129 research outputs found
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Impact of disturbances on serpulid reef and soft-sediment macrofauna in Baffin Bay, Texas
No full textA thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Coastal and Marine System ScienceIn subtropical regions, low inflow estuaries are influenced by long residence times that promote hypersalinity and are intermittently affected by acute rainfall events; extreme cold temperatures, while uncommon, can also occur. Baffin Bay, TX, USA experienced a sustained period (~7 days) of freezing temperatures during “Winter Storm Uri” in February 2021, and experienced an acute freshwater flooding event three months later with a 20 unit drop in salinity. This study used benthic macrofauna from soft-sediment and serpulid reef habitats as indicators for understanding the impact of successive freeze and flood disturbances on this low inflow estuarine ecosystem. Traditional community analyses were supplemented by stable isotope analysis of basal food resources and resource use by an abundant benthic predator and economically important fisheries species, black drum (Pogonias cromis). Successive disturbances in 2021 had minimal effects on soft-sediment benthic macrofauna abundance, biomass, richness, and diversity, with values falling within historically measured ranges. Serpulid reef benthic macrofauna were lower in biomass and richness following Winter Storm Uri, and higher in abundance and richness after freshwater flooding, with values outside of historic records. Despite this fluctuation during 2021 disturbances, serpulid reef macrofauna remained higher in abundance, biomass, and richness and more stable in community composition than soft-sediment macrofauna. Greater prey availability and reliability on serpulid reefs may be important for higher-level consumers. Stable isotope results indicate reliance of black drum on benthic macrofauna prey resources in both Baffin Bay and the adjacent Upper Laguna Madre in 2021. Understanding the response of benthic macrofauna indicators to environmental disturbance from acute freeze and flood events can inform future resource management strategies, particularly in light of increasing climate variability and water resource development.Coastal and Marine System Science ProgramCollege of Scienc
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Characterizing the unfished oyster reef community of Sabine Lake Estuary relative to surrounding marsh edge and nonvegetated bottom habitats.
No full text"A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Fisheries and Mariculture."Sabine Lake is an approximately 360 km2 estuary on the Texas-Louisiana border formed by the union of the Neches and Sabine Rivers. The estuary is unique in terms of its large oyster reef complex with no record of commercial harvest as far back as the 1960’s. However, after substantial oyster mortalities in Louisiana estuaries due to hurricane activity and freshwater releases post-Macondo oil spill, Louisiana has shown strong interest in opening their portion of Sabine Lake to supplement lost commercial harvest. The overarching goal of this research project was to describe oyster population structure and community composition of finfishes and invertebrates on this naturally functioning reef system compared to nearby nonvegetated bottom and marsh edge habitats. Live and dead oyster abundances were significantly different among seasons, with spring 2013 having the highest live oyster abundance, and fall 2011 having the highest dead oyster abundance. Approximately half (45%) of all live oyster heights measured were ≥ 80 mm, while the largest recorded height was 203 mm in spring 2013. The high abundance of large oysters collected within Sabine Lake Estuary may offer unique ecosystem services compared to commercially fished reefs with low, or scattered vertical relief. Oyster reef and nonvegetated deep (> 3m) habitats had significantly lower total faunal densities than the marsh edge habitat throughout all seasons. The highest species diversity and richness were observed in the nonvegetated deep habitat, while the oyster reef habitat had a higher diversity than both marsh edge and shallow nonvegetated habitats. The highest abundances of dominant crustaceans, transient, and resident fishes were found within the marsh edge habitat. Despite observing lower densities of organisms, our community analysis provides evidence that the oyster reef habitats support a unique community of fishes and crustaceans compared to the marsh edge and nonvegetated habitats. Characterizing and understanding the true value of the unfished oyster reef, marsh edge, and nonvegetated habitats will enhance natural resource management decisions in the future, by incorporating potential effects due to commercial fishing activities.Life SciencesCollege of Science and Engineerin
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Relative Habitat Value Of Alternative Substrates Used In Oyster Reef Restoration
No full textOyster reef habitats have declined from historic levels due to a variety of reasons, including overharvest, disease, and degraded water quality. The harvesting of oysters has led to a loss of reef habitat for both oysters and reef-associated fauna. When oysters spawn, the larval oysters, or spat, depend on hard substrate for settlement and growth. Oyster shell is the preferred substrate for use in restoration because it most closely matches natural reef habitat, but it is often expensive and in limited supply. This study incorporated field and laboratory experiments to assess the relative habitat value of alternative substrates (crushed concrete, porcelain, crushed limestone, and river rock, as well as oyster shell) for larval oyster recruitment as well as reef resident fishes and macro-invertebrates. Replicate trays of each substrate type were deployed in St. Charles Bay, TX for four months during spring and summer 2012 and assessed for oyster recruitment and faunal diversity and density. Concrete, river rock, limestone and porcelain had similar spat recruitment densities compared to oyster shell (1300-2300 spat). Spat shell heights were also larger on these substrates (13-16 mm), while spat on porcelain substrates were slightly smaller (10-13 mm). All substrates except bare sediment had similar fauna species densities (200-500 individuals m-2). Limestone had lower fauna diversity (H���; 0-1) than concrete and shell (1-2). Laboratory experiments compared the effectiveness of these substrates in providing prey refuge from pinfish and blue crab predators. All substrates performed similarly resulting in very low (<20 %) prey mortality rates for either predator. Results may enable future restoration plans to be implemented at a lower cost while providing similar habitat functions
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Long-term ecological assessment of faunal dynamics and production on a large, restored oyster reef in the Gulf of Mexico
No full textCrassostrea virginica oyster reefs, which are valued for providing essential fish habitat and other ecosystem services, were historically abundant throughout the Western Atlantic and U.S. Gulf of Mexico, yet have been severely degraded throughout their native range over the past century. The potential for oyster reefs to recover lost ecosystem services is a field that requires further research, in part due to the complex food webs that oyster reefs support by way of provision of high abundances of prey resources and habitat for vulnerable life stages of many fish and invertebrates. Because the majority of oyster reef restoration experiments are small-scale, it is unclear how fisheries benefits scale up for much larger restored reefs. Better understanding is needed on whether previous experimental findings are able to translate to large-scale restoration practices to advance our knowledge of oyster reef restoration. Half Moon Reef in Matagorda Bay, TX, was a large, historically productive reef rendered functionally extinct in the early 1900s due to overharvesting. In 2013, 23 of the original 200 ha were restored, followed by 4.5 years of ecological monitoring to assess faunal development and fisheries enhancement benefits. On a seasonal basis from July 2014 to January 2019, oysters were collected by hand from the restored reef while fish and macroinvertebrate samples were collected via suction sampling and modified epibenthic sled surveys on and off the reef. These data were used to assess oyster population and faunal community dynamics, including estimates of oyster disease and augmented faunal production from the restored reef. Data were also used to develop monitoring recommendations for key restoration metrics such as oyster population dynamics, oyster disease development, and faunal community development. Oyster population growth was typical of newly restored reefs, with the highest densities of newly settled oysters immediately post-restoration. Prevalence and severity of oyster infection by Perkinsus marinus were relatively low and indicative of early stage infection. After 1.5 years, faunal community composition on the restored reef was distinct from unrestored sites. Estimations of enhanced production were similar to previous studies except for stone crabs (Menippe adina), which were an order of magnitude higher than previous estimates (11.0 kg 10 m-2 y-1 versus 1.0 kg 10 m-2 y-1). Because restored reefs are generally small scale and monitored over a short timeframes of 1-2 years, this study provided the unique opportunity to assess longer-term thresholds of change in faunal metrics. Results indicated that monitoring timeframes of greater than 1 year may be required to properly document oyster population dynamics, faunal community succession, and seasonal dynamics of restored reef fauna. When reservoir reefs are distant from the restored reef, it may require greater than 4.5 years to observe the full onset of P. marinus (Dermo) disease within the restored oyster population. This study builds on previous meta-analyses of relatively small reefs monitored for short time scales encompassing a large geographic range by calculating the per-unit-area enhanced production of a large restored reef monitored over a relatively long time scale. Resource managers planning for future restoration projects in the Gulf of Mexico, particularly with the goal of enhancing faunal production of higher trophic levels, will benefit from assessments of large-scale restoration projects.Life SciencesCollege of Science and Engineerin
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Developing a bioassessment framework to inform tidal stream management along a hydrologically variable coast
No full textWater body impairments related to coastal development threaten aquatic life and ecosystem services associated with estuaries. Tidal streams are transitional river-estuary systems that are both ecologically and economically important, but are at high risk for anthropogenic impairment due to their location in areas of rapid coastal development and within the receiving zone of upstream runoff. Although management action is needed to assess how these stressors affect faunal assemblages in tidal streams, natural spatiotemporal variability in tidal and salinity regimes poses a challenge to defining biotic community baseline conditions, and resource managers often lack standardized bioassessment protocols. The goal of this study was to develop multimetric indices of biotic integrity (IBIs) for nekton and benthic macroinfauna in tidal streams along the lower Texas coast, providing a practical bioassessment tool for resource management. Fifteen tidal stream sites were classified into degraded “test” or least-impaired “reference” conditions based on surrounding land use, historical water quality, and watershed population density. Sites were sampled twice per year in the spring and summer of 2020 and 2021 for nekton and benthic macroinfauna, water quality, and physical habitat characteristics. Metrics from historical IBI studies and from directly measured changes in nekton and benthic macroinfauna communities were evaluated. Ten univariate nekton metrics and 6 benthic macroinfauna metrics were selected to create each IBI, encompassing a range of attributes from taxon-level abundances, functional groups, and diversity measures. Although natural spatiotemporal variability and a continuum of degradation among sites made some individual metrics difficult to interpret, the IBIs were generally successful in differentiating test and reference conditions. Recommendations for future refinement of tidal stream IBIs include incorporation of long-term monitoring data, further regionalizing the IBIs based on major climatic regions, sampling multiple sites along the longitudinal salinity gradient, and refining scoring criteria based on stream characteristics. The resulting IBIs represent a significant first step in bioassessment development for Texas tidal streams and provide a useful tool to inform resource management decisions.Physical and Environmental SciencesCollege of Science and Engineerin
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Analyses of biological communities and development of indices of biotic integrity for monitoring tidal streams along the upper Texas coast
No full textTidal streams along the upper Texas coast are characterized by large heterogeneity in abiotic
conditions and biotic communities, posing challenges to managers seeking to assess their
ecological condition and develop effective management strategies. There is currently no
standardized protocol for assessing ecological condition in Texas tidal stream systems. The goal
of the current study was to create multimetric indices of biotic integrity (IBIs) from nekton and
benthic macroinfaunal community metrics that were effective in discriminating between
degraded “test” and non-degraded “reference” streams (classified by watershed land-cover data).
Fifteen tidal streams were sampled twice per year in 2018 and 2019 to assess water quality,
nekton, and benthic macroinfaunal dynamics. In order to create the multimetric indices of biotic
integrity, multiple univariate metrics were assessed to determine the extent to which they
differentiated between test and reference sites. Selected metrics were used as components in
developing the multimetric IBIs, which give higher scores to samples that have similar biotic
characteristics to our reference condition samples. Multivariate analyses provided a
complementary approach to selection of IBI metrics by visualizing, comparing, and identifying
community-level changes as well as taxa that associate with the test or reference condition.
Results indicated that overall differences in biological communities between test and reference
sites were often not extremely strong. Multivariate analyses indicated nekton communities
exhibited stronger differentiation between test and reference samples whereas benthic
macrofaunal communities were influenced more by year to year variations. However, several
univariate metrics highlighted components of communities that did differ between test and
reference sites, and these metrics were used to form the IBI. Comparing IBIs for both nekton
and benthic macroinfauna can provide a more comprehensive understanding of biotic integrity in
tidal streams than focusing on one or the other. Results should be interpreted with some caution
but could help inform water resource management decisions that seek to support aquatic life use
while balancing human needs for food, recreation, and industry.Life SciencesCollege of Science and Engineerin
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Evaluating habitat provision by restored intertidal and subtidal oyster reefs in St. Charles Bay, Texas
No full textEstuarine habitats, such as Crassostrea virginica oyster reefs, are critical to the resilience of coastal environments and provide many ecosystem services. To address declining oyster populations, oyster reef restoration has become a widespread management strategy to recover and restore lost ecosystem functions and biodiversity. While traditional restoration practices in Texas have focused on subtidal oyster reefs to ameliorate harvest impacts, there is growing interest in restoring intertidal reefs to maximize habitat benefits. This study evaluates the development of oyster populations and epifaunal communities on concurrently restored intertidal and subtidal oyster reefs in St. Charles Bay, TX, USA. In May 2022, 2.4 ha of oyster reef complex were restored in intertidal (0.5 m depth) and subtidal (1.5 m depth) areas using recycled oyster shells. Epifaunal and oyster dynamics were measured on the restored reefs and nearby natural reference reefs for 12 months (epifauna) and 18 months (oysters) following restoration. Results indicate distinct timelines for oyster population and epifaunal community development: restored subtidal reefs progressed faster, reaching peak oyster densities of 2203 ind. m-2 and similar epifaunal community composition to natural reference within 6 months post- restoration. In contrast, intertidal reefs reached peak oyster densities of 390 ind. m-2 at 12 months post- restoration with dissimilar epifaunal community compositions compared to natural reefs. Spat recruitment to restored intertidal and restored subtidal reefs occurred immediately following restoration, and oysters grew rapidly during the first 3 months, averaging 0.97- 0.95 mm d-1. Submarket size oysters (25- 75 mm) were observed on both restored intertidal and restored subtidal reefs just 1 month after restoration, and market size oysters (≥ 76 mm) occurred on the restored subtidal reefs within 6 months. Large quantities of drift algae were deposited on the restored intertidal reefs in August 2022 and persisted for 4- 6 months, which may have affected oyster and epifaunal recruitment and growth. On restored subtidal reefs, epifaunal densities, biomass, diversity, and community composition became similar to natural reference reefs within 6 months following restoration. On restored intertidal reefs, although epifauna diversity became similar to natural reefs within 12 months, epifaunal community composition remained distinct throughout the 18-month study period. The findings of this study offer important insights into key differences in restored intertidal and subtidal oyster reef development, making it possible to evaluate the ecological tradeoffs of restoration approaches and inform future restoration efforts.Physical and Environmental SciencesCollege of Scienc
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Reef restoration facilitates habitat provisioning for oysters and motile epifauna
No full textSevere degradation of oyster reef habitat over the past century has led to associated losses
in ecological and economic benefits. Common oyster reef restoration goals target replacement of
lost ecosystem services, including habitat provision, by replacing the ecological functions of lost
reef habitats. The goal of this study was to monitor development of faunal communities on a
restored oyster reef in the Gulf of Mexico. In July 2017, more than 1 M tons of reclaimed oyster
shell were used to restore 1.83 ha of oyster reef complex (~610 linear m) in St. Charles Bay,
Texas. Oysters, epifauna, and infauna were sampled monthly for the first three months after
construction, and then were sampled quarterly for a total of 19 months at the restored reef and
nearby reference sites. Within the first three months after construction, mean oyster densities
increased by more than three times, growth rates peaked at 0.41 mm d-1
, and the restored oyster
population shifted from 100 % spat to more than 90 % submarket size oysters. Although
Perkinsus marinus infection was detected on every sampling date on the reference reef, only a
single infected oyster was observed on the restored reef. Reef location—away from infected
source populations— and other hydrological factors such as current speed and direction, may
have impeded disease development. Epifaunal density, biomass, and diversity, became similar to
that of the reference reef within four months after construction, but a shift in epifaunal
community assemblages occurred between the first and the second year after construction,
indicating monitoring periods of more than one year are necessary to capture faunal community
development on a restored reef. The structure provided by the restored reef was conducive to
oyster and epifaunal community development and may have supported ecological resistance
since minimal impacts to reef structure were observed in the wake of Hurricane Harvey. Infaunal
density, diversity, and biomass did not differ between sites adjacent (less than 5 m) versus distant
(~30 m) from the restored reef and were governed more by salinity than presence of the restored
reef. The recruitment and densities of oysters indicate that the restored reef met proposed success
metrics within 19 months after construction, and that restored reefs can successfully replace
ecosystem services, such as habitat provision, lost due to degradation.EngineeringCollege of Science and Engineerin
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Effects of extreme freshwater events and perkinsus marinus on crassostrea virginica stress response
No full textEstuarine salinity is one of the most important factors affecting oyster (Crassostrea virginica) growth and Perkinsus marinus disease characteristics. The combined effect of increased freshwater inflows and P. marinus infection on oyster physiology is important to understand for improving the predictions of oyster response to increasing climate variability. This study determined the effects of rapid declines in salinity, such as those oysters experience after a strong storm or flood, and P. marinus infection on the scope for growth of oysters from the Laguna Madre, a hypersaline estuarine system. Scope for growth was assessed by determining clearance rate, absorption efficiency, ammonia excretion rate, and oxygen consumption rate for oysters at six salinity treatments: 10, 15, 20, 25, 30, and 35. Salinity did not have a significant effect on clearance rate, absorption efficiency, or oxygen consumption rate, but did significantly affect the rate of ammonia excretion. Scope for growth ranged from 37.25 J hr-1 g dry weight-1 to 867.46 J hr-1 g dry weight-1, and demonstrated a decreasing trend from the lowest to highest salinity treatments, indicating reduced growth potential with increasing salinity. Perkinsus marinus infection intensity ranged from low to moderately heavy, but did not have a significant effect on oyster scope for growth. Oyster condition index increased with increasing salinity treatment, likely reflecting Laguna Madre oyster tolerance for high salinities. Regardless, oysters experiencing rapid reductions in salinity demonstrated increased physiological function compared to oysters that remained at the control salinity 35, indicating that the normally high salinities of the Laguna Madre may not present optimal conditions for oyster growth. Results of this study improve understanding of oyster response to rapid decreases in salinity conditions influenced by human and climate-driven changes.Life SciencesCollege of Science and Engineerin
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Salinity disturbance affects community structure and organic matter on a restored Crassostrea virginica oyster reef in Matagorda Bay, Texas
No full textOyster reefs are one of the most degraded marine habitats, with estimated 85-91% global habitat loss compared to historic levels (Beck et al. 2011, Lotze et al. 2006). However, the restoration of oyster reefs is becoming a widely recognized tool to ameliorate the effects of habitat loss. Half Moon Reef, once a highly-productive 2 km2 Crassostrea virginica oyster reef located in Matagorda Bay, Texas, was harvested to depletion in the early 20th century. In 2014, The Nature Conservancy restored 0.23 km2 of reef—one of the largest oyster reef restorations in the country. In the three years following reef restoration, two salinity disturbances (prolonged salinities <10) provided a unique opportunity to determine the effects of large salinity variations on oyster reef community structure and quality of organic matter.
Oyster growth generally increased over the 3-year study period, enhancing habitat provisioning for reef fauna. Reef-resident species metrics showed strong positive correlations with salinity. Following a low salinity event (25 to 9) one year post-restoration, the reef-resident fauna shifted from a community dominated by pioneer organisms to one comprising larger and more resilient crustaceans and gastropods. A second low salinity event two years post-restoration did not show a similar response, indicating the presence of larger oysters facilitated species that may otherwise not exist in high disturbance environments. Fauna from adjacent areas showed no patterns with distance from the reef, indicating restoration did not influence faunal communities away from the physical reef structure. As salinity decreased, suspended particular organic matter became more 13C-depleted whereas surface sediment organic matter did not show significant change. Carbon/chlorophyll a and carbon/nitrogen ratios of suspended particulate organic matter indicated the quality of organic matter was higher following low salinity events, implying pulses of freshwater inflow increased autochthonous production. Surface sediment organic matter and suspended particulate organic matter contributed nearly equally to assimilation by oysters. Results were integrated into a conceptual diagram to visualize the effects of salinity on oyster reef communities, providing a tool that natural resource managers can use for a broader perspective on the effects of salinity variations on oyster reef communities.Life SciencesCollege of Science and Engineerin
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