Abstract in English:Abstract We evaluate how the concentrations of inorganic nutrients and chlorophyll a vary in a heterogeneous area (Equatorial SW Atlantic), covering a gradient from stations closer to the coast to others more distant associated or not with turbid-zone reefs. Vertical temperature (27.9 ± 0.10 °C; mean ± standard deviation) and salinity (36.2 ± 0.14) profles showed that the water column is well mixed (0-30 m depth). The oligotrophic condition was marked by low concentrations of phosphate (0.30 ± 0.22 µM) and dissolved inorganic nitrogen (0.64 ± 0.74 µM). Moreover, dissolved reactive silicon (DSi) was low in most samples (< 2.0 µM), but higher (>10 µM) in nearshore stations, probably related to continental runoff and/or resuspension of the bottom sediments. The pelagic phytoplankton biomass indicated that chlorophyll a (0.25 ± 0.08 µg L-1) was low, positively correlated with light and negatively correlated with nutrients, indicating possible phytoplankton uptake. Chlorophyll a concentrations were lower in stations closer to the coast and higher in some stations near the reefs, indicating that the latter could be more prone to phytoplankton development and depletion of nutrients, especially DSi. Therefore, although oligotrophy is present along this coast, we found some unexpected heterogeneity of nutrient and chlorophyll a distributions, which were probably infuenced by benthic-pelagic coupling due to the presence of extensive reefs, sponge gardens (18-30 m depth), and the proximity to the coast. These results highlight the importance of understanding the heterogeneity of ocean productivity, especially in lesser known low-latitude areas, which showed distinct nutrient and chlorophyll a levels related to the occurrence of tropical reefs that are capable of supporting important fsh stocks and unique biological communities.
Abstract in English:Abstract Measurements of the marine carbonate system on tropical and subtropical continental margins are poorly distributed in space and time, with many uncertainties persisting regarding the role of carbon exchanges at the ocean-atmosphere interface in these areas. To calculate sea-to-air CO 2 fluxes in Marine Ecoregions along the Brazilian continental margin (4°N to 34°S), we used data from the Surface Ocean CO 2 Atlas (SOCAT v2020), collected up to 400 km from the coast, at the surface (5 m), between 1991 and 2018, with the aim of investigating the role of ecoregions as potential sinks or sources of atmospheric CO 2. The temperature and salinity of seawater presented variability in the north-south direction mainly because of the broad latitudinal range, reflecting typical patterns of tropical (T = 27.4°C ±1.49; S = 36.4 ±1.91) and subtropical waters (T = 22.8°C ±3.41; S = 35 ±2.91), in addition to the greater or lesser influence of river inputs in each ecoregion. The pCO 2 values in the surface waters varied from 121.81 (Amazon) to 478.92 μatm (Eastern), differing significantly between ecoregions and showing an expected decadal increasing trend, both in the atmosphere and in the seawater. The calculated values of CO 2 fluxes showed non-homogeneous spatio-temporal variations, from -24.37 mmol m-2 d-1 (Rio Grande) to 9.87 mmol m- 2 d-1 (Southeastern). Throughout the analyzed time series, we observed that the Northeast, Amazon and Eastern ecoregions acted predominantly as sources of CO 2 and the Southeastern ecoregions and, mainly, Rio Grande, acted predominantly as sinks of atmospheric CO 2.
Abstract in English:Abstract Picoplankton are central global carbon (C) cycling players and often dominate the ocean plankton communities, especially in low latitudes. Therefore, evaluating picoplankton temporal dynamics is critical to understanding microbial stocks and C fluxes in tropical oceans. However, the lack of studies on low-latitude picoplankton communities translates into a common conception that there is an absence of seasonality. Herein, we studied the temporal variation in abundance (measured by flow cytometry), and carbon flux (taking bacterial production and respiration as proxies) of the picoplanktonic community for the first time, as well as their environmental drivers in a low-latitude (05° 59’ 20.7″S 035° 05’ 14.6″W) Atlantic coastal station. We performed monthly samplings between February 2013 and August 2016 in a novel microbial observatory – hereafter called the Equatorial Atlantic Microbial Observatory – established on the northeastern Brazilian Atlantic coast. Our results revealed stability in temporal dynamics of picoplankton, despite a considerable inter-annual variation, with some related to the El Niño (ENSO) event in 2015. However, weak environmental relationships found were not enough to explain the variation in picoplankton’s abundance, which suggests that other factors such as biological interactions may lead to picoplankton abundance variation over time. Heterotrophic bacteria dominated picoplankton during the entire study period and between photosynthetic counterparts, and Synechococcus showed greater relative importance than picoeukaryotes. These results bring a novel perspective that picoplankton may exhibit more pronounced fluctuations in the tropical region when considering inter-annual intervals, and is increasing prokaryotic contribution to carbon cycling towards the equator.
Abstract in English:Abstract This study identified the marine protected areas (MPAs) affected by the most extensive oil spill recorded on the Southwestern Atlantic coast, Brazil (2019/2020). We found that 81 MPAs suffered the direct or indirect effects of spilled oil, producing chemical, biological and socioenvironmental impacts over approximately 3.0% of the 2,659 protected areas currently established in Brazil. Although estimates suggest a moderate volume of spilled oil, the incident reached wide coastal strips, probably producing more damage to MPAs than other cases worldwide. Further, the generated negative impacts affected the already fragile environmental protection system in Brazil, potentially leading to negative impacts on global networks of MPAs and worldwide biodiversity.
Abstract in English:Abstract This study investigates the impact of winds, tides, and river discharges on the coastal current and salinity variability of Southern Brazil’s inner shelf. Data on wind speed, current, surface salinity, and temperature were collected for analysis from a metocean buoy of the Brazilian Coastal Monitoring System (SiMCosta). The observed current time series can be interpreted as a sum of highly variable flows correlated with local wind stress, and a residual mean current flowing southward along the coast at a few centimeters per second. Tidal currents were predominantly diurnal, albeit negligible, representing approximately 1.7% of the current variance in the region. We observed a prevalence of northwest winds and southeastward currents on the inner shelf, as well as an intermittent flow in both the alongshore and cross-shore directions due to meteorological frontal system passages. The power spectrum of both current components presented similar frequency patterns, indicating the prevalence of high-energy events in periods of 3 to 10 days over the entire time series. The alongshore current is highly correlated (r=0.73, p<0.05) with alongshore wind and a delay of 3 hours. In the low- (period >40 h) and high-frequency (period <40 h), the temporal lags were of 5 and 3 hours, respectively, with correlations of 0.79 (p<0.05) and 0.60 (p<0.05). The wavelet analysis has shown that high-energy events in alongshore wind stress are more common between August and October and less often between February and March, with similar surface currents and salinity patterns. A decrease in surface salinity during the winter season was observed due to the high level of Patos Lagoon’s outflow. Mean daily salinity correlated negatively with Patos Lagoon’s outflow, however part of this variability is associated with the intrusion of Patos Lagoon’s plume and the passage of frontal systems.
Abstract in English:Abstract Cyanobacterial blooms are a potential threat to human communities and ecosystems. Since the late 1980s, researchers have reported harmful cyanobacterial colonies in Patos Lagoon (PL), the largest coastal lagoon in South America. Most studies concerning harmful blooms in PL have focused on its biology and on its southernmost estuarine region, with little information about its displacement inside the lagoon and the influence of physical forces on its dynamics. This study uses satellite-derived information (normalized difference chlorophyll-a index – NDCI), river discharge data, and meteorological data (wind speed and direction, rainfall, and air temperature) to analyze two bloom episodes in PL, during the austral summer of 2019/2020, specifically in its larger, limnic portion. A 30-year meteorological time series was used to contrast the same summer period. Two remote sensing images from Sentinel-2 were taken of PL margins, near their central portion. The summer of 2019/2020 was drier when compared with the historical data, characterizing low river discharge. This environmental condition was coupled with high temperature, which implies thermal stratification in summer even at 2-m depth sites, which might have promoted cyanobacterial growth and accumulation inside PL. Moreover, weak winds (<<6 m s−1) seemed to accumulate cyanobacterial patches on the water surface, including after vertical mixing caused by strong winds (>6 m s−1). The NDCI values represented the two days of blooms, with higher values occurring under higher water temperatures and low wind speeds.
Abstract in English:Abstract This study analyzed the influence of strong and moderate El Niño-Southern Oscillation (ENSO) events on the seasonal and interannual variabilities of the sea surface temperature (SST) in the Western Equatorial Atlantic (WEA) Ocean and how the precipitation over the state of Maranhão, in Brazil, responds to the zonal teleconnection. To evaluate the ENSO magnitude and phase in the four Niño regions (1+2, 3, 3.4, and 4), the SODA 3.3.1 oceanic reanalysis database for the period from 1980 to 2015 was used. Our results showed that the La Niña phase with moderate magnitude was the most predominant among the 70 events analyzed, with Niño 3.4 presenting the highest number (20) of ENSO events (both positive and negative phases). At lag = 0, we found that significant negative correlations prevailed between the WEA SST anomalies and ENSO index, with the region of Niño 3.4 showing the most significant correlations (r = −0.25). The whole events of El Niño and La Niña were, respectively, accompanied by a cooling and a heating of up to −0.6°C or +0.8°C in the WEA Ocean. The WEA SST anomalies during El Niño and La Niña events have, respectively, reduced and increased the precipitation in Maranhão around ± 100 mm in a quarter. Strong El Niño events influence a greater precipitation deficit in Maranhão than moderate El Niño events. Moderate La Niña events have more pronounced influence on the precipitation over Maranhão than strong La Niña events do, especially on the negative anomalies. Our results showed that the central, northern, and eastern tip sectors of the state are the most affected by this zonal teleconnection. We concluded that ENSO’s significant influences on the WEA SST seasonal variability, added to the performance of the Atlantic Meridional Mode (Soares, 2019), determine the quality of the rainy season (March–April–May) in the state of Maranhão.
Abstract in English:Abstract Marginal reefs can provide meaningful information about the structure and dynamics of ecosystems under suboptimal environmental conditions. In addition to their different characteristics, these environments can also occur in urbanized areas. In this note, we characterize marine animal forests (MAFs) on turbid-zone reefs on an urban coast in the equatorial southwestern Atlantic. Overall, the sandstone ferruginous reefs (6-10 m depth) exhibited a flat topography and gentle slope (1-2 m above the seabed). Benthic cover is composed mainly of sponge gardens and ascidians. In addition, we found a low-relief coral carpet with only one massive reef-building coral (Siderastrea stellata) and Zoantharia. The ascidians and sponges had a higher diversity (at least 15 species) than the cnidarians (two species) in these forests. The main animals forming this seascape are weedy and stress-tolerant species adapted to challenging environmental conditions, such as swell waves, mesotidal regimes, moderate turbidity waters, and periodic burial. In this regard, these conditions and human impacts have shaped a unique MAF. Remarkably, the studied formations seem similar to high-latitude marginal reefs or low-latitude reefs under the influence of upwelling, which sustains soft corals and non-framework building coral communities along with sponges and ascidians. In particular, the shallow MAFs along the semi-arid coast of Brazil seem to lack some of the characteristics of low-latitude reefs under high sedimentation, whose structure was described as coral rubble within sedimentary matrices. This suggests that factors other than periodic burials and low light availability affected these MAFs. These overlooked forests are widespread in this area and have been neglected in studies, despite their richness (> 31 taxa) and valuable ecosystem goods and services. In the context of urbanized areas subject to climate change and pollution impacts, jetties, and dredging activities, it is necessary to consider these lush forests in impact assessments and conservation policies.
Abstract in English:Abstract This study evaluated the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in Santos Bay (SB) and the adjacent Santos Continental Shelf (SCS) in Brazil. Biliary metabolites were measured in several fish species to establish a baseline for future monitoring programs. Bile samples from different species of fish were collected monthly from July to December 2005 in SB, and in August 2005 and February 2006 on SCS. Metabolite concentrations were determined using high-performance liquid chromatography with fluorescence detectors. Naphthalene, phenanthrene, and benzo[a]pyrene metabolite concentrations ranged from 24 to 810 µg g -1 of bile, 1.8 to 68 µg g -1 of bile, and below the limit of quantitation to 1.3 µg g -1 of bile, respectively. Despite its high concentrations, the levels of naphthalene metabolites were in regions of low-contamination, while benzo[a]pyrene metabolite were in the same range as those reported in moderately contaminated areas, which may indicate pyrolytic contamination by PAHs. No significant differences in the metabolite concentrations were found between the SB and the SCS samples or during the periods of collection. Future studies with a single biomonitoring species should be conducted, considering age, sex, and feeding condition of the individuals. The metabolite data presented in this study is an important baseline information for this urbanized region, which hosts several sources of contaminants.