Foraging Behavior Of The Blue-Crab, Callinectes-Sapidus, On Juvenile Oysters, Crassostrea-virginica - Effects Of Prey Density And Size

Blue crabs (Callinectes sapidus) are major predators of juvenile oysters (Crassostrea virginica) in Chesapeake Bay, yet little information exists on the foraging behavior and predatorprey dynamics for this predator-prey system. Laboratory experiments assessed functional responses of blue crabs to six densities of three size-classes of juvenile American oysters. Behavioral subcomponents of the crabs\u27 functional response were quantified: total and successful encounter rates, proportional attack success, persistence time in unsuccessful encounters, and breaking, eating and handling times in successful encounters. Specific opening techniques were used by crabs for the three oyster size-classes. Blue crabs exhibited a hyperbolic type II functional response regardless of oyster size, with an inverse relationship between predation rates and increasing oyster size. Crab persistence times with oysters were positively correlated with attack success rates at three oyster size-classes, and inversely related to prey density, suggesting higher selectivity by blue crabs at higher oyster densities. Oysters \u3e30 mm shell-height may be near the critical size for crushing by large crabs as a result of increased variations in (I) shell to crab strength ratios, (2) opening techniques with oyster attachment site and growth geometry, and (3) oyster density. These findings indicate that crab acceptance or rejection sequences of bivalve prey depend on prey density and size, that predation by large male C. sapidus can lead to local extinction of juvenile oysters (x = 15- 35 mm SH) regardless of density and, that increasing shell-height provides a refuge from predation

Ontogenetic diet shifts in Nassau grouper: Trophic linkages and predatory impact

Understanding which fauna and flora from seagrass beds serve as primary food for reef-based commuters is critical in defining trophic linkages between shallow-water habitats of tropical oceanic regions. Although numerous studies have documented the relative importance of crustaceans in the diet of reef fishes associated with tropical seagrass meadows, it is unknown if trophic importance corresponds to a significant effect on prey distribution and abundance patterns. We quantified size-specific diet of juvenile Nassau grouper (Epinephelus striatus) inhabiting natural and artificial patch reefs, and manipulated the density of artificial patch reefs (0, 8, and 16 patch reefs per ha) to examine the predatory impact of patch reef associates on nocturnally foraging crabs. Stomach content analysis indicated an ontogenetic shift in diet, where small grouper (TL) consumed mainly brachyuran crabs and other small crustaceans, and large grouper (\u3e30 cm TL) consumed primarily fish. Mid-size fish (20.0-29.9 cm TL) were transitional in diet, with crustaceans occurring more frequently than fish. Diet was least diverse for large fish, and nearly identical for mid-size and small fish. Similar numbers of prey taxa were ingested in natural and artificial patch reefs. Before patch reefs were deployed in the field, nighttime band censuses revealed a mean density of 3 crabs per 240 m(2) (ranges = 0-8 crabs/transect) in nearby seagrass beds. After patch reefs were deployed, crab densities dropped by one-half to 43-fold in sites with patch reefs compared to control sites (0 patch reefs). There was a negative and significant relationship between grouper density (no. ha(-1)) and crab density (no. 240 m(-2)) at all sites and locations combined. These results suggest that patch reef associated predators have a significant predatory impact on nocturnally foraging crabs in adjacent seagrass meadows, and highlight an important trophic link between tropical patch reef and seagrass habitats

Survival of juvenile Caribbean spiny lobster: effects of shelter size, geographic location and conspecific abundance

The Caribbean spiny lobster Panulirus argus seeks structured shelter throughout its benthic phase, often forming aggregations within shelters. Casitas - concrete, low-relief, artificial shelters - are effective in aggregating lobsters, and are used to harvest spiny lobster in the Caribbean. However, casitas may also enhance populations of P. argus, by providing shelter from predation. In this study we examined the effects of various shelter features upon the survival of juvenile P. argus. Juvenile lobsters were tethered at several artificial shelter treatments in Florida Bay, Florida, USA, to test the efficacy of casitas as refuge from predation. Survival of juveniles was analyzed with respect to 4 shelter types (2 casita sizes, a simulated natural shelter and a no-shelter control) within 2 locations in Florida Bay. In general, casita availability significantly increased survival. The geographic location of artificial shelter placement also significantly affected survival; the degree of survival enhancement was apparently linked to the availability of natural shelter. Furthermore, there was a quantitative relationship between lobster survival and lobster abundance within shelters, which was tempered by local predation pressure. Survival of tethered individuals was highest when the number of conspecifics was high and predator abundance was low. While larger shelters allowed for larger lobster aggregations and usually contained more lobsters, lobsters tethered to large shelters that contained relatively few conspecifics sustained higher mortality, probably due to their increased vulnerability to larger casita-associated predators. Thus, the survival of juvenile P. argus is controlled not only by physical features of the shelter, but also by the relative abundance of conspecifics and predators in shelter-providing habitats

The Impact of Rural Pensions in China on Labor Migration

We study the impact of China’s new rural pension program on promoting migration of labor by applying a regression discontinuity analysis to this new pension program. The results reveal a perceptible difference in labor migration among adult children whose parents are just above and below the age of pension eligibility: The adult children with a parent just attaining the pension-eligible age are more likely to be labor migrants compared with those with a parent just below the pension-eligible age. We also find that with a pension-eligible parent, the adult children are more likely to have off-farm jobs. These abrupt changes in household behavior at the cutoff suggest that these households are credit constrained. In addition, we find that the pension’s effect on migration is greater among adult children with a parent in poor health; pension-eligible elderly report that they are more likely to use inpatient services when needed and less likely to rely on adult children for care when they are ill. These results suggest that (expectations regarding) providing care for elderly parents has constrained labor migration from China\u27s rural areas to some extent, and that the new rural pension program has helped to relax this constraint

Differentiation of human adipose-derived stem cells into neuron/motoneuron-like cells for cell replacement therapy of spinal cord injury

Human adipose-derived stem cells (hADSCs) are increasingly presumed to be a prospective stem cell source for cell replacement therapy in various degenerative and/or traumatic diseases. The potential of trans-differentiating hADSCs into motor neuron cells indisputably provides an alternative way for spinal cord injury (SCI) treatment. In the present study, a stepwise and efficient hADSC trans-differentiation protocol with retinoic acid (RA), sonic hedgehog (SHH), and neurotrophic factors were developed. With this protocol hADSCs could be converted into electrophysiologically active motoneuron-like cells (hADSC-MNs), which expressed both a cohort of pan neuronal markers and motor neuron specific markers. Moreover, after being primed for neuronal differentiation with RA/SHH, hADSCs were transplanted into SCI mouse model and they survived, migrated, and integrated into injured site and led to partial functional recovery of SCI mice. When ablating the transplanted hADSC-MNs harboring HSV-TK-mCherry overexpression system with antivirial Ganciclovir (GCV), functional relapse was detected by motor-evoked potential (MEP) and BMS assays, implying that transplanted hADSC-MNs participated in rebuilding the neural circuits, which was further confirmed by retrograde neuronal tracing system (WGA). GFP-labeled hADSC-MNs were subjected to whole-cell patch-clamp recording in acute spinal cord slice preparation and both action potentials and synaptic activities were recorded, which further confirmed that those pre-conditioned hADSCs indeed became functionally active neurons in vivo. As well, transplanted hADSC-MNs largely prevented the formation of injury-induced cavities and exerted obvious immune-suppression effect as revealed by preventing astrocyte reactivation and favoring the secretion of a spectrum of anti-inflammatory cytokines and chemokines. Our work suggests that hADSCs can be readily transformed into MNs in vitro, and stay viable in spinal cord of the SCI mouse and exert multi-therapeutic effects by rebuilding the broken circuitry and optimizing the microenvironment through immunosuppression

Mosquito control practices and perceptions: An analysis of economic stakeholders during the Zika epidemic in Belize, Central America.

The tourist-based economy of Belize, a tropical hub for eco-tourism, is at high risk to be disproportionately impacted by established and emerging mosquito-borne diseases such as Zika. An online survey was used to probe economic stakeholders working in the Belize tourism industry about their mosquito control practices and perceptions. Responses demonstrated that the respondents have good working knowledge of mosquitoes and mosquito-borne illnesses. Most businesses surveyed engage in some means of mosquito control, either through larval source reduction or use of insecticides on the premises. Larvicide use was significantly correlated with a general willingness to use insecticides, as well as belief that treatment of water will reduce mosquito densities and disease transmission. A majority of the respondents agreed that they would be interested in buying a new larvicide to be used on the business premises if it were shown to be safe and effective. The safety of mosquito control products for humans, animals, plants, and the environment in general, followed by product effectiveness, are the most critical determinants of mosquito control purchasing decisions. A majority of respondents agreed that control of mosquitoes and mosquito-borne illnesses is central to the success of their tourist-based industry. Respondents expressed significant concern that the Zika epidemic was over-sensationalized by the media, and that this negatively impacted their livelihoods. The respondents, many of whom are associated with eco/sustainable businesses, also voiced concerns that chemical pesticides could have a negative impact on human health and the environment and expressed a desire for balance between effective mosquito control and preservation of the rich biodiversity of Belize. This study provided a framework for further engagement activities in Belize and other Caribbean nations, uncovered both concerns and support for emerging mosquito control technologies, and revealed opportunities for further debate and educational outreach efforts