Amazon River plume habitats shape planktonic cnidarian assemblages in the Western Atlantic.

The impact of the Amazon River freshwater plume on planktonic cnidarians over neritic and oceanic provinces is unknown. To provide further knowledge we took advantage of an oceanographic cruise performed in October 2012 in the Western Atlantic off the North Brazilian coast (8°N, 51°W-3.5°S, 37°W). A complex and dynamic system was observed, with strong currents and eddies dispersing the plume over a large area. Our results show that the Amazon River shapes marine habitats with a thin highly productive surface layer compressed by a deeper oxygen minimum zone both over the shelf and in the open ocean. We hypothesized that such habitat structure is particularly advantageous to planktonic cnidarians, which have low metabolic rates, being able to survive in hypoxic zones, resulting in high species richness and abundance. Over the shelf, distinctions were sharp and the area under the influence of the plume presented a diverse assemblage occurring in large abundance, while outside the plume, the hydromedusa Liriope tetraphylla was dominant and occurred almost alone. Divergences in the oceanic province were less pronounced, but still expressive being mostly related to the abundance of dominant species. We concluded that Amazon River plume is a paramount physical feature that profoundly affects the dynamics of the mesoscale habitat structure in the Western Equatorial Atlantic Ocean and that such habitat structure is responsible for shaping planktonic cnidarian assemblages both in neritic and oceanic provinces.

The Amazon River plume, a barrier to animal dispersal in the Western Tropical Atlantic.

The dispersal of marine organisms can be restricted by a set of isolation mechanisms including hard barriers or hydrological features. In the Western Atlantic Ocean, the Amazon River discharge has been shown to act as a biogeographical barrier responsible for the differences in reef fish communities between Caribbean Sea and Northeast Brazil continental shelves. Here, we compare the diversity of all Animalia phyla from biogeographic ecoregions along the Tropical Western Atlantic continental shelf to test the hypothesis that the Amazon River plume spatially structures species diversity. For that, we used beta diversity estimators and multivariate ecological analysis on a database of species occurrence of the whole animal kingdom including 175,477 occurrences of 8,375 species from six ecoregions along the Western Tropical Atlantic. Results of the whole animal kingdom and the richest phyla showed that the Caribbean Sea and Tropical Brazil ecoregions are isolated by the Amazon River Plume, broadening and confirming the hypothesis that it acts as a soft barrier to animal dispersal in the Western Tropical Atlantic. Species sharing is larger northwestwards, in direction of the Caribbean than the opposite direction. Beyond species isolation due to local characteristics such as low salinity and high turbidity, our results suggest the dominant northwestward currents probably play a major role in animal dispersion: it enhances the flux of larvae and other planktonic organisms with reduced mobility from Brazil to Caribbean and hinders their contrary movement. Thus, the Amazon area is a strong barrier for taxa with reduced dispersal capacity, while species of pelagic taxa with active swimming may transpose it more easily.

Short-term variation of plankton spatial distribution at a subtropical mixed estuarine system.

The horizontal distribution of plankton communities in a subtropical mixed estuarine system over one tidal cycle was investigated. Hydrological and planktonic samples were obtained twice on 17 July 2007 in a transect with ten stations in the Babitonga Bay estuary, south Brazil (~26°S). Hydrological variables did not vary spatially or tidally during samplings. However, in the cluster analyses both phyto and zooplankton were structured according to their estuarine position and in the inner stations also by the tidal condition. Phytoplankton abundances were higher during flood tide in the inner estuary (max. 122,583 ind.L-1), where diatoms dominated, particularly Diploneis bombus. However, the density at ebb tide increased towards outer estuary (max. >100,000 ind.L-1) and flagellates, mostly Gymnodinium spp., became abundant. Zooplankton abundances were higher at intermediate stations during both tides (max. 13,691 ind.m-3). The innermost stations were dominated by the copepod Acartia tonsa, while in the outermost stations Temora turbinata and the polychaete larvae Loimia sp. dominated. The results demonstrate how variable the estuarine plankton horizontal structure can be over short time-scales even in mixed estuarine systems under relatively homogeneous conditions, highlighting the importance to consider such temporal scales for a more accurate understanding of the dynamics of these communities.

Teissiera polypofera: first record of the genus Teissiera (Hydrozoa: Anthoathecata) in the Atlantic Ocean.

Specimens of Teissiera polypofera Xu, Huang & Chen, 1991 were found in waters off the northeast Brazilian coast between 8.858°S, 34.809°W and 9.005°S, 34.805°W and 56 to 717 m depth. The genus can be distinguished from other anthomedusae by the two opposite tentacles with cnidophores and four exumbrellar cnidocyst pouches with ocelli. Specimens were assigned to Teissiera polypofera due to the long and narrow manubrium transposing bell opening and polyp buds with medusoid buds on it, issuing from the base of manubrium. This study represents the first record of the genus in the Atlantic Ocean.

Foraminiferal assemblage structure from Brazilian tropical urbanized beaches (~7°S).

Foraminifera are diversified protists with high ecological and bioindicator importance. Physical-chemical parameters of the environment can be evaluated through the taphonomic analysis of the test coloring, because once they settle in the sediment their tests begin to behave as sedimentary particles. Five urbanized tropical Brazilian beaches were sampled in this study in order to characterize the diversity, abundance, taxonomic and taphonomic structure of Foraminifera assemblages. General environmental characterization such as granulometric analysis, temperature and salinity was also performed. A total of 69 foraminiferan species were found, dominated by Quinqueloculina lamarckiana, Archaias angulatus, Amphistegina lessonii, Ammonia tepida and Eponides repandus. A large predominance of dead tests (>90%) was found, and only them were considered in further analyses. The cluster based on the taxonomic composition formed two groups, separating Miramar from the other beaches. Miramar was dominated by Ammonia tepida (18.9%), Sorites marginalis (16.8%), Quinqueloculina lamarckiana (13.9%) and Textularia agglutinans (10.2%), and had the highest density, number of species and diversity, what may be related with the sheltered nature of this beach and the dominance of fine sand. The other four beaches have high oceanic influence and the medium and coarse sand predominated. In these beaches Quinqueloculina lamarckiana dominated, representing between 30.9 and 38.7% of total foraminiferans. The taphonomic analysis indicates that Miramar presents a high deposition of tests and a low hydrodynamic energy, since the majority of tests were white. In Bessa, Manaíra and Seixas most of the tests were brownish, which is characteristic of beaches with high hydrodynamic energy, which causes the tests to be constantly brought to the oxidation zone.

Ingestion of microplastic by ontogenetic phases of Stellifer brasiliensis (Perciformes, Sciaenidae) from the surf zone of tropical beaches.

Microplastics (<5 mm) are present in marine ecosystems worldwide where they can be ingested by a wide range of organisms from different trophic levels. In this study we analyzed the gastrointestinal tract of 443 specimens of Stellifer brasiliensis (124 juveniles, 254 subadults, and 65 adults) sampled in tropical beaches adjacent to the Paraíba River estuary. We found 1-3 microplastics in 42 fishes (9.48%), averaging 1.31 ± 0.52 microplastics per fish. The number of ingested microplastics by the different ontogenetic stages was statistically similar, but the adults had a higher ingestion frequency (13.8%). Among subadults, the condition factor of fishes that ingested microplastics was significantly smaller (p < 0.05) than those that had not ingested them. The ingestion of microplastics by the different ontogenetic stages of S. brasiliensis reflects the availability of this pollutant in the studied environment and highlights the vulnerability of fishes and other organisms through food webs.

Diel Vertical Dynamics of Gelatinous Zooplankton (Cnidaria, Ctenophora and Thaliacea) in a Subtropical Stratified Ecosystem (South Brazilian Bight).

The diel vertical dynamics of gelatinous zooplankton in physically stratified conditions over the 100-m isobath (~110 km offshore) in the South Brazilian Bight (26°45'S; 47°33'W) and the relationship to hydrography and food availability were analyzed by sampling every six hours over two consecutive days. Zooplankton samples were taken in three depth strata, following the vertical structure of the water column, with cold waters between 17 and 13.1°C, influenced by the South Atlantic Central Water (SACW) in the lower layer (>70 m); warm (>20°C) Tropical Water in the upper 40 m; and an intermediate thermocline with a deep chlorophyll-a maximum layer (0.3-0.6 mg m-3). Two distinct general patterns were observed, emphasizing the role of (i) physical and (ii) biological processes: (i) a strong influence of the vertical stratification, with most zooplankton absent or little abundant in the lower layer. The influence of the cold SACW on the bottom layer apparently restricted the vertical occupation of most species, which typically inhabit epipelagic warm waters. Even among migratory species, only a few (Aglaura hemistoma, Abylopsis tetragona eudoxids, Beroe sp., Thalia democratica, Salpa fusiformis) crossed the thermocline and reached the bottom layer. (ii) A general tendency of partial migrations, with variable intensity depending on the different species and developmental stages; populations tended to be more widely distributed through the water column during daylight, and to become more aggregated in the upper layer during the night, which can be explained based on the idea of the "hunger-satiation hypothesis", maximizing feeding and minimizing the chances of being predated.