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Author: McMahon, Robert
Email: r.mcmahon@uta.edu
Phone: 8174802524
Organization: The University of Texas at Arlingtom
Address:
Box 19498, Department of Biology,
Arlington,
TX,
76017
Abstract Title: THE POPULATION DYNAMICS OF ZEBRA MUSSELS IN TEXAS LAKES BELTON, RAY ROBERTS AND TEXOMA 2016-2017. Robert F. McMahon* and Heather Arterburn, Department of Biology, The University of Texas at Arlington, Arlington, TX.
Abstract Text: Zebra mussel (Dreissena polymorpha) populations were sampled monthly from June 2016 - August 2017 in three Texas water bodies; Lakes Texoma (infested 2009), Ray Roberts (infested 2012) and Belton (infested 2013). At monthly site visits, mussels (n >100) were randomly sampled from house brick substrata previously suspended at a depth of 1.5-2.0 m from marina floating docks, returned to the laboratory, and their shell lengths measured to the nearest 0.1 mm. Analysis of resulting mussel cohort size distributions allowed estimation of growth rates and life spans through time. Vertical, 60 μm mesh plankton net tows determined presence of mussel veliger larvae indicating reproductive/settlement periods. Field examination of previously deployed 15.2 by 20.3 cm nylon scrub pad settlement monitors allowed determination of juvenile settlement periods and densities as well as that of previously settled mussel cohorts as estimated by size distributions after which settlement monitors were re-submerged. Surface water temperatures were measured hourly with a data logger over the collecting period while pH, and oxygen and calcium concentrations were determined at each collection. In all three lakes, mussel populations had spring and fall reproduction/settlement periods leading to settlement of spring and fall juvenile cohorts. Both cohorts sustained rapid growth rates (up to 3.0 cm shell length in 1-1.5 years) and attenuated life spans of ≈1-1.9 years compared to populations in the cooler waters of northeastern North America and Europe which require 3-5 years growth to attain similar shell lengths. Spring reproduction was initiated at a water temperature of ≈18°C and inhibited as summer water temperatures approached 30°C. Fall reproduction was initiated at temperatures >30°C and ceased at <18°C. Early maturity and rapid growth allow Texas mussels to attain high densities 1-2 years after invasion. Mussel densities on settlement monitors indicated that mussels in Lakes Texoma and Belton displayed increased settlement rates and population densities in spring 2017 after a previous period of extensive population decline in 2015 and 2016 associated with extreme water level variation during the 2015 spring flooding event. On Lake Belton, a notable surface water hypoxia event was recorded on 09/25/2016 with O2 concentration declining to 15.1% of full air O2 saturation, well below the 30% considered the zebra mussel’s incipient lower limit. This hypoxia event resulted in a complete loss of mussels from the settlement monitors and an extensive mussel density reduction at the study site if not throughout the reservoir. Lake Belton zebra mussel densities did not recover from this event until spring 2017. In contrast, zebra mussel densities in Lake Ray Roberts remained very low after the 2015 flood though the end of collection on August 2017 likely due to a sustained decline in surface water pH below 7.4 required for veliger development to settled juveniles from October 2016 through the end of the sampling period. As such, our results suggest that Texas zebra mussel populations are likely to undergo boom/bust population dynamics similar to those of populations in the northeastern U.S. and Europe.
Conference
Year: TIPPC_2018
Presentation Type: Oral Presentation
Presenter Type (Student or Regular): Regular
Session: 4. Research
Submission Date: 2018-09-06
