Nils Edvin Asp

An extensive reef system at the Amazon River mouth

A novel Amazonian reef biome was discovered, encompassing large rhodolith and sponge beds under low light, low oxygen, and high POC. Large rivers create major gaps in reef distribution along tropical shelves. The Amazon River represents 20% of the global riverine discharge to the ocean, generating up to a 1.3 × 106–km2 plume, and extensive muddy bottoms in the equatorial margin of South America. As a result, a wide area of the tropical North Atlantic is heavily affected in terms of salinity, pH, light penetration, and sedimentation. Such unfavorable conditions were thought to imprint a major gap in Western Atlantic reefs. We present an extensive carbonate system off the Amazon mouth, underneath the river plume. Significant carbonate sedimentation occurred during lowstand sea level, and still occurs in the outer shelf, resulting in complex hard-bottom topography. A permanent near-bottom wedge of ocean water, together with the seasonal nature of the plume’s eastward retroflection, conditions the existence of this extensive (~9500 km2) hard-bottom mosaic. The Amazon reefs transition from accretive to erosional structures and encompass extensive rhodolith beds. Carbonate structures function as a connectivity corridor for wide depth–ranging reef-associated species, being heavily colonized by large sponges and other structure-forming filter feeders that dwell under low light and high levels of particulates. The oxycline between the plume and subplume is associated with chemoautotrophic and anaerobic microbial metabolisms. The system described here provides several insights about the responses of tropical reefs to suboptimal and marginal reef-building conditions, which are accelerating worldwide due to global changes.

Wave refraction and longshore transport patterns along the southern Santa Catarina coast

Based on the wave climate for the southern Brazilian coast, wave refraction has been modelled in order to obtain the refracted wave heights and directions along the southern Santa Catarina coast, providing the needed information for potential longshore drift estimates. According to its coastline orientation, different sectors of the coast present varying longshore drift patterns. Estimates have been made for the yearly-averaged wave climate as well as for each season, showing thereby the longshore drift patterns along the year. Based on the results of the potential longshore drift intensities and directions and on the shoreline outline in plan, it has been possible to identify a strongly drift-dominated coast in the south turning to a mixed drift and swash dominated coast towards the north of the studied area. Contrasting patterns of longshore drift between the southern and northern portion of the coastline indicate a sediment surplus in the central portion, making sediment available for cross-shore transport processes, either on- or offshore. Considering long-term aspects, the longshore drift patterns are in agreement with the coastal infilling process which has mainly been driven by persistent surplus from littoral sediment drift.

The dynamics of a frictionally-dominated Amazonian estuary

A hidrodinâmica, morfologia e sedimentologia do estuario do Taperacu foram investigadas. Este e um entre varios estuarios do litoral amazonico que integram a maior extensao continua de manguezais do mundo, apresentando uma descarga de agua doce muito reduzida, atipica para a regiao. Os resultados revelam grandes bancos arenosos que ocupam em grande parte a porcao central do estuario. Areias muito finas e bem selecionadas de origem marinha prevalecem. Fases de enchente mais curtas, com velocidades de corrente substancialmente mais altas, sao observadas na porcao superior do estuario, como esperado para um estuario raso e dominado por friccao. Por outro lado, uma vazante mais intensa poderia ocorrer como resultado de grandes areas de manguezais associadas e intenso preenchimento estuarino, sendo que ambas as condicoes sao observadas no Taperacu. Neste caso, a prevalencia da enchente parece estar associada a ausencia de uma descarga fluvial efetiva. Alem disso, alguns canais de mare conectam o Taperacu com seu vizinho estuario do Caete, o que contribuiria para o dominio de enchente. Como um todo, os resultados demonstram uma complexa interacao de aspectos de configuracao (friccao, drenagem fluvial, conexoes com estuarios vizinhos, preenchimento e grandes areas intermareais) na determinacao dos padroes hidrodinâmicos, contribuindo para o entendimento dos estuarios da regiao amazonica.

Mud in the surf: Nature at work in a Brazilian bay

Massive discharge of mud from coastal rivers is a well-documented phenomenon. However, in areas with limited historical and instrumental records it is often difficult to assess the nature and history of the process. This article looks at Tijucas Bay, in southern Brazil (Figure 1a) (an area that was the landfall region in March 2004 for South Americas first recorded hurricane [Bossack, 2004]), to examine the time frame for extensive deposition of fluid muds in the nearshore (Figure 1b). The new geological data suggest that whereas recent human activities (e.g., massive sand mining) along the Tijucas River may be important in increasing the suspended sediment discharge, the shift to a mud-dominated regime was part of the natural evolution of this coastal plain.

Divergence of cryptic species of Doryteuthis plei Blainville, 1823 (Loliginidae, Cephalopoda) in the Western Atlantic Ocean is associated with the formation of the Caribbean Sea

Although recent years have seen an increase in genetic analyses that identify new species of cephalopods and phylogeographic patterns, the loliginid squid of South America remain one of the least studied groups. The suggestion that Doryteuthis plei may represent distinct lineages within its extensive distribution along the western Atlantic coasts from Cape Hatteras, USA (36°N) to northern Argentina (35°S) is consistent with significant variation in a number of environmental variables along this range including in both temperature and salinity. In the present study D. plei samples were obtained from a large number of localities along the western Atlantic coasts to investigate the distribution of these possible species in a phylogeographic context. Phylogeographic analyses were performed using the mitochondrial Cytochrome Oxidase I gene and nuclear Rhodopsin gene. Divergence times were estimated using Bayesian strict clock dating with calibrations based on fossil records for divergence from the lineage containing Vampyroteuthis infernalis (162mya), the probable origins of the North American loliginids (45mya), and the European loliginids (20mya) and fossil statolith from Doryteuthis opalescens (3mya). Our results suggest a deep genetic divergence within Doryteuthis plei. The currently described specie consists of two genetically distinct clades (pair-wise genetic divergence of between 7.7 and 9.1%). One clade composed of individuals collected in northwestern Atlantic and Central Caribbean Atlantic waters and the other from southwestern Atlantic waters. The divergence time and sampling locations suggest the speciation process at approximately 16Mya, which is in full agreement with the middle Miocene orogeny of the Caribbean plate, ending up with the formation of the Lesser Antilles and the adjacent subduction zone, coinciding with a particularly low global sea level, resulting in the practical absence of continental shelves at the area, and therefore an effective geographic barrier for D. plei. Furthermore, this study also provides evidence of previously undocumented sub-population structuring in the Gulf of Mexico.

Mangrove sedimentary characteristics and implications for crab Ucides cordatus (Crustacea, Decapoda, Ucididae) distribution in an estuarine area of the Amazonian region

At the coastal zone sediments, water and organisms interact intensely. At equatorial tidal-dominated coast mangroves are abundant. These areas are well-known for their ecological importance. Considering the mangroves of Atlantic South America, the mangrove crab, Ucides cordatus has ecological and economic prominence. High densities of this crab are found on the Amazon coast. This study investigates the sediment distribution of the Braganca mangrove area (Amazon coast, Brazil) and its correlations with vegetation and mangrove crab distribution. Sediments of 47 sites, as well as crabs from sites with different sediment and vegetation, were sampled. Results show that surface sediment of the area is mainly composed by silt (59%), with 21% sand and 20% clay. Variations in sorting and skewness are the product of local variations in clay and sand content. The vegetation type was significantly correlated to mangrove crab characteristics, abundance and weight/size. Sediment characteristics are also substantially different according to the vegetation type. Areas where Avicennia germinans prevails have more sand and clay than areas of Rizophora mangle, in which silt is dominant and crabs were significantly heavier. The present results have showed that the distribution of sediments, crabs and vegetation at mangrove areas are strongly correlated. Thus, they should be studied in conjunction.

Características sedimentares fluviais associadas ao grau de reservação da mata Ciliar - Rio Urumajó, Nordeste Paraense

Rivers are the main ways of sediment transport from inland to the coastal zone and oceans. Despite direct influence of climate, the vegetation coverage plays a central role in liquid and solid fluvial discharge. In this context, the present work aimed to study the fluvial sedimentology of the Urumajo River (Para, Brazil) in relation to the preservation state of riparian vegetation. Sediment samples were collected at five sites (A to E), including a five-sample transversal profile at each site. The sites were distributed from the source to the estuarine area. The characteristics and preservation state of the riparian vegetation were analyzed at each site as well. The collected sediments were submitted to grain size analysis, where mean grain size, median, asymmetry, selection and kurtosis were obtained. The results made it possible to recognize the regular characteristics (sites A and C), which included median sand as the main sediment class and well-sorted and approximate symmetric grain size distribution, directly related to the well-preserved riparian vegetation at sites A and C. On the other hand, sites B, D and E showed substantial differences in relation to the regular pattern. This fact could be associated to the vegetation degradation at those sites, resulting in margin erosion. Furthermore, at site E, reflexes of tide influence on the sediment characteristics could be observed, subsidizing the estuary delimitation.

Patterns of Genetic Variability in Island Populations of the Cane Toad (Rhinella marina) from the Mouth of the Amazon.

The Amazonian coast has several unique geological characteristics resulting from the interaction between drainage pattern of the Amazon River and the Atlantic Ocean. It is one of the most extensive and sedimentologically dynamic regions of the world, with a large number of continental islands mostly formed less than 10,000 years ago. The natural distribution of the cane toad (Rhinella marina), one of the world’s most successful invasive species, in this complex Amazonian system provides an intriguing model for the investigation of the effects of isolation or the combined effects of isolation and habitat dynamic changes on patterns of genetic variability and population differentiation. We used nine fast-evolving microsatellite loci to contrast patterns of genetic variability in six coastal (three mainlands and three islands) populations of the cane toad near the mouth of the Amazon River. Results from Bayesian multilocus clustering approach and Discriminant Analyses of Principal Component were congruent in showing that each island population was genetically differentiated from the mainland populations. All FST values obtained from all pairwise comparisons were significant, ranging from 0.048 to 0.186. Estimates of both recent and historical gene flow were not significantly different from zero across all population pairs, except the two mainland populations inhabiting continuous habitats. Patterns of population differentiation, with a high level of population substructure and absence/restricted gene flow, suggested that island populations of R. marina are likely isolated since the Holocene sea-level rise. However, considering the similar levels of genetic variability found in both island and mainland populations, it is reliable to assume that they were also isolated for longer periods. Given the genetic uniqueness of each cane toad population, together with the high natural vulnerability of the coastal regions and intense human pressures, we suggest that these populations should be treated as discrete units for conservation management purposes.

Perspectives on the Great Amazon Reef: extension, biodiversity and threats

Here we provide a broad overview of the Great Amazon Reef System (GARS) based on the first-ever video surveys of the region. This footage supports four major hypotheses: 1) the GARS area may be six times larger than previously suggested (up to 56,000 km2); 2) the GARS may extend deeper than previously suggested (up to 220 m); 3) the GARS is composed of a greater complexity and diversity of habitats than previously recognized (e.g. reef platforms, reef walls, rhodolith beds, and sponge bottoms); and 4) the GARS represents useful system to test whether a deep corridor connects the Caribbean Sea to the Southwest Atlantic Ocean. We also call attention to the urgent need to adopt precautionary conservation measures to protect the region in the face of increasing threats from extractive oil and gas practices. With less than 5% of the potential area of the GARS surveyed so far, more research will be required to inform a systematic conservation planning approach and determine how best to establish a network of marine protected areas. Such planning will be required to reconcile extractive activities with effective biodiversity conservation in the GARS.

Benthic Estuarine Assemblages of the Brazilian North Coast (Amazonia Ecoregion)

Despite its ecological and economical importance, the Brazilian North Coast (BNC) or Amazonia Ecoregion sensu Spalding et al. (Bioscience 57:573–583, 2007), was poorly studied until the 1980s, when major interdisciplinary coastal research programs began. The Amazon and other major rivers strongly influence the BNC, causing seasonally reduced surface salinity and significant sediment deposition. From February to March, monthly accumulated rainfall is 400 mm or more and estuarine salinity varies between 0 and 10, but reaches over 40 in the dry season. Mangrove vegetation, with narrow seaward fringes of salt marsh, dominates the BNC. Macrotides between 4 and 7 m expose large areas of muddy to sandy sediments at low tide. Tidal amplitude is twice as large during spring tides, inundating large areas of mangrove. Tidal export, as well as riverine discharge, determines BNC dissolved nutrient profiles. Despite high turbidity, BNC estuaries have high phytoplankton biomasses and washout of benthic microalgae may also contribute to high chlorophyll-a concentrations. Though benthic diversity is low, secondary productivity in sediments is high, and important for nutrient cycling, especially in mangrove forest. The uca-crab (Ucides cordatus) is economically important in the region. Strong gradients in salinity, along both the coast and individual estuaries, determine the relative abundance of freshwater and marine benthic taxa but abundance and diversity are lower in the wet season. Although relatively conserved, there is increasing pressure on the BNC through urban expansion, organic pollution, mangrove logging, and over-harvesting of coastal resources. With only 17 protected and especially managed areas along the BNC, the implementation of conservation policies is, so far, unsatisfactory.