Environmental forcing on phytoplankton biomass and primary productivity of the coastal ecosystem in Ubatuba region, southern Brazil

Abstract

A time series of chlorophyll a and in situ primary production sampled over a period of 33 days during summer in Ubatuba region, southeastem Brazil, was subjected to multivariate and harmonic analysis. Principal Component Analysis has revealed four factors interpreted as (i) South Atlantic Central Water forcing; (ii) Transient ftontal systems and rain fali forcings; (iii) Wind forcing normal to the coast; (iv) Wind forcing parallel to the coast, as main factors in the variability of the phytoplankton biomass and primary productivity. Splitting of the time series according to four main events which had profound effects on the physicochemical characteristics of the region showed the following variations in the primary productivity integrated over the photic layer (g C m-2 day-1): mixing&#8594;stratification period, 0.40 ± 0.11; heavy rainfall, 1.24± 0.28; stratification after rainfall, 0.74± 0.10; stratification&#8594;mixing period, 0.90± 0.27; stratification after deep mixing, 0.63 ± 0.28. Harmonic analysis revealed two indistinguishable significant peaks of the phytoplankton biomass - one at a period of 8.25 days and one at a period of 6.6 days, contributing, respectively, about 17 and 32% ofthe total variance. Atmospheric forcing showed a characteristic period,of 200-264 hours while phytoplankton biomass response ranged over the 144-192 hours time scales and primary productivity was best related to the environment 360 hours before. Relative to total nitrogen' and ' biomass primary productivity oscillations were lagged about 96-144 hours. The interruption of steady-state conditions by transient atmospheric ev~nts and wind field intensification are the determining factors driving phytoplankton changes in this coastal environment.<br>Uma série temporal de clorofila a e produção primária obtida em um período de 33 dias durante o verão na região de Ubatuba, sudeste do Brasil, foi submetida à análise multivariada e harmônica. A Análise de Componentes Principais revelou quatro fatores interpretados como (i) Água Central do Atlântico Sul; (ii) Sistemas ftontais transientes e chuvas; (iii) Ventos normais à costa; (iv) Ventos paralelos à costa. Estes fatores atuam como forçantes ambientais na determinação da variabilidade observada na biomassa fitoplanctônica e produtividade primária. A divisão da séríe temporal de acordo com quatro eventos modificadores das características fisicoquímicas da região mostrou a seguinte variabilidade na produção primária integrada (g C m,2 dia,l) na camada eufótica: coluna de água homogênea em processo de estratificação térmica- 0,4O±0, 11; coluna de água estratificada e chuvas intensas- 1,24±0,28; coluna de água misturada em fase de estratificação térmica após intensas chuvas- 0,74:f:0,10; coluna de água estratificada em fase de processo de mistura- 0,90±0,27; coluna de água homogênea em fase de estratifição térmica após intensa mistura- 0,63±0,28. A Análise Harmônica revelou dois picos de biomassa significativos- um com período de 8,25 dias e outro com período de 6,6 dias, contribuindo, res...

Microbial biomass response to different quantities and sources of organic matter in Brazilian coastal sediments

“…The coastal water (CW) in Ubatuba has a salinity of 32-33 and temperatures of ≥25°C (Castro-Filho et al 1987). Given the presence of only small-sized rivers in the enclosed bays, minimal riverine input accounts for the meso-oligotrophic characteristics of the CW (Castro & Miranda 1998;Gaeta et al 1999). Nutrient concentrations (e.g.…”

“…nitrate, phosphate) are low during most of the year and the phytoplankton community is dominated by nanoplanktonic species (Aidar et al 1993;Gaeta et al 1999). In spring and summer, however, upwelling of cold and nutrient-rich water (South Atlantic Central Water, SACW: salinity ≤36.4 and temperature ≤20°C) to the euphotic zone and higher rainfall can drive sporadic blooms of opportunistic diatoms (Castro-Filho et al 1987;Aidar et al 1993;Gaeta et al 1999). Short-term sediment resuspension events, which are frequent during passage of cold fronts (i.e.…”

Benthic responses to organic matter variation in a subtropical coastal area off SE Brazil

“…The study site, located in Ubatuba, a city located at the tropical ⁄ subtropical boundary of SE Brazil, is characterized by the presence of small bays and is exposed to river run-off (Mahiques et al 1998) and slight variations in water temperature. Sporadic increases in new production are driven by the higher rainfall during summer and by the presence of the cold and nutrient-rich South Atlantic Central Water (SACW) in the inner shelf (>20 m depth) (Castro Filho et al 1987;Aidar et al 1993;Gaeta et al 1995Gaeta et al , 1999. Blooms of opportunistic diatoms can be observed during SACW advection in the euphotic zone.…”

“…Blooms of opportunistic diatoms can be observed during SACW advection in the euphotic zone. However, nanoflagellates dominate the phytoplanktonic community for most of the year, when the low salinity Coastal Water mass is present (Gaeta et al 1995(Gaeta et al , 1999Yoshinaga et al 2008). Lipid biomarkers extracted from the sediments revealed that phytoplankton-derived material constitutes the main source of organic carbon in the sediments of Ubatuba, whereas terrestrial material derived from continental run-off accounts for a small contribution to the total organic carbon pool, even during summer, when the precipitation is higher (Yoshinaga et al 2008).…”

“…In addition to planktonic sources of organic matter, microphytobenthic production in sediment is believed to be a major contributor to the pool of sedimentary organic matter (Corbisier et al 1997). Furthermore, physical disturbances are likely to affect the availability of food for the benthic system, either flushing out organic matter from exposed sites or stimulating both primary (Gaeta et al 1995(Gaeta et al , 1999Mahiques et al 1998) and secondary production (Corbisier et al 1997), during of cold fronts, after the resuspension of sediments.…”