Search

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.

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.

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.

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.

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.

We used data from 1984 samples taken approximately monthly over 11 yr (1982 to 1992) with a 2.6 m 2 drop sampler to quantify and compare nekton densities in Spartina alterniflora marsh edge and over adjacent shallow nonvegetated bottom (SNB) in Carancahua Cove, Galveston Bay estuary, Texas, USA. We also used a Geographic Information System (GIS), aerial photography, and population models to track changes in wetland area and trends in fishery populations over time. Decapod crustaceans were less speciose than fishes (35 vs. 60 species) in our samples, but this taxo- nomic group accounted for most (91%) of the animals we collected. Annual variability in animal abundance was high. Most species peaked in abundance during spring or fall, and were absent or occurred at low densities during winter. Mean densities of all abundant decapod crustaceans and several abundant fishes in our study were significantly greater in marsh vegetation than over SNB. Based on our GIS analysis, we estimated that 61% of the wetlands in the study area were converted to open water between 1982 and 1995; marsh edge (marsh within 1 m of the shoreline) was reduced by 70% during the same period. Our fishery models showed that brown shrimp Farfantepenaeus aztecus, white shrimp Litopenaeus setiferus, and blue crab Callinectes sapidus populations also declined substantially during this period as the area of wetlands and marsh edge was reduced. A marsh-terracing project in 1999 replaced some open water with marsh, and our models show that populations of these fishery species rebounded in response to this recent restoration effort.

In 1997, white spot syndrome virus (WSSV) was discovered in shrimp culture facilities in South Carolina, USA. This disease was known to cause devastating mortalities in cultured popula- tions in Southeast Asia and prompted concern for the health of wild populations in the USA. Our study surveyed wild shrimp populations for the presence of WSSV by utilizing molecular diagnostics and bioassay techniques. A total of 1150 individuals (586 Litopenaeus setiferus, 477 Farfantepenaeus aztecus and 87 F. dourarum) were examined for the presence of WSSV DNA by PCR. A total of 32 individuals tested positive and were used in a bioassay to examine the transmission of disease to healthy individuals of the culture species L. vannamei. DNA sequencing of PCR products from a pos- itive individual confirmed that the positive individuals carried WSSV DNA. Significant mortalities were seen in test shrimp injected with tissue extracts from heavily infected wild shrimp. These data confirm the existence of WSSV in wild shrimp stocks along the Atlantic Coast and that the virus can cause mortalities in cultured stocks.

We measured variation in low-tide abundance of juvenile white shrimp Litopenaeus setiferus in subtidal creek channels relative to the amount of intertidal drainage area and creek edge in an adjacent tidal marsh. Samples were collected over a 2 yr period (1998 and 1999) and included 201 384 individual shrimp taken by cast net during July to November from 4 different tidal creek sub- systems in the Sapelo Island National Estuarine Research Reserve on the coast of Georgia (USA). Total drainage areas of the sub-systems ranged from 0.59 to 1.19 km 2 . Variation in intertidal and subtidal areas, and creek edge (interface between the vegetated marsh and open water) within the upper, middle and lower reaches of each sub-system was measured from high-resolution scaled (1:16 000) aerial photographs. Shrimp were most abundant and smaller in the upper reaches of tidal channels, where the adjacent intertidal drainage area and vegetated marsh edge were greatest. Regression analysis of shrimp abundance, measured as mean catch per unit effort, showed a strong positive relationship (p < 0.001; R 2 = 0.86) with the amount of intertidal marsh edge in associated reaches (upper, middle or lower) of the creek sub-systems. Distribution and abundance of shrimp within tidal creeks probably reflected a link between estuarine landscape structure and accessibility of resources in the vegetated marshes that support shrimp production. Among the implications for management of shrimp resources in marsh habitats, we recommend a precautionary approach in making land-use decisions that would reduce structural complexity of marsh landscapes, particularly in the upper reaches of tidal creeks where juvenile white shrimp are concentrated and complex networks of creek channels enhance access to intertidal resources within the estuarine nursery.