Vertical migration of the crab Carcinus maenas first zoea in an estuary: implications for tidal stream transport

The first zoea of Carcinus maenas (L.) was intensively sampled in the Canal de Mira (Ria de Aveiro, Portugal) during the winter and spring of 1990. Each sampling period included a series of 25 h fixed-station plankton sampling cycles (12 in winter and 9 in spring), conducted at 1 station located in the lower part of the Canal. Plankton samples were collected every hour, at several depths along the water column, with the use of a pump. Hydrological measurements (salinity, temperature and current velocity and direction) were taken immediately before the collection of the plankton samples. The average depth of the zoeae changed in phase with the tide: larvae reached their highest position in the water column during ebb and their lowest during flood. The extent and phasing of the vertical displacements were such that the first zoea occupied a significantly higher position during the span of the ebb than during flood (p < 0.001). It was also demonstrated that the larvae were significantly closer to the surface during the night (p < 0.05). The pattern of vertical dispersion of the zoeae changed cyclically, with a period equivalent to the tidal half-cycle. Maximum aggregation usually occurred during periods of high current velocity and was independent from water stratification. These observations support the hypothesis that C. maenas first zoea performs an active vertical migration synchronised with tidal and daily cycles. Analysis of the zoeae instantaneous velocity showed that shifts of vertical position according to the phases of tide and day influenced their transport velocity, due to vertical differences of water velocity in the estuarine shear current system. During ebb the larvae were transported at a velocity that exceeded the vertically integrated water velocity; the reverse relationship was observed during flood (p < 0.001). The larvae were also transported faster during the night than during the day (p < 0.05). These results demonstrate that selective tidal stream transport can be generalised in the sense of a unidirectional transport mechanism in estuaries that can enhance exportation

Larval abundance patterns of Carcinus-Maenas (Decapoda, Brachyura) in Canal de Mira (Ria de Aveiro, Portugal)

Larval stages of Carcinus maenas (L.) were intensively sampled in the Canal de Mira (Ria de Aveiro, Portugal) during 2 lunar months: February 12 to March 11 and May 9 to June 7, 1990. Each sampling period included fifteen 25 h fixed-station sampling cycles beginning at intervals of 4 tide cycles. Within each 25 h sampling cycle, plankton samples were collected hourly at several depths using a pump. Analysis of the data from these sampling periods indicated tidal and diel cycles of abundance of first stage C. maenas larvae. A semilunar component was also identified. These patterns were expressed as peaks of abundance during ebb tides, with highest peaks during nocturnal neap ebb tides around the first and last quarters of the moon. Peaks of nocturnal abundance could occur at any time during the night but consistently followed high water. In contrast, megalopae were present in the samples primarily during nocturnal flood tides. Intermediate zoeal stages of C. maenas were not collected. As indicated by an analysis of variance, the main effects of phases of the tide and day on the abundance of first zoeae and megalopae were significant (p < 0.05). These results provide evidence that a component with semilunar periodicity is associated with the release of C. maenas larvae. That the release activity occurs well after sunset is also an additional interesting feature of these observations, inasmuch as larval release in decapods is usually concentrated within the first few hours after dusk. These observations support earlier observations that it is the time during the day-night cycle of high tide, as opposed to tidal amplitude, which is the important factor promoting synchrony with the lunar cycle

Planktonic stages of Processa macrodactyla (Decapoda: Caridea: Processidae) reared in the laboratory

Two ovigerous females of the processid shrimp Processa macrodactyla were caught in April 1997 at 13 m depth in coastal waters of Rota, Cádiz Bay, south-western Spain (36°36′N 6°18′W). Rearing was terminated after nine zoeal stages, when larvae moulted to the first juvenile instar. Descriptions of the appendages of every instar have been made so as to: (1) compare the larval morphology with that of other previous described known species in the genus Processa (P. canaliculata, P. edulis, P. elegantula, P. modica, P. nouveli); and (2) with those larvae not ascribed to a certain species in order to facilitate the specific identification of unknown collected planktonic larvae. When describing P. macrodactyla some characters remained, with few exceptions, invariable in their setation form ZI to ZIV or ZV, to then change and maintain until the last zoeal stage. This can be due to intermediate moults, with the result that some larvae unite the characters of Stages ZIV and ZV and others those of ZV and ZVI

Cannibalism, post-settlement growth rate and size refuge in a recruitment-limited population of the shore crab Carcinus maenas.

Previous studies on intra-specific interactions among green shore crabs have been undertaken in very large populations, in which individuals concentrate at high densities in physically complex substrates. Under such conditions, cannibalism and interference competition often override initial density patterns delivered by larval supply. In this study, we focused on a Carcinus maenas population receiving a low supply of settlers. We reported crab abundance in habitats of different physical structure, and measured cannibalistic interactions, in different substrates, at a prey density expected only after a major recruitment event. Different predator and prey sizes were used to verify if juveniles froma critical range attain a size refugewhen coexistingwith subadults, which are still commonly found in the nursery habitat. Virtually no juvenile shore crabs were found on sandy habitats, and differences between sparsely and densely vegetated cover were only detected shortly after a settlement pulse, indicating that nursery habitats are under their carrying capacity most of the time. Even under extreme high densities, cannibalism on juveniles of 10 mm carapace width (CW) remained undetected, and predation on crabs half this sizewas only significant in lowand mediumZostera cover,when larger predators (20–25 mmCW)were included in experimental plots. The allometricmodel predicted the non-linear decrease of predation rate as a function of relative prey size, with a nearly asymptotic value of one prey consumed each 5 d by one predator in a square metre, when relative prey size attains 0.6. Such a relationship is expected for ‘cruising’ predators which rely on encounter rate. Growth estimates obtained using time series of the catch of distinct juvenile stages in artificial collectors indicated that crabs surviving 50 d after settlement have attained a size refuge from predation by larger conspecific

Completeness of Retention Data and Determinants of Attrition in Birth Cohorts of Very Preterm Infants: A Systematic Review

Background: Birth cohorts provided essential knowledge for clinical and public health decision-making. However, little is known about retention and determinants of attrition in these specific longitudinal studies, although characterizing predictors of attrition sets the path to mitigate its occurrence and to promote valid inferences. We systematically reviewed retention in follow-ups of birth cohorts of very preterm or very low birth weight infants and the determinants of attrition. PROSPERO registration number: CRD42017082672. Methods: Publications were identified through PubMed®, Scopus, Web of Science, and Cochrane Library databases from inception to December 2017. Studies were included when reporting at least one of the following: retention at follow-ups, reasons for attrition, or characteristics of non-participants. Quality assessment was conducted using the completeness of the report of participation features in the articles. Non-participant's characteristics were presented using descriptive statistics. Local polynomial regression was used to describe overall retention trends over years of follow-up. Results: We identified 57 eligible publications, reporting on 39 birth cohorts and describing 83 follow-up evaluations. The overall median retention was 87% (p25–p75:75.8–93.6), ranging from 14.6 to 100%. Overall, retention showed a downward trend with increasing child age. Completeness of retention report was considered “enough” in only 36.8% of publications. Considering the 33 (57.9%) publications providing information on participants and non-participants, and although no formal meta-analysis was performed, it was evident that participants lost to follow-up were more often male, had foreign-born, multiparous, and younger mothers, and with a lower socioeconomic status. Conclusion: This systematic review evidenced a lack of detailed data on retention, which may threaten the potential use of evidence derived from cohort studies of very preterm infants for clinical and public health purpose. It supports the requirement for a standardized presentation of retention features responding to current guidelines.This work was supported by RECAP-Preterm project that is funded by the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 733280. This study was also funded by Foundation for Science and Technology—FCT (Portuguese Ministry of Science, Technology and Higher Education), under the Unidade de Investigação em Epidemiologia—Instituto de Saúde Pública da Universidade do Porto (EPIUnit) (info:eu-repo/grantAgreement/FCT/6817 - DCRRNI ID/UIDB/04750/2020/PT); Ana Cristina Santos holds a FCT Investigator contract info:eu-repo/grantAgreement/FCT/Investigador FCT/IF/01060/2015/CP1319/CT0001/PT

Preconditioning triggered by carbon monoxide (CO) provides neuronal protection following perinatal hypoxia-ischemia

Perinatal hypoxia-ischemia is a major cause of acute mortality in newborns and cognitive and motor impairments in children. Cerebral hypoxia-ischemia leads to excitotoxicity and necrotic and apoptotic cell death, in which mitochondria play a major role. Increased resistance against major damage can be achieved by preconditioning triggered by subtle insults. CO, a toxic molecule that is also generated endogenously, may have a role in preconditioning as low doses can protect against inflammation and apoptosis. In this study, the role of CO-induced preconditioning on neurons was addressed in vitro and in vivo. The effect of 1 h of CO treatment on neuronal death (plasmatic membrane permeabilization and chromatin condensation) and bcl-2 expression was studied in cerebellar granule cells undergoing to glutamate-induced apoptosis. CO's role was studied in vivo in the Rice-Vannucci model of neonatal hypoxia-ischemia (common carotid artery ligature +75 min at 8% oxygen). Apoptotic cells, assessed by Nissl staining were counted with a stereological approach and cleaved caspase 3-positive profiles in the hippocampus were assessed. Apoptotic hallmarks were analyzed in hippocampal extracts by Western Blot. CO inhibited excitotoxicity-induced cell death and increased Bcl-2 mRNA in primary cultures of neurons. In vivo, CO prevented hypoxia-ischemia induced apoptosis in the hippocampus, limited cytochrome c released from mitochondria and reduced activation of caspase-3. Still, Bcl-2 protein levels were higher in hippocampus of CO pre-treated rat pups. Our results show that CO preconditioning elicits a molecular cascade that limits neuronal apoptosis. This could represent an innovative therapeutic strategy for high-risk cerebral hypoxia-ischemia patients, in particular neonates

Characterization of the Megalopal Premoult Stages of the Green Crab, Carcinus Maenas (Decapoda, Portunidae), from Laboratory Culture

The premoult stages of Carcinus maenas (L.) megalopae were described from laboratory-reared larvae. Characterization of the premoult stage sequence was based upon a time sequence of morphological modifications of the distal segment of the second maxilliped, the uropod, and the telson. An intermoult plus seven premoult stages were identified, following a sequence of morphological modifications similar to the one described in previous studies of brachyuran decapods. The later premoult stages D3 D3 and D4 D4 mentioned by Drach were not observed, possibly owing to both the low calcification of the megalopae cuticle and the short duration of these moult stages. The knowledge of the time series of moult events will assist in the evaluation of the development state and competence of megalopae throughout the several phases of dispersal and recruitment, based on the observation of their morphological characters