Biologie de Penaeus duorarum en Côte d'Ivoire. 3. Étude des variations quotidiennes des rendements et leur relations avec l'hydroclimat. Essai de généralisation au Golfe de Guinée

Hydroclimatic conditions in the Gulf of Guinea between Senegal and Nigeria are briefly described emphasizing the seasonal variations of transparency. Analysis of the Abidjan based shrimp fleet allowed to the description of the seasonal variations of activity rhythms for Côte d'Ivoire, Ghana, and Nigeria. These rhythms are different between seasons, between fishing grounds, and sometimes even between depths on a given ground. These variations follow the turbidity ones. Diurnal activity is observed in very turbid waters, nocturnal and transition activity in clearer ones. The authors assume that the basic behaviour is a nocturnal one, but that the shrimp-trawlers catches reflect some apparently different ones resulting from diel variations in the stock availability. To explain the apparently diurnal behaviour observed most of the year over the whole Gulf of Guinea it is suggested that these generally benthic shrimps become nectonic at night when turbidity is very high. The results obtained in Ivory Coast, Ghana and Nigeria are compared to those from Senegal where hydroclimatic conditions are different. The similarities are emphasized. The differences in observed behaviour are supposedly caused by the cold season water temps which are sufficiently low to disturb the nor mal activity rhythm.

Seasonal variation in the chemical composition of pomfrets. Pt. 1. Black pomfret (Parastromateus niger)

Seasonal variations in proximate composition of the different parts such as head, middle, tail and skin of black pomfret (Parastromateus niger) are reported over three years on monthly basis. The lean and fatty conditions of fish are discussed on the basis of spawning period, food and feeding activity, size group appearance and the gonadal maturity of the pomfret.

Seasonal variability in penaeid prawn larval abundance in the Mandovi and Zuari estuaries, Goa

Seasonal variations in the occurrence and abundance of penaeid prawn larvae in the Mandovi and Zuari estuaries of Goa were studied. Larvae and post-larvae of commercially important species viz. Metapenaeus dobsoni (Miers), M.affinis (H. Milne Edwards). M. Monoceros (Fabricius), Penaeus merguiensis de Man and Parapenaeopsis stylifera (H. Milne Edwards) were recorded in that order of abundance. Protozoea and mysis stages were dominant in surface zooplankton collections while the post-larvae were more in the bottom samples. Based on larval density, M. dobsoni appeared to be a continuous breeder. The active spawning periods in other species were during the late post-monsoon and pre-monsoon seasons varying with the species. Peak recruitment of post-larvae in the estuaries was observed mostly during southwest monsoon months (June to September). Penaeid prawn larval ingression was more in the Zuari estuary compared to the Mandovi estuary. Their numerical abundance gradually decreased towards the upstream areas. The feasibility of large scale collection of penaeid prawn larvae for aquaculture is indicated.

Salinity and temperature variations of the surface waters in the Jaffna Lagoon

Salinity and temperature in the sea surface of the Jaffna Lagoon were observed from August 1967 to July 1968. Peak surface temperatures were recorded during April and the lowest temperature recorded was in December. The seasonal variations of surface temperature closely followed a similar pattern in all locations of the lagoon. Salinity values in the lagoon surface were very high during the period from May to August and were relatively low during the period from October to December. Monsoon, rainfall, exchange of water between the lagoon and the sea and within the lagoon, and the currents in the Palk Bay might have been the factors which influenced the salinity structure of the surface waters of the lagoon during this period.

Stable isotope variations in particulate organic matter and a planktivorous fish in the Yangtze River

Temporal and spatial changes in delta(13) C and delta 15 N of particulate organic matter (POM) and Hemiculter leucisculus were studied in the Yangtze River of China. Isotopic signatures of POM showed seasonal variations, which was assumed to be associated with allochthonous organic input and autochthonous phytoplankton growth. delta C-13 of H. leucisculus was 1.1 % higher than that of POM, which suggested that the food source of H. leucisculus was mostly from the POM. A mass balance model indicated the trophic position of H. leucisculus in the food web of Yangtze River was estimated to be 2.0 - 2.1, indicating that this fish mainly feeds on planktonic organic matter, which agreed with previous gut content analysis.

Seasonal variation of virioplankton in a eutrophic shallow lake

Lake Donghu is a typical eutrophic freshwater lake in which high abundance of planktonic viruses was recently revealed. In this study, seasonal variation of planktonic viruses were observed at three different trophic sites, hypertrophic, eutrophic, and mesotrophic regions, and the correlation between their abundances and other aquatic environmental components, such as bacterioplankton, chlorophyll a, burst size, pH, dissolved oxygen, and temperature, was analyzed for the period of an year. Virioplankton abundance detected by transmission electron microscope (TEM) ranged from 5.48 x 10(8) to 2.04 x 10(9) ml(-1) in all the sites throughout the study, and the high abundances and seasonal variations of planktonic viruses were related to the trophic status at the sampled sites in Lake Donghu. Their annual mean abundances were, the highest at the hypertrophic site (1.23x10(9) ml(-1)), medium at the eutrophic site (1.19x10(9) ml(-1)), and the lowest at the mesotrophic site (1.02x10(9) ml(-1)). The VBR (virus-to-bacteria ratio) values were high, ranging from 49 to 56 on average at the three sampled sites. The data suggested that the high viral abundance and high VBR values might be associated with high density of phytoplankton including algae and cyanobacteria in this eutrophic shallow lake, and that planktonic viruses are important members of freshwater ecosystems.

Spatial and temporal variations of sound speed at the PN section

Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone. Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance are almost equivalent.

Circulation in the western tropical Pacific Ocean and its seasonal variation

An assimilation data set based on the GFDL MOM3 model and the NODC XBT data set is used to examine the circulation in the western tropical Pacific and its seasonal variations. The assimilated and observed velocities and transports of the mean circulation agree well. Transports of the North Equatorial Current (NEC), Mindanao Current (MC), North Equatorial Countercurrent (NECC) west of 140degreesE and Kuroshio origin estimated with the assimilation data display the seasonal cycles, roughly strong in boreal spring and weak in autumn, with a little phase difference. The NECC transport also has a semi-annual fluctuation resulting from the phase lag between seasonal cycles of two tropical gyres' recirculations. Strong in summer during the southeast monsoon period, the seasonal cycle of the Indonesian throughflow (ITF) is somewhat different from those of its upstreams, the MC and New Guinea Coastal Current (NGCC), implying the monsoon's impact on it.

Seasonal and spatial variation in abundance and egg production of Paracalanus parvus (Copepoda: Calanoida) in/out Jiaozhou Bay, China

The spatial distribution of stage-specific abundance and reproduction of the copepod Paracalanus parvus were studied from October 2005 to September 2006 in the Jiaozhou Bay. This copepod occurred continuously in this bay throughout the year. The species reached the lowest abundance in April and peaked in June. From October to December, distribution center mainly occurred in offshore water and at the mouth of the bay. In winter, early copepodites and adults gradually decreased and till February, most of the population was only comprised of CIV-CV stages. Overwintering copepodites matured in March and males tended to mature before female. From May to September, each stage occurred in the population and gradually reached high abundance. Temperature and chlorophyll a (Chl-a) concentration in the three stations can't clearly explain the seasonal variation in stage-specific abundance, so we surmised the important effect of the Yellow Sea. Egg production rate (EPR) reached its lowest in winter and peaked in June at 60.8 eggs female(-1) day(-1) in nearshore water. In the warming period, EPR in nearshore water was statistically higher and EPR > 10 eggs female(-1) day(-1) lasted longer than that in offshore water, showing the importance of nearshore water for recruitment of R parvus. Our study showed that EPR was positively related to temperature and total chlorophyll a in offshore water and mouth of the bay. In nearshore water, the relationships between EPR and temperature and Chl-a in three size fractions were not the same as those in offshore water, suggesting complicated ecosystem in such a eutrophic area in warming period. (C) 2008 Elsevier Ltd. All rights reserved.

Physical controls on the seasonal migration of the North Pacific transition zone chlorophyll front

The large seasonal migration of the transition zone chlorophyll front (TZCF) is of interest because a number of marine fauna, both commercial and endangered, appear to track it. Herein we examine the physical dynamics driving this seasonal migration of the TZCF. Vertical processes, traditionally viewed as controlling the dynamical supply of nutrients to surface waters, prove insufficient to explain seasonal variations in nutrient supply to the transition zone. Instead, we find that the horizontal Ekman transport of nutrients from higher latitudes drives the TZCF's southward migration. The estimated horizontal transport of nitrate supports up to 40% of new primary productivity in the region annually and nearly all of new primary productivity in the winter. The significance of horizontal advection to the North Pacific transition zone supports revising the paradigm that nutrients are supplied to surface waters from below. © 2010 by the American Geophysical Union.

Seasonal Sedimentation Of Phytoplankton To The Deep-Sea Benthos

Until recently the deep sea was considered to be a particularly stable environment1, free from seasonal variations. However, atmospheric storms may cause periodicity in deep-ocean currents2 and nepheloid layers3 while seasonality in the particulate flux to the deep sea is known to occur in the Sargasso Sea4,5 and Panama Basin6. Evidence is presented here of a similar seasonal pulse of detrital material to bathyal and abyssal depths in temperate latitudes; this material seems to be derived directly from the surface primary production and to sink rapidly to the deep-sea benthos. Considerable sedimentation occurs soon after the spring bloom and continues throughout the early summer. This process acts as a pathway for the descent of carbon from the euphotic zone, providing a periodic food source for the deep pelagic and benthic communities.

Seasonal variability of fine-sediment in the Tamar estuary

Measurements describing the intratidal, spring-neap and seasonal variations of fine, cohesive, suspended particulate matter (SPM) concentrations at two sites (Calstock and Halton Quay) within the upper reaches of the Tamar Estuary, UK, are presented. The data were obtained using two, near-bed instrument packages. Correlations of daily-averaged SPM concentrations and fluxes with both runoff and tidal range during the separate deployments often showed a significant dependence on these variables. Where statistically significant, increasing tidal range led to enhanced SPM levels because of resuspension of bed sediments.

Ecological comparative study of the rock-rose scrubs of Madrid, II. Soil-pH seasonal fluctuation

During twao years soil and litter pH of 31 permanent plots grown by several rock-rose scrubs (jarales) of Cistion laurifolii at different dynamic stages have been measured. Acidily records show the existence of important seasonal variations and according to a certain rythm. The different syntaxa are characterized as for this ecological factor and the results for these matorrals are compared with other data of heath-scrubs. Adult jaral-phases tend to decrease soil pH when compared with younger dwarf-scrubs-phases, nevertheless upper soil levels generally remain less acidic. Multivariable analysis do not show preference of t he different syntaxa for a certain soil-pH range.

Seasonal and geographical differences in aflatoxin exposures in Senegal

The aim of the study was to determine the geographical and seasonal variations in aflatoxin dietary exposure levels in adults from Senegal. A total of 168 adults (50% male) were recruited from three districts: Nioro du Rip (n=90), located in the Sudan Savannah agro-ecological zone where rainfall is sufficient for groundnut growth; Saint-Louis (n=40) and Mboro (n=38), located in the Sahel zone where groundnuts are produced under irrigated conditions. Diet information and samples were collected at groundnut harvest and post-harvest seasons. Plasma aflatoxin-albumin adducts (AF-alb) and total aflatoxin in household groundnut samples were measured by ELISA and a quantitative thin layer chromatography method, respectively. The blood AF-alb geometric mean was 45.7 pg/mg albumin (range 5.5-588.2 pg/mg). Nioro du Rip had a higher AF-alb level at harvest than Saint-Louis and Mboro (80.0 vs 15.6 and 33.3 pg/mg, P<0.001). Similar trends were observed at post-harvest (P<0.05). Seasonal trends were not consistent across the districts as Nioro du Rip had a higher AF-alb level at harvest than post-harvest (80.0 vs 58.6 pg/mg, P=0.026), whereas Saint-Louis had a higher level at post-harvest than harvest (25.6 vs 15.6 pg/mg, P=0.032). It is clear that aflatoxin exposure is prevalent in adults from Senegal and that season and geographical location are strong determinants of aflatoxin exposure.

Time-lapse monitoring of fluid induced geophysical property variations within an unstable earthwork using P-wave refraction

A significant portion of the UK’s transportation system relies on a network of geotechnical earthworks (cuttings and embankments) that were constructed more than 100 years ago, whose stability is affected by the change in precipitation patterns experienced over the past few decades. The vulnerability of these structures requires a reliable, cost- and time-effective monitoring of their geomechanical condition. We have assessed the potential application of P-wave refraction for tracking the seasonal variations of seismic properties within an aged clay-filled railway embankment, located in southwest England. Seismic data were acquired repeatedly along the crest of the earthwork at regular time intervals, for a total period of 16 months. P-wave first-break times were picked from all available recorded traces, to obtain a set of hodocrones referenced to the same spatial locations, for various dates along the surveyed period of time. Traveltimes extracted from each acquisition were then compared to track the pattern of their temporal variability. The relevance of such variations over time was compared with the data experimental uncertainty. The multiple set of hodocrones was subsequently inverted using a tomographic approach, to retrieve a time-lapse model of VPVP for the embankment structure. To directly compare the reconstructed VPVP sections, identical initial models and spatial regularization were used for the inversion of all available data sets. A consistent temporal trend for P-wave traveltimes, and consequently for the reconstructed VPVP models, was identified. This pattern could be related to the seasonal distribution of precipitation and soil-water content measured on site.