White Shrimp Litopenaeus Setiferus Research Articles

Salinity Selection by Juvenile Brown Shrimp (Farfantepenaeus aztecus) and White Shrimp (Litopenaeus setiferus) in a Gradient Tank

Changes in freshwater inflow and salinity patterns may affect the nursery value of estuarine systems for penaeid shrimp, but the relationship between salinity and shrimp abundance is complex and likely confounded by other environmental variables. Laboratory experiments can provide insights into salinity selection, and we designed an experimental gradient tank to examine salinity preferences of juvenile brown shrimp and white shrimp. Our design uses gently flowing water to eliminate various physical constraints often associated with selection experiments. We conducted experiments with juvenile brown shrimp (12 trials) and white shrimp (seven trials), to examine selection for salinities along a gradient from 1 to 42. Data were analyzed using contingency tables and log-linear modeling to examine relationships with salinity and possible interactions with temperature. Both brown shrimp and white shrimp were present in all salinities examined within the experimental range. In general, brown shrimp showed a preference for salinities from 17 to 35 and demonstrated avoidance for the extreme low salinities along the gradient. Results for white shrimp were not statistically significant, and this species did not appear to avoid low salinities. There was no effect of water temperature on the observed selection patterns for brown or white shrimp. Our results suggest that although salinity preferences likely exist for these species, strong distribution trends associated with salinity gradients in estuaries are likely caused by other environmental factors.

Motor neurons in the escape response circuit of white shrimp (Litopenaeus setiferus).

Many decapod crustaceans perform escape tailflips with a neural circuit involving giant interneurons, a specialized fast flexor motor giant (MoG) neuron, populations of larger, less specialized fast flexor motor neurons, and fast extensor motor neurons. These escape-related neurons are well described in crayfish (Reptantia), but not in more basal decapod groups. To clarify the evolution of the escape circuit, I examined the fast flexor and fast extensor motor neurons of white shrimp (Litopenaeus setiferus; Dendrobranchiata) using backfilling. In crayfish, the MoGs in each abdominal ganglion are a bilateral pair of separate neurons. In L. setiferus, the MoGs have massive, possibly syncytial, cell bodies and fused axons. The non-MoG fast flexor motor neurons and fast extensor motor neurons are generally found in similar locations to where they are found in crayfish, but the number of motor neurons in both the flexor and extensor pools is smaller than in crayfish. The loss of fusion in the MoGs and increased number of fast motor neurons in reptantian decapods may be correlated with an increased reliance on non-giant mediated tailflipping.

Blue crabs Callinectes sapidus as potential biological reservoirs for white spot syndrome virus (WSSV).

White spot syndrome virus (WSSV) is a virulent pathogen of cultured shrimp and was first detected in farms in South Carolina (USA) in 1997 and subsequently in wild shrimp in 1999. We screened groups of 1808 wild Atlantic white shrimp Litopenaeus setiferus and 300 blue crabs Callinectes sapidus collected from South Carolina, Georgia, and Florida for the presence of WSSV using the Shrimple® immunoassay-strip test, with all positives and random subsets of negatives tested by TaqMan real-time PCR and in infectivity bioassays. Of 87 shrimp and 11 crabs that tested positive using the Shrimple® test, only a single C. sapidus was confirmed to be infected with WSSV by PCR and the infectivity bioassay. The data indicate that the prevalence of WSSV in these species is low in these southeastern US regions, but that C. sapidus may serve as a biological reservoir.

Shrimp consumption after deepwater horizon: no evidence of excess risks for vietnamese americans.

Shrimp consumption after deepwater horizon: no evidence of excess risks for vietnamese americans.

Estimating Natural Mortality Rates of Juvenile White Shrimp Litopenaeus setiferus

Comparisons of natural mortality rates can be used to identify essential habitat and nursery areas for fishery species. We estimated and compared natural mortality rates of juvenile white shrimp Litopenaeus setiferus using length-frequency and mark-recapture data and attempted to identify factors that may affect these mortality rates. Daily instantaneous natural mortality rates (95 % confidence interval (CI)) obtained from length-frequency data by following individual cohorts were 0.043 (0.031–0.054) and 0.014 (0.0–0.039). Combining all length-frequency data, converting to age-frequency data, and using two types of catch-curve analyses yielded estimates of 0.069 (0.042–0.095) and 0.060 (0.046–0.073). Mark-recapture estimates obtained in a separate study from two ponds were 0.129 (0.054–0.203) and 0.014 (−0.048–0.076). These estimates are comparable to previously reported values for this species, but we are the first to report a measure of precision with our estimates. In the mark-recapture study, mortality rates appeared to be related to predator abundance in ponds and flooding patterns of the surrounding marsh. The only mortality rate significantly different from any of the other estimates was the lower of the two length-frequency estimates, but this result should be interpreted with caution because of the uncertainty in that estimate, relative imprecision of our estimates, and confounding factors between the methods we used to estimate mortality. Despite this caveat, the results from our study can be used to improve population models for L. setiferus and our understanding of the role of marsh habitats as nursery areas.

A targeted health risk assessment following the Deepwater Horizon oil spill: polycyclic aromatic hydrocarbon exposure in Vietnamese-American shrimp consumers.

Background: The Deepwater Horizon oil spill of 2010 prompted concern about health risks among seafood consumers exposed to polycyclic aromatic hydrocarbons (PAHs) via consumption of contaminated seafood.Objective: The objective of this study was to conduct population-specific probabilistic health risk assessments based on consumption of locally harvested white shrimp (Litopenaeus setiferus) among Vietnamese Americans in southeast Louisiana.Methods: We conducted a survey of Vietnamese Americans in southeast Louisiana to evaluate shrimp consumption, preparation methods, and body weight among shrimp consumers in the disaster-impacted region. We also collected and chemically analyzed locally harvested white shrimp for 81 individual PAHs. We combined the PAH levels (with accepted reference doses) found in the shrimp with the survey data to conduct Monte Carlo simulations for probabilistic noncancer health risk assessments. We also conducted probabilistic cancer risk assessments using relative potency factors (RPFs) to estimate cancer risks from the intake of PAHs from white shrimp.Results: Monte Carlo simulations were used to generate hazard quotient distributions for noncancer health risks, reported as mean ± SD, for naphthalene (1.8 × 10–4 ± 3.3 × 10–4), fluorene (2.4 × 10–5 ± 3.3 × 10–5), anthracene (3.9 × 10–6 ± 5.4 × 10–6), pyrene (3.2 × 10–5 ± 4.3 × 10–5), and fluoranthene (1.8 × 10–4 ± 3.3 × 10–4). A cancer risk distribution, based on RPF-adjusted PAH intake, was also generated (2.4 × 10–7 ± 3.9 × 10–7).Conclusions: The risk assessment results show no acute health risks or excess cancer risk associated with consumption of shrimp containing the levels of PAHs detected in our study, even among frequent shrimp consumers.Citation: Wilson MJ, Frickel S, Nguyen D, Bui T, Echsner S, Simon BR, Howard JL, Miller K, Wickliffe JK. 2015. A targeted health risk assessment following the Deepwater Horizon Oil Spill: polycyclic aromatic hydrocarbon exposure in Vietnamese-American shrimp consumers. Environ Health Perspect 123:152–159; http://dx.doi.org/10.1289/ehp.1408684

Juvenile growth and mortality effects on white shrimp Litopenaeus setiferus population dynamics in the northern Gulf of Mexico

Processes regulating juvenile growth and mortality of white shrimp Litopenaeus setiferus in coastal nurseries may be particularly important in regulating offshore adult population size and sustainability. To advance the integration of these processes into fishery stock assessments, and to provide a better understanding of the functional role of coastal nurseries for fishery species, we explored the potential effects of variable juvenile growth and survival on white shrimp population growth rate. We developed a population model that incorporates available information on vital rates (growth, mortality, fecundity) for each shrimp life stage. We used the model to explore the potential impacts of variability in juvenile growth and mortality rates on the overall population growth rate. Modest changes in juvenile growth and mortality rates were projected to have a greater impact on stock size than the full range in fishing mortality over the past few decades. These results suggest that variability in juvenile survival may be a strong driver of adult stock size and that the processes that regulate juvenile growth and mortality need to be properly understood for the effective management of coastal nurseries and shrimp stocks.

Effect of Deepwater Horizon Oil on Growth Rates of Juvenile Penaeid Shrimps

Marsh shoreline, an important habitat for juvenile penaeid shrimps, was extensively oiled in coastal Louisiana by the Deepwater Horizon oil spill of 2010. The effect of this spill on growth was examined for brown shrimp Farfantepenaeus aztecus and white shrimp Litopenaeus setiferus held for 7 days in field mesocosms in Barataria Bay during May and August 2011, respectively. The experiments each had 10 treatment combinations, five apparent oil levels, each one with and without added food. Mesocosms were placed in northern Barataria Bay along shorelines that varied in oiling (designated as heavy, moderate, light, very light, or none based on NOAA surveys), and shrimp in half the mesocosms received additional food. Polycyclic aromatic hydrocarbon (PAH) concentrations determined from sediment cores collected at each mesocosm were significantly higher at heavy and moderate than very light shorelines and also higher at moderate than light and none shorelines. Brown shrimp grew more slowly at heavy than very light or none shorelines, and a statistically significant negative relationship was detected between brown shrimp growth rates and sediment PAH concentrations. In August, PAH sediment concentrations had decreased significantly from the values measured in May, no significant difference in white shrimp growth rates was detected among oiling levels, and no relationship was detected between white shrimp growth and sediment PAH concentrations. Both brown shrimp and white shrimp grew more rapidly in mesocosms where food was added. Our study shows that exposure to nonlethal concentrations of petroleum hydrocarbons can reduce growth rates of juvenile penaeid shrimps.

Acute Effects of Drought on Emergent and Aquatic Communities in a Brackish Marsh

Plants and animals in brackish marshes are adapted to live within a wide, yet finite, range of conditions. Events that shift the environmental state beyond that range can dramatically alter habitats and, potentially, the numerous ecosystem services they provide. A prolonged exceptional drought in Texas (October 2010–January 2012) provided a unique opportunity to understand how brackish wetland habitats respond to an extreme environmental event. We examined marshes in the Lower Neches Wildlife Management Area (Texas, USA) that fell within the drought affected area, including restored areas and an adjacent reference marsh. To test our hypothesis that the brackish marsh community would be sensitive to drought conditions, we quantified emergent plant and submerged aquatic vegetation (SAV) and animal (invertebrates, fish) characteristics in summer 2010 and 2011. In spite of its severity, the exceptional drought of 2011 did not have a negative impact on emergent plant communities: biomass, stem density, and chlorophyll a concentrations were the same in pre-drought and drought years in all restored and reference areas. In contrast, SAV biomass was reduced by up to 100 % in the drought year. Some fish and invertebrate densities were also reduced by an order of magnitude or more, possibly due to the loss of SAV. Aquatic faunal species composition was markedly different in the drought year, largely due to the loss of the hydrobiid snail Probythinella protera and the gain of some marine species, including Gulf menhaden (Brevoortia patronus), brown shrimp (Farfantepenaeus aztecus), and white shrimp (Litopenaeus setiferus). By altering aquatic the plant and animal community, this drought event may subsequently reduce trophic support for higher consumers, or contribute to a decline in water quality. Restoration monitoring programs that only focus on relatively stress-resistant, emergent wetland plant communities may underestimate the sensitivity of these ecosystems to extreme environmental events like droughts.

Hydrodynamic regulation of salt marsh contributions to aquatic food webs

Vegetated salt marsh habitats are widely considered critical for supporting many species of nekton, yet direct evidence of the processes controlling marsh habitat use for most species remains elusive. We related salt marsh flooding patterns and nekton trophic dynamics among 14 sites spanning 2500 km across the northern Gulf of Mexico (GoM) and southern Atlantic coasts of the USA. Functional access for nekton to marsh vegetation (edge flooded to ≥5 cm depth) ranged from 90% access in the western GoM and Pamlico Sound. Food web mixing models based on stable isotope analysis show that the impor- tance of Spartina trophic support for common nekton may be regulated by the duration of marsh surface flooding. In particular, the potential contribution of Spartina production was positively related to indices of marsh surface flooding for brown shrimp Farfantepenaeus aztecus, white shrimp Litopenaeus setiferus, small (≤60 mm carapace width) blue crabs Callinectes sapidus, grass shrimp Palaemonetes pugio, and killifish Fundulus heteroclitus/grandis. The value of Spartina salt marsh production to several common species of nekton appears to depend, at least in part, on direct access to the vegetated marsh surface, which is regulated by hydrodynamics. Hence, the substantial geographic and temporal variability in marsh flooding regulates the func- tional roles and value of these tidal wetlands for aquatic organisms.

L-leucine, l-methionine, and l-phenylalanine share a Na+/K+-dependent amino acid transporter in shrimp hepatopancreas

Hepatopancreatic brush border membrane vesicles (BBMV), made from Atlantic White shrimp (Litopenaeus setiferus), were used to characterize the transport properties of (3)H-L-leucine influx by these membrane systems and how other essential amino acids and the cations, sodium and potassium, interact with this transport system. (3)H-L-leucine uptake by BBMV was pH-sensitive and occurred against transient transmembrane concentration gradients in both Na(+)- and K(+)-containing incubation media, suggesting that either cation was capable of providing a driving force for amino acid accumulation. (3)H-L-leucine uptake in NaCl or KCl media were each three times greater in acidic pH (pH 5.5) than in alkaline pH (pH 8.5). The essential amino acid, L-methionine, at 20mM significantly (p<0.0001) inhibited the 2-min uptakes of 1mM (3)H-L-leucine in both Na(+)- and K(+)-containing incubation media. The residual (3)H-L-leucine uptake in the two media were significantly greater than zero (p<0.001), but not significantly different from each other (p>0.05) and may represent an L-methionine- and cation-independent transport system. (3)H-L-leucine influxes in both NaCl and KCl incubation media were hyperbolic functions of [L-leucine], following the carrier-mediated Michaelis-Menten equation. In NaCl, (3)H-L-leucine influx displayed a low apparent K M (high affinity) and low apparent J max, while in KCl the transport exhibited a high apparent K M (low affinity) and high apparent J max. L-methionine or L-phenylalanine (7 and 20mM) were competitive inhibitors of (3)H-L-leucine influxes in both NaCl and KCl media, producing a significant (p<0.01) increase in (3)H-L-leucine influx K M, but no significant response in (3)H-L-leucine influx J max. Potassium was a competitive inhibitor of sodium co-transport with (3)H-L-leucine, significantly (p<0.01) increasing (3)H-L-leucine influx K M in the presence of sodium, but having negligible effect on (3)H-L-leucine influx J max in the same medium. These results suggest that shrimp BBMV transport (3)H-L-leucine by a single L-methionine- and L-phenylalanine-shared carrier system that is enhanced by acidic pH and can be stimulated by either Na(+) or K(+) acting as co-transport drivers binding to shared activator sites.

Decapod Utilization of Adjacent Oyster, Vegetated Marsh, and Non-Vegetated Bottom Habitats In A Gulf of Mexico Estuary

Abstract Few studies have compared oyster habitat use with adjacent vegetated and non-vegetated habitats. We investigated habitat use by six common, estuarine, invertebrate species. In order to better understand the species-specific use of oyster and adjacent habitats within the salt marshes of Grand Bay NERR, MS, we examined the abundance patterns and size distributions among oyster, vegetated marsh edge (VME), and non-vegetated bottom (NVB) for three seasons (Fall 2003, Spring 2004, Summer 2004) for the following species: blue crab Callinectes sapidus, brown shrimp Farfantopenaeus aztecus, white shrimp Litopenaeus setiferus, daggerblade grass shrimp Palaemonetes pugio, flatback mud crab Eurypanopeus depressus, and oystershell mud crab Panopeus simpsoni. Three main trends emerged concerning habitat use: 1) the three crab species (juvenile C. sapidus, E. depressus, P. simpsoni) occupied oyster and VME habitats in higher abundances relative to NVB with minor to moderate fluctuations in seasonal abundance. ...

Survey of protozoan, helminth and viral infections in shrimp Litopenaeus setiferus and prawn ­Macrobrachium acanthurus native to the Jamapa River region, Mexico

We surveyed protozoan and metazoan parasites as well as white spot syndrome virus (WSSV) and infectious hypodermal hematopoietic necrosis virus (IHHNV) in white shrimp Litopenaeus setiferus and the palaemonid prawn Macrobrachium acanthurus native to the lower Jamapa River region of Veracruz, Mexico. The presence of parasites and the infection parameters were evaluated in 113 palaemonid prawns collected during the northwind (n = 45), rainy (n = 38) and dry seasons (n = 30) between October 2007 and July 2008, and in 91 shrimp collected in the rainy season between May and June 2008. In L. setiferus, ciliates of the subclass Apostomatia (Ascophrys sp.) were evident in gills, and third-stage larvae of the nematode Physocephalus sexalatus were evident in the stomach. Cestodes of the genus Prochristianella were evident in the hepatopancreas, while some gregarines of the genus Nematopsis, as well as unidentified larval cestodes, were observed in the intestine. Histology identified Ascophrys sp. in association with gill necrosis and tissue melanization. Slight inflammation was observed in intestinal epithelium near cestode larvae. In M. acanthurus, epibionts of the protozoans Epistylis sp., Acineta sp. and Lagenophrys sp. were observed under uropods, periopods and pleopods. An unidentified ciliate of the Apostomatia was also found in the gills, and Nematopsis was identified in the intestine. No histopathology was observed in association with these parasites. Moreover, neither WSSV nor IHHNV were detected by the polymerase chain reaction (PCR) in any of the L. setiferus or M. acanthurus analysed.

Pulsed Ultraviolet Light Reduces Immunoglobulin E Binding to Atlantic White Shrimp (Litopenaeus setiferus) Extract

Pulsed ultraviolet light (PUV), a novel food processing and preservation technology, has been shown to reduce allergen levels in peanut and soybean samples. In this study, the efficacy of using PUV to reduce the reactivity of the major shrimp allergen, tropomyosin (36-kDa), and to attenuate immunoglobulin E (IgE) binding to shrimp extract was examined. Atlantic white shrimp (Litopenaeus setiferus) extract was treated with PUV (3 pulses/s, 10 cm from light source) for 4 min. Tropomyosin was compared in the untreated, boiled, PUV-treated and [boiled+PUV]-treated samples, and changes in the tropomyosin levels were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). IgE binding of the treated extract was analyzed via immunoblot and enzyme-linked immunosorbent assay (ELISA) using pooled human plasma containing IgE antibodies against shrimp allergens. Results showed that levels of tropomyosin and IgE binding were reduced following PUV treatment. However, boiling increased IgE binding, while PUV treatment could offset the increased allergen reactivity caused by boiling. In conclusion, PUV treatment reduced the reactivity of the major shrimp allergen, tropomyosin, and decreased the IgE binding capacity of the shrimp extract.

Polypocephalus sp. Infects the Nervous System and Increases Activity of Commercially Harvested White Shrimp (Litopenaeus setiferus)

Larval tapeworms (Polypocephalus sp.) reside within the central nervous system of decapod crustaceans. Living within the nervous system would seem to create an excellent opportunity for the parasites to manipulate the behavior of their hosts, so we tested the hypothesis that behavior of white shrimp ( Litopenaeus setiferus ) would be correlated with the level of parasitic infection. We videorecorded the behavior of L. setiferus for 8 hr, then examined the nervous system and digestive glands for parasite infection. Larval Polypocephalus sp. were found in the nerve cord, often in large numbers, but only very rarely in the digestive gland, which was typically infected by the larval stage of the nematode, Hysterothylacium sp. There were significantly more Polypocephalus larvae in the abdominal and thoracic ganglia than the subesophageal ganglia and brain. Walking, but not swimming, was significantly and positively related to the number of Polypocephalus sp. lodged in nervous tissue, as well as shrimp carapace length. Polypocephalus sp. is 1 of only a few parasites residing inside the host nervous system and it may, therefore, be suitable for investigating mechanisms of parasite manipulation of invertebrate host behavior.

Variation in penaeid shrimp growth rates along an estuarine salinity gradient: Implications for managing river diversions

Freshwater inflows from river diversions may affect nekton populations by altering the salinity and temperature of estuarine waters. To investigate the influence of these environmental variables on the growth and survival rates of brown shrimp Farfantepenaeus aztecus and white shrimp Litopenaeus setiferus, we conducted field experiments in May and September 2007 to expose experimental animals to the range of different combinations of salinity and water temperature that commonly occur in an estuarine environment. Growth rates for shrimp held in mesocosms for approximately 7 days were compared among four locations and three treatments; locations were identified by the dominant marsh vegetation and distance from the Gulf of Mexico (low to high salinity: Intermediate, Brackish, Saline UE = Saline Up Estuary, Saline DE = Saline Down Estuary). At each location, the treatments were replicated four times and included shallow water with additional food, shallow water without food added, and deeper water (an attempt to expose animals to lower temperatures). Our experiments were designed to test the null hypothesis that shrimp growth and survival rates did not differ by location or treatment. Both brown shrimp and white shrimp grew more slowly at the Intermediate than higher salinity locations. Potential prey (benthic infauna) biomass was relatively low at both the Intermediate and Brackish locations in May, and both shrimp species consistently grew faster in mesocosms where food was added. We conclude that reduced growth in low salinity environments is likely due to the combined effects of increased metabolic costs and less food in these areas. River diversions that reduce estuarine salinities over a large portion of available habitat during peak recruitment periods may reduce overall growth rates and shrimp productivity in the affected areas.

Growth and mortality of juvenile white shrimp Litopenaeus setiferus in a marsh pond

Despite the widely held view that certain estuarine habitats are more valuable as nurseries because they provide enhanced growth and reduced mortality, there remain few estimates of growth and mortality rates in support of this paradigm. We conducted field caging experiments and collected weekly nekton samples in shallow open-water habitat in a marsh pond during summer and fall 2007 in Galveston Bay, Texas, USA, to estimate growth and morality rates of juvenile white shrimp Litopenaeus setiferus. Growth rates (mean ± 1 SE) were lower during the summer experiment (0.77 ± 0.05 mm d–1) than the fall (0.91 ± 0.04 mm d–1), and high summer water temperatures may have inhibited shrimp growth. Cohort analysis to derive mortality estimates from 15 weekly sampling trips failed due to extended periods of continuous recruitment, the lack of clearly identifiable cohorts, and high temporal variability in abundance estimates. Catch-curve analysis provided estimates of mean daily instantaneous mortality (Z) during the sampling period of 0.181 for post-larvae and early juveniles 28 mm. The mortality estimates must be interpreted with caution due to potential problems meeting the assumptions of catch-curve analysis. Despite the challenges, comparisons of vital rates among habitats are required to validate long-held paradigms on the functioning of estuarine nurseries and the importance of various coastal habitats in the support of fishery species.

Effects of Marsh Terracing on Nekton Abundance at Two Locations in Galveston Bay, Texas

We evaluated two marsh terracing restoration projects (GI=Galveston Island State Park, PM=Pierce Marsh) to compare nekton density and biomass between locations and among habitat types (open water pre-construction, open water post-construction, terrace marsh, terrace pond). Most (72%) animals collected were decapod crustaceans. Few differences in nekton abundance were observed over time (pre-construction versus post-construction open water). Comparisons of pre-construction to post-construction open water showed that the locations differed environmentally (e.g., turbidity) and in populations of nekton species. Density and biomass of gulf menhaden Brevoortia patronus and spot Leiostomus xanthurus in spring and density of white shrimp Litopenaeus setiferus in fall were higher at PM than GI, whereas densities and biomass of blue crab Callinectes sapidus, density of pink shrimp Farfantepenaeus duorarum, and biomass of brown shrimp Farfantepenaeus aztecus in the fall were higher at GI than PM. Despite location differences, constructing terraces appeared to benefit fishery species at both locations. Densities of brown shrimp, blue crab, white shrimp (fall), and pink shrimp (fall) and the biomass of brown shrimp, blue crab, and white shrimp (fall) were higher in terrace marsh than open water. Marsh terracing appears to be an effective tool for enhancing fishery habitat in degraded coastal systems.

Do Decapod Crustaceans Have Nociceptors for Extreme pH?

BackgroundNociception is the physiological detection of noxious stimuli. Because of its obvious importance, nociception is expected to be widespread across animal taxa and to trigger robust behaviours reliably. Nociception in invertebrates, such as crustaceans, is poorly studied.Methodology/Principal FindingsThree decapod crustacean species were tested for nociceptive behaviour: Louisiana red swamp crayfish (Procambarus clarkii), white shrimp (Litopenaeus setiferus), and grass shrimp (Palaemonetes sp.). Applying sodium hydroxide, hydrochloric acid, or benzocaine to the antennae caused no change in behaviour in the three species compared to controls. Animals did not groom the stimulated antenna, and there was no difference in movement of treated individuals and controls. Extracellular recordings of antennal nerves in P. clarkii revealed continual spontaneous activity, but no neurons that were reliably excited by the application of concentrated sodium hydroxide or hydrochloric acid.Conclusions/SignificancePreviously reported responses to extreme pH are either not consistently evoked across species or were mischaracterized as nociception. There was no behavioural or physiological evidence that the antennae contained specialized nociceptors that responded to pH.

Using nekton growth as a metric for assessing habitat restoration by marsh terracing

We conducted field growth experiments to evaluate marsh-terracing restoration in Galveston Bay, Texas (USA). Growth rates were compared for selected species held in mesocosms for ~7 d within 4 habitat type treatments: terrace marsh edge (TerM), terrace pond (TerP), reference marsh edge (RefM), and reference pond (RefP). Environmental variables were measured during each experiment, and values measured inside the experimental mesocosms generally tracked outside values. Mean daily growth rates were 0.7 to 1.9 mm (30 to 143 mg) for brown shrimp Farfantepenaeus aztecus, 0.4 to 1.2 mm (8 to 67 mg) for white shrimp Litopenaeus setiferus, 0.3 to 0.6 mm (15 to 194 mg) for blue crab Callinectes sapidus, and 0.1 to 0.4 mm (0.3 to 3 mg) for daggerblade grass shrimp Palaemonetes pugio. No difference was detected in growth rates among treatments for blue crab and daggerblade grass shrimp. White shrimp growth rates in August 2002 were higher in TerP than RefP, and in October 2002, were higher in RefP than TerM. Brown shrimp grew more rapidly in RefM than TerM in early May 2003, but mean growth rates were similar in both habitat types later in May 2003, and significantly lower than growth rates in RefP and TerP. Even though growth rates were not consistently higher in terrace habitat types, production rates may be higher in terrace fields than over shallow non-vegetated bottom (the habitat type replaced by marsh terracing); much higher densities of fishery species in terrace habitats more than compensate for occasionally lower growth rates there. However, our production rates should be used cautiously, because we did not include mortality rates in these estimates. We recommend using a combination of different metrics, including mortality rate, to assess secondary productivity of marsh terracing or other restoration projects.