An inverse latitudinal biodiversity pattern in asellote isopods (Crustacea, Peracarida) from the Southwest Atlantic between 35° and 56°S

Fil: Biancalana, Florencia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto Argentino de Oceanografia. Universidad Nacional del Sur. Instituto Argentino de Oceanografia; Argentina

TABLE 2. - Number of Asellota isopods collected in the Beagle Channel

This work documents the occurrence of drillholes on muricid Trophon geversianus shells from a Holocene raised marine deposit in the Beagle Channel, located on the extreme southern tip of South America (~ 55ºS).Based on drillhole morphology and previous data under laboratory conditions these predatory holes are attributed to conspecifics, thus suggesting cannibalism.It appears that when food is scarce and the alternative prey (Tawera gayi and other clams) is not available, T. geversianus may increase the frequency of cannibalism in order to compensate for the loss of bivalve prey.Cannibalism therefore developed at ca. 4000 yr.BP as a response to the lack of clams, which would have disappeared during a sudden hydrological local event that affected the filter feeders.

Fil: Lopez Gappa, Juan Jose. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina

The crab Halicarcinus planatus is the only hymenosomatid crab that inhabits the southern tip of South America and is the only decapod species that reproduces twice a year in the Beagle Channel. In this article, we study the moult cycle in the field (moult frequency, analysis of size frequency distribution) and linked it with growth studied in the laboratory (absolute and per cent growth increment, Hiatt function). Hiatt functions were similar for males and females. Moult frequency was seasonal: in early austral spring and in austral summer. In females, the pubertal moult is the terminal moult, whereas males continue moulting after attaining the size of morphometric maturity. Moult increment was highly variable. The relationship between absolute moult increment and crab size was described by a quadratic function. Per cent growth increment decreased with size, and relationships were different for each sex: linear for females and quadratic for males. Seven and eight modal groups explained the size frequency distributions for females and males from the field, respectively, and revealed the existence of two cohorts of recruits per year. Further modal analysis was mainly hampered by the high variability of size increment that could make any moulting individual fall in its own or one of two following modal groups. The antagonism between growth and reproduction was evident in small males. We hypothesize that the terminal pubertal moult is an advantageous feature that allows females to maximize their investment in reproduction after their terminal moult, which allows this species to have two spawnings per year.

Contaminants in the southern tip of South America: Analysis of organochlorine compounds in feathers of avian scavengers from Argentinean Patagonia

Current knowledge on the pyramidellids from the southern tip of South America appears restricted to a couple of species described in the beginning of the 20th century and a few taxa subsequently reported from this area, including some species recognized as new, but never formally described. This study fills this gap in the knowledge by performing the first revision on the diversity of Pyramidellidae occurring in the Magellanic Province. The material for this study arises from extant collections made along the Atlantic and Pacific coasts of Patagonia, the Beagle Channel, the Magellan Strait and in Burdwood Bank; this information was supplied with specimens from museum collections. As part of this study, eight pyramidellid species, belonging to the genera Turbonilla, Fargoa, Menestho and Brachystomia are recognized from the Magellanic Province, including five species new to science: Turbonilla deseadensis n. sp., Menestho beaglensis n. sp., M. patagonica n. sp., Brachystomia conica n. sp. and B. tenuilirata n. sp. The distinctive characters of Menestho, a genus frequently misunderstood in the past, are also discussed. The presence of Menestho and Brachystomia are here documented for the first time for the southern tip of South America. In addition, a neotype for Turbonilla strebeliStrebel, 1905 (nonVerrill, 1880) is here designated.

Predictions based on animal ecology are critical to model human-specific decisions in zooarchaeology. However, information about the past distribution of prey is rare, and evaluations normally rely on modern ecological parameters to fill in the gaps. These assumptions often are problematic since species distributions are likely to have fluctuated over time as a consequence of different environmental factors, or as the by-product of cumulative human impacts. Stable isotope studies, including bulk and compound specific isotope analysis, have the potential to address this problem by providing a suitable paleoecological framework. A number of studies have suggested that variation in carbon and nitrogen stable isotope values among marine animals can be explained by differences in the isotopic composition between nearshore and offshore ecosystems, and/or by changes in trophic levels in marine food webs. In this chapter, we provide a long-term perspective on the interaction between Beagle Channel hunter-gatherer-fisher societies and marine resources of the southern tip of South America through the application of stable isotope ecology. We address changes in the foraging behavior of Otariids in response to human predation, the human use of offshore patches during the late Holocene, and the isotopic paleoecology to understand human dietary variations in the region.

ABSTRACT. Epipelagic medusae collected in the Magellan region (Southern Patagonian Zone) during spring 2009 were analyzed. A total of 25 species of medusae were identified (23 hydromedusae and 2 scyphomedusae). The highest level of abundance of medusae was found in the Almirantazgo and Agostini fjords, and the Beagle Channel. 12 medusae species were recorded for the first time in the Magellan region. Six dominant species were found: Clytia simplex (19.8%), Rophalonema funerarium (16.2%), Aurelia aurita (15.9%), Bougainvillia muscoides (15.5%), Proboscidactyla stellata (8.9%) and Obelia spp. (6.0%). Most of the dominant species were collected in shallow strata (0-50 m), with less saline waters ( R. funerarium , which was mainly collected above depths of 25 m in more saline waters (30-33). These results confirm the success of several species in the colonization of the inland waters of the Southern Patagonian Zone.

The Beagle Channel (BC) is a long and narrow interoceanic passage (∼270 km long and 1–12 km wide) with west-east orientation and complex bathymetry connecting the Pacific and Atlantic oceans at latitude 55°S. This study is the first integrated assessment of the main oceanographic features of the BC, using recent oceanographic observations from cruises, moored instruments and historical observations. The waters transported into the BC are supplied mainly by the Cape Horn Current, which carries Subantarctic Water (SAAW) at depth (100 m below surface) along the Pacific Patagonian continental shelf break. SAAW enters the continental shelf via a submarine canyon at the western entrance of the BC. The SAAW is diluted by fresh, nutrient depleted (nitrate, phosphate and silicic acid) Estuarine Water (EW) from Cordillera Darwin Ice Field (CDIF) forming modified SAAW (mSAAW). Freshwater inputs from the CDIF generate a two-layer system with a sharp pycnocline which delimits the vertical distribution of phytoplankton fluorescence (PF). Two shallow sills (<70 m) along the BC contribute to EW and mSAAW mixing and the homogenization of the entire water column east of the sills, coherent with Bernoulli aspiration. The central section of the BC, extending ∼100 km toward the east, is filled by a salty (31–32) variety of EW. In winter, this central section is nearly vertically homogeneous with low nutrient concentrations (0.9–1.1 μM PO4 and 7.5–10 μM NO3) and PF. The temporal variability of seawater temperature from 50 to 195 m in the central section of the BC was found to be mostly dominated by the annual and semiannual cycles and influenced by tidal forcing. The middle section of the BC was less influenced by oceanic inputs and its basin-like structure most likely favors retention, which was observed from the weakly stratified water column at the mooring site. Toward the east, the central section bathymetry is disrupted at Mackinlay Strait where another shallow sill separates the middle channel from the shallow eastern entrance that connects to the Atlantic Ocean. In this section, a weakly stratified two-layer system is formed when the eastward surface outflow (salty-EW) flows over a deeper, denser tongue of oceanic mSAAW.

Fil: Salariato, Diego Leonel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Botanica Darwinion. Academia Nacional de Ciencias Exactas, Fisicas y Naturales. Instituto de Botanica Darwinion; Argentina

Sea lions have been one of the main resources used by Holocene hunter–gatherers in Southern Patagonia, but many aspects of their exploitation still remain to be studied if we are to understand the variability involved in human-pinniped relationships since the human peopling of the region at the end of the Pleistocene. In this chapter, Southern Patagonia is defined as the southern tip of South America, from Santa Cruz river (50°S) to Cape Horn (55°S). The main pinniped species in this region are the Southern sea lion (Otaria flavescens) and the South American fur seal (Arctocephalus australis). The former weighs 300 kg (males) and 150 kg (females), and the latter, 140 kg (males) and 50 kg (females). Besides their body size, these two species differ in the loci they use for mating and pupping, as well as in the waters where they feed (King 1983; Jefferson et al. 1993; Bastida and Rodriguez 2003).

The crab Halicarcinus planatus (Fabricius, 1775) is the only member of Hymenosomatidae that inhabits the southern tip of South America, and it is the only decapod species that reproduces twice a year in the Beagle Channel. In this study, we analysed seasonal variations in development duration, body size, biomass (dry weight), and elemental composition (CHN) of larvae from a population living at the southernmost limit of the species’ geographic range. Compared to offspring produced in December (early summer), larvae released in August (late winter) were on average larger and heavier, and they showed a higher carbon content (suggesting a larger lipid fraction). This pattern of intraspecific variation in larval size and biomass corresponds with minimum primary productivity in sub-Antarctic regions during winter, suggesting that large winter eggs may represent a reproductive adaptation to a regular pattern of variation in nutritional conditions, including food limitation in winter. As an additional or alternative explanation, also strong salinity fluctuations occurring in summer might reduce larval quality in the December cohort. In conclusion, seasonal variation in larval size and biomass may be related to variations in nutritional and/or physical factors.

Frequent sampling of zooplankton is essential to understand their annual dynamics. However, in polar and subpolar ecosystems, such sampling is rare. This study comparatively analysed, for the first time, the annual mesozooplankton succession in the northwest nearshore and external zones of Ushuaia Bay in the sub-Antarctic Beagle Channel by monthly sampling over two years. The nearshore zone, with shallow waters and strong continental and anthropogenic influence, was characterised by the year-round occurrence of the euryhaline copepod Eurytemora americana and adventitious taxa. The mesozooplankton community exhibited pronounced monthly and year-to-year variability but, as a general seasonal trend, winter assemblages were dominated by the copepod Oithona similis and adventitious nematodes, whereas the spring–summer ones were dominated by E. americana, the cladoceran Podon leuckarti and Cirripedia nauplii. In the external zone, the copepods Drepanopus forcipatus and Ctenocalanus citer were found throughout the year. The annual succession showed a clearer seasonal pattern. Main shifts in community structure occurred in late winter–spring and late summer–autumn, when a high representation of meroplankton and appendicularians was closely associated with phytoplankton blooms. The higher temporal variability in the nearshore community was partially related to variable contributions of adventitious taxa to assemblage composition and may be also reflecting stressful conditions for plankton species linked to freshwater and urban discharges reported within the bay. This study allowed filling the temporal gaps in previous research and providing a more complete picture of the annual mesozooplankton dynamics in the Beagle Channel, generating hypotheses at the community and population levels for future research.

A total of 3142 specimens of Pagurus comptus (White, 1847) were collected on the kelp beds in the Beagle Channel, Argentina, during 1999-2001. Fifteen of these hermit crabs were infested by a bopyrid provisionally identified as Anathelges cf. hyptius (Thompson, 1902). Of these parasites, 10 were attached to their hosts' pleons, whereas the remaining five were found inside the branchial chambers of the hermit crabs. All branchial parasites were immature females though one of them harboured a male. This is the first time that a postlarval stage of Anathelges is recorded inside the branchial chamber of its host. Whether this location is normal or erratic is unknown. This collection of Anathelges has made it possible for us to describe and illustrate four sequential female stages of this parasite, to extend the geographic range of distribution of this genus to the southern tip of South America, and to discuss the taxonomic value of some of the characters used to distinguish species in this genus.