Productivity of dinoflagellate blooms on the west coast of South Africa, as measured by natural fluorescence

The biomass and productivity of phytoplankton populations inshore on the west coast of South Africa were investigated towards the end of the upwelling season, a period when high-biomass dinoflagellate blooms arecommon. Productivity was estimated from natural fluorescence measurements (PNF), using photosynthesis (P) v. irradiance (E) relationships (PE) and by means of the in situ 14C-method (PC). A linear regression of PNF productivity against PC and PE productivities yielded a slope of 0.911 and an r2 of 0.83 (n = 41). Physical and biological variability was high inshore, reflecting alternating periods of upwelling and quiescence. Mean chlorophyll inshore (within a 12 m water column) ranged from 0.7 to 57.8 (mean = 8.9) mg.m-3, mean PNF productivity ranged from 8.4 to 51.0 (mean = 24.6) mgC.m-3.h-1 and daily integral PNF productivity from 0.8 to 4.8 (mean = 2.3) gC.m-2.day-1. Transects sampled during active and relaxation phases of upwelling had different chlorophyll distributions. High chlorophyll concentrations (sometimes >50 mg.m-3) were associated with surface blooms within the region of the upwelling front. Estimates of daily water-column PNF productivity within these frontal blooms ranged from 4.0 to 5.6 gC.m-2.day-1. With relaxation of wind stress, blooms dominated by dinoflagellates flooded shorewards and often formed red tides. Chlorophyll concentrations of>175 mg.m-3 and productivity rates > 500 mgC.m-3.h-1 and 12 gC.m-2.day-1 were measured during a particularly intense red tide. Offshore, the water column was highly stratified with a well-defined subsurface chlorophyll maximum layer within the pycnocline region. Estimates of daily water-column PNF productivity ranged from2.4 to 4.0 gC.m-2.day-1 offshore. The high productivity of shelf waters on the West Coast in late summer can be ascribed largely to dinoflagellate populations and their success in both upwelling systems and stratified conditions

Seasonal changes in phytoplankton biomass on the Western Agulhas bank, South Africa

Data on temporal and spatial changes in phytoplankton biomass and distribution on the western Agulhas Bank during the main spawning season of pelagic fish were obtained from monthly cruises conducted betweenAugust and March in 1993/94 and September and March in 1994/95. The period was divided into three oceanographic seasons based on different levels of upwelling activity: late winter (August and September), spring(October–December) and summer (January–March). Cross-shelf and vertical distribution patterns of chlorophyll changed markedly during these seasonal periods, reflecting changes in hydrographic structure and in nutrient availability. During late winter, chlorophyll was evenly distributed in the deep, upper-mixed layer (>40 m) across the shelf. A clump-forming Thalassiosira sp. contributed to the moderately high mean chlorophyllconcentration (1.9 mg·m–3) in the upper 30 m. In October and/or September, warming of surface waters inshore gave rise to a modest (2–5 mg chl·m–3) spring bloom, typical of the temperate zone. This was terminated in November by an influx across the shelf of warm, nutrient-impoverished water. Upwelling was sporadic and weak in spring. Summer was characterized by intense, episodic upwelling inshore, with pronounced cross-shelf thermal gradients, intensified by the presence of water of Agulhas origin along the shelf-edge. During an upwelling cycle, rapid hydrographic and biological changes occur over four phases: onset of upwelling, sustained upwelling, quiescence and downwelling. The upwelling productive zone, bounded by the 20°C isotherm, varied fro

Identification and classification of vertical chlorophyll patterns in the Benguela upwelling system and Angola-Benguela front using an artificial neural network

Information on the vertical chlorophyll structure in the ocean is important for estimating integrated chlorophyll a and primary production from satellite. For this study, vertical chlorophyll profiles from the Benguela upwelling system and the Angola-Benguela front were collected in winter to identify characteristic profiles. A shifted Gaussian model was fitted to each profile to estimate four parameters that defined the shape of the curve: the background chlorophyll concentration (B0), the height parameter of the peak (h), the width of the peak (&#963) and the depth of the chlorophyll peak (zm). A type of artificial neural network called a self-organizing map (SOM) was then used on these four parameters to identify characteristic profiles. The analysis identified a continuum of chlorophyll patterns, from those with large surface peaks (>10 mg m-3) to those with smaller near-surface peaks

The effect of sea temperature and food availability on the spawning success of Cape Anchovy engraulis capensis in the Southern Benguela

Data on the thermal structure, copepod biomass and production, and total number of eggs of the Cape anchovy Engraulis capensis were obtained from monthly surveys during the periods August 1993 – March1994 and September 1994 – March 1995 on the western Agulhas Bank and off the South-Western Cape, South Africa. Previous work suggested that anchovy spawn on the western Agulhas Bank in temperaturesbetween 16 and 19°C, where they feed predominantly on copepods. This study shows that the western Bank is a more suitable spawning area for anchovy, having greater thermal stability, a larger area of 16–19°Cwater and a more consistent food environment than off the South-Western Cape. Also, copepod production on the western Bank was highest in 16–19°C water. To identify factors controlling the area of this watermass, a cluster analysis was used on a suite of hydrographic variables. Three periods were identified: winter (August-September), spring (October-December) and summer (January-March), reflecting changes in theextent of the 16–19°C water and anchovy spawning, both of which peaked during spring. Spring was further characterized by infrequent surface upwelling. During summer, upwelling frequently reached the surface andthe upwelling front migrated offshore, constricting the area of 16–19°C water. It is hypothesized that spawning success in anchovy is dependent upon the extent of suitable spawning habitat, both spatially (16–19°Cwater) and temporally (spring). To put this concept into a predictive framework, the number of anchovy eggs was regressed against the area of 16–19°C water; a significant, positive relationship (p < 0.001, r2 = 0.56, n = 17) was found. An implication of the hypothesis is that the duration of spawning may be important to recruitment

Towards screening Barrett’s Oesophagus: current guidelines, imaging modalities and future developments

Barrett’s oesophagus is the only known precursor to oesophageal adenocarcinoma (OAC). Although guidelines on the screening and surveillance exist in Barrett’s oesophagus, the current strategies are inadequate. Oesophagogastroduodenoscopy (OGD) is the gold standard method in screening for Barrett’s oesophagus. This invasive method is expensive with associated risks negating its use as a current screening tool for Barrett’s oesophagus. This review explores current definitions, epidemiology, biomarkers, surveillance, and screening in Barrett’s oesophagus. Imaging modalities applicable to this condition are discussed, in addition to future developments. There is an urgent need for an alternative non-invasive method of screening and/or surveillance which could be highly beneficial towards reducing waiting times, alleviating patient fears and reducing future costs in current healthcare services. Vibrational spectroscopy has been shown to be promising in categorising Barrett’s oesophagus through to high-grade dysplasia (HGD) and OAC. These techniques need further validation through multicentre trials

Seasonal changes in phytoplankton biomass on the western Agulhas Bank, South Africa

Data on temporal and spatial changes in phytoplankton biomass and distribution on the western Agulhas Bank during the main spawning season of pelagic fish were obtained from monthly cruises conducted between August and March in 1993/94 and September and March in 1994/95. The period was divided into three oceanographic seasons based on different levels of upwelling activity: late winter (August and September), spring (October-December) and summer (January-March). Cross-shelf and vertical distribution patterns of chlorophyll changed markedly during these seasonal periods, reflecting changes in hydrographic structure and in nutrient availability. During late winter, chlorophyll was evenly distributed in the deep, upper-mixed layer (>40 m) across the shelf. A clump-forming Thalassiosira sp. contributed to the moderately high mean chlorophyll concentration (1.9 mg.m(-3)) in the upper 30 m. In October and/or September, warming of surface waters inshore gave rise to a modest (2-5 mg chl.m(-3)) spring bloom, typical of the temperate zone. This was terminated in November by an influx across the shelf of warm, nutrient-impoverished water. Upwelling was sporadic and weak in spring. Summer was characterized by intense, episodic upwelling inshore, with pronounced cross-shelf thermal gradients, intensified by the presence of water of Agulhas origin along the shelf-edge. During an upwelling cycle, rapid hydrographic and biological changes occur over four phases: onset of upwelling, sustained upwelling, quiescence and downwelling. The upwelling productive zone, bounded by the 20 degrees C isotherm, varied fro

The effect of sea temperature and food availability on the spawning success of Cape anchovy Engraulis capensis in the southern Benguela

Data on the thermal structure, copepod biomass and production, and total number of eggs of the Cape anchovy Engraulis capensis were obtained from monthly surveys during the periods August 1993 - March 1994 and September 1991 - March 1995 on the western Agulhas Bank and off the South-Western Cape, South Africa. Previous work suggested that anchovy spawn on the western Agulhas Bank in temperatures between 16 and 19 degreesC, where they feed predominantly on copepods. This study shows that the western Bank is a more suitable spawning area for anchovy, having greater thermal stability, a larger area of 16-19 degreesC water and a more consistent food environment than off the South-Western Caps. Also, copepod production on the western Bank was highest in 16-19 degreesC water. To identify factors controlling the area of this water mass, a cluster analysis was used on a suite of hydrographic variables. Three periods were identified: winter (August-September), spring (October-December) and summer (January March), reflecting changes in the extent of the 16-19 degreesC water and anchovy spawning, both of which peaked during spring. Spring was further characterized by infrequent surface upwelling. During summer, upwelling frequently reached the surface and the upwelling front migrated offshore, constricting the area of 16-19 degreesC water. It is hypothesized that spawning success in anchovy is dependent upon the extent of suitable spawning habitat, both spatially (16-19 degreesC water) and temporally (spring). To put this concept into a predictive framework, the number of anchovy eggs was regressed against the area of 16-19 degreesC water; a significant, positive relationship (p < 0.001, r(2) = 0.56, n = 17) was found. An implication of the hypothesis is that the duration of spawning may be important to recruitment