Geology topics

Thomas M. Soniat

Publications and source records attributed to Thomas M. Soniat.

5 recordsLinked to original sources

USGS2017

Interactive effects of water temperature and salinity on growth and mortality of eastern oysters, Crassostrea virginica: A meta-analysis using 40 years of monitoring data

Despite nearly a century of exploitation and scientific study, predicting growth and mortality rates of the eastern oyster ( Crassostrea virginica ) as a means to inform local harvest and management activities remains difficult. Ensuring that models reflect local population responses to varying salinity and temperature combinations requires locally appropriate models. Using long-term (1988 to 2015) monitoring data from Louisiana's public oyster reefs, we develop regionally specific models of temperature- and salinity-driven mortality (sack oysters only) and growth for spat (<25 mm), seed (25–75 mm), and sack (>75 mm) oyster size classes. The results demonstrate that the optimal combination of temperature and salinity where Louisiana oysters experience reduced mortality and fast growth rates is skewed toward lower salinities and higher water temperatures than previous models have suggested. Outside of that optimal range, oysters are commonly exposed to combinations of temperature and salinity that are correlated with high mortality and reduced growth. How these combinations affect growth, and to a lesser degree mortality, appears to be size class dependent. Given current climate predictions for the region and ongoing large-scale restoration activities in coastal Louisiana, the growth and mortality models are a critical step toward ensuring sustainable oyster reefs for long-term harvest and continued delivery of the ecological services in a changing environment.

Louisiana↗

USGS2013

Differences in extreme low salinity timing and duration differentially affect eastern oyster ( Crassostrea virginica ) size class growth and mortality in Breton Sound, LA

Understanding how different life history stages are impacted by extreme or stochastic environmental variation is critical for predicting and modeling organism population dynamics. This project examined recruitment, growth, and mortality of seed (25–75 mm) and market (>75 mm) sized oysters along a salinity gradient over two years in Breton Sound, LA. In April 2010, management responses to the Deepwater Horizon oil spill resulted in extreme low salinity (<5) at all sites through August 2010; in 2011, a 100-year Mississippi River flood event resulted in low salinity in late spring. Extended low salinity (<5) during hot summer months (>25 °C) significantly and negatively impacted oyster recruitment, survival and growth in 2010, while low salinity (<5) for a shorter period that did not extend into July (<25 °C) in 2011 had minimal impacts on oyster growth and mortality. In 2011, recruitment was limited, which may be due to a combination of low spring time salinities, high 2010 oyster mortality, minimal 2010 recruitment, cumulative effects from 10 years of declining oyster stock in the area, and poor cultch quality. In both 2010 and 2011, Perkinsus marinus infection prevalence remained low throughout the year at all sites and almost all infection intensities were light. Oyster plasma osmolality failed to match surrounding low salinity waters in 2010, while oysters appeared to osmoconform throughout 2011 indicating that the high mortality in 2010 may be due to extended valve closing and resulting starvation or asphyxiation in response to the combination of low salinity during high temperatures (>25 °C). With increasing management of our freshwater inputs to estuaries combined with predicted climate changes, how extreme events affect different life history stages is key to understanding variation in population demographics of commercially important species and predicting future populations.

Louisiana↗

USGS2013

Predicting the effects of proposed Mississippi River diversions on oyster habitat quality; application of an oyster habitat suitability index model

In an attempt to decelerate the rate of coastal erosion and wetland loss, and protect human communities, the state of Louisiana developed its Comprehensive Master Plan for a Sustainable Coast. The master plan proposes a combination of restoration efforts including shoreline protection, marsh creation, sediment diversions, and ridge, barrier island, and hydrological restoration. Coastal restoration projects, particularly the large-scale diversions of fresh water from the Mississippi River, needed to supply sediment to an eroding coast potentially impact oyster populations and oyster habitat. An oyster habitat suitability index model is presented that evaluates the effects of a proposed sediment and freshwater diversion into Lower Breton Sound. Voluminous freshwater, needed to suspend and broadly distribute river sediment, will push optimal salinities for oysters seaward and beyond many of the existing reefs. Implementation and operation of the Lower Breton Sound diversion structure as proposed would render about 6,173 ha of hard bottom immediately east of the Mississippi River unsuitable for the sustained cultivation of oysters. If historical harvests are to be maintained in this region, a massive and unprecedented effort to relocate private leases and restore oyster bottoms would be required. Habitat suitability index model results indicate that the appropriate location for such efforts are to the east and north of the Mississippi River Gulf Outlet.

Louisiana↗

USGS2012

A shell-neutral modeling approach yields sustainable oyster harvest estimates: a retrospective analysis of the Louisiana state primary seed grounds

A numerical model is presented that defines a sustainability criterion as no net loss of shell, and calculates a sustainable harvest of seed (<75 mm) and sack or market oysters (≥75 mm). Stock assessments of the Primary State Seed Grounds conducted east of the Mississippi from 2009 to 2011 show a general trend toward decreasing abundance of sack and seed oysters. Retrospective simulations provide estimates of annual sustainable harvests. Comparisons of simulated sustainable harvests with actual harvests show a trend toward unsustainable harvests toward the end of the time series. Stock assessments combined with shell-neutral models can be used to estimate sustainable harvest and manage cultch through shell planting when actual harvest exceeds sustainable harvest. For exclusive restoration efforts (no fishing allowed), the model provides a metric for restoration success-namely, shell accretion. Oyster fisheries that remove shell versus reef restorations that promote shell accretion, although divergent in their goals, are convergent in their management; both require vigilant attention to shell budgets.

Journal of Shellfish Research↗

USGS1988

Field validation of a habitat suitability index model for the American oyster

A habitat suitability index (HSI) model, developed for the American oyster, Crassostrea virginica , along the Gulf of Mexico, was field tested on 38 0.1-ha reef and nonreef sites in Galveston Bay, Texas. The HSI depends upon six (HSI1) or, optionally, eight (HSI2) variables. The six variables are percent of bottom covered with suitable cultch (V 1 ), mean summer water salinity (V 2 ), mean abundance of living oysters (V 3 ) (a gregarious settling factor), historic mean water salinity (V 4 ), frequency of killing floods (V 5 ), and substrate firmness (V 6 ). The optional variables are the abundance of the southern oyster drill Thais haemostoma (V 7 ), and the intensity of the oyster pathogen Perkinsus marinus (V 8 ). The HSI values were lowest at high and low salinity sites and highest at intermediate-salinity sites. To validate the model, the hypothesis that the output of the HSI model was correlated with oyster density was therefore tested. A significant correlation was found between HSI1 and oyster density (Kendall Tau Beta correlation coefficient, τ=0.674, p<0.001, n=38); however, a statistical independence problem exists with the above test, that is, oyster density is both the independent standard for the test and a variable in the model. A regression model was constructed to test the relationship between log-transformed oyster density values (dependent variable) and the other variables of the model (independent variables). Most variation (r 2 =0.72, r=0.85) in the log-transformed density values were explained by a regression model that contained V 2 , V 4 , V 5 , V 6 , V 7 , and V 8 as independent variables. The regression model was useful in constructing a modified HSI model (MHSI). A significant correlation (τ=0.674, p<0.05, n=10) was found between MHSI1 values and oyster densities from reefs closed to harvesting. The MHSI improves upon the original model by (i) simplifying the model structure, (ii) removing the requirement to measure V 3 , (iii) accounting better for the negative effects of high salinity, disease, and parasitism upon oysters, and (iv) eliminating the statistical independence problem by dropping V 3 from the model. The MHSI should be tested against a new, independently-collected data set.

Texas↗