Implications of a fluctuating fish predator guild on behavior, distribution, and abundance of a shared prey species: the grass shrimp Palaemonetes pugio

In some systems, the identity of a prey species' dominant predator(s) may not be constant over time. In cases in which a prey species exhibits different responses to various predator species, such changes in predator identity may have population-wide consequences. Our goals were to determine (1) whether mortality of and refuge use by the grass shrimp, Palaemonetes pugio, were predator-specific, and (2) how effects of prey size and habitat interacted with predator type. Striped bass (Morone saxatilis) exerted twice as much predation pressure as mummichog (Fundulus heteroclitus), although not equally as great on large (female) and small (male) shrimp. Mummichog, which fed preferentially on large shrimp, forced a partitioning of habitat between the two shrimp size classes. In contrast, large and small shrimp occupied similar habitats when subjected to striped bass, which fed on both size classes equally. Refuge use of grass shrimp depended on predator type. In the presence of mummichog, which occupied shallower depths in the water column than striped bass, shrimp stayed deep and close to structural habitat. Striped bass, which were deeper, caused shrimp to move high in the water column away from structural habitat. When both predators were present, shrimp distribution was similar to that when only striped bass were present, striped bass predation rate was enhanced, and overall mortality was higher than with either predator alone. Results suggest that at times when mummichogs are the dominant predators, large (female) shrimp experience higher predation than small (male) shrimp and are physically separated from their potential mates. When striped bass are more abundant, male and female shrimp may share a similar, shallow, less structure-oriented distribution and be subjected to higher mortality. When both predators are present, mortality rates may be higher still. This predator-, size-, and habitat-specificity of grass shrimp behavior suggests significant population and distribution consequences of fluctuating predator guilds and fluctuating cover of structural habitats in the field.     

Diel variation in predator abundance, predation risk and prey distribution in shallow-water estuarine habitats

Predation by visual predators is often affected by light conditions and may therefore exhibit strong diel variation. The dominant predators on grass shrimp, Palaemonetes pugio, are finfish predators that are thought to locate their prey by visual cues. We examined the response of grass shrimp to diel variation in predation risk in the nearshore shallow waters of the Chesapeake Bay. We used diel shoreline seines to assess the relative abundance of predators. We assessed the relative risk of predation with shrimp tethered at refuge (30 cm) and nonrefuge (60 cm) depths. To measure grass shrimp response to predation risk, we used dipnets to monitor habitat use. Four predominantly visual predators dominated the shoreline seine catches, Fundulus heteroclitus, Micropogonias undulatus, Morone americana and Morone saxatilis. Total predator abundance had a diel component, with dramatic nighttime decreases in total abundance, whereas guild composition and relative abundance remained unchanged. Relative predation risk for tethered shrimp exhibited significant time by habitat interaction. During the day, depth negatively affected survivorship of tethered shrimp while at night overall survivorship increased and there was no effect of depth. Shrimp habitats use reflected diel predation risks. Abundances in the near shore were highest during the day with decreased abundances at night. Together, the seine and tethering data highlight the importance for a refuge (e.g., shallow water) from predation during the daytime and a relaxation of predation pressure at night.     

Effects of hypoxia on movements and behavior of selected estuarine organisms from the southeastern United States

Hypoxia, or low dissolved oxygen, remains a common occurrence in estuarine waters as human activity in coastal areas expands. Fish kills, probably the most recognized indicator of these and other water quality problems, have significantly increased in recent years in many Southeastern United States estuaries. While entire aquatic communities are impacted by changes in available oxygen, estuarine organisms serve as appropriate indicators of these changes as they exhibit complex physiological and behavioral responses to hypoxia. The consequences of hypoxia for these species depend on their ability to detect and avoid areas of low dissolved oxygen. We conducted a series of two-way, replicated choice experiments with juvenile spot (Leiostomus xanthurus), pinfish (Lagodon rhomboides), croaker (Micropogonias undulatus), menhaden (Brevoortia tyrannus), white mullet (Mugil curema), mummichog (Fundulus heteroclitus), and brown shrimp (Penaeus aztecus) to determine their ability to detect and avoid specific levels of hypoxia. Additional data on organisms' movement patterns, aquatic surface respiration, and ventilation rates were collected. All species tested could detect and avoid 1 mgl(-1) dissolved oxygen. The hypoxia avoidance response differed among species, as some species exhibited an avoidance threshold while others exhibited a graded avoidance response. These data supply baseline information necessary to assess how some mobile estuarine organisms respond behaviorally to oxygen concentrations, and to understand how hypoxia more broadly impacts fish populations and estuarine community health.     

Do Decapod Crustaceans Have Nociceptors for Extreme pH?

Background

Nociception 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 Findings

Three 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/Significance

Previously 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.     

Recruitment of the infaunal bivalve Soletellina alba (Lamarck, 1818) (Bivalvia: Psammobiidae) in response to different sediment types and water depths within the intermittently open Hopkins River estuary

Studies examining recruitment processes for soft-sediment macroinvertebrate fauna in intermittent estuaries are rare and most studies of active habitat selection have been tested in the laboratory rather than the field. The present field study examined whether recruitment of the infaunal bivalve Soletellina alba was influenced by water depth and sediment particle size in the intermittent Hopkins River estuary, southern Australia. The number of recruits in sediment trays differed between water depths, but active habitat selection was not evident across treatments of varying sediment particle size. The use of sediments with varying particle sizes also provided an opportunity to identify potential discontinuities in body-size distributions of recruits associated with varying habitat architecture. The length (mm) of recruits was converted to the same scale used to express sediment particle size (i.e. phi units: ? = − log₂ of sediment particle size). The size of recruits differed across water depths, but did not differ across treatments with fine (? = 3) versus coarse (? = 1) sediment, and no relationships were apparent between bivalve size and sediments consisting of varying particle size. These patterns of recruitment do not correspond with the distribution of adult S. alba within the Hopkins River estuary. Previous sampling has shown that abundances of juvenile and adult S. alba are variable across time, site and water depth, but are often greater at the deeper water depth (1.05 m below the Australian Height Datum). However, recruitment during the present study was greatest at the shallower water depth (0.05 m below AHD), and the apparent absence of active habitat selection suggests that the distribution of adults is unlikely to be attributable to differences in recruitment associated with sediments of varying particle size.     

Swimming abilities of juvenile estuarine fishes: implications for passage at water control structures

The capability of early life history stage fishes to access nursery habitat within managed salt marshes is dependent on their ability to negotiate water control structures (WCSs). Knowledge of swimming ability and hydrodynamic preferences is essential to assess the impact of WCSs on fish movement in managed marshes. These data, however, are lacking for many common estuarine fishes, and the utility of the data for the few species examined thus far is limited. We examined critical swimming speeds and derived linear relationships between fish size and swimming speed for juveniles of six common estuarine fish species of the southeast U.S. and northern Gulf of Mexico coasts. White mullet Mugil curema displayed the greatest swimming ability among these six species and was able to swim against currents ≥ 30 cm s^?1 higher than the other species examined at the same size. The remaining species displayed lower critical swimming speeds and were classified into groups of moderate (pinfish Lagodon rhomboides, striped mullet Mugil cephalus) or slow (silver perch Bairdiella chrysoura, spotfin mojarra Eucinostomus argenteus, spot Leiostomus xanthurus) swimmers. Our results suggest that high-flow conditions at WCSs would likely preclude the passage of all but the largest juvenile fishes, and passage for most juveniles would occur under low-flow conditions; these flows at WCSs are dictated largely by site-specific tidal and weather conditions.     

Living benthic foraminifera of the Okhotsk Sea: Faunal composition,standing stocks and microhabitats

Live (Rose Bengal stained) benthic foraminifera were investigated in surface sediment samples from the Okhotsk Sea to reveal the relationship between faunal characteristics and environmental parameters. Live benthic foraminifera were quantified in the size fraction > 125 µm in the upper 8 cm of replicate sediment cores, recovered with a multicorer at five stations along the Sakhalin margin, and at three stations on the southwestern Kamchatka slope. The stations are from water depths between 625 to 1752 m, located close or within the present Okhotsk Sea oxygen minimum zone, with oxygen levels between 0.3 and 1.5 ml l^- 1. At the high-productivity and ice-free Kamchatka stations, live benthic foraminifera are characterized by maximal standing stocks (about 1700-3700 individuals per 50 cm²), strong dominance of calcareous species (up to 87-91% of total live faunas), and maximal habitat depths (down to 5.2-6.7 cm depth). Vertical distributions of total faunal abundances exhibit a clear subsurface maximum in sediments. At the Sakhalin stations, which are seasonally ice-covered and less productive, live benthic foraminifera show lower standing stocks (about 200-1100 individuals per 50 cm²), lower abundance of calcareous species (10-64% of total live faunas), and shallower habitat depths (down to 2.5-5.4 cm depth). Faunal vertical distributions are characterized by maximum in the uppermost surface sediments. It is suggested that 1) lower and strongly seasonal organic matter flux, caused by the seasonal sea ice cover and seasonal upwelling, 2) lower bottom water oxygenation (0.3-1.1 ml l^- 1), and 3) more pronounced influence of carbonate undersaturated bottom water along the Sakhalin margin are the main factors responsible for the observed faunal differences. According to species downcore distributions and average living depths, common calcareous species were identified as preferentially shallow, intermediate and deep infaunal. Foraminiferal microhabitat occupation correlates with the organic matter flux and the depth of the oxygenated layer in sediments.     

Environmental influences on the spatial distribution of European hake (Merluccius merluccius) and red mullet (Mullus barbatus) in the Mediterranean

Generalised additive models (GAMs) were used to test the hypotheses that red mullet (Mullus barbatus) and hake (Merluccius merluccius) abundances are related to the bathymetry, spatial location and the temperature-based variability of the NE Mediterranean. Data were collected during a 2-year period (1996–1997) of quasi-synoptic sampling using demersal trawl surveys in the northern Aegean Sea. The results of this study supported these hypotheses. It was found that geographic position and sea bottom characteristics influence the temporal distribution patterns of red mullet and hake. Data are presented that reveal species-specific aggregation patterns and an important habitat utilisation of the area. The modelled species’ abundances showed a strongly non-linear dependence on the explanatory covariates. This study, although not directly dealing with spawning, also provided evidence that red mullet and hake demonstrate environmental and bathymetric preferences in the months posterior to spawning. Mean red mullet abundance was consistently highest in areas with warmer bottom waters in the east and west than in the centre, these areas having shallower depths (35–60 m) and bottom temperatures around 19°C. The red mullet appeared to avoid the cold bottom waters (<16°C) of the deeper regions. Results indicated that areas with the highest hake abundances were located in waters of ∼160 m having bottom temperature of ∼16°C and avoided the shallower waters (<70 m) regardless of their bottom temperature. The present findings also suggested that colder bottom waters at all depths were associated with lower-than-average hake abundance. Red mullet and hake preferences for areas with specific bathymetric and ocean environmental conditions are believed to be linked to the oceanography of the NE Mediterranean ecosystem.     

Living benthic foraminifera of the Okhotsk Sea: Faunal composition, standing stocks and microhabitats

Live (Rose Bengal stained) benthic foraminifera were investigated in surface sediment samples from the Okhotsk Sea to reveal the relationship between faunal characteristics and environmental parameters. Live benthic foraminifera were quantified in the size fraction > 125 µm in the upper 8 cm of replicate sediment cores, recovered with a multicorer at five stations along the Sakhalin margin, and at three stations on the southwestern Kamchatka slope. The stations are from water depths between 625 to 1752 m, located close or within the present Okhotsk Sea oxygen minimum zone, with oxygen levels between 0.3 and 1.5 ml l^- 1. At the high-productivity and ice-free Kamchatka stations, live benthic foraminifera are characterized by maximal standing stocks (about 1700-3700 individuals per 50 cm²), strong dominance of calcareous species (up to 87-91% of total live faunas), and maximal habitat depths (down to 5.2-6.7 cm depth). Vertical distributions of total faunal abundances exhibit a clear subsurface maximum in sediments. At the Sakhalin stations, which are seasonally ice-covered and less productive, live benthic foraminifera show lower standing stocks (about 200-1100 individuals per 50 cm²), lower abundance of calcareous species (10-64% of total live faunas), and shallower habitat depths (down to 2.5-5.4 cm depth). Faunal vertical distributions are characterized by maximum in the uppermost surface sediments. It is suggested that 1) lower and strongly seasonal organic matter flux, caused by the seasonal sea ice cover and seasonal upwelling, 2) lower bottom water oxygenation (0.3-1.1 ml l^- 1), and 3) more pronounced influence of carbonate undersaturated bottom water along the Sakhalin margin are the main factors responsible for the observed faunal differences. According to species downcore distributions and average living depths, common calcareous species were identified as preferentially shallow, intermediate and deep infaunal. Foraminiferal microhabitat occupation correlates with the organic matter flux and the depth of the oxygenated layer in sediments.     

Seasonal and daily movements of the bluntnose sixgill shark (<Emphasis Type="Italic">Hexanchus griseus</Emphasis>) in the strait of Georgia from satellite tag data

The bluntnose sixgill shark (Hexanchus griseus Bonnaterre 1788) is a large, deepwater apex predator that, in a few unique locations such as the Strait of Georgia, Canada, occupies shallow, inshore waters as juveniles. The occurrence of pregnant females in the Strait of Georgia suggests that this is an important area for parturition and juvenile rearing. Bluntnose sixgill sharks are listed under the Canadian Species at Risk Act, and an understanding of their behaviour in habitat selection during important life stages is an important component for conservation measures. We employed satellite tags to identify the daily and seasonal depth and thermal habitats of juvenile bluntnose sixgill sharks in the Strait of Georgia. Tag release and depth information suggests that juvenile bluntnose sixgill sharks within the Strait of Georgia remain there until they mature and migrate to offshore deepwaters. The dominant depth habitat utilized by the juvenile sharks in our study was deepwater (>200 m), with only occasional occupation of depths <100 m, indicating that even within coastal areas, juveniles still prefer deepwater. Overall the sharks occupied shallower depths at night than during the day with increased vertical activity in both the day and night compared to crepuscular periods. Seasonally, the sharks occupied shallower depths in the summer than in winter, but inconsistency in the temperatures with which those depths were associated suggests that their vertical behaviour is influenced by local foraging opportunities and not by thermoregulation.     

First documentation of detailed behaviors of endangered adult Sakhalin taimen <Emphasis Type="Italic">Parahucho perryi</Emphasis> in the Bekanbeushi River system,eastern Hokkaido,Japan, using bio-logging and acoustic telemetry concurrently

Behavior of adult Parahucho perryi was examined using bio-logging and acoustic telemetry concurrently in the Bekanbeushi River system, eastern Hokkaido, Japan, in 2009 and 2010. Based on 46.1–87.9 h data from five P. perryi (69.0–80.0 cm fork length) caught from Lake Akkeshi, they used upstream (n = 2), midstream (n = 3), and downstream (n = 4) habitats. Large variability in diel activity and depth occupation existed in each stream habitat; however, fish in the downstream habitat tended to be more active than those in the upper habitats and mainly occupied shallower depths than mean bottom depth in this habitat.     

Comparison of Protein Expression Profiles of the Hepatopancreas in Fenneropenaeus chinensis Challenged with Heat-inactivated Vibrio anguillarum and White Spot Syndrome Virus

Fenneropenaeus chinensis (Chinese shrimp) culture industry, like other Penaeidae culture, has been seriously affected by the shrimp diseases caused by bacteria and virus. To better understand the mechanism of immune response of shrimp to different pathogens, proteome research approach was utilized in this study. Firstly, the soluble hepatopancreas protein samples in adult Chinese shrimp among control, heat-inactivated Vibrio-challenged and white spot syndrome virus-infected groups were separated by 2-DE (pH range, 4–7; sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and pH range, 3–10; tricine-SDS-PAGE). Then the differentially expressed protein spots (≥1.5-fold or ≤0.67-fold averagely of controls) were analyzed by LC-ESI-MS/MS. Using Mascot online database searching algorithm and SEQUEST searching program, 48 and 49 differentially expressed protein spots were successfully identified in response to Vibrio and white spot syndrome virus infection, respectively. Based on these results, we discussed the mechanism of immune response of the shrimp and shed light on the differences between immune response of shrimp toward Vibrio and white spot syndrome virus. This study also set a basis for further analyses of some key genes in immune response of Chinese shrimp.     

Mesophotic depths as refuge areas for fishery-targeted species on coral reefs

Coral reefs are subjected to unprecedented levels of disturbance with population growth and climate change combining to reduce standing coral cover and stocks of reef fishes. Most of the damage is concentrated in shallow waters (<30 m deep) where humans can comfortably operate and where physical disturbances are most disruptive to marine organisms. Yet coral reefs can extend to depths exceeding 100 m, potentially offering refuge from the threats facing shallower reefs. We deployed baited remote underwater stereo-video systems (stereo-BRUVs) at depths of 10–90 m around the southern Mariana Islands to investigate whether fish species targeted by fishing in the shallows may be accruing benefits from being at depth. We show that biomass, abundance and species richness of fishery-targeted species increased from shallow reef areas to a depth of 60 m, whereas at greater depths, a lack of live coral habitat corresponded to lower numbers of fish. The majority of targeted species were found to have distributions that ranged from shallow depths (10 m) to depths of at least 70 m, emphasising that habitat, not depth, is the limiting factor in their vertical distribution. While the gradient of abundance and biomass versus depth was steepest for predatory species, the first species usually targeted by fishing, we also found that fishery-targeted herbivores prevailed in similar biomass and species richness to 60 m. Compared to shallow marine protected areas, there was clearly greater biomass of fishery-targeted species accrued in mesophotic depths. Particularly some species typically harvested by depth-limited fishing methods (e.g., spearfishing), such as the endangered humphead wrasse Cheilinus undulatus, were found in greater abundance on deeper reefs. We conclude that mesophotic depths provide essential fish habitat and refuge for fishery-targeted species, representing crucial zones for fishery management and research into the resilience of disturbed coral reef ecosystems.     

Fish predation on juvenile brown shrimp, Penaeus aztecus Ives: The effect of simulated Spartina structure on predation rates

The effect of artificial Spartina structure on the predation rates of four estuarine fish on juvenile brown shrimp (Penaeus aztecus Ives) was examined under laboratory conditions. Vegetative structure reduced predation rates of pinfish and Atlantic croaker but did not affect predation rates of red drum and speckled trout. Pinfish and Atlantic croaker were inefficient predators, needing several strikes before successfully capturing prey. This inefficiency, necessitating repeated detection of prey organisms, probably contributed to the reduced predation rates by these fish in vegetated treatments. Although pinfish and speckled trout appeared to be strictly visual feeders, Atlantic croaker and red drum could apparently detect and feed upon shrimp through other sensory mechanisms. Differences in the mode of feeding among the fish, however, did not appear to be related to the effect of vegetative structure on predation rates. Over all of the experiments, predation rates on shrimp (50–69 mm) ranged between ≈2 and 13 shrimp·fish^?1·day^?1, and there was a positive relationship between the number of shrimp eaten and the size of the predator.     

Up‐and‐down shift in residence depth of slickheads (Alepocephalidae) revealed by otolith stable oxygen isotopic composition

Otolith δ¹⁸O profiles for four slickhead species (Alepocephalidae) suggested that Alepocephalus umbriceps, Talismania okinawensis and Rouleina watasei migrated hundreds of metres to shallower depths during the juvenile to young stages before returning to their original depth or even deeper waters. Xenodermichthys nodulosus gradually shifted residence depth from shallow to deeper water during their life. These migratory patterns indicated that the slickheads examined had allopatric residence depths at different life stages, which might enhance the pelagic survival and growth rates of the juvenile and young fishes.     

Spatial distribution and habitat suitability indices for non‐spawning and spawning adult Chinese sturgeons below Gezhouba Dam,Yangtze River: Effects of river alterations

The study objectives were to identify the horizontal and vertical distributions of adult Chinese sturgeon (Acipenser sinensis) in relation to the Habitat Suitability Index (HSI) in order to assess the utility of the only remaining spawning grounds by adults and to understand the effects of river alterations on habitat use. Twenty‐five adults were surgically implanted with ultrasonic transmitters and located by mobile tracking and fixed monitoring stations during the 2006–2009 spawning seasons. Fish locations and depths along with water depth and bottom characteristics (topography, velocity, and embeddedness) were measured during tracking and used to determine HSI curves for non‐spawning and spawning adults. Most fish locations (91%) were on the spawning grounds (GZD to Miaozui reaches). Horizontal distribution differed before and after spawning, among years, and between the sexes. Adults used deeper depths during the day than at night (P < 0.001), while also preferring shallower depths on the day of spawning rather than the days before and after. Mature females used deeper water than other females (P < 0.001). Comparison of horizontal and vertical distributions before and after river alterations found fewer adults using the grounds impacted by a diversion dike which was built on the spawning grounds. Adults also used shallower depths after the Three Gorges Dam regulated river flow over the spawning grounds. The HSI model and the use of Weighed Usable Areas (WUA) for mature and immature adults indicated suitable habitat was available, but was reduced by the river alterations resulting in reduced spawning success and placing the population into a situation close to extirpation.     

Metabolic flexibility allows bacterial habitat generalists to become dominant in a frequently disturbed ecosystem

Ecological theory suggests that habitat disturbance differentially influences distributions of habitat generalist and specialist species. While well-established for macroorganisms, this theory has rarely been explored for microorganisms. Here we tested these principles in permeable (sandy) sediments, ecosystems with much spatiotemporal variation in resource availability and physicochemical conditions. Microbial community composition and function were profiled in intertidal and subtidal sediments using 16S rRNA gene amplicon sequencing and metagenomics, yielding 135 metagenome-assembled genomes. Community composition and metabolic traits modestly varied with sediment depth and sampling date. Several taxa were highly abundant and prevalent in all samples, including within the orders Woeseiales and Flavobacteriales, and classified as habitat generalists; genome reconstructions indicate these taxa are highly metabolically flexible facultative anaerobes and adapt to resource variability by using different electron donors and acceptors. In contrast, obligately anaerobic taxa such as sulfate reducers and candidate lineage MBNT15 were less abundant overall and only thrived in more stable deeper sediments. We substantiated these findings by measuring three metabolic processes in these sediments; whereas the habitat generalist-associated processes of sulfide oxidation and fermentation occurred rapidly at all depths, the specialist-associated process of sulfate reduction was restricted to deeper sediments. A manipulative experiment also confirmed habitat generalists outcompete specialist taxa during simulated habitat disturbance. Together, these findings show metabolically flexible habitat generalists become dominant in highly dynamic environments, whereas metabolically constrained specialists are restricted to narrower niches. Thus, an ecological theory describing distribution patterns for macroorganisms likely extends to microorganisms. Such findings have broad ecological and biogeochemical ramifications.Subject terms: Microbial ecology, Microbial communities     

Experimental assessment of trophic impacts from a network model of a seagrass ecosystem: Direct and indirect effects of gulf flounder, spot and pinfish on benthic polychaetes

Trophic cascades are predicted to occur when the abundance of predators is increased, directly reducing the abundance of the intermediate prey and indirectly increasing the abundance of the prey at the base of a food web. Mixed trophic impact analysis of a network model developed for Apalachee Bay, near St. Marks, FL, USA predicted such a trophic cascade, in that increased abundance of juvenile gulf flounder Paralichthys albigutta (x¯ = 149 mm SL, effective trophic level 3.9) should have a negative impact on juvenile spot Leiostomus xanthurus (x¯ = 30 mm SL, effective trophic level 2.9) and a positive impact on benthic polychaetes (effective trophic levels 2.3 for deposit feeders and 3.0 for predatory polychaetes) in Halodule wrightii seagrass beds. We tested the predictions of the mixed trophic impact analysis by manipulating the abundance of the high trophic-level species (juvenile gulf flounder) in a cage-exclusion study in the North River, near Harkers Island, NC, USA. We compared the polychaete communities in St. Marks, FL and Harkers Island, NC, and showed that they are 51% similar (Jaccard's Index) at the family level, with the same eight dominant families (Nereidae, Capitellidae, Syllidae, Spionidae, Cirratulidae, Terebellidae, Sabellidae, and Maldanidae) present in both locations. We used 24 open-bottom cages to enclose the benthos and its seagrass-associated animal communities. We manipulated each cage by assigning it to one of the following treatments: (1) inclusion of fishes in upper and intermediate trophic levels (1 juvenile gulf flounder and 10 juvenile spot, the flounder + spot treatment); (2) inclusion of the intermediate predator (10 juvenile spot with no gulf flounder, the spot-only treatment); and (3) no fish added (unmanipulated controls). Core samples taken within the cages provided pre- and post-experimental measures of polychaete density and biomass, and the difference in density and biomass were used as response variables. At the end of the experiment, we collected, weighed, and analyzed the gut contents of all juvenile spot present in the cages. Juvenile pinfish (Lagodon rhomboides, x¯ = 30 mm SL) were present at the end of the study, having arrived as larvae or being trapped during cage set-up, and these fish were also examined, because they also eat polychaetes and their natural densities exceeded our introduced spot densities. Significant differences among treatments were detected for the polychaete family Terebellidae for both the change in density and biomass (pre-experiment − post-experiment). Densities of the Terebellidae changed in the direction predicted by the network model's impact analysis, declining in the cages with spot added compared with the control cages. Analyses of the other response variables (post-experiment spot and pinfish densities and biomass, difference between pre- and post-experiment polychaete densities and biomass for other families, and post-experiment spot and pinfish stomach content biomass) showed no significant differences among treatments. Several variables (Nereidae densities, pinfish densities and biomass, and pinfish stomach content biomass) varied between cages with low and high seagrass cover (significant blocking effect, P < 0.001). Nereidae densities declined significantly in cages with high (73%) rather than with low coverage (31% cover) of seagrass. Pinfish density and biomass were significantly greater in the high seagrass cages at the end of the experiments (P < 0.001), suggesting that dense seagrass attracted them. We conclude that the high density of pinfish in dense seagrass was responsible for the decline in density of the Nereidae. The direct effect of intermediate predators (pinfish feeding on polychaete prey) can be influenced by preferential recruitment of fishes to structurally complex habitats. The direction of change of indirect effects, but not the magnitude, in multi-trophic-level food webs can be predicted by the mixed trophic impact analysis of network models. However, these indirect effects are likely to be small in magnitude relative to direct effects and may be difficult to detect experimentally, especially in low-power experimental caging studies with natural fluctuations in recruitment rates of competitor species.     

Protection of Shrimp Penaeus monodon from WSSV Infection Using Antisense Constructs

White spot syndrome caused by white spot syndrome virus (WSSV) is one of the most threatening diseases of shrimp culture industry. Previous studies have successfully demonstrated the use of DNA- and RNA-based vaccines to protect WSSV infection in shrimp. In the present study, we have explored the protective efficacy of antisense constructs directed against WSSV proteins, VP24, and VP28, thymidylate synthase (TS), and ribonucleotide reductase-2 (RR2) under the control of endogenous shrimp histone-3 (H3) or penaedin (Pn) promoter. Several antisense constructs were generated by inserting VP24 (pH3–VP24, pPn–VP24), VP28 (pH3–VP28, pPn–VP28), TS (pH3–TS, pPn–TS), and RR2 (pH3–RR2) in antisense orientation. These constructs were tested for their protective potential in WSSV infected cell cultures, and their effect on reduction of the viral load was assessed. A robust reduction in WSSV copy number was observed upon transfection of antisense constructs in hemocyte cultures derived from Penaeus monodon and Scylla serrata. When tested in vivo, antisense constructs offered a strong protection in WSSV challenged P. monodon. Constructs expressing antisense VP24 and VP28 provided the best protection (up to 90 % survivability) with a corresponding decrease in the viral load. Our work demonstrates that shrimp treated with antisense constructs present an efficient control strategy for combating WSSV infection in shrimp aquaculture.     

The ecology of eelgrass, Zostera marina (L.), fish communities. I. Structural analysis

Fish populations utilizing eelgrass, Zostera marina (L.), beds in two different estuarine areas near Beaufort, North Carolina were analysed and compared to determine aspects of their community structure. The fish community of the eelgrass beds was characterized by low diversity and high standing crops of biomass and energy, both of which showed seasonal variation. Wide temperature fluctuations related to the overall shallowness of the beds probably regulated the diversity of fishes utilizing the beds. This community was dominated by pinfish, Lagodon rhombiodes (L.), which comprised 45% and 67% of the fish biomass in the Phillips Island and Bogue Sound beds, respectively.Changes in total body caloric content were probably related to developmental stages and changes in diet. Adult fish often had significantly higher weight-specific caloric contents than juvenile fish. Monthly or seasonal variations in caloric content of the organic matter of pinfish had little influence on the caloric content within the various sizes of pinfish.There was a significant correlation between fish biomass, temperature, and Zostera biomass. Fish biomass was highest when temperature and grass biomass were at a maximum. In general, water depth over the beds had little effect on the standing crop of fish within the bed, but cooler waters which occurred at night, darkness, or both, had a large effect.