use During Low-Flow

EAHCP Study #14-14-697-HCP Parvathi Nair1 Weston Nowlin1 Benjamin Schwartz1 Randy Gibson2 Thomas Hardy1

1Department of Biology

Texas State University San Marcos, TX 78666

2USFWS

SMARC San Marcos, TX 78666

Comal Springs Riffle Beetle and Spring Flows

Comal Springs Riffle Beetle Plastron

Comal Springs Riffle Beetle and Spring Flows

O2

Comal Springs Riffle Beetle and Spring Flows

Temperature

Comal Springs Riffle Beetle and Spring Flows

Temperature O2 demand

Comal Springs Riffle Beetle and Spring Flows

Temperature

Comal Springs Riffle Beetle and Spring Flows

Temperature

O2

Comal Springs Riffle Beetle and Spring Flows

Temperature

O2

O2 for plastron function

Study Objectives

• Examine effect of increasing temperature and

decreasing DO on performance of H. comalensis – Separate effects of each factor – Not direct assessment of plastron function

• Explore use of non-listed surrogate species
• Compare temperature and DO responses among

surrogate species and H. comalensis

Hypotheses

• All species will exhibit threshold temperatures and

DO concentrations, beyond which beetles will exhibit a reduction in performance

• Spring-ass0ciated species (H. comalensis and H.

glabra) will exhibit smaller ranges in temperature and DO than the surface associated species (H. vulnerata).

Elmid Species Examined

H.comalensis H.glabra H.vulnerata

Critical Limit Methodology

Beetle Collection

Finnegan Springs (Devils River) Comal Springs (SMARC)

Beetle Housing

• SMARC and FAB
• Ambient temperatures (22-

23oC), DO >4 mg/L

• Plastic flow-through

chambers

• Issues with H. vulnerata

– Die off over a 2-week period in August, re-collected in September – Seasonality?

Experimental System

Experimental Design

• Examined responses to short-term and long-term

changes in DO and temperature

– Short term = minutes to hours – Long-term = Days

• Short term experiments

– Responses to rapid environmental changes, no time for acclimation – Thresholds not indicative of responses over longer time periods

• Long term experiments

– Limits of acclimation – Allows for longer term deleterious effects to manifest

Short Term Experiments

• Short Term DO

– Start at 4 mg/L, decreased 1mg/L every few minutes – 3 min observation period – Temperature maintained at 23oC

• Short Term Temperature

– Start at 23oC, increase temperature by 1oC every few minutes – Maintained DO >4 mg/L – 3 minute observation period

• n = 16 H. glabra, n = 12 H. comalensis
• Examined for Loss Of Response (LOR)

– Other consistent behaviors noted

• At LOR, individuals moved to recovery chambers

Recovery Chambers

Long Term Experiments

• Only H. glabra

– Flows at Comal Springs, mortality issues – Funding and time

• Long Term DO

– Start at 4 mg/L, decreased 1mg/L over 24-h period – Observed every 2-3 hours over day – Temperature at 23oC

• Long Term Temperature

– Start at 23oC, increase 1oC every 24 hours – Maintained DO >4 mg/L – Observed every 2-3 hours

• n = 16 and 12

Data analysis

• Critical temperature and DO thresholds

determined as mean of observed LOR (or other recognizable behavioral responses)

• Differences among species for short term

experiments assessed with one-way ANOVA

• Long term thresholds for H.glabra compared to

data in literature for other elmids and dryopids

Short term DO Results

• H. glabra

– No LOR even at 0 mg/l DO for 3 minutes

• H. comalensis

– No LOR even at 0 mg/l DO for 3 minutes

• Recovery chamber

– Observed for 1-h

– No lasting exposure effects

Short term Temperature Results

Rapid movement

45.17

31.6 28.8

F1, 26 = 9.92 p = 0.004

Short term Temperature Results

Uncoordinated movement

45.17 F1, 21 = 3.99 p = 0.059

37.3 40.2

Short term Temperature Results

LOR

45.2 49.9 F1,26= 23.08 p < 0.001

Short term Temperature Recovery

• H.comalensis

– All individuals recovered within one hour.

• H. glabra

– All individuals recovered within an hour except one

Long term DO Results

• H. glabra only

– LOR at mean DO concentration 0.48 mg/L (0 – 1 mg/L) – LOR after an average of 10.2-h at <1 mg/L

– All beetles recovered within 3-h

Long term Temperature Results

• H. glabra only

– Rapid agitated movements at around 34.7 0C – LOR at 36.30C – On an average 177.6 -h spent at temperatures above 300C before LOR

• Recovery chamber

– Only 3/12 individuals recovered after 4-h

Implications of Low DO

• Not sensitive to rapid changes in DO
• Findings consistent with other studies on elmids
• Stenelmis quadrimaculata exhibited LOR after

an average of 60-h at 0 mg/L (Harpster 1944)

Implications of high temperature

• Short term experiments

– Rapid movement onset at 28 – 32oC – Threshold temperature for both species high – H. comalensis had significantly lower than H. glabra

• Long term experiment with H. glabra

– Stress at 30-340C

• Findings consistent with other studies on elmids

– Stenelmis quadrimaculata exhibited LOR at 30-330C (Harpster,1944)

Potential use of surrogate

• H. vulnerata

– Utility as surrogate unknown

• H. glabra

– Promising in terms of DO responses – Limited utility as threshold temperature 50C greater

Future studies

• Long term threshold study for H. comalensis.
• Future studies to clearly identify long term

thresholds for DO and temperature by holding beetles for weeks-months

• Surrogate studies in Habitat Connectivity Study

(later today)

Dewatering Issues

• Decline in mean

daily discharge since 2010

• Marked decline in

beetle habitat

• Movement of beetle

into hyporheos?

Acknowledgements

• Funding- EAHCP
• Help-Michael Markowski, Dan Huston,

McLean Worsham, Amelia Everett, and Duane Friedman