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Trainer V.L.,National Oceanic and Atmospheric Administration | Pitcher G.C.,South African Department of Environmental Affairs and Tourism | Pitcher G.C.,University of Cape Town | Reguera B.,Spanish Institute of Oceanography | Smayda T.J.,University of Rhode Island
Progress in Oceanography | Year: 2010

Comparison of harmful algal bloom (HAB) species in eastern boundary upwelling systems, specifically species composition, bloom densities, toxin concentrations and impacts are likely to contribute to understanding these phenomena. We identify and describe HABs in the California, Canary, Benguela and Humboldt Current systems, including those that can cause the poisoning syndromes in humans called paralytic shellfish poisoning (PSP), diarrhetic shellfish poisoning (DSP), and amnesic shellfish poisoning (ASP), as well as yessotoxins, ichthyotoxins, and high-biomass blooms resulting in hypoxia and anoxia. Such comparisons will allow identification of parameters, some unique to upwelling systems and others not, that contribute to the development of these harmful blooms.


Pitcher G.C.,South African Department of Environmental Affairs and Tourism | Pitcher G.C.,University of Cape Town | Figueiras F.G.,CSIC - Institute of Marine Research | Hickey B.M.,University of Washington | Moita M.T.,Institute Investigacao das Pescas e do Mar IPIMAR
Progress in Oceanography | Year: 2010

The upwelling systems of the eastern boundaries of the world's oceans are susceptible to harmful algal blooms (HABs) because they are highly productive, nutrient-rich environments, prone to high-biomass blooms. This review identifies those aspects of the physical environment important in the development of HABs in upwelling systems through description and comparison of bloom events in the Benguela, California and Iberia systems. HAB development is dictated by the influence of wind stress on the surface boundary layer through a combination of its influence on surface mixed-layer characteristics and shelf circulation patterns. The timing of HABs is controlled by windstress fluctuations and buoyancy inputs at the seasonal, event and interannual scales. Within this temporal framework, various mesoscale features that interrupt typical upwelling circulation patterns, determine the spatial distribution of HABs. The inner shelf in particular provides a mosaic of shifting habitats, some of which favour HABs. Changes in coastline configuration and orientation, and bottom topography are important in determining the distribution of HABs through their influence on water stratification and retention. A spectrum of coastline configurations, including headlands, capes, peninsulas, Rías, bays and estuaries, representing systems of increasing isolation from the open coast and consequent increasing retention times, are assessed in terms of their vulnerability to HABs. © 2010 Elsevier Ltd. All rights reserved.


Gibbons M.J.,University of the Western Cape | Janson L.A.,South African Department of Environmental Affairs and Tourism | Ismail A.,University of the Western Cape | Samaai T.,South African Department of Environmental Affairs and Tourism
Journal of Biogeography | Year: 2010

Aim Using the genus as the unit of analysis, we examine the relationship between richness, distribution and life cycle strategy for all currently recognized marine Hydrozoa. Location The global marine environment. Methods A global dataset detailing the number of species per genus and the mean date of first description (as a proxy for geographic range size) per genus was assembled for all currently recognized marine Hydrozoa. Differences in means per genus were examined by dominant life cycle strategy (holoplanktic, meroplanktic and benthic) using nonparametric ANOVA and resampling methods. Results By comparison with benthic taxa, holopelagic genera are (on average) significantly less species rich and were described at a significantly earlier date. Taxa with meroplanktic life cycles have a richness and a date of first description that is mid-way between the two extremes. Main conclusions Following from previous work showing that there is a negative relationship between the date of first description and geographic range size, our data indicate that holopelagic taxa not only have fewer species per genus but also have a wider distribution than benthic taxa. These quantitative results are in agreement with long-standing intuitions, and should be applicable to other taxa. They run counter to some recent genetic observations that suggest taxa having planktic larvae might nevertheless show restricted distributions; we argue that this inference reflects a lack of sampling of holopelagic taxa, and a call is made to provide empirical evidence from this realm. © 2009 Blackwell Publishing Ltd.


von der Heyden S.,Stellenbosch University | Lipinski M.R.,South African Department of Environmental Affairs and Tourism | Matthee C.A.,Stellenbosch University
Molecular Phylogenetics and Evolution | Year: 2010

Cape hake, Merluccius paradoxus, is a valuable commercially exploited demersal species. Using the 5′ mtDNA control region we show that 96% of 1013 fishes sampled over a three-year period share one of two dominant haplotypes; 19 haplotypes were recovered in total, suggesting a genetically homogenous population of fish. Accordingly, haplotype and nucleotide diversities are low (h = 0.53, π = 0.0014); an asymptotic haplotype accumulation curve suggests that few additional haplotypes exist. Comparing h and π with other fish species shows that M. paradoxus and other southern African fish species have remarkably low genetic diversity values compared with other global marine fishes. Despite low genetic variability, frequency differences among M. paradoxus haplotypes suggest weakly structured populations between Namibia and South Africa. However, given the remarkably homogeneous mtDNA population genetic structure between fishes sampled along 1800 km, it is clear that faster evolving markers such a microsatellites are also needed before inferences can be made regarding stock identification and management of this species. © 2009 Elsevier Inc. All rights reserved.


Travers M.,IRD CRHMT | Watermeyer K.,University of Cape Town | Shannon L.J.,University of Cape Town | Shannon L.J.,South African Department of Environmental Affairs and Tourism | Shin Y.-J.,IRD CRHMT
Journal of Marine Systems | Year: 2010

Ecosystem models provide a platform allowing exploration into the possible responses of marine food webs to fishing pressure and various potential management decisions. In this study we investigate the particular effects of overfishing on the structure and function of the southern Benguela food web, using two models with different underlying assumptions: the spatialized, size-based individual-based model, OSMOSE, and the trophic mass-balance model, Ecopath with Ecosim (EwE). Starting from the same reference state of the southern Benguela upwelling ecosystem during the 1990s, we compare the response of the food web to scenarios of overfishing using these two modelling approaches. A scenario of increased fishing mortality is applied to two distinct functional groups: i) two species of Cape hake, representing important target predatory fish, and ii) the forage species anchovy, sardine and redeye. In these simulations, fishing mortality on the selected functional groups is doubled for 10 years, followed by 10 years at the initial fishing mortality. We compare the food web states before the increase of fishing mortality, after 10 years of overfishing and after a further 10 years during which fishing was returned to initial levels. In order to compare the simulated food web structures with the reference state, and between the two modelling approaches, we use a set of trophic indicators: the mean trophic level of the community and in catches, the trophic pyramid (biomass per discrete trophic level), and the predatory/forage fish biomass ratio. OSMOSE and EwE present globally similar results for the trophic functioning of the ecosystem under fishing pressure: the biomass of targeted species decreases whereas that of their potential competitors increases. The reaction of distant species is more diverse, depending on the feeding links between the compartments. The mean trophic level of the community does not vary enough to be used for assessing ecosystem impacts of fishing, and the mean trophic level in the catch displays a surprising increase due to the short period of overfishing. The trophic pyramids behave in an unexpected way compared to trophic control theory, because at least two food chains with different dynamics are intertwined within the food web. We emphasize the importance of biomass information at the species level for interpreting dynamics in aggregated indicators, and we highlight the importance of competitive groups when looking at ecosystem functioning under fishing disturbance. Finally, we discuss the results within the scope of differences between models, in terms of the way they are formulated, spatial dimensions, predation formulations and the representation of fish life cycles. © 2009 Elsevier B.V. All rights reserved.


Pichegru L.,Percy FitzPatrick Institute | Gremillet D.,CNRS Center of Evolutionary and Functional Ecology | Crawford R.J.M.,University of Cape Town | Crawford R.J.M.,South African Department of Environmental Affairs and Tourism | Ryan P.G.,Percy FitzPatrick Institute
Biology Letters | Year: 2010

No-take zones may protect populations of targeted marine species and restore the integrity of marine ecosystems, but it is unclear whether they benefit top predators that rely on mobile pelagic fishes. In South Africa, foraging effort of breeding African penguins decreased by 30 per cent within three months of closing a 20 km zone to the competing purse-seine fisheries around their largest colony. After the fishing ban, most of the penguins from this island had shifted their feeding effort inside the closed area. Birds breeding at another colony situated 50 km away, whose fishing grounds remained open to fishing, increased their foraging effort during the same period. This demonstrates the immediate benefit of a relatively small no-take zone for a marine top predator relying on pelagic prey. Selecting such small protected areas may be an important first conservation step, minimizing stakeholder conflicts and easing compliance, while ensuring benefit for the ecosystems within these habitats. © 2010 The Royal Society.


Hutchings K.,University of Cape Town | Griffiths M.H.,South African Department of Environmental Affairs and Tourism
African Journal of Marine Science | Year: 2010

Biological data for Umbrina robinsoni were obtained from fish sampled monthly during 2001-2002 by shore-angling in the warm-temperate De Hoop Marine Protected Area (MPA) (n = 312), and by means of spearfishing during three trips (May, September and January 2001-2002) in the Kosi Bay region of the subtropical Maputaland MPA (n = 354). Annuli in otolith sections were validated by means of marginal increment analyses and fluorochrome marking (oxytetracycline). Maximum ages recorded were 12 and 16 years at Kosi Bay and De Hoop respectively. Kosi Bay fish obtained a significantly greater asymptotic length than De Hoop fish and mean length-at-age (for ages 2-10 years) was significantly greater. The fitted von Bertalanffy growth equations for combined sexes were: Lt = 594 (1 - e-0.183 (t + 2.42)) for De Hoop and Lt = 875 (1 - e-0.151 (t + 2.49)) for Kosi Bay. Trends in mean monthly gonadosomatic indices and proportions of histologically validated macroscopic gonad stages indicated a summer spawning season (November-February) at De Hoop and year-round spawning at Kosi Bay. Relative condition peaked in both spring and autumn at De Hoop but showed little seasonal variation in the Kosi Bay region. Kosi Bay females attained 50% sexual maturity at a significantly larger size (48 vs 39 cm) but at younger age (2.8 vs 3.4 years) than those at De Hoop. Analysis of maturity schedules indicates that current sizes at maturity are plastic responses that maximise lifetime fecundity within local regimes of somatic growth and natural mortality. The instantaneous rate of natural mortality was substantially higher at Kosi Bay than at De Hoop (M = 0.35 vs M = 0.26). © NISC (Pty) Ltd.


Probyn T.A.,South African Department of Environmental Affairs and Tourism | Bernard S.,University of Cape Town | Pitcher G.C.,South African Department of Environmental Affairs and Tourism | Pienaar R.N.,University of Witwatersrand
Harmful Algae | Year: 2010

The detection of brown tide dominated by the pelagophyte Aureococcus anophagefferens in Saldanha Bay in 1997 was the first occurrence of such blooms outside the north-east coast of the USA. Repeated brown tides in a semi-isolated aquaculture facility in the bay have resulted in poor oyster yields during bloom periods threatening the economic viability of the farming venture. The dramatic economic and ecological consequences of brown tides in the USA initiated a considerable research effort for over two decades that has revealed a number of ecophysiological adaptations of Aureococcus proposed to confer an advantage over competing phytoplankton. The aim of the present study was to investigate certain physiological and ecological characteristics of natural brown tide assemblages to provide a comparison with findings from elsewhere. Investigations were conducted on a number of occasions between 1998 and 2003 during visible brown tide events in a semi-isolated oyster culture facility within Saldanha Bay. Microscope counts revealed that Aureococcus was the most abundant phytoplankton species present during these blooms amounting to 96.7% of total phytoplankton and other nanoplankton numbers. Size fractionated experiments confirmed that primary productivity was dominated by the <10 μm fraction (87.4%). Nitrogen (N) uptake rates based both on calculations from kinetic parameters and on direct measurements using 15N isotopes show reduced N as NH4 and urea to be far more important than oxidised N as NO3 (f-ratio between 0.04 and 0.24). Organic N as urea provided an important N resource for these brown tides. Uptake affinity estimated from the initial slope of the Michaelis-Menten equation did not reveal any marked preference for either N source; the small contribution from NO3 being dictated largely by low environmental concentrations. There was a marked separation of primary production and N uptake in the vertical such that C/N assimilation ratios ranged from 28.5 at the surface to 1.6 at depth. Depth integrated values more closely approximated the Redfield ratio. Studies investigating the effect of irradiance on primary productivity and N uptake were consistent with a low-light adapted species with light saturation parameters of 71-102 μmol m-2 s-1 for photosynthesis and 14-68 μmol m-2 s-1 for N uptake. Dark uptake of reduced N was in excess of 50% of maximum rates in the light. The findings of this study support the idea of a species well adapted to growth in turbid waters that are poor in dissolved inorganic nutrients, particularly as NO3, though with significant supplies of organic N. A salient characteristic of Saldanha Bay brown tides was the co-occurrence of a Chrysochromulina sp. that may have exerted some degree of grazing control over Aureococcus. © 2009 Elsevier B.V. All rights reserved.


Soule M.A.,Fisheries Resource Surveys Cc | Hampton I.,Fisheries Resource Surveys Cc | Lipinski M.R.,South African Department of Environmental Affairs and Tourism
ICES Journal of Marine Science | Year: 2010

Estimates of the target strength (TS) of the loliginid squid Loligo reynaudii at 120 kHz were made from ex situ experiments on 38 caged, but free-swimming animals, and at 38 and 120 kHz from 17 in situ experiments on spawning aggregations in the wild conducted from a research vessel and from small boats. The cage experiments suggested that the backscattering cross section is proportional to mantle length (ML), which would not be expected from simple considerations of ML in relation to wavelength. A similar relationship was found during the in situ experiments conducted from the research vessel. The TS estimates from the research vessel agreed well with those from the cage experiments, for both of the two methods used to extract squid TS distributions from the overall TS distributions, but were some 2-3 dB lower than those from the small boats. This suggests that in situ estimates are affected by the vessel and/or the way in which squid react to it. It is concluded that ex situ experiments on L. reynaudii TS are of most value as a complement to in situ experiments, which should be made concurrently while surveying, using systems capable of having higher volume resolution than in the current experiments, to maximize the applicability of the estimates to the survey data. © 2010 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.


Downey N.J.,South African Department of Environmental Affairs and Tourism | Roberts M.J.,South African Department of Environmental Affairs and Tourism | Baird D.,Stellenbosch University
ICES Journal of Marine Science | Year: 2010

Spawning aggregations of chokka squid are influenced by environmental conditions. Acoustic telemetry was used to monitor the behaviour of spawning squid in relation to environmental variability. During the November squid-fishery closed seasons of 2003-2006, hexagonal VR2 receiver arrays were moored on and around active spawning aggregations in Kromme Bay, South Africa. In all, 45 squid were tagged (V9P-6L-S256 transmitters) and released within these arrays. Three presence-absence behaviours were identified: (i) arrival on the spawning site at dawn and departure after dusk, (ii) continuous presence for a number of days, and (iii) presence interrupted by frequent but short periods of absence. Movement between spawning sites was both diurnal and nocturnal. Squid presence at the monitored sites increased after dawn and decreased towards and after dusk. Occasionally, a core aggregation of squid remained on the spawning sites at night. Temperature data at the sites indicated occasional upwelling, and although the role of temperature in the spawning process is not well understood, data suggest that it is linked to the continuation and or interruption of spawning after an aggregation has formed. The initial formation of spawning aggregations appears to be triggered by upwelling events. © 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.

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