Discovery of a Species Rich Assemblage of Freshwater Mussel Species in the Metropolitan Lake Houston, Harris County, Texas
Steve Johnson1*, Lori Johnson1, Stephen Van Kampen Lewis2, Mike Farris3, Chris Collins3, Jeff Fox3, Raymond Thomas Sankey4, and Eric C. Munscher4
1SWCA Environmental Consultants, 15 Research Drive, Amherst, MA 01002. 2SWCA Environmental Consultants, 4407 Monterey Oaks, Austin, TX, USA 78749. 3SWCA Environmental Consultants, 4949 N Loop 1604 W, Suite 235, San Antonio, TX, USA 78249. 4SWCA Environmental Consultants, 10245 West Little York Road, Houston, TX, USA 77040. *Corresponding author.
Urban Naturalist, No. 48 (2022)
Freshwater mussels are one of the most imperiled taxa globally. North American mussels have experienced rapid declines throughout the 20th and into the 21st centuries. These declines are primarily associated with habitat degradation through water quality and impacts from invasive species. In Texas, most rivers have been altered by reservoir construction, which are thought to provide suboptimal mussel habitat, including Lake Houston reservoir in Houston, Texas. We performed a 44 person-hour freshwater mussel survey to detect the presence/absence of state-listed freshwater mussels within Lake Houston, as requested by Texas Parks and Wildlife Department. We relocated 1,190 native freshwater mussels out of the project site in Lake Houston. We documented the presence of 15 mussel species within the project area, including 12 live species and recent “dead” shells of two additional species, as well as a much older shell of a 15th species. No state or federally listed species were observed. Overall, mussel density was 0.098 per square meter (980 per hectare). The total number of individuals found for each species ranged from 1 to 397, and species catch per unit effort (CPUE) ranged from 0.02 to 9.02 mussels per hour. Cyclonaias pustulosa and Quadrula apiculata were the most abundant species observed and were found at the greatest densities. The presence of Tritogonia nobilis was one of the most unexpected observations made. The Mussels of Texas database (MoTX) has no records of this species in the San Jacinto Basin, and the nearest observation was approximately 65 kilometers north of Lake Houston, in the Trinity River Basin. Our results suggest that, despite ecological impacts from damming and sediment deposition from frequent extreme flood events, many of the freshwater mussel species found in other portions of the San Jacinto River are persisting and could even be flourishing within Lake Houston. Our findings suggest that freshwater mussels could be a significant ecological component of the lake.
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No. 48 Urban Naturalist 2022
Discovery of a Species Rich
Assemblage of Freshwater
Mussel Species in the
Metropolitan Lake Houston,
Harris County, Texas
Steve Johnson, Lori Johnson, Stephen Van Kampen
Lewis, Mike Farris, Chris Collins, Jeff Fox, Raymond
Thomas Sankey, and Eric C. Munscher
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Cover Photograph: Collection of surveyed mussels. Photograph © Stephen Van Kampen Lewis.
S. Johnson et al.
2022 No. 48
2022 Urban Naturalist 48:1–12
Discovery of a Species Rich Assemblage of
Freshwater Mussel Species in the Metropolitan
Lake Houston, Harris County, Texas
Steve Johnson1*, Lori Johnson1, Stephen Van Kampen Lewis2, Mike Farris3, Chris
Collins3, Jeff Fox3, Raymond Thomas Sankey4, and Eric C. Munscher4
Abstract - Freshwater mussels are one of the most imperiled taxa globally. North American mussels
have experienced rapid declines throughout the 20th and into the 21st centuries. These declines are
primarily associated with habitat degradation through water quality and impacts from invasive species.
In Texas, most rivers have been altered by reservoir construction, which are thought to provide
suboptimal mussel habitat, including Lake Houston reservoir in Houston, Texas. We performed a 44
person-hour freshwater mussel survey to detect the presence/absence of state-listed freshwater mussels
within Lake Houston, as requested by Texas Parks and Wildlife Department. We relocated 1,190
native freshwater mussels out of the project site in Lake Houston. We documented the presence of 15
mussel species within the project area, including 12 live species and recent “dead” shells of two additional
species, as well as a much older shell of a 15th species. No state or federally listed species were
observed. Overall, mussel density was 0.098 per square meter (980 per hectare). The total number
of individuals found for each species ranged from 1 to 397, and species catch per unit effort (CPUE)
ranged from 0.02 to 9.02 mussels per hour. Cyclonaias pustulosa and Quadrula apiculata were the
most abundant species observed and were found at the greatest densities. The presence of Tritogonia
nobilis was one of the most unexpected observations made. The Mussels of Texas database (MoTX)
has no records of this species in the San Jacinto Basin, and the nearest observation was approximately
65 kilometers north of Lake Houston, in the Trinity River Basin. Our results suggest that, despite
ecological impacts from damming and sediment deposition from frequent extreme flood events, many
of the freshwater mussel species found in other portions of the San Jacinto River are persisting and
could even be flourishing within Lake Houston. Our findings suggest that freshwater mussels could
be a significant ecological component of the lake.
Freshwater mussels (order Unionida) are considered one of the most imperiled taxa in
North America, experiencing rapid declines throughout the 20th and into the 21st centuries
(Bogen 1993, Lydeard et al. 2004). It has been estimated that 30 freshwater mussel taxa native
to North America have been pushed to extinction during the last century (Vaughn 2018). Approximately
195 species (65%) of the 300 species native to North America are currently listed
as vulnerable, threatened, or endangered (Haag and Williams, 2014, Vaughn, 2017). The high
degree of biodiversity loss not only impacts species richness but is also having extreme impacts
on “abundant” and “common” species, resulting in substantial declines in relative abundance
and biomass (Lindenmayer et al. 2011). Relative abundance and biomass have become
important metrics in valuing ecosystem functionality (Gaston and Fuller 2007, Lindenmayer
et al. 2011). The more abundant and the more biomass a species or species group contributes
to the system, generally the more the ecosystem is reliant on that and/or those species.
1SWCA Environmental Consultants, 15 Research Drive, Amherst, MA 01002. 2SWCA Environmental
Consultants, 4407 Monterey Oaks, Austin, TX, USA 78749. 3SWCA Environmental Consultants, 4949
N Loop 1604 W, Suite 235, San Antonio, TX, USA 78249. 4SWCA Environmental Consultants, 10245
West Little York Road, Houston, TX, USA 77040. *Corresponding author: email@example.com.
Associate Editor: Jann Vendetti, Natural History Museum of Los Angeles County.
S. Johnson et al.
2022 No. 48
Water quality issues (i.e., pollution, temperature fluctuations), invasive species (Dreissena
polymorpha Pallas [Zebra Mussel] and Corbicula sp. [Asian Clam]), river damming
and reservoir creation, and the subsequent habitat alteration and degradation that result from
these activities have all been identified as major factors in the decline of freshwater mussels
throughout North America (Haag and Williams 2014, Vaughn and Taylor 1999, Williams et
al. 1993). In East Texas, the Sabine-Trinity Province includes the Sabine, Neches, Trinity,
and San Jacinto River basins. This province is considered to be the diversity hotspot for
freshwater mussels within the state (Haag 2010, Burlakova et al. 2011). The San Jacinto
River is located in the Sabine-Trinity Province Watershed and has undergone significant
degradation in the last 90 years (Burlakova et al. 2011). In 2006, it was considered the 9th
most endangered river in the United States, primarily due to sediment loading and bank erosion
originating from sand mining operations (American Rivers, 2006). In addition, urban
development and water diversion are identified as two major impacts to the Trinity/San Jacinto
Basin (Winemiller et al. 2010). Between 2005 and 2009, 5 sites within the San Jacinto
River Basin were surveyed for unionid assemblages (Burlakova et al. 2011). Evidence of
only 9 extant species was found, based on live and recently-dead individuals. This led to
the assumption that up to 20 of the 29 species (70%) historically found in the San Jacinto
River may now be extirpated.
Lake Houston in Harris County was created 65 years ago by damming the San Jacinto
River approximately 27 kilometers northeast of downtown Houston (Fig. 1). The City of
Houston recently proposed a new raw water intake structure in the southern portion of Lake
Figure 1. Lake Houston in relation to Sabine-Trinity Province, as described by Haag (2010) and Burlakova
et al. (2011). Inset shows survey location within the lake.
S. Johnson et al.
2022 No. 48
Houston. As part of the environmental permitting process, we performed a freshwater mussel
survey to detect the presence/absence of state-listed freshwater mussels within or near
the project area. All native freshwater mussels detected were to be collected and relocated
to a nearby location within Lake Houston to protect them from potential impacts from the
Prior to the start of surveys, we identified 32 native mussel species with the potential to
occur within or near the San Jacinto River Basin (Howells 2014), including 3 species listed
by the State of Texas as threatened (Pleurobema riddellii Lea [Louisiana Pigtoe], Lampsilis
satura Lea [Sandbank Pocketbook], and Fusconaia chunii [Lea] [Texas Pigtoe]). To the
best of our knowledge, there have been 4 freshwater mussel surveys in Lake Houston prior
to our study (Randklev et al. 2020). The most recent survey, in 2005, found evidence for 7
extant species in the lake, as well as evidence of 4 additional species, but these were only
represented by old shells (Burlakova et al. 2011).
We developed protocols for surveying and relocating both state-listed and common
freshwater mussels, which were reviewed and approved by Texas Parks and Wildlife Department
(TPWD). The designated survey area included the project footprint and a 20-meter
buffer around it within 80 meters of the shoreline. The project footprint included a bridge
and pier structure to support 2 concrete water pipelines extending 290 meters from the
shoreline to a 70 x 37-meter water intake structure extending the project out to approximately
360 meters from shore. The entire survey area was 12,140 square meters (1.2 hectare) in
size. The outermost portion of the survey area was approximately 1.1 kilometers from the
original channel of the San Jacinto River (Fig. 1).
We conducted transect surveys and mussel translocations between March 25 and April
25, 2019, when water temperatures exceeded 60 degrees Fahrenheit, per TPWD protocols
for aquatic relocation. Transects were laid out such that the entire survey area was surveyed,
with the objective of removing all native mussels from the potential impact area. Transect
ends were mapped using GPS equipment. Transects consisted of two-meter-wide corridors
demarcated with weighted line. Two biologists worked side by side and conducted tactile
searches for all freshwater mussels present. The first 20 transects were laid out parallel to
shore. The remaining transects were laid out perpendicular to shore. In total, 44 transects
were surveyed. Wading and/or snorkeling were/was used for surveys conducted in less than
1 meter of water. For surveys within depths of 1 to 2 meters, divers used a hookah system
(surface pump with airlines to divers below) and in depths greater than 2 meters, SCUBA
equipment was utilized. We relied entirely on tactile methods of mussel detection due to
extremely low visibility of Lake Houston. During surveys, we systematically raked our
fingers through all soft substrates to depths of up to 10 centim eters.
We collected all detected native mussels and placed them in mesh dive bags for the duration
of the survey. At the end of each transect survey, the collected mussels were processed and
identified to species. A subset of all collected mussels had their shell length measured to the
nearest millimeter and photographed, including at least one representative from each native
species encountered. Native mussels were kept out of the water for no more than ten minutes
during processing and were stored in freshwater following processing until relocation. Mussels
were typically held in captivity for two to four hours, and never longer than six hours.
The total number of mussels collected, survey duration, and number of surveyors were
recorded for each transect. Catch per unit effort (CPUE) for each transect was calculated by
S. Johnson et al.
2022 No. 48
dividing the number of mussels captured by total person hours to determine number of mussels
encountered during 1 survey hour to determine a CPUE value indicating the number of
mussels encountered during 1 person-hour. CPUE was also calculated for the sections of the
survey area (combining sets of transects) as well as for the entire survey area.
All collected mussels were translocated approximately 2 kilometers northeast of the
survey area to a designated relocation area. Four species of native mussel were observed in
the relocation area prior to transplanting mussels: Cyclonaias pustulosa Lea (Pimpleback),
Lampsilis teres Rafinesque (Yellow Sandshell), Plectomerus dombeyanus Valenciennes
(Bankclimber), and Quadrula apiculata Say (Southern Mapleleaf). All relocation area
resident mussels appeared to be healthy and thriving, with both juvenile and adult mussels
present, indicating this site was suitable for mussel relocation.
We conducted a GIS analysis using 2018 bathymetry data collected by the Texas Water
Development Board (Leber et al. 2019) to calculate the amount of area within Lake Houston
with the same range of depths as our survey area, assuming that substrate and habitat types
remain relatively consistent throughout the lake at these depths. Using this information and
the overall CPUE value we calculated for the survey area, we estimated the total number of
mussels for the portion of the lake within depth range of our study.
Depths observed within the survey area ranged from 0 to 7.9 meters. This included a
gradual slope of the lake bottom with water depths ranging from 0 to 2.3 meters for the first
80 meters from shore, steeper slopes with water depths ranging from 2.3 to 4.6 meters from
80 to 120 meters from shore, and a more gradual slope with water depths ranging from 4.6 to
7.9 meters from 120 to 355 meters from shore at the end of the survey area. We observed fine
sand with embedded coarse gravel and flat expanses of marl (lime-rich mudstone) within the
first 80 meters of the survey area, a combination of sand and silt on the steeper slope from
80 to 120 meters from shore, and mostly soft to very soft silt/clay throughout the remainder
of the survey area. The range of depths at which each substrate type was observed, as well
as average depth of each substrate type can be found in Table 1.
We conducted 44 person-hours of surveys and relocated 1,190 native freshwater mussels.
We documented the presence of 15 mussel species within the survey area, including 12 live
species and recently dead shells of two additional species, as well as a much older shell of
a 15th species (Table 2). No state- or federally-listed species were observed. Overall mussel
density was 0.098 per square meter (980 per hectare). The total number of individuals found
Table 1. Range of depths (in meters) at which each substrate type* was observed, along with the average
depth of each substrate type.
Substrate Type Depth Range Average Depth
FSaMG 0–1.37 0.76
FSaMGC 1.37–1.98 1.65
SaSiMG 1.83–2.23 2.06
SaSi 2.23–4.57 3.53
SaSiC 2.23–5.49 3.75
SiC 4.57–7.92 6.43
*FSaMG = fine sand/marl/gravel, FSaMGC = fine sand/marl/gravel/clay, SaSiMG = sand/silt/marl/gravel,
SaSi = sand/silt, SaSiC = sand/silt/clay, SiC = silt/clay.
S. Johnson et al.
2022 No. 48
for each species ranged from one to 397, and species CPUE ranged from 0.02 to 9.02. C. pustulosa
and Q. apiculata were the most abundant species observed and were found at the greatest
densities. Mussels were found in all observed substrate types, including fine soft sand, soft
sand/silt, dense clay/marl with embedded coarse gravel, and very soft silt/clay. Shell length
and wear data were collected for 517 individuals, representing all 12 live species observed.
CPUE for each transect ranged from 0 mussels per person-hour (first transect closest to
shore) to 152 mussels per person-hour (100–165 meters from shore at depths of 2.3 to 4.6
meters), with an average CPUE of 32.8 mussels per person-hour. There appeared to be a
noticeable pattern to mussel density and the frequency of detection within the survey area,
with mussels being encountered at greater frequencies approximately halfway through the
survey area. To illustrate this pattern, we broke the survey area into nine survey segments
of approximately similar sizes based on transect configuration, and calculated CPUE values
for each segment (Fig. 2).
The highest segment CPUE values were observed in segments E (64.8), F (98.8), and G
(54.8) which correspond to the slope observed approximately 80 meters from shore and continuing
into the flatter terrain beyond. Species richness was also calculated for each survey
segment and there was a slight overall decrease in species richness as distance from shore
increased (Fig. 2). Species richness ranged from 5 to 8 species per segment. The highest species
richness was observed in segments A and B, the 2 segments closest to shore. Three species
were found in every survey segment: Pimpleback, Pyganodon grandis Say (Giant Floater),
and Southern Maple Leaf. Several species only occurred in the first 3 transects at depths of
0–0.6 meters, including Lampsilis hydiana Lea (Louisiana Fatmucket), Yellow Sandshell,
Leptodea fragilis Rafinesque (Fragile Papershell), Toxolasma texasiense Lea (Texas Lilliput),
and Leaunio lienosus Conrad (Little Spectacle Case, formerly Villosa lienosa). Three species
only occurred in the outer 6 segments at depths of 1.4 to 7.6 meters: Megalonaias nervosa
Table 2. Mussel species observed in Lake Houston, Harris County, TX during 2019 survey, including
total number of individuals, Catch Per Unit Effort (CPUE), density for each species, and depths.
Density indicates mussels per square meter. Depths is the range of depths (in meters) each species
was observed in.
Scientific Name Common Name # of Individuals CPUE Density Depths
Plectomerus dombeyannus Bank Climber 177 4.02 0.0146 0.1–6.1
Potamilus purpuratus Bleufer Shells only N/A N/A N/A
Truncilla truncata Deertoe Shells only N/A N/A N/A
Utterbackiana suborbiculata Flat Floater 17 0.39 0.0014 1.4–7.9
Leptodea fragilis Fragile Papershell 4 0.09 0.0003 0.3–1.5
Pyganodon grandis Giant Floater 58 1.32 0.0048 0.1–7.9
Tritogonia nobilis Gulf Mapleleaf 130 2.95 0.0107 2.3–7.9
Leaunio lienosa Little Spectacle Case 1 0.02 0.0001 0.6–1.5
Lampsilis hydiana Louisiana Fatmucket 3 0.07 0.0002 0.4–0.9
Cyclonaias pustulosa Pimpleback 397 9.02 0.0327 0.1–7.9
Quadrula apiculata Southern Mapleleaf 350 7.95 0.0288 0.1–7.9
Toxolasma texasiense Texas Lilliput 3 0.07 0.0002 0.4–0.9
Amblema plicata Threeridge Shells only N/A N/A N/A
Megalonaias nervosa Washboard 43 0.98 0.0035 1.4–7.9
Lampsilis teres Yellow Sandshell 7 0.16 0.0006 0.1–1.5
S. Johnson et al.
2022 No. 48
Rafinesque (Washboard), Tritogonia nobilis (Conrad) (Gulf Mapleleaf; formerly Quadrula
nobilis), and Utterbackiana suborbiculata Say (Flat Floater).
CPUE may be more dependent on substrate type than depth (Fig. 3). It is also possible
that depth and substrate are autocorrelated. We conducted a simple linear regression of
Depth (independent variable) versus CPUE (dependent variable) resulting in a P-value of
0.06 and R2 value of 0.08, indicating there is a significant correlation at the 90 percent confidence
interval. In contrast, our ANOVA analysis of substrate versus CPUE provided a pvalue
of <0.0001. While there appears to be a slight increase in CPUE values as one moves
into deeper waters, there is a much more dramatic increase once course gravel and marl are
no longer present. CPUE then drops off somewhat when sand is no longer present. Species
richness does not appear to follow this same pattern (Fig. 4). Richness remains relatively
constant across the substrate types observed.
Few introduced species were encountered during surveys. We observed 17 Flat Floaters,
believed to have been introduced to Texas in the mid-1900’s (Howells 2014), and approximately
12 individuals of Asian Clam. Per TPWD protocols, all invasive species found were
destroyed. No evidence of Zebra Mussel was observed.
A search of the Mussels of Texas database (MoTX) for all species occurrences within
Lake Houston, the East Fork of the San Jacinto River, the West Fork of the San Jacinto
Figure 2. CPUE (mussels per hour) and Species Richness values for nine 2019 survey segments in
Lake Houston. Each segment is made up of transects covering the entire segment.
S. Johnson et al.
2022 No. 48
Figure 3. Averaged CPUE and Water Depth (meters) for each observed mix of substrate types.
Figure 4. Averaged Species Richness and Water Depth (meters) for each observed mix of substrate types.
S. Johnson et al.
2022 No. 48
River, and the San Jacinto River (Randklev et al. 2020) indicated the total number of species
observed within the river system was 24 (Table 3). Of these, only 16 had been observed
since 2005, and only 12 species have been observed in Lake Houston (11 since 2005). In
each of these surveys, some species were only represented by shells. Our research indicates
there have been at least 4 surveys in Lake Houston since 1995 on the following dates: June
18, 1996; June 26, 1996; and October 7, 2005; and our survey in the spring of 2019 (Table
4). The June 18, 1996, survey appears to have occurred in the same general portion of the
lake as our survey, while the other surveys occurred approximately 9.7 kilometers north
(upstream) of our survey site. Cyclonaias pustulosa and Q. apiculata were the only species
observed alive during all four surveys.
The most recent Lake Houston mussel survey recorded in the MoTX database occurred
on October 7, 2005 (Burlakova et al. 2011). As noted earlier, this survey found evidence for
11 freshwater mussel species, but only 7 were found alive. In contrast, we observed 12 live
species, and 3 additional species based on shells. This included 3 live species not previously
observed in Lake Houston: T. nobilis, T. texasiense, and L. lienosus. The differences in species
richness between our survey and other surveys in Lake Houston illustrates the value
of increasing survey duration and area. For instance, the Burlakova et al. 2005 survey (Personal
Communication) was 3 person-hours in duration, compared to our 44 person-hours.
While the amount of area surveyed was not documented, it was likely far less than the 1.2
hectare we surveyed. In addition, Burlakova et al. may not have used SCUBA equipment or
surveyed at depths greater than 1 meter. Total CPUE was similar for their survey and ours
(24 and 32.8, respectively). Although total CPUE was lower for the Burlakova et al. (2005)
survey, the highest CPUE they recorded for a single species (Q. apiculata) was 15.3, nearly
twice as high as our value. In addition, their CPUE for P. dombeyannus (5.7) was also larger
than our value of 4.02. In contrast, our CPUE for C. pustulosa (9.02) was larger than the
Burlakova et al. (2005) CPUE of 1.0 for this species. We believe the ranges in CPUE values
between the 2 surveys reflect differences in mussel distribution between the two survey
areas rather than in mussel detection skills, and the increased number of species detected
was due primarily to increased duration and area surveyed.
There appears to be no relationship between segment CPUE and segment species
richness indicating that the number of different species present did not necessarily
increase with increasing mussel density. We hypothesize that higher mussel density is
occurring in the optimal habitat for the most abundant species, while increased species
richness can be observed in areas that support both common and rarer species. The most
common species observed within survey segments E, F, and G (the three segments with
the highest CPUE values), in descending order of abundance were C. pustulosa, Q.
apiculata, T. nobilis, and P. dombeyannus, which are also the 4 most abundant species
within the entire survey area.
The presence of T. nobilis was unexpected (Figs. 5–6). The MoTX database has no
records of this species for the San Jacinto Basin, and the nearest observation was approximately
65 kilometers north of Lake Houston, in the Trinity River Basin. However, Howells
(2014) states the range of this species in Texas is from the San Jacinto River north and east
to the Red River. It is possible this species has been overlooked, at least within Lake Houston,
due to its apparent preference for deeper water. We did not observe T. nobilis within the
shallower portion of the survey area, only at depths between 3.7 and 7.6 meters. Another
unexpected species was L. lienosus, which was previously known from the upper sections
of the East and West Forks of the San Jacinto River, with the closest observation to Lake
Houston approximately 30 kilometers north on the East Fork.
Table 3. Summary of mussel species observations in the San Jacinto River system based on search of Mussels of Texas Database and the results of 2019 survey of site in
Lake Houston, Harris County, TX.
Scientific Name San Jacinto River (MoTX) Lake Houston (MoTX) 2019 Lake Houston Survey Notes (MoTX) Most Recent Observation*
Amblema plicata X X X 9/17/2015
Arcidens confragosus X One record No Date
Cyclonaias pustulosa X X X 10/7/2005
Fusconaia chunii (East Fork Only) One record 9/16/2016
Fusconaia flava (East Fork Only 7/27/2017
Glebula rotunda (West Fork Only) One Record 7/31/1996
Lampsilis hydiana X X X 10/7/2005
Lampsilis satura (West Fork Only) 7/14/1979
Lampsilis teres X X X 10/7/2005
Leaunio lienosa (East Fork Only) X 7/27/2017
Leptodea fragilis X X X 10/7/2005
Megalonaias nervosa X X 10/7/2005
Plectomerus dombeyanus X X X 10/7/2005
Pleurobema riddellii (East Fork Only) 8/15/1986
Potamilus purpuratus X X X 10/7/2005
Pyganodon grandis X X X 10/7/2005
Quadrula apiculata X X X 10/7/2005
Strophitus undulatus (East Fork Only?) One Record No Date
Toxolasma texasiense X X 9/17/2015
Tritogonia nobilis X
Tritogonia verrucosa (West Fork Only) One Record 7/27/2009
Truncilla truncata X X X 10/7/2005
Utterbackia imbecillis X One Record 7/14/1979
Utterbackiana suborbiculata X X One Record 9/23/1982
* Prior to 2019 Survey
S. Johnson et al.
2022 No. 48
The water quality of Lake Houston has long been a potential concern for the region.
The lake is a major public water supply as well as a recreational lake used by the greater
Houston metropolitan area (Sneck-Fahrer et al. 2005). The issues of concern for this waterbody
stem from nutrient enrichment (phosphorus and nitrate / nitrite) loading and, for
aquatic fauna, the amount of dissolved oxygen in the water (Sneck-Fahrer et al. 2005).
Our results indicate that, despite impacts from damming and sediment deposition from
frequent extreme floods, many of the freshwater mussel species found in other portions
of the San Jacinto River are persisting and perhaps flourishing within Lake Houston. This
mussel diversity may represent a significant ecological component of the lake, as mussels
are foundational species that provide ecosystem services including food sources for
numerous species (Haag 2012, Vaughn 2018). Based on 2018 bathymetry data (Leber et
al. 2019), approximately 3,860 hectares of Lake Houston have a depth from zero to 7.9
meters. Based on our calculated overall mussel density for the entire survey area, and
assuming that depth can be used as a surrogate for substrate as they relate to CPUE, we
estimate there may be 3,783,486 or more mussels occupying the portion of Lake Houston
with the same range of depths we surveyed (0 to 7.9 meters). This population estimate is
only perfunctory and would benefit from additional sampling at various depths at other
locations within the lake. Additional work is needed to ascertain mussel extent and diversity
within Lake Houston. Additionally, extensive surveys should be carried out in other
impoundments within the Sabine-Trinity Province in order to document the status of their
The authors acknowledge Ravi Kaleyatodi, Project Manager for the City of Houston’s Northeast
Water Purification Plant (NEWPP) Expansion Project for obtaining authorization for publishing this
Table 4. Species observed during four surveys in Lake Houston between 1996 and 2019 including species
represented by shells only.
Scientific Name Common Name 1996a 1996b 2005 2019
Amblema plicata Threeridge X X X
Cyclonaias pustulosa Pimpleback X X X X
Lampsilis hydiana Louisiana Fatmucket X X X
Lampsilis teres Yellow Sandshell X X X
Leaunio lienosa Little Spectacle Case X
Leptodea fragilis Fragile Papershell X X X
Megalonaias nervosa Washboard X X X
Plectomerus dombeyannus Bank Climber X X X
Potamilus purpuratus Bleufer X X X
Pyganodon grandis Giant Floater X X X
Quadrula apiculata Southern Mapleleaf X X X X
Toxolasma texasiense Texas Lilliput X
Tritogonia nobilis Gulf Mapleleaf X
Truncilla truncata Deertoe X X
Utterbackiana suborbiculata Flat Floater X
Total Species 2 10 11 15
S. Johnson et al.
2022 No. 48
Figure 5. Top Photos: Two of the 130 live Tritogonia nobilis observed in Lake Houston in 2019, right
photo shows more elongated form of older mussel. Bottom photo: interior view of shell of T. nobilis.
Photos by S. Johnson.
Figure 6. Detail of collected shell of Tritogonia
nobilis showing diagnostic paired rows of horizontal,
shelf-like pustules from the beak to the
margin on posterior slope. Photo by S. Johnson.
S. Johnson et al.
2022 No. 48
paper. We also acknowledge Paul Walker and Susan Berkey, both of Carollo Engineers, who are SWCA’s
immediate client and who represent the consulting engineer for the design and implementation
of the multi-year water treatment infrastructure construction project. We wish to thank Jason Carlisle,
Carollo’s on-site construction coordinator, who assisted SWCA in obtaining site access and helped us
stay safe during completion of our study. Finally, we wish to thank Heather Biggs, Chris Maldonado,
Clint Robertson, Adam Whisenant, and Colleen Roco of TPWD who provided the appropriate state
permits for this work and provided valuable suggestions and insight into our proposed sampling protocol
and proposed freshwater mussel release sites.
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