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Lamont T.,Oceans and Coastal Research | Lamont T.,University of Cape Town | Barlow R.G.,Bayworld Center for Research and Education | Barlow R.G.,University of Cape Town | Kyewalyanga M.S.,University of Dar es Salaam
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2014

Investigations of primary production (PP) were undertaken in the southern Benguela ecosystem during two research surveys in October 2006 and May 2007. Significant differences in environmental conditions, as well as biomass and PP, were observed between October and May. During October, integrated biomass and PP were significantly higher, ranging from 20.43 to 355.01mgm-2, and 0.71 to 6.98gCm-2d-1, respectively, than in May, where the range was 47.92-141.79mgm-2, and 0.70-3.35gCm-2d-1, respectively. Distribution patterns indicated low biomass and PP in newly upwelled water along the coast, higher biomass and PP in the mid-shelf region, while lower values were observed at and beyond the shelf edge. Latitudinal variations showed consistently higher biomass and PP in the St. Helena Bay region compared to biomass and PP south of Cape Town. During both surveys, phytoplankton communities were comprised primarily of diatoms and small flagellates, with no significant differences. Phytoplankton adaptation to environmental variability was characterised by increased Pm B and Ek under elevated temperatures and irradiance, while no clear relationships were evident for αB. Generalised Additive Models (GAMs) showed that photosynthetic parameters were all significant predictors of photosynthesis rates (Pz), with Pm B being the most important, accounting for 36.97% of the deviance in Pz. However, biomass levels and environmental conditions exerted a much greater influence on Pz, with irradiance explaining the largest proportion (68.24%) of the deviance. Multiple predictor GAMs revealed that 96.26% of the deviance in Pz could be explained by a model which included nitrate, chlorophyll a, and irradiance. © 2014 Elsevier Ltd.

Brewin R.J.W.,Plymouth Marine Laboratory | Brewin R.J.W.,National Center for Earth Observation | Sathyendranath S.,Plymouth Marine Laboratory | Sathyendranath S.,National Center for Earth Observation | And 7 more authors.
Remote Sensing of Environment | Year: 2015

Phytoplankton size structure is an important indicator of the state of the pelagic ecosystem. Stimulated by the paucity of in situ observations on size structure, and by the sampling advantages of autonomous remote platforms, new efforts are being made to infer the size-structure of the phytoplankton from oceanographic variables that may be measured at high temporal and spatial resolution, such as total chlorophyll concentration. Large-scale analysis of in situ data has revealed coherent relationships between size-fractionated chlorophyll and total chlorophyll that can be quantified using the three-component model of Brewin et al. (2010). However, there are variations surrounding these general relationships. In this paper, we first revise the three-component model using a global dataset of surface phytoplankton pigment measurements. Then, using estimates of the average irradiance in the mixed-layer, we investigate the influence of ambient light on the parameters of the three-component model. We observe significant relationships between model parameters and the average irradiance in the mixed-layer, consistent with ecological knowledge. These relationships are incorporated explicitly into the three-component model to illustrate variations in the relationship between size-structure and total chlorophyll, ensuing from variations in light availability. The new model may be used as a tool to investigate modifications in size-structure in the context of a changing climate. © 2015 Elsevier Inc.

Barlow R.,Bayworld Center for Research and Education | Barlow R.,University of Cape Town | Gibberd M.-J.,University of Cape Town | Lamont T.,University of Cape Town | And 3 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2016

Surface pigment data from a transect along the eastern boundary of the Atlantic Ocean was analysed using CHEMTAX to yield more detailed information on the composition of phytoplankton communities. Total chlorophyll a concentrations varied from 0.03 mg m-3 in a northern oligotrophic region to 30.3 mg m-3 in the Benguela ecosystem. Diatoms dominated the Benguela, while both diatoms and haptophytes were the major groups in the Canary ecosystem and the temperate NE Atlantic. Prochlorococcus was the most prominent group in the southern oligotrophic region (15.5°S-15°N) although haptophytes were also a significant component of the population. In contrast, haptophytes dominated the northern oligotrophic region (21°-40°N). Photo-pigment indices indicated that chlorophyll b was mainly associated with prasinophytes and chlorophyll c with diatoms. Elevated photosynthetic carotenoids were due to increased proportions of haptophytes, but also linked with diatoms and dinoflagellates. Photoprotective carotenoids were more prominently associated with Prochlorococcus and to a lesser extent to Synechococcus. © 2016 Elsevier Ltd.

Lamont T.,Oceans and Coastal Research | Lamont T.,University of Cape Town | Van Den Berg M.A.,Oceans and Coastal Research | Barlow R.G.,University of Cape Town | Barlow R.G.,Bayworld Center for Research and Education
Journal of Physical Oceanography | Year: 2016

The Agulhas Current is a fast western boundary current flowing along the South African east coast, strongly influencing oceanographic variability on the adjacent KwaZulu-Natal shelf. Hydrographic observations in January 2010, July 2010, and July 1989 have been used to describe variations in geostrophic currents and water masses and to elucidate mechanisms of change in circulation and thermohaline structure. Differences in wind forcing, precipitation, and solar insolation caused modifications in stratification and mixing that resulted in seasonal changes in surface temperature, salinity, and mixed layer depth ZMLD between the austral summer and winter surveys. During January 2010, surface temperatures were elevated and there was a large range in salinity as the upper 10 m was influenced by river outflow and rainfall. In July 2010 and 1989, surface temperatures were lower and the salinity range was significantly less. The ZMLD in January 2010 was much shallower, varying between 5 and 40 m, while deeper ZMLD, from 9 to 107 m, was found in July 2010 and 1989. Cross-shelf, alongshore, and vertical variations in water masses during July 2010 and July 1989 were driven by deviations in the position of the inshore edge of the Agulhas Current and the influence of offshore cyclonic eddies. In January 2010, the close proximity of the current to the coast and shelf break caused increased Ekman veering in the bottom layers along the shelf edge and slope in the north and recirculation in the south. © 2016 American Meteorological Society.

Vinas M.D.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Blanco-Bercial L.,University of Connecticut | Bucklin A.,University of Connecticut | Verheye H.,Oceans and Coastal Research | And 3 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2015

Calanoides carinatus sensu lato (s.l.) (Krøyer, 1848) is known to occur in the North and South Atlantic, Indian, and tropical western Pacific Oceans, and the Mediterranean Sea. In highly productive areas, this species may dominate the copepod biomass and occupy a pivotal position in the pelagic food webs that support commercial fisheries. Despite the species' ecological importance, its taxonomic status and biogeographic range are not certain. An international collaborative project was carried out to examine the molecular phylogeography and population genetics of C. carinatus of the Atlantic Ocean. A total of 55 specimens were identified from 13 samples collected from neritic populations of the SW (23°S-47°S), SE (16°S-34°S) and NE (11°N-44°N) Atlantic Ocean. A 708 base-pair (bp) region of the mitochondrial cytochrome c oxidase subunit I (mtCOI) gene was amplified. DNA sequences were trimmed to a final aligned length of 484bp for analysis. A parsimony haplotype network (constructed with TCS Ver. 1.2.1) had no shared haplotypes between the SE and SW Atlantic samples. In contrast, SE and NE Atlantic samples had broadly shared haplotypes, although several individuals from the NE Atlantic had very divergent haplotypes. Based on all samples analyzed, neutrality tests were both positive and significant (Tajima's D=2.374, p<0.05; Fu's FS=29.378, p<0.001) and haplotype diversity (Hd) was 0.81. NE and SE Atlantic samples were pooled for analysis (based on average pairwise Tamura-Nei distance between C. carinatus s.l. individuals=0.024). Between SW and NE/SE Atlantic populations, average pairwise distance=0.556 and ϕST=0.956 (p<0.0001). Phylogeographic analysis of mtCOI sequence variation indicates that C. carinatus s.l. comprises two genetically divergent and geographically distinct species. Since the type locality of the species is in Brazilian waters, we consider the SW Atlantic type to represent C. carinatus sensu stricto (s.s.), with a biogeographical range restricted to the SW Atlantic Ocean. Further, we consider the NE/SE Atlantic type to be an undescribed, cryptic sibling species. © 2015 Elsevier B.V.

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