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This study reports on the abundance, biomass and reproductive traits of Oncaea venusta , a common pelagic copepod in tropical oceans, in a coastal area influenced by bottom intrusions of the cold and nutrient-rich South Atlantic Central Water (SACW). In addition to O. venusta abundance and biomass, we estimated egg production and weight-specific fecundity rates by applying the egg-ratio method and incubation experiments, at monthly intervals over 3 years (July 2005–June 2008), to understand potential SACW influences on reproductive patterns. Mean abundance and biomass were low, and no differences were detected with and without SACW intrusions. Mean clutch size (±SD) was 65.1 ± 28.9 eggs female−1 and egg production rates averaged 7.6 ± 12.4 and 9.3 ± 5.2 eggs female−1 day−1 (viability >80%), for the egg-ratio method and incubation experiments, respectively, corresponding to a female weight-specific fecundity from 0.03 ± 0.05 to 0.04 ± 0.06 day−1. Oncaea venusta abundance and biomass were positively correlated with temperature, but no SACW influence on the reproductive rates was recorded. The egg production rate and the female weight-specific fecundity were influenced by the chlorophyll a concentration and the sex ratio. Although egg production and female weight-specific fecundity rates had peak values during intrusion events, no immediate impact on population abundance was observed within the same time interval. [ABSTRACT FROM AUTHOR]

The inner shelf waters off Southeastern Brazil are periodically enriched by bottom intrusions of the cold and nutrient-rich South Atlantic Central Water ( SACW), which is transported offshore by the Brazil Current. This study examined the temporal contrasts in abundance and structure of pelagic copepod assemblages in a neritic station off Ubatuba, in relation to hydrography and phytoplankton biomass, to investigate the effects of SACW bottom intrusions on copepod population dynamics during three consecutive years. The water-column characteristics shifted from a well-mixed, more turbid and phytoplankton-poor scenario during subsidence conditions to a stratified, less turbid and high Chl- a concentration scenario during SACW bottom intrusions, leading to increased copepod diversity, abundance, and biomass. The rise in copepod diversity during SACW intrusions was related to the contribution of oceanic species in addition to coastal water species. The copepod community was numerically dominated by small-sized species, such as Oncaea waldemari, Oithona plumifera, and clausocalanid and paracalanid copepodids, regardless of seasonality and SACW intrusions. Some large calanoid species contributed considerably to the total copepod biomass during intrusions. In addition to confirming that SACW seasonal intrusions play a key role in pelagic processes off Southeast Brazil, this study showed that the multiannual variability of SACW seasonal intrusions is important in regulating the structure and dynamics of copepod communities in this subtropical area. [ABSTRACT FROM AUTHOR]

The analysis of plankton size distributions in response to physical and biological forcing is relevant to the understanding of marine ecological processes. In this study, we evaluated the influence of seasonal intrusions of the South Atlantic Central Water (SACW) on zooplankton vertical distribution and normalized biomass size spectra (NBSS) on the inner shelf off subtropical Brazil. Monthly sampling was performed at a fixed station for 5 years and zooplankton samples were analyzed with a ZooScan system. SACWintrusions led to increases in nitrate, chlorophyll and zooplankton biomass in different depth strata. NBSS slopes and intercepts varied between SACW intrusion and retraction phases and stratification was a key factor explaining seasonal fluctuations in NBSS parameters. The zooplankton interannual variability was related to the changing strength of SACW intrusions during the time series, as indicated by surfacing 18 and 20°C isotherms in certain years and intrusion phases, indicative of transient upwelling. We conclude that the temporal components of zooplankton variability in this subtropical coastal ecosystem were governed by SACW intrusions, affecting the vertical distribution of zooplankton biomass and size structure. [ABSTRACT FROM AUTHOR]

Abstract: We studied the temporal and vertical variability in larvacean abundance and secondary production on a fixed station off southeast Brazil, from January 2007 to December 2008. Larvacean biomass was derived from length–weight regressions, and growth rates were estimated from an empirical model. We identified eleven larvacean species. Oikopleura longicauda occurred throughout the studied period and was the most abundant species, followed by Oikopleura fusiformis. Fritillaria haplostoma, O. fusiformis and O. longicauda were found mainly above the thermocline, whereas Oikopleura dioica and Fritillaria pellucida preferred bottom layers. Higher abundance and biomass were observed in warmer months, when the water column was stratified as a result of the bottom intrusions of the cold and nutrient-rich South Atlantic Central Water. Secondary production mirrored the biomass seasonal pattern. Larvacean biomass equaled to less than 10% of copepod biomass during the same period, but larvacean production comprised on average 77% that of copepods, whereas the production of discarded houses and fecal pellets comprised up to 2800% of larvaceans secondary production. This confirms the potential significance of larvaceans in the carbon flux in tropical and subtropical coastal regions. [Copyright &y& Elsevier]

We measured grazing by herbivorous zooplankton (<200 μm fraction) in coastal and slope regions of the South Brazil Bight. Using the dilution technique, we performed nine experiments during the austral summer, when nutrient-rich South Atlantic Central Water is present on the shelf, and five during winter. These experiments provide the first estimates of microzooplankton grazing in the western South Atlantic Ocean. Model II regression showed a strong relationship between phytoplankton intrinsic growth rates and grazing, with a slope of 0.64 (±0.28; 95% confidence interval) indicating that microzooplankton grazing could account for the majority of phytoplankton mortality. Both phytoplankton growth and microzooplankton grazing were higher during the summer upwelling season, compared to winter. For the two experiments that were conducted in oligotrophic slope water, grazing accounted for >80% of phytoplankton production. A comparison of incubations with and without added inorganic nutrients showed no consistent stimulation of phytoplankton growth (slope of enriched versus unenriched treatments not significantly different from 1). Estimates from microscopic counts of heterotrophic organisms >10 μm indicated that copepod nauplii comprised the largest share of the microzooplankton biomass (mean 62.4 ± 5.8% SE). Grazing estimates were not correlated with microzooplankton biomass, whether or not nauplii were included, suggesting that most of the grazing was done by nano-sized zooplankton. [ABSTRACT FROM AUTHOR]

Abstract: The biomass size spectrum provides valuable information about the functioning of plankton systems. We evaluated hydrographic and bathymetric influences on biomass size spectra and on vertical distributions of plankton and seston above the Abrolhos Bank and in adjacent oceanic areas off Eastern Brazil. We used both in situ Laser Optical Particle Counter (LOPC) and preserved plankton samples analyzed with a ZooScan system to determine seston and plankton abundances, size distributions, and biomasses. Shelf stations, including those on the Abrolhos Bank, had higher particle concentrations and mesozooplankton biomasses than the vertically stratified oceanic stations. The latter were influenced by cold, nutrient-rich South Atlantic Central Water (SACW) below the mixed layer, particularly toward the south of the study area. Small particles (<1mm) were more abundant above and within the pycnocline, whereas large particles (>1mm) had a more heterogeneous vertical distribution, but were more abundant above the pycnocline, especially at the oceanic stations. Calanoid copepods usually dominated the mesozooplankton biomass spectra, but were accompanied by cyclopoids, appendicularians, and ostracods, the latter being particularly abundant during nighttime stations on the Abrolhos Bank. Both LOPC and ZooScan data showed significant differences in NBSS slopes and intercepts between shelf and oceanic stations. The higher intercepts and steeper slopes over the shelf are characteristic of higher productivity. The shallower slopes and presence of more biomass in larger particles indicate a more important contribution of large organisms and higher energy transfer efficiencies at the open ocean stations. Our results highlight the importance of the Abrolhos Bank for pelagic production in an otherwise oligotrophic ocean. [Copyright &y& Elsevier]