Atlantic Coast Of Patagonia Research Articles

Seasonal periodicity and reproduction of brown algae (Phaeophyceae) at Puerto Deseado (Patagonia)

Abstract Puerto Deseado is a locality on the Atlantic coast of Patagonia (47°45′ S, 65°54′ W) with a ria (fjord-like estuary) several kilometres long that follows the course of Rio Deseado. From 1969 to 1972, we followed the development of 50 species of mostly intertidal brown macroalgae at five sites, one outside the ria and four within. Collections and observations were made at least once monthly to determine species identities, vegetative and reproductive states of the thalli, and variations between the different sites. Several environmental factors were used to describe the sites, including seawater temperature, season, and hydrodynamics. In summer, there were more species, coincident with the highest proportion of plurilocular sporangia. In contrast, unilocular sporangia appeared mostly in autumn. The difference between the five sites was well defined: nine species from the outermost site did not occur inside the ria, and only 13 species were found at all five sites. The number of species gradually declined towards the interior of the ria. The aim of this study was to document brown algal vegetation at the beginning of the 1970s to provide a baseline dataset before the start up of large-scale port activity.

Seasonal dynamic of macroalgae in intertidal pools formed by beds of Crassostrea gigas (Mollusca, Bivalvia) on the north Patagonian Atlantic coast

Abstract Intertidal pools represent restricted habitats for macroalgal assemblages, and their structure is determined by physical and biotic factors. The establishment of the exotic oyster Crassostrea gigas on the north Patagonian Atlantic coast led to the formation of intertidal pools; these provide habitats for macroalgal settlement. We aimed to determine the composition, distribution and abundance of the macroalgal assemblage inhabiting these pools, and to establish the structuring variables. Several biotic and abiotic variables were evaluated in 36 pools in winter and summer. Correlations were calculated and permutation analysis of variance and constrained redundancy analysis were conducted to determine the structuring variables. Unlike other Patagonian coasts, richness was low and pools were characterized by a dominance of red algae. Richness was higher in winter, while diversity was lower because of the dominance of Polysiphonia abscissa, which had the highest percentage of occurrence. Temperature was a putative factor determining seasonal richness and diversity. Elevation and surface area of the pools were structuring factors for assemblage biomass. We demonstrated distinct assemblage dynamics. Polysiphonia abscissa developed large populations in winter, which declined towards the summer, while Gelidium maggsiae and Gelidiella calcicola formed dense turfs during summer stress.

Holocene Beach Ridges and Coastal Evolution in the Cabo Raso Bay (Atlantic Patagonian Coast, Argentina)

Abstract The Holocene evolution of the Cabo Raso bay (Atlantic Patagonian coast) was reconstructed by means of geomorphological, stratigraphic, and palaeontological analyses, assisted by radiocarbon dating. Six beach ridges were individuated and mapped in the field, as well as some rocky erosional landforms, e.g., inner margins of marine terraces. Thanks to quarry sections, the internal structure of beach ridges, their relationship with continental deposits, and the fossil contents were determined. Two specimens of Aulacomya atra and Brachidontes purpuratus were radiocarbon dated at 6055 and 4500 ± 20 YBP, respectively. The bedrock outcrops at the base of an analysed section allowed us to associate the age of the samples collected to the elevation of the marine transgression surface upon which the entire deposit rests. Because a beach ridge is a regressive form, the elevation of the base of the dated deposit was assumed to be equivalent to or slightly lower than the maximum sea-level stationing, represent...

Paleoseismicity and seismic hazard in southern Patagonia (Argentina-Chile; 50°–55°S) and the role of the Magallanes-Fagnano transform fault

Patagonia, including the island of Tierra del Fuego, lies in southernmost South America at the junction of the South American, Antarctic, and Scotia tectonic plates. Historical and instrumental records have documented several local earthquakes of damaging magnitude, posing a threat to the rapidly growing population of 300,000 and the expanding industrial and service infrastructure. Short and inaccurate instrumental records of local seismic events and a diffuse epicenter distribution not clearly related to the recognized seismogenic structures have hindered an adequate evaluation of the seismic hazard for this region. To improve this situation, a paleoseismological study was carried out on two gravelly strandplains on the Atlantic coast of Patagonia. Surveying combined ground-probing radar, vertical electric sounding, and seismic refraction. Coseismic normal faults buried beneath the strandplain bodies were revealed and related to the morphology of the strandplains. The faults have probable ages between 0.9 and 6.4 kyr BP and a recurrence rate of about 1 kyr. The more likely source for these structures is the Magallanes-Fagnano fault, a continental transform fault that crosses Tierra del Fuego. The distance of more than 300 km from the buried coseismic structures to the trace of the Magallanes-Fagnano fault argues for high-magnitude earthquake activity on this fault throughout the Holocene. Urban development on soft glacial and alluvial substrates increases the hazard.

Archaeological littoral sites on the northern coast of Santa Cruz: Valuable evidence of sea level changes on the continental Patagonian coasts (Argentina)

Geological studies are fundamental to archaeologists as they provide essential data to understand certain processes involved in the present archaeological record. When working on marine coastal archaeology, the information provided by geomorphologic studies with regards to the evolution and dynamics of coastal marine lines is essential to assess the availability and accessibility of certain marine coastal areas, and their resources, to human populations of the past. This is also the key to reach correct cultural interpretations. However, on certain occasions, archaeological information can also offer valuable alternative data for geologists to reach geological interpretations, for instance when working on the evolution and changes of coastal sea lines. In this case, spatial and temporal scales must be regarded. This idea is supported on the experience gained through research done on the Patagonian Atlantic coast at the two archaeological localities introduced in this paper: Cabo Blanco, where we evaluate models of evolution of the coastline with a number of radiocarbon dates from excavated sites; and Punta Medanosa, where we discuss the temporal depth of the formation of the coastal ridges for the mid-Holocene transgression.

The eggs and hatchlings of the octopusRobsonella fontaniana(Cephalopoda: Octopodidae)

Very little is known about the life history ofRobsonella fontaniana. In particular, there are no descriptions of the early life stages that enable correct identification of samples taken from the wild. In this work, eggs and hatchlings are described from egg clutches obtained in the field with brooding females and incubated until hatching. Individual eggs exhibited marked differences in stages of embryonic development within egg clutches or even within a single egg string. For one clutch collected at early stages of embryonic development, embryogenesis took 91 days at 11.5 °C and for a second clutch at intermediate developmental stages it took 68 days at 11 °C and 39 days at 14 °C. For the later clutch the hatching period lasts 25 days at 14 °C. The eggs and paralarvae were small, with an egg length of 3.9–5.2 mm, a dorsal mantle length of 2–3 mm and a total paralarvae length of 3.4–6.0 mm. Chromatophore shape and distribution presented a very distinctive pattern. Characteristics of the eggs, egg strings and paralarvae make it possible to distinguish the early stagesof R. fontanianafrom those of other octopodid species found off the Atlantic coast of Patagonia.

A baseline paleoecological study for the Santa Cruz Formation (late–early Miocene) at the Atlantic coast of Patagonia, Argentina

Coastal exposures of the Santa Cruz Formation (late–early Miocene, southern Patagonia, Argentina) between the Coyle and Gallegos rivers have been a fertile ground for recovery of Miocene vertebrates for more than 100 years. The formation contains an exceptionally rich mammal fauna, which documents a vertebrate assemblage very different from any living community, even at the ordinal level. Intensive fieldwork performed since 2003 (nearly 1200 specimens have been collected, including marsupials, xenarthrans, notoungulates, litopterns astrapotheres, rodents, and primates) document this assertion. The goal of this study is to attempt to reconstruct the trophic structure of the Santacrucian mammalian community with precise stratigraphic control. Particularly, we evaluate the depauperate carnivoran paleoguild and identify new working hypotheses about this community. A database has been built from about 390 specimens from two localities: Campo Barranca (CB) and Puesto Estancia La Costa (PLC). All species have been classified as herbivore or carnivore, their body masses estimated, and the following parameters estimated: population density, on-crop biomass, metabolic rates, and the primary and secondary productivity. According to our results, this model predicts an imbalance in both CB and PLC faunas which can be seen by comparing the secondary productivity of the ecosystem and the energetic requirements of the carnivores in it. While in CB, the difference between carnivores and herbivores is six-fold, in PLC this difference is smaller, the secondary productivity is still around three times that of the carnivore to herbivore ratio seen today. If both localities are combined, the difference rises to around four-fold in favour of secondary productivity. Finally, several working hypotheses about the Santacrucian mammalian community and the main lineages of herbivores and carnivores are offered.

Vulnerability of the Atlantic Patagonian coast to tsunamis generated by submarine earthquakes located in the Scotia Arc region. Some numerical experiments

The Scotia Arc is one of two regions in the Atlantic Ocean with greater potential for tsunami generation from seismic and volcanic sources. A numerical modeling study was undertaken to determine tsunami generation from postulated sources along the Arc and tsunami wave amplification or attenuation along the Patagonian continental shelf. Sea level oscillation represented by a simple sinusoidal wave function applied at the boundary of the numerical grid, which simulated the tsunami entering the computational domain, was implemented as forcing. The validation of this model was carried out by comparing the maximum amplitudes recorded and simulated at Santa Teresita and Mar del Plata (Buenos Aires province) after the occurrence of earthquake and subsequent tsunami in Sumatra (December 2004). From numerical simulations it can be seen that the tsunami propagation is highly affected by bathymetric refraction on the Patagonian continental shelf and the wave amplitude is significantly attenuated on the inner continental shelf. Maximum amplifications were obtained around Malvinas (Falkland) Islands and Burdwood bank because the wave propagates almost without refracting and the shoaling effect is highly significant there.

Correlation of marine beds based on Sr- and Ar-date determinations and faunal affinities across the Paleogene/Neogene boundary in southern Patagonia, Argentina

The San Julián and Monte León formations (“Patagonian”) are exposed along the Atlantic coast of Patagonia, whereas in the west equivalent rocks are known as Centinela Formation. Sixteen 87Sr/ 86Sr measurements on the oyster Crassostrea? hatcheri (Ortmann) from the San Julián and Centinela formations and an 40Ar/ 39Ar-date from a whole-rock sample from the Centinela Formation yielded ages that allow more precise correlation between the two areas. 87Sr/ 86Sr measurements from the San Julián Formation yielded ages between 23.83 and 25.93 Ma, while for the Centinela Formation the ages ranged between 21.24 and 26.38 Ma. The 40Ar/ 39Ar analysis of a sample of the Centinela Formation yielded an age of 20.48 ± 0.27 Ma. The age data suggest a late Oligocene (Chattian) age for the San Julián Formation and the lowermost beds of the Centinela Formation (northernmost exposures). The Monte León Formation along the East coast and the entire section of the Centinela Formation in the southern area – and the middle and upper beds of this same unit in the northernmost localities – were deposited at the end of the Oligocene and early Miocene (Chattian–Burdigalian). The invertebrate fauna present in these units shows diverse preservation patterns that makes these fossils, especially the mollusks, not useful – at this stage – for correlation purposes.

Blood and Intestinal Parasites in Wild Psittaciformes: A Case Study of Burrowing Parrots (Cyanoliseus Patagonus)

Quantifying parasites is essential for understanding the ecological and evolutionary implica- tions of parasites on their hosts. It is also crucial for many conservation attempts carried out in endan- gered groups of birds, like the Psittaciformes. The aim of the present study was to test for the presence of blood and intestinal parasites of Burrowing Parrots (Cyanoliseus patagonus) (Psittaciformes) breeding in a large colony at the Atlantic coast of Patagonia, Argentina. Although Burrowing Parrots in this colony have

A prediction come true: the green crab invades the Patagonian coast

We report the finding of the European green crab on the Atlantic coast of Patagonia. A total of 61 specimens were found in Camarones bay (Chubut Province, Argentina) in November 2003 and January 2004. Carapace widths ranged between 39.9 and 71.4 mm for females, and 51.4 and 81.4 mm for males. All of the females were sexually mature, and most had already spawned. Size frequency distributions and temperature conditions in the area suggest that the species had been introduced at least 3–4 years before our finding (1999–2000). The analysis of surface seawater temperature in the native and non-native ranges of distribution of the species suggests that the crab would be able to colonize the eastern coast of South America from southern Brazil (29°S) to the mouth of the Magellan Strait (52°S). Possible areas of introduction to the region and vectors are discussed.

THE GENUS TROPHON MONFORT, 1810 (GASTROPODA: MURICIDAE) IN THE TERTIARY OF PATAGONIA

Species of Trophon Montfort, 1810 are well known from Tertiary rocks exposed over a wide area of Patagonia. All nominal species referable to the genus were revised and, where necessary, synonymized. Valid species were redescribed and reillustrated, based on type material and additional material collected at other localities ranging from Península Valdés to south of the mouth of the Santa Cruz River (along the Atlantic coast of Patagonia) to Lake Pueyrredón (along the foothills of the Andes). Of the 17 nominal species, only six are considered valid, i.e., Trophon sowerbyi new name (replacement for Fusus patagonicus Sowerby, 1846 in Darwin non d'Orbigny), Trophon santacruzensis Ihering, 1897, Trophon camachoi new species, Trophon leanzai Brunet, 1997, Trophon contortus Brunet, 1997, and Trophon inornatus Pilsbry, 1897.

Polynostratigraphy and palaeoenvironments across the Oligocene-Miocene boundary within the Centinela Formation, southwestern Argentina

Abstract Palynological analysis of the Centinela Formation, exposed in the foothills of the Patagonian Andes, has revealed the presence of pollen, dinoflagellate cysts, and chlorococcalean and prasinophycean algae. These groups are here reported from the Centinela Formation for the first time. Sporomorph and dinoflagellate cyst assemblages suggest a Late Oligocene and Early Miocene age. These results coincide with a 87 Sr/ 86 Sr age close to the age of the Oligocene-Miocene boundary obtained from the lower part of the section. Palynological information from the Centinela Formation permits correlation with Upper Oligocene and Lower Miocene units cropping out along the Atlantic Patagonian coast. Assemblages from the lower part of the section suggest that the beds were deposited under marine, near-shore palaeoenvironmental conditions with a strong continental influence. In the middle part of the section, high dinoflagellate cyst ratios coincide with a maximum flooding surface recorded in the Centinela Formation. Towards the top of the Centinela Formation, the sporomorph assemblages reflect the development of vegetation adapted to coastal environments, which agrees with the sparse occurrence of marine palynomorphs. A new dinoflagellate species, Hystrichostrogylon sulcatum , is proposed. This species appears to range across the Oligocene-Miocene boundary and is particularly abundant in the lowest Miocene.

Imminent extinction of the guanay cormorant on the Atlantic South American coast: a conservation concern?

Guanay cormorants Phalacrocorax bougainvilli aredistributed mostly on the Pacific coast of Peru and northern Chile. A smallpopulation of around 50 pairs was described on the Patagonian Atlantic coast inthe late 1960s. Further records have revealed a progressive decrease of thispopulation. During 1999 we looked for guanay cormorants at those Atlanticcolonies where the species was recorded in the past. Only four individuals weredetected in one colony (Punta Lobería), and all of them were mated withking cormorants P. albiventer. In addition, we recordedhybrids between guanay and king cormorants mated with pure king and imperialcormorants P. atriceps. Causes of the population declineare unknown. Since guanay cormorants inhabiting the Atlantic coast could be agenetically differentiated population, we emphasize the need for molecularstudies. If genetic polymorphism is detected, the capture of remnant individualsin order to constitute a genetic stock should be considered.

ESR dating stratigraphically well-constrained marine terraces along the Patagonian Atlantic coast (Argentina)

Abstract ESR dating of marine mollusc shells is an important tool in coastal geomorphology as well as in palaeosea-level and other research. Some severe problems, however, remain as far as the accuracy of the dating results are concerned. Case studies of Patagonian Middle and Younger Quaternary marine terraces help to illustrate the potential of an improved ESR dating technique. It can be demonstrated that a discrimination of Holocene, Last Interglacial, Penultimate Interglacial and “older” samples is possible. A chronostratigraphic separation of the well-known Last Interglacial substages 5a, 5c, and 5e is still missing, partly due to the misleading accuracy of ESR dating results. Consequently, it cannot be decided yet whether the morphologically well-conserved Last and Penultimate Interglacial age substages result from a relative sea-level fall (glacioeustatic and/or decreasing wind intensities) during the one and the same interglacial highstand shortly after the 5e or 7 transgression maximum or whether they were deposited during the much younger sea-level sub-highstands, e.g. 5c, 5a or 7c, or 7a.

Direct and Indirect Effects of the Highseas Fisheries on the Marine Mammal Populations in the Northern and Central Patagonian Coast

Since 1989, interactions between marine mammals and fisheries have been monitored along the Atlantic Patagonian coast. The Argentinian national fishing fleet in the area is composed of approximately 208 vessels (75% trawlers; 16% jiggins; 9% longliners). The fleet operates the year-round from eight harbours between Escondida Island and San Jorge Gulf (80 000 naut. miles2). The important target species are: hake (Merluccius hubbsi), shortfin squid (IIlex argentinus) and shrimp (Pleoticus muelleri), while several tons of other fish are discarded. The dusky dolphin (Lagenorhynchus obscurus), the Commerson's dolphin (Cephalorhynchus commersonii) and the southern sea lion (Otaria flavescens) are incidentally caught. The dolphins become entangled mainly in mid-water trawls at night, while the sea lions become entangled in any kind of trawl. Annual mortality rates obtained are 170-480 sea lions (mostly males; figure estimated to be 1–2% of the population size in the area), 70–200 dusky dolphins (70% females) and 25–170 Commerson's dolphins. Feeding habits of top predators, fish catch and bycatch of the fishery were also studied. Dusky dolphins in the area prey mainly on anchovy and squid, while hake was the most important food item for Commerson's dolphins and male southern sea lions. Squid is also important prey for sea lions and overlaps in size with the fish taken by the commercial fishery. Fishing areas for squid taken by jigging vessels overlap in part with those of foraging sea lions. Even though the commercial size for hake is 30 cm or larger, smaller hakes are largely discarded by the fishery. A combination of operational and specific interactions have been detected. At present, mortality rates seem to be low and there is insufficient evidence of competition for prey species. However, there is concern about the large amounts of fish (particularly hake) discarded by the fishery.

REDESCRIPTION OF TYRINNA NOBILIS BERGH, 1898 (OPISTHOBRANCHIA: CHROMODORIDIDAE) FROM PATAGONIA, ARGENTINA

The chromodond nudibranch Tyritma nobiiis, described originally by Bergh, 1898 from Chile, has been collected on the Atlantic coast of Patagonia (Argentina) We have made a redescription which includes the presence of a vestibular gland, absent in the Bergh's description, and provided information on the biology of the living animal* Tynnna nobihs was compared with other nominal species assigned to the genera Cadlina and Tyrinna. Tynnna pusae Marcus, 1959 was synonymised with T. nobdis, and Cadlina bumayi Ortea, 1988 was included in Tynnna. The presence of a ramifying vestibular gland in T nobiiis, was discussed in relation to phylogeny of the family Chromodorididae

Long range long term transport and decay of PAHs in a semiarid coastal area of Argentina

The transport and decay processes of environmental PAHs (Polynuclear Aromatic Hydrocarbons) are important in defining the exposures and risks which they may pose to organisms and man. In southeastern Patagonia, at about 42° S, westerly winds are very active in long range transport of top soil dust and air suspended particulate matter, a phenomenon which is similar to what occurs in other semi‐desert areas of the world. The transport of air suspended particulate around a small town at the atlantic coast of Patagonia was studied by means of a net of continuous monitors (dust gauges and high volume samplers) during 5.5 years. The sampling stations were located at various distances up to about 25 km of a single industrial source which emits PAHs as well as inorganic fluorides at about a constant, continuous and known rate. The concentration of 16 PAHs as well as inorganic F in the dust and in the air, and the rates of advective mass transport per unit of wind erosive power were recorded. The long term analysis of these variables (6‐month moving average regression models) confirms that the emission and dispersion systems have been in relative steady condition during the last years. This simple spatial and temporal situation allows the computation of average long term decay rates of several individual PAHs, by comparing the distribution and transport patterns of these compounds with that of inorganic F‐, which is used as a conservative tracer. A box model of unit angular volumes of the atmosphere centered at the emission source was fitted to the profiles of PAH and F‐concentration at increasing distance from the source. An algorithm to relate spatial rates of decay and transport with temporal rates of decay of several PAHs, based on their known emission rates at the source, is presented. Some PAHs of low molecular weight (<200) were observed to be transported more efficiently than F‐ or heavier PAHs. Environmental decay rates vary from 0.059 g/g/day (Anthracene) to ‐0.62 g/g/day (Fluoranthene), which correspond to half‐lives of 11.5 and 1.1 days respectively. The average half‐life of a group of 12 PAHs investigated is 4.33 days.

Site Fidelity and Survival Differences between Two Groups of New World Red Knots (Calidris canutus)

Abstract During the boreal winter, New World Red Knots (Calidris canutus rufa) principally occupy two areas widely separated in latitude. The larger group of approximately 100,000 birds is distributed along the Patagonian Atlantic coast, the smaller group of about 10,000 along Florida's Gulf coast. Resightings of banded individuals showed no interchange between these groups. The annual survival rate of knots marked in Florida is twice that of marked knots that winter in Patagonia. During northward migration Florida knots were sighted significantly less often at a major New Jersey stopover site than knots marked in Argentina. Whether this segregation is maintained during the breeding season is unknown. Wing and culmen lengths did not differ between the groups. The higher survival of individuals from the smaller Florida group, which presumably migrates a much shorter distance than the Argentina birds, runs counter to current evolutionary theories on the benefits of migration.

Observations on the Occurrence and Origin of Petroleum in Argentina and Bolivia

This paper, based on observations in 1917, outlines the geographic and geologic range of petroleum indications in Argentina and the Atlantic watershed of Bolivia, and discusses the probable mother-rocks. Besides the Comodoro Rivadavia field on the Atlantic coast of Patagonia, where petroleum is produced in quantity, seepages and other evidences of oil are scattered along a sub-Andine belt over fifteen hundred miles long from southwestern Argentina to north central Bolivia, and range through many thousands of feet of the sedimentary series. The original sources appear to be sediments containing organic remains in formations of widely different ages, ranging from Devonian to Cretaceous. The chief source beds are here postulated as being the marine Devonian and Cretaceous in the northern Argentine-Bolivian belt; fresh or brackish water Upper Triassic near Mendoza; marine Upper Jurassic-Lower Cretaceous in southwestern Argentina; and marine Cretaceous or older beds on the Atlantic Coast.