Trophic shift in young-of-the-year Mugilidae during salt-marsh colonization.

This study investigated the trophic shift of young-of-the-year (YOY) thinlip grey mullet Liza ramada and golden grey mullet Liza aurata during their recruitment in a salt marsh located on the European Atlantic Ocean coast. Stable-isotope signatures (δ(13) C and δ(15) N) of the fishes followed a pattern, having enrichments in (13) C and (15) N with increasing fork length (LF ): δ(13) C in fishes < 30 mm ranged from -19.5 to -15.0‰, whereas in fishes > 30 mm δ(13) C ranged from -15.8 to -12.7‰, closer to the level in salt-marsh food resources. Large differences between the δ(15) N values of mugilids and those of food sources (6·0‰ on average) showed that YOY are secondary consumers, similar to older individuals, when feeding in the salt marsh. YOY mugilids shift from browsing on pelagic prey to grazing on benthic resources from the salt marsh before reaching 30 mm LF. The results highlight the role of European salt marshes as nurseries for juvenile mugilids.

Methodology of light response curves: application of chlorophyll fluorescence to microphytobenthic biofilms.

The light response curve methodology for microphytobenthic biofilms was studied by comparing the two most usual approaches used in pulse amplitude modulated (PAM) fluorometry. The non-sequential light curve (N-SLC) method is characterized by independent measures of the photosynthetic activity across a light gradient whereas the rapid light curve (RLC) method consists of successive measures on the same sample exposed to a stepwise increase of light intensities. Experiments were carried out on experimental microphytobenthic biofilms prepared from natural assemblages and acclimated to dark conditions. In preliminary experiments, N-SLCs were constructed from fluorescence induction curves performed at 12 different photon flux densities (PFDs). A minimum of 50 s of illumination was necessary to reach a stable light response curve; shorter illumination times resulted in underestimating the physiological parameters (α the light utilization coefficient in light-limited conditions and rETRmax the maximum rate of photosynthesis efficiency) of the light response curve. For the comparison between N-SLCs and RLCs, the same time of illumination (50 s) was used for each light step of RLCs so that N-SLCs differed from RLCs only by the way the amount of light was delivered, i.e., a light dose accumulation for RLC. The experimental results showed the difference between the two photobiological response curves. In the lower range of PFDs, RLCs exhibited a larger value of α; in this light-limited part of the response curve the incremental increase of PFDs limited the development of NPQ and resulted in a better optimization of electron transport rate for RLC. In the higher range of PFDs, the trend was reversed and the RLC showed a lower value of rETRmax than the N-SLC did; this is attributed to the light dose accumulation which likely led to a more efficient dispersion of energy, as illustrated by a higher non-photochemical quenching (NPQ). In conclusion, these results confirm that parameters derived from both methods differ in their value and do not bear the same physiological information.

[Short-term dynamics of intertidal microphytobenthos biomass. Mathematical model]. / La dynamique à court terme de la biomasse du microphytobenthos intertidal. Formalisation mathématique.

We formulate a deterministic mathematical model to describe the dynamics of the microphytobenthos of intertidal mudflats. It is 'minimal' because it only takes into account the essential processes governing the functioning of the system: the autotrophic production, the active upward and downward migrations of epipelic microalgae, the saturation of the mud surface by a biofilm of diatoms and the global net loss rates of biomass. According to the photic environment of the benthic diatoms inhabiting intertidal mudflats, and to their migration rhythm, the model is composed of two sub-systems of ordinary differential equations; they describe the simultaneous evolution of the biomass 'S' concentrated in the mud surface biofilm--the photic layer--and of the biomass 'F' diluted in the topmost centimetre of the mud--the aphotic layer. Qualitatively, the model solutions agree fairly well with the in situ observed dynamics of the S + F biomass. The study of the mathematical properties of the model, under some simplifying assumptions, shows the convergence of solutions to a stable cyclic equilibrium, whatever the frequencies of the physical synchronizers of the production. The sensitivity analysis reveals the necessity of a better knowledge of the processes of biomass losses, which so far are uncertain, and may further vary in space and time.

Transvaginal versus transabdominal Doppler auscultation of fetal heart activity: a comparative study.

OBJECTIVE: Our purpose was to determine whether transvaginal Doppler auscultation is more sensitive than transabdominal auscultation for the detection of fetal heart rate in the first trimester of pregnancy. STUDY DESIGN: In a prospective study 141 patients between 6 weeks and 11 weeks 6 days of gestation underwent both transvaginal and transabdominal Doppler evaluation by use of continuous-wave Doppler instruments for detection of fetal heart rate. Transvaginal ultrasonography was used as the gold standard to establish fetal cardiac activity and to help assign gestational age. The two methods of auscultation were compared for accuracy in different gestational age ranges. Sensitivities and specificities were calculated, and associations were investigated with chi 2 analysis. The direction of disagreement between modalities was tested with the McNemar chi 2 test. RESULTS: Transvaginal auscultation outperformed transabdominal auscultation in every gestational age range. Transvaginal Doppler auscultation performed significantly better than transabdominal Doppler auscultation at 8 weeks to 8 weeks 6 days (p < or = 0.004) and 9 weeks to 9 weeks 6 days (p < or = 0.006). In pregnancies with cardiac activity, fetal heart rate can be successfully detected transvaginally in 60.5% of pregnancies at 8 weeks to 8 weeks 6 days and in 87.5% of pregnancies at 9 weeks to 9 weeks 6 days of gestation. This compares with successful transabdominal detection rates of 22.9% and 56% at 8 and 9 weeks, respectively. As gestational age advances both methods became increasingly sensitive for the detection of fetal heart rate. The earliest fetal heart rate detected transvaginally was at 6 weeks 0 days of gestation compared with 7 weeks 0 days transabdominally. The transvaginal Doppler method was also more successful in detecting the fetal heart rate in women with a retroverted uterus (p < or = 0.01). CONCLUSION: By use of continuous-wave Doppler instrumentation, transvaginal auscultation is significantly better than transabdominal auscultation in detecting fetal heart rate between 8 weeks to 8 weeks 6 days and 9 weeks to 9 weeks 6 days of gestation. Use of transvaginal auscultation has potential in the evaluation of first-trimester fetal cardiac activity.

The clinical implications of subchorionic placental lucencies.

Forty-six patients were identified at a perinatal diagnostic referral center as having subchorionic placental lucencies. These lucencies varied from simple to multicystic and covered up to 50% of the subchorionic placental surface. Clinical follow-up of 40 patients demonstrated no increase in the incidence of adverse pregnancy outcome. We conclude that these pregnancies are not at higher risk when the subchorionic placental lucencies are not associated with other intraplacental or fetal anomalies.