Palaemonetes Research Articles

Habitat partitioning by native and alien fishes and decapods in novel habitats of the upper San Francisco Estuary

The rate of alien species introductions is increasing in aquatic ecosystems, but many invaders appear to co-exist with previous residents, resulting in persistent mixed assemblages of non-coevolved organisms. This study focuses on species’ habitat partitioning of edge habitats in the San Francisco Estuary, a highly altered novel ecosystem that supports mixed assemblages of native and alien fishes and macroinvertebrates. We used minnow traps to address two questions about the demersal assemblage along levees in large tidal sloughs: (1) What is the relative abundance of demersal fish and macroinvertebrate species in shallow water adjacent to levee edges? and (2) Do native and alien species occupy different habitat types? We used our findings to address the broader question: do native and non-native species show habitat segregation, suggesting development of assemblage structure similar to that of co-evolved assemblages? Results indicate that habitat partitioning occurs among some clusters of species, but not all. Native Prickly Sculpin was found most often near riprapped levee edges, while alien Yellowfin Goby occupied adjacent muddy habitat, and the alien Shimofuri Goby showed no preference. Where two non-native species of caridean shrimp co-occurred, Siberian Prawn occupied unvegetated mud, while Oriental Grass Shrimp used primarily riprap. However, when only Siberian Prawn was present, it showed no preference for habitat type. Habitat associations changed slightly in response to seasonal shifts in habitat and spawning requirements. This study demonstrates that non-coevolved assemblages of organisms can develop resource partitioning to assist co-existence in novel habitats.

Importance of patch size variation for the population persistence of a decapod crustacean in seagrass beds

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 570:157-171 (2017) - DOI: https://doi.org/10.3354/meps12126 Importance of patch size variation for the population persistence of a decapod crustacean in seagrass beds Yuichi Shinomiya1, Susumu Chiba2,*, Makoto Kanamori3, Shigeyuki Hashizume1, Kenji Yoshino4, Seiji Goshima1 1Laboratory of Benthology, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan 2Department of Aquatic Bioscience, Tokyo University of Agriculture, Abashiri, Hokkaido 099-2493, Japan 3Hakodate Fisheries Research Institute, Fisheries Research Department, Hokkaido Research Organization, Hakodate, Hokkaido 040-0051, Japan 4Institute of Lowland and Marine Research, Saga University, Saga, Saga 840-8502, Japan *Corresponding author: s2chiba@bioindustry.nodai.ac.jp ABSTRACT: To understand the effects of patch attributes of seagrass beds on the persistence of an animal population, we examined shifts in patch utilization that occur with the life stages of a decapod crustacean, Hokkai shrimp Pandalus latirostris, inhabiting only eelgrass beds. The abundance of juveniles did not relate to the abundance of prey or patch size, but adult abundance decreased significantly when patches were smaller. Edge effects were suggested for adults. Since patch size and shoot density were inseparable structures at our study site, we conducted an experiment using artificial seagrass units (ASUs) to clarify structures that were effective as shrimp habitat. This experiment showed that while adults recruited mainly to the small patches regardless of shoot density, juveniles, though much smaller in number, recruited to all patch types. Adults frequently emerged from natural patches to bare spaces at night, while juveniles seldom used the bare spaces at all. When we experimentally released shrimps between ASUs at night, adults generally used the bare spaces while juveniles randomly moved to all habitat types. We tethered adults in the interior of seagrass patches and bare spaces during both daytime and nighttime, and found that the predation rate was high only in bare spaces during daytime. We demonstrated that the habitat functions of seagrass patches can vary with the life stages of this decapod crustacean, and suggest that spatial management of various sizes of patches is crucial for population persistence of Hokkai shrimp. KEY WORDS: Behavioral habitat shift · Habitat structure · Diurnal behavior · Population management · Eel grass · Grass shrimp · Pandalidae Full text in pdf format PreviousNextCite this article as: Shinomiya Y, Chiba S, Kanamori M, Hashizume S, Yoshino K, Goshima S (2017) Importance of patch size variation for the population persistence of a decapod crustacean in seagrass beds. Mar Ecol Prog Ser 570:157-171. https://doi.org/10.3354/meps12126 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 570. Online publication date: April 27, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Methylmercury Bioaccumulation in an Urban Estuary: Delaware River, USA

Spatial variation in mercury (Hg) and methylmercury (MeHg) bioaccumulation in urban coastal watersheds reflects complex interactions between Hg sources, land use, and environmental gradients. We examined MeHg concentrations in fauna from the Delaware River estuary, and related these measurements to environmental parameters and human impacts on the waterway. The sampling sites followed a north to south gradient of increasing salinity, decreasing urban influence, and increasing marsh cover. Although mean total Hg in surface sediments (top 4cm) peaked in the urban estuarine turbidity maximum and generally decreased downstream, surface sediment MeHg concentrations showed no spatial patterns consistent with the examined environmental gradients, indicating urban influence on Hg loading to the sediment but not subsequent methylation. Surface water particulate MeHg concentration showed a positive correlation with marsh cover whereas dissolved MeHg concentrations were slightly elevated in the estuarine turbidity maximum region. Spatial patterns of MeHg bioaccumulation in resident fauna varied across taxa. Small fish showed increased MeHg concentrations in the more urban/industrial sites upstream, with concentrations generally decreasing farther downstream. Invertebrates either showed no clear spatial patterns in MeHg concentrations (blue crabs, fiddler crabs) or increasing concentrations further downstream (grass shrimp). Best-supported linear mixed models relating tissue concentration to environmental variables reflected these complex patterns, with species specific model results dominated by random site effects with a combination of particulate MeHg and landscape variables influencing bioaccumulation in some species. The data strengthen accumulating evidence that bioaccumulation in estuaries can be decoupled from sediment MeHg concentration, and that drivers of MeHg production and fate may vary within a small region.

Assessment of ocean acidification and warming on the growth, calcification, and biophotonics of a California grass shrimp

Cryptic colouration in crustaceans, important for both camouflage and visual communication, is achieved through physiological and morphological mechanisms that are sensitive to changes in environmental conditions. Consequently, ocean warming and ocean acidification can affect crustaceans’ biophotonic appearance and exoskeleton composition in ways that might disrupt colouration and transparency. In the present study, we measured growth, mineralization, transparency, and spectral reflectance (colouration) of the caridean grass shrimp Hippolyte californiensis in response to pH and temperature stressors. Shrimp were exposed to ambient pH and temperature (pH 8.0, 17 °C), decreased pH (pH 7.5, 17 °C), and decreased pH/increased temperature (pH 7.5, 19 °C) conditions for 7 weeks. There were no differences in either Mg or Ca content in the exoskeleton across treatments nor in the transparency and spectral reflectance. There was a small but significant increase in percent growth in the carapace length of shrimp exposed to decreased pH/increased temperature. Overall, these findings suggest that growth, calcification, and colour of H. californiensis are unaffected by decreases of 0.5 pH units. This tolerance might stem from adaptation to the highly variable pH environment that these grass shrimp inhabit, highlighting the multifarious responses to ocean acidification, within the Crustacea.

Effects of salinity on oil dispersant toxicity in the grass shrimp, Palaemonetes pugio

Chemical dispersants can be a useful tool to mitigate oil spills, but the potential risks to sensitive estuarine species should be carefully considered. To improve the decision making process, more information is needed regarding the effects of oil spill dispersants on the health of coastal ecosystems under variable environmental conditions such as salinity. The effects of salinity on the toxicity of two oil dispersants, Corexit® 9500 and Finasol® OSR 52, were examined in this study. Corexit® 9500 was the primary dispersant used during the 2010 Deepwater Horizon oil spill event, while Finasol® OSR 52 is another dispersant approved for oil spill response in the U.S., yet considerably less is known regarding its toxicity to estuarine species. The grass shrimp, Palaemonetes pugio, was used as a model estuarine species. It is a euryhaline species that tolerates salinities from brackish to full strength seawater. Adult and larval life stages were tested with each dispersant at three salinities, 5, 20, and 30 ppt. Median acute lethal toxicity thresholds and oxidative stress responses were determined. The toxicity of both dispersants was significantly influenced by salinity, with greatest toxicity observed at the lowest salinity tested. Larval shrimp were significantly more sensitive than adult shrimp to both dispersants, and both life stages were significantly more sensitive to Finasol than to Corexit. Oxidative stress in adult shrimp, as measured by increased lipid peroxidation activity, occurred with exposure to both dispersants. These data will assist environmental managers in making informed decisions regarding dispersant use in future oil spills.

Linking wading bird prey selection to number of nests

Establishing a link between food availability and productivity is often central to the recovery of declining populations; however, differences in prey selection may influence how populations are affected by changes in prey availability. We determined prey selection and prey availability for 3 wading bird species, and investigated the effects of prey availability on the number of nests initiated by 6 wading bird species in the Florida Everglades, USA. To determine prey selection, we compared food items recovered from tricolored heron (Egretta tricolor), snowy egret (Egretta thula), and little blue heron (Egretta caerulea) nestlings to aquatic prey availability from throw-traps across the Everglades landscape from 2012 to 2014. Tricolored heron and snowy egret prey composition was statistically similar across years, with the majority of prey biomass coming from relatively large (>1.9 cm) marsh fish. Little blue heron prey composition differed from the other wading bird species, and contained a higher percentage of grass shrimp (Palaemonetes paludosus) and exotic fish species. Numbers of small heron nests were positively influenced by the availability of large marsh fish across the landscape, whereas numbers of nests for other wading bird species (wood stork [Mycteria americana], great egret [Ardea alba], white ibis [Eudocimus albus]) were not. Our results suggest differences among wading bird species in their prey selection and availability. Although small heron foraging may seem restricted by their specialization on marsh fishes, their short nesting cycles allow for the phenological flexibility to delay nesting until foraging conditions are optimal. Conversely, wood storks with longer nesting cycles are more temporally constrained but have greater flexibility in prey items and foraging range. The annual number of small heron nests may be more robust to hydrological variability as a result of management action or global change than the number of wood stork nests. The temporal constraints of nesting by wood storks indicate that management of supporting wetland systems should provide continuous habitat availability during the nesting season. © 2016 The Wildlife Society.

Influence of a Trematode Parasite (Microphallus turgidus) on Grass Shrimp ( Palaemonetes pugio ) Response to Refuge and Predator Presence.

The grass shrimp ( Palaemonetes pugio ) is a staple prey species in the diet of many ecologically and economically important species such as blue crab and striped bass and is commonly infected with a trematode parasite, Microphallus turgidus. To complete its life cycle, M. turgidus must be consumed as a metacercaria by a bird or mammal definitive host. Previous research has found that infected grass shrimp behave more conspicuously than uninfected shrimp around predators, which include mummichogs ( Fundulus heteroclitus ). In addition, grass shrimp are more likely to avoid predation when they have access to coarse woody debris (CWD). Aquaria experiments revealed that uninfected shrimp significantly reduce the amount of time spent swimming in the presence of a fish predator, whereas infected shrimp did not exhibit this predation avoidance behavior. Uninfected shrimp also increased predator avoidance behavior ("backthrusts") in the absence of CWD, whereas infected shrimp did not. These findings suggest that M. turgidus does not influence grass shrimp usage of CWD, but it alters shrimp swimming and backthrust behavior, thereby rendering infected shrimp more susceptible to predation. The implications of increased predation by a fish (nonhost or possible paratenic host) versus by a bird or mammal (definitive host) for parasite transmission are discussed.

Mechanisms That Generate Resource Pulses in a Fluctuating Wetland.

Animals living in patchy environments may depend on resource pulses to meet the high energetic demands of breeding. We developed two primary a priori hypotheses to examine relationships between three categories of wading bird prey biomass and covariates hypothesized to affect the concentration of aquatic fauna, a pulsed resource for breeding wading bird populations during the dry season. The fish concentration hypothesis proposed that local-scale processes concentrate wet-season fish biomass into patches in the dry season, whereas the fish production hypothesis states that the amount of dry-season fish biomass reflects fish biomass production during the preceding wet season. We sampled prey in drying pools at 405 sites throughout the Florida Everglades between December and May from 2006–2010 to test these hypotheses. The models that explained variation in dry-season fish biomass included water-level recession rate, wet-season biomass, microtopography, submerged vegetation, and the interaction between wet-season biomass and recession rate. Crayfish (Procambarus spp.) biomass was positively associated with wet-season crayfish biomass, moderate water depth, dense submerged aquatic vegetation, thin flocculent layer and a short interval of time since the last dry-down. Grass shrimp (Palaemonetes paludosus) biomass increased with increasing rates of water level recession, supporting our impression that shrimp, like fish, form seasonal concentrations. Strong support for wet-season fish and crayfish biomass in the top models confirmed the importance of wet-season standing stock to concentrations of fish and crayfish the following dry season. Additionally, the importance of recession rate and microtopography showed that local scale abiotic factors transformed fish production into the high quality foraging patches on which apex predators depended.

Effects of Culture Area, Stocking Density, and Shrimp and Fish Polyculture on the Cost Efficiency of Hard Clam, Meretrix meretrix, Culture: A Case Study of Hard Clam Farms in Yunlin, Taiwan

AbstractUsing the hard clam farms in Yunlin, Taiwan as examples, this study analyzes the effects of culture area, stocking density, and shrimp and fish polyculture on the cost efficiency (CE) of hard clam farming. A data envelopment analysis (DEA) is used to estimate the farms' technical efficiency (TE), allocative efficiency (AE), and CE values. The findings show that the mean TE, AE, and CE values of hard clam farms are 0.74, 0.57, and 0.43, respectively. The TE value is higher than the AE value, which indicates that cost inefficiency is mainly attributable to poor AE. Tobit regression results suggest that there are positive relationships between CE and both culture area and operator experience. Hard clam stocking density and age of the operators have negative effects on CE. Hard clam culture areas larger than 2 ha and a stocking density of 1.1–1.2 million hard clams per hectare have higher CEs than smaller culture areas and smaller or larger stocking densities. The use of sand shrimp, white shrimp, kuruma shrimp, and grass shrimp for polyculture and the use of milkfish and silver sea bream for polyculture are both associated with high CEs.

Do You See What I See? Using Ethograms to Observe Animal Behavior

The process of exploration and the methods that scientists use to conduct research are fundamental to science education. In this activity, authentic scientific practices are used to develop hypotheses to explain the natural world. Students observe grass shrimp in aquaria and construct an ethogram, which is a compilation of the observable behaviors an animal exhibits. They then conduct an experiment, just as real scientists would, to determine how changes in the environment alter shrimp behavior. This activity is designed for a fourth-grade science class and allows students to experience the excitement of observing a live organism while learning about scientific inquiry, and also reinforces quantification and graphing skills. “Do You See What I See” covers Next Generation Science Standards and addresses the science and engineering practices of engaging in argument from evidence.

Influence of Microphallus szidati Martorelli, 1986 (Trematoda) on the fecundity of the second intermediate host, Palaemonetes argentinus Nobili, 1901 (Decapoda: Natantia)

Fil: Merlo, Matias Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Biologia. Laboratorio de Parasitologia; Argentina

The freshwater grass shrimpPalaemonetes antennariusin the diet of fish in Lake Bracciano (Central Italy)

We evaluated the importance of the freshwater grass shrimp Palaemonetes antennarius as trophic source for the lacustrine fish of the Lake Bracciano (Central Italy) analyzing 6120 stomach contents of 10 species. Shrimp was recorded for all size classes of the investigated species with a variation in frequency and abundance depending on seasons. P. antennarius was occasionally preyed by cyprinids, and systematically by small individuals of carnivorous fish. Our findings acquire more importance if we take the shrimps ecological niche into account, as it is potentially acting as detritivorous/generalist and predator of benthic invertebrates as well. This feeding behavior makes P. antennarius an important network ring, being a taxon that ought to receive the same attention recommended for other freshwater decapods as proposed for Austropotamobius pallipes and Potamon fluviatile .

Mesopredator foraging success in eelgrass (Zostera marina L.): Relative effects of epiphytes, shoot density, and prey abundance

In seagrass habitats, structural complexity influences predator foraging success and prey survival by moderating encounter rates and behaviors of predators and prey. Studies of the effects of structural complexity on predator–prey interactions typically vary seagrass shoot density, biomass, or architecture. Filamentous epiphytic algae commonly grow on seagrass blades and add structure to seagrasses, but the effect of epiphytes on the outcome of predator–prey interactions has rarely been explored. This study determined the relative effects of simulated seagrass epiphytes, eelgrass (Zostera marina) shoot density, and prey density on the foraging behaviors of a common predator, the juvenile giant kelpfish Heterostichus rostratus (Girard, 1854) and on escape responses of their prey, grass shrimp Hippolyte californiensis (Holmes, 1895). Juvenile giant kelpfish hunted for grass shrimp in a laboratory experiment in which two levels of grass shrimp density were crossed with three levels of structural complexity (low density artificial eelgrass, low density artificial eelgrass with artificial epiphytes, and high density artificial eelgrass). Increased structural complexity had variable effects on juvenile kelpfish activity levels, but enhanced their success at catching prey after detection, resulting in no net effect of structural complexity on the total number of prey captured. Grass shrimp made fewer escape attempts in high vs. low structural complexity, which may have enhanced kelpfish foraging success because kelpfish rarely pursued fleeing prey. Prey density did not influence kelpfish behaviors or the total amount of prey they consumed. These results suggest that it is important to consider how different forms of habitat complexity affect the mechanisms by which predators hunt for prey in structured marine habitats.

Variability Is Not the Villain: Finding Patterns in Complex Natural Images

ABSTRACTEveryone needs strong observational skills to solve challenging problems and make informed decisions. However, many students expect to find exact answers to their questions by using the internet and do not understand the role of uncertainty, especially in decision making and scientific research. Humans and other animals choose among many options by using information about their environment. During this activity, students use their observational skills to analyze data from images of grass shrimp and a highly variable salt-marsh habitat as case studies for prioritizing different pieces of information. They gain an increased appreciation of natural variability and learn to build a consensus in a scenario that has no correct answer.

Movements and site fidelity of grass shrimp (Palaemonetes pugio and P. vulgaris) in salt marsh intertidal creeks

Grass shrimp are abundant residents of shallow-water habitats in US Atlantic and Gulf coast estuaries. Mark-recapture events determined the extent and direction of their movements in meso-tidal salt marsh creeks at North Inlet, South Carolina. Microwire-tagged Palaemonetes vulgaris demonstrated high fidelity for a dock in a subtidal channel. In the 48 days following release, 11 % of the 422 tagged shrimp were recaptured and 99 % of all recaptures were made there an average of 14 days post-release. Palaemonetes pugio, which favored the use of shallow intertidal areas, exhibited moderate fidelity for pools within creek beds with 53 % of the recaptured shrimp collected at the release site. Higher fidelity was observed for confluences of intertidal creeks and the subtidal channels. Of the 5565 shrimp released with coded microwire tags, 7.5 % were recaptured and 98 % of those recaptures were at release sites up to 53 days later. During another event, P. pugio released 235 m from their origin demonstrated relatively low fidelity for the new site and a lack of homing behavior. Of the 544 tagged shrimp, 3 % were recaptured; only 40 % of those recaptured were from the release site. Site fidelity is a mechanism by which previously discovered large and consistent differences in grass shrimp use of neighboring intertidal creek basins can be sustained over weeks, seasons, and years. Spatial variations and the tendency of these keystone organisms to resist relocation by tidal currents and occupy certain areas for extended periods should be considered in decisions about proposed alterations to creeks and shorelines.

The Effect of Temperature on Synchronization of Brood Development of the Bopyrid Isopod Parasite Probopyrus pandalicola with Molting of Its Host, the Daggerblade Grass Shrimp Palaemonetes pugio.

The bopyrid isopod Probopyrus pandalicola is a hematophagous ectoparasite that sexually sterilizes some palaemonid shrimps, including female daggerblade grass shrimp Palaemonetes pugio. The reproduction of parasitic isopods is thought to occur synchronously with host molting because the brood would be unsuccessful if molting occurred before the larvae were free swimming. Temperature affects the length of the molting cycle of shrimp, and therefore may also affect the incubation time of isopod broods. The purpose of the present study was to determine the effect of temperature on brood development of the parasite and on the degree of synchronization with the molting of its host. Parasitized P. pugio were monitored daily at 2 experimental temperatures, 23 and 15 C, in temperature-controlled chambers for the duration of a full parasite reproductive cycle. Developmental stage was determined by the visible coloration of the brood through the exoskeleton of the host, and was designated as egg, embryo I, embryo II, or epicaridium larvae. Temperature significantly affected median brood incubation time, which was only 11 days at 23 C, as compared to 35 days at 15 C. The final developmental stage (epicaridium larvae) was 3 times shorter at 23 C (median 3 days; n = 45) than at 15 C (median 9 days; n = 15). Temperature significantly affected the intermolt period of parasitized shrimp, which was shorter at 23 C (median 12 days) than at 15 C (median 37 days). A smaller percentage of the intermolt period elapsed between larval release and shrimp molting at 23 C (0.0%) than at 15 C (3.1%), indicating closer synchronization between host molting and parasite reproduction at the warmer temperature. At 15 C, the isopods utilized a smaller proportion of the time that was available for brood incubation during the intermolt period of their host. Brood size ranged from 391 to 4,596 young and was positively correlated with parasite and host size. Because development progressed more rapidly at 23 C, warmer temperatures could increase the prevalence of P. pandalicola. The corresponding reduction in the abundance of ovigerous grass shrimp as a result of sexual sterilization by bopyrids could adversely impact estuarine ecosystems, as grass shrimp are a crucial link in transferring energy from detritus to secondary consumers.

True metabolizable energy of American black duck foods

ABSTRACTUnderstanding the true metabolizable energy (TME) of foods is critical to estimating the energetic carrying capacity of landscapes for migrating and wintering waterfowl. We estimated gross energy, nutrient composition, and TMEN (TME corrected for zero nitrogen balance) for 7 foods that are commonly found in the diet of American black duck (Anas rubripes) and other waterfowl wintering along the Atlantic Coast. TMEN values ( ± SE) were 3.66 ± 0.12 kcal/g for mummichog (Fundulus heteroclitus), 2.02 ± 0.12 kcal/g for grass shrimp (Palaemonetes intermedius, P. pugio, and P. vulgaris), 1.57 ± 0.11 kcal/g for fiddler crabs (Uca minax, U. pugilator, and U. pugnax), 1.42 ± 0.13 kcal/g for sea lettuce (Ulva lactuca), 1.39 ± 0.12 kcal/g for saltmarsh cordgrass seeds (Spartina alterniflora), 1.10 ± 0.14 kcal/g for widgeon grass vegetation (Ruppia maritima), and 0.77 ± 0.16 kcal/g for saltmarsh snails (Melampus bidentatus). TMEN estimated for foods in this study will assist conservation planners in carrying out bioenergetics modeling along the Atlantic Coast. © 2014 The Wildlife Society.

The effects of the parasite Probopyrus pandalicola (Packard, 1879) (Isopoda, Bopyridae) on the behavior, transparent camouflage, and predators of Palaemonetes pugio Holthuis, 1949 (Decapoda, Palaemonidae)

The bopyrid isopod Probopyrus pandalicola (Packard, 1879) is a large, noticeable, hematophagous ectoparasite of palaemonid shrimps, including the daggerblade grass shrimp Palaemonetes pugio Holthuis, 1949. Bopyrids affect grass shrimp physiology and may also affect predator-prey dynamics. The purpose of this study was to determine whether the isopod affected the behavior and/or camouflage of grass shrimp, thereby altering the predation preferences of the mummichog Fundulus heteroclitus (Linnaeus, 1766). To determine whether the isopod affected predator preference through behavioral and/or camouflage alterations, paired combinations of unparasitized, parasitized, and marked shrimp were presented to mummichogs. One branchiostegite of some of the unparasitized shrimp was marked with black paint to mimic the bopyrid parasite. Mummichog predation preference and shrimp behavior immediately prior to predation events were recorded. All shrimp behavior was classified as motionless, walking, swimming, or backward thrusting. Immediately prior to predation, parasitized shrimp swam more () and backward thrusted less () than unparasitized shrimp. Mummichogs exhibited a preference for the more active shrimp (80.7% of shrimp; ), and also for the less camouflaged (parasitized or marked) shrimp (81.5% of shrimp; ) if there was no difference in shrimp behavior. Parasitized shrimp were preferentially consumed (51/85 shrimp) when paired with unparasitized shrimp (), but not with marked shrimp (). A 30-min activity budget was created for each type of shrimp both in the presence and absence of predators; neither the parasite nor marking affected their behavior over 30 min (). The major finding of this study was that P. pandalicola affected the predation preferences of F. heteroclitus by altering the behavior and/or camouflage of the grass shrimp. Parasitization alters predator-prey dynamics by decreasing the camouflage and the frequency of backward-thrusting behavior by the host when it is threatened by predation, which thereby decreases the ability of shrimp to escape from predators.

Size-Selective Foraging of Adult Mummichogs, Fundulus heteroclitus, in Intertidal and Subtidal Habitats

Intertidal marshes provide an important foraging habitat for resident marsh fishes. However, few studies have considered whether the importance of intertidal foraging is uniform across the adult-size range of marsh fishes or whether size-selective foraging, which has been demonstrated in intertidal habitats, also occurs in subtidal habitats. This study compares diet composition of adult mummichogs (Fundulus heteroclitus) in Hoffler Creek, VA, USA, foraging in intertidal salt marshes with the diet of individuals foraging in the subtidal creek and considers the effect of fish size on gut fullness and consumption of major intertidal and subtidal diet items. Gut fullness was significantly greater in the intertidal salt marsh for small mummichogs (40–60 mm total length), and small mummichogs were significantly more likely than larger individuals to consume several major intertidal diet items, including copepods and ostracods. However, gut fullness was greater in the subtidal creek for large mummichogs (70–90 mm total length (TL)) due to consumption of grass shrimp (Palaemonetes spp.). This diet item was rarely consumed by large mummichogs in the marsh or by smaller mummichogs in either habitat. Modifications to the marsh landscape that affect prey resources for fishes may, therefore, have differing impacts across adult size classes. Although subtidal habitats are not frequently considered important for foraging of marsh fishes, access to shallow, subtidal water may allow larger adults to take advantage of additional prey resources, such as shrimp.

Sexual sterilization of the daggerblade grass shrimp Palaemonetes pugio (Decapoda: Palaemonidae) by the bopyrid isopod Probopyrus pandalicola (Isopoda: Bopyridae).

Probopyrus pandalicola is a bopyrid isopod that infects several palaemonid shrimp species, including the daggerblade grass shrimp Palaemonetes pugio . The parasite can have several negative effects on its host, including loss of hemolymph, reduced reproductive potential, and decreased molting frequency and growth. To date, there are conflicting reports on whether Probopyrus pandalicola affects the reproductive capability of both male and female daggerblade grass shrimp. The purpose of this study was to determine whether infection by Probopyrus pandalicola resulted in the sexual sterilization of Palaemonetes pugio , and if the reproductive capability of male and/or female shrimp was restored after the bopyrid was removed. We found that parasitized and deparasitized males were able to fertilize the eggs of unparasitized females successfully, as 18.9 ± 7.1% and 42.7 ± 5.2% of the females paired with them became ovigerous in 4 wk, respectively. Neither parasitized nor deparasitized females became ovigerous when placed with unparasitized males during the 4-wk period. However, 45.4 ± 20.6% of deparasitized females did become ovigerous within 10 wk. Despite the fact that female shrimp are able to reproduce again when no longer parasitized, the majority of females remain infected with the bopyrid for their entire lives. Therefore, the sexual sterilization of female shrimp could potentially have a significant impact on estuarine food webs, as grass shrimp are conduits of detrital energy and a food source for many recreationally and commercially important species in estuaries on the East Coast of the United States and in the Gulf of Mexico.