scholarly journals Seasonal distribution of nutrients and primary productivity on the eastern continental shelf of Venezuela as influenced by the Orinoco River

1993 ◽  
Vol 98 (C2) ◽  
pp. 2245-2257 ◽  
Author(s):  
Jaime Bonilla ◽  
William Senior ◽  
John Bugden ◽  
Oliver Zafiriou ◽  
Ronald Jones
Keyword(s):  
Continental Shelf ◽  
Primary Productivity ◽  
Seasonal Distribution ◽  
Orinoco River

scholarly journals Seasonal Distribution of Nutrients and Primary Productivity on the Eastern Continental Shelf of Venezuela as Influenced by the Orinoco River

2016 ◽  
Author(s):  
JAIME BONILLA ◽  
William James Senior
Keyword(s):  
Continental Shelf ◽  
Primary Productivity ◽  
Coastal Upwelling ◽  
Nutrient Status ◽  
Dry Season ◽  
Wet Season ◽  
Orinoco River ◽  
Carbon 14 ◽  
Low Salinity ◽  
The Caribbean

Nitrogenous nutrients, dissolved silicate, and salinity were measured in surface waters and shallowhydrocasts along similar cruise tracks during the spring (dry season) and fall (wet season) of 1988. Bothcruises transected the eastern Caribbean, transited the Gulf of Paria, ran parallel to the Orinoco Deltaand into the main channel of the Orinoco River. Trends in primary productivity were also measuredby daily carbon 14 incubations. In both seasons, samples covered the range from highly oligotrophicand transparent to highly productive and rich in biogenic and abiogenic particulate matter. Most of theOrinoco outflow appears to turn N to NW and remains in shallow waters off Venezuela andsurrounding Trinidad, permitting benthic regeneration of river-borne nutrients. However, the role ofthe Orinoco and associated low-salinity coastal waters in fertilizing large areas of the easternCaribbean basin, as suggested by satellite imagery, can be approximated crudely from the nutrientcomposition at Boca de Dragon, which is representative of the nutrient status of these waters as theyflow into deeper Caribbean waters. Additional nutrients may be supplied to the area primarily fromAmazon-derived water entering the Caribbean Basin further north, with some coastal upwelling alongthe continental shelf in the dry season.

scholarly journals Distribution of paracalanidae species (Copepoda, Crustacea) in the continental shelf off Sergipe and Alagoas States, Northeast Brazil

2006 ◽  
Vol 54 (4) ◽  
pp. 173-181 ◽  
Author(s):  
Hortência Maria Pereira Araujo
Keyword(s):  
Continental Shelf ◽  
Rainy Season ◽  
Environmental Variables ◽  
Dominant Species ◽  
Seasonal Distribution ◽  
Northeast Brazil ◽  
Oceanic Water ◽  
Density Values ◽  
Oceanic Species ◽  
Parvocalanus Crassirostris

The spatial and seasonal distribution of the Paracalanidae species were studied in eighteen stations in the continental shelf off Sergipe and Alagoas States, northeast Brazil, in December, 2001 and 2003, and in June, 2002 and 2003. The Paracalanidae family was constituted by coastal and shelf species such as Parvocalanus crassirostris, Paracalanus quasimodo, P. indicus and P. aculeatus and oceanic species, Calocalanus pavo and Acrocalanus longicornis. Density values were higher in stations located at 10 m isobath with respect to those located at 20 and 30 m depths. Paracalanidae abundance presented differences between seasons with values higher in June (2002, 2003) than in December (2001, 2002). All species were more abundant in the rainy season except Parvocalanus crassirostris. Paracalanus quasimodo was the dominant species with average densities of 949, 740 and 41 ind.m-3 in December months and 4231, 2389 and 1185 ind.m-3 in June months, at stations with local depths of 10, 20 and 30 m, respectively. Canonical correspondence analysis showed that salinity and temperature were the environmental variables that presented significant correlation with the distribution of Paracalanidae species, probably because these variables are influenced by the estuarine waters and by the dynamic of oceanic water masses in the continental shelf.

scholarly journals Size and sex composition of two species of the genus Atlantoraja (Elasmobranchii, Rajidae) caught by the bottom trawl fisheries operating on the Uruguayan continental shelf (southwestern Atlantic Ocean)

2011 ◽  
Vol 59 (4) ◽  
pp. 357-364 ◽  
Author(s):  
Luis Orlando ◽  
Ines Pereyra ◽  
Laura Paesch ◽  
Walter Norbis
Keyword(s):  
Continental Shelf ◽  
Significant Variation ◽  
Length Distribution ◽  
Seasonal Distribution ◽  
Size At Maturity ◽  
Southwestern Atlantic ◽  
Spatial And Seasonal Variation ◽  
Southwestern Atlantic Ocean ◽  
Trawl Fisheries ◽  
Size And Sex Composition

In this work we analyzed the spatial and seasonal variation of length distribution, sexual proportion and mature dominance for Atlantoraja cyclophora and A. castelnaui, at the Uruguayan continental shelf. There were significant differences in total length (TL) composition between sexes, being females bigger than males for both species. Atlantoraja cyclophora showed a relatively uniform length distribution between inner and outer shelf. There were no major variations in the sex compositions and in the mature dominance between seasons, suggesting no temporal variation. Atlantoraja castelnaui showed a significant variation in its spatial and seasonal distribution. Individuals were smaller in inner shelf, pointing out the existence of juvenile zone in areas up to 50 m depth. A tendency to capture smaller individuals towards the end of the year was observed. In all seasons over 50% of females were caught below the estimated size at maturity, suggesting that this species is highly susceptible to exploitation.

Spatial and seasonal distribution of eggs and larvae of sandy sprat, Hyperlophus vittatus (Clupeidae), off south-western Australia

1996 ◽  
Vol 47 (8) ◽  
pp. 971 ◽  
Author(s):  
DJ Gaughan ◽  
WJ Fletcher ◽  
RJ Tregonning
Keyword(s):  
Continental Shelf ◽  
Western Australia ◽  
Surf Zone ◽  
Temporal Distribution ◽  
Seasonal Distribution ◽  
Spawning Season ◽  
Marine Waters ◽  
Spawning Areas ◽  
Spatio Temporal ◽  
Eggs And Larvae

Ichthyoplankton surveys were employed to determine the distribution and spawning season of Hyperlophus vittatus off south-western Australia. Eggs and larvae of H. vittatus were sampled with 500-μm-mesh bongo-nets monthly during 1992, and less regularly during 1993, close to the beach and at 5.5 and 11 km offshore in four areas within the region of the fishery. The spatio-temporal distribution and abundance of eggs indicates that H. vittatus spawns in nearshore marine waters from May to September, with a peak in June and July. Larvae were rarer and less abundant than the eggs and therefore were less reliable indicators of spawning areas and season. Samples taken along transects across the continental shelf in July of both 1993 and 1994 indicated that H. vittatus did not spawn further than 14 km from the coast. Samples taken in July 1994 just beyond the surf zone at beaches, and at corresponding sites 5.5 km offshore, at 3.7-km intervals along 150 km of coastline indicated that H. vittatus spawns throughout the distribution of the fished stock off south-westem Australia.

scholarly journals The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

2015 ◽  
Vol 12 (21) ◽  
pp. 17781-17816
Author(s):  
D. R. Clark ◽  
C. E. Widdicombe ◽  
A. P. Rees ◽  
E. M. S. Woodward
Keyword(s):  
Continental Shelf ◽  
Primary Productivity ◽  
Mixed Layer Depth ◽  
Nutrient Concentrations ◽  
New Production ◽  
Phytoplankton Productivity ◽  
Upwelling System ◽  
Upwelled Water ◽  
Shelf Slope ◽  
N Assimilation

Abstract. The lagrangian progression of biogeochemical processes was followed in a filament of the Mauritanian upwelling system, North West Africa, during offshore advection. Inert duel tracers sulphur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical and chemical characteristics were measured including phytoplankton productivity, nitrogen assimilation and regeneration. Freshly upwelled water contained high nutrient concentrations (NO3− = 9.0 ± 0.1 μmol L−1; PO43− = 0.7 ± 0.1 μmol L−1; Si = 2.7 ± 0.1 μmol L−1) but was depleted in N compared to Redfield stoichiometry (N:P = 13.9:1). A maximum primary productivity rate of 0.7 mol C m−2 d−1 was measured on the continental shelf, associated with N-assimilation rates of 43.8 nmol L−1 h−1 for NO3−, 32.8 nmol L−1 h−1 for NH4+ and a phytoplankton community dominated by diatoms and flagellates. Indicators of phytoplankton abundance and activity decreased as the labelled water mass transited the continental shelf slope into deeper water, possibly linked to the mixed layer depth exceeding the light penetration depth. By the end of the study, primary productivity rates of 0.1 mol C m−2 d−1 were measured, associated with N-assimilation rates of 3.9 nmol L−1 h−1 for NO3−, 6.1 nmol L−1 h−1 for NH4+ and lower nutrient concentrations (NO3− = 4.6 ± 0.3 μmol L−1; PO43− = 0.4 ± 0.1 μmol L−1; Si = 0.9 ± 0.1 μmol L−1). Nitrogen regeneration and assimilation took place simultaneously; NH4+ was regenerated at 9.4–85.0 nmol L−1 h−1; NH4+ was oxidised at 0.30–8.75 nmol L−1 h−1; NO2− was oxidised at 25.55–81.11 nmol L−1 h−1. Results highlight the importance of regenerated NH4+ in sustaining phytoplankton productivity and indicate that the upwelled NO3− pool contained an increasing fraction of regenerated NO3− as it advected offshore. By calculating this fraction and incorporating it into an f ratio formulation we estimated that of the 12.38 Tg C of annual regional production, 4.73 Tg C was exportable.

Sign in / Sign up

Export Citation Format

Share Document