Browsing by Author "Palma, Alvaro T."

Now showing 1 - 9 of 9
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    Antarctic shallow suhtidal echinoderms: is the ecological success of broadcasters related to ice disturbance?
    (SPRINGER, 2007) Palma, Alvaro T.; Poulin, Elie; Silva, Marcelo G.; San Martin, Roberto B.; Munoz, Carlos A.; Diaz, Angie D.
    One characteristic pattern found in the marine Antarctic shallow environments is the unusually high proportion of species with protected and pelagic lecitotrophic development modes. However, species with planktotrophic development generally appear as the most conspicuous types of organisms in these environments. The Antarctic shallow benthos is considered as one of the most disturbed in the world, mainly due to the action of ice, thus one could hypothesize that such an environment should favor organisms with high dispersal capability. In order to test this general hypothesis, for two consecutive summers (2004-2005) and at two locations, we quantified the abundance and size distribution of most echinoderms present along bathymetric transects. Our results show the predominance of broadcasters (i.e., Sterechinus neumayeri and Odontaster validus) at a location where disturbances are common, while brooders (e.g., Abatus agassizii) only occurred at shallower depths of the least disturbed location. These results not only corroborate the hypothesis that local disturbance is an important factor generating these ecological patterns, but also suggest how ice-related disturbances could represent a major selecting agent behind the patterns of species diversity at an evolutionary scale in Antarctica.
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    Coastal brachyuran decapods
    (2006) Palma, Alvaro T.; Pardo, L. M.; Veas, R.; Cartes, C.; Silva, M.; Manriquez, K.; Diaz, A.; Munoz, C.; Ojeda, F. P.
    The importance of coastal morphology, and its influence on the magnitude of larval delivery and subsequent recruitment patterns of brachyuran decapods, was investigated at a broad range of spatial and temporal scales along the central coast of Chile. Larvae were quantified through plankton net towing as well as by using artificial settlement collectors deployed at different depths, while the abundance of benthic stages was quantified via in situ SCUBA airlifting and visual surveys. The abundance of young-of-the-year (YOY) and of individuals older than 1 yr (> 1 yr) was compared between sites with contrasting conditions of coastal exposure at peninsulas several hundred kilometers apart. Additionally, we pursued a temporally more detailed surveying program, which included more species, at the southernmost peninsula. From our results we conclude that: (1) in general, the abundance of Paraxanthus barbiger, the most abundant species throughout, was greater at all locations in 2003 compared with 2004 and it was also greater (particularly > 1 yr individuals) at protected sites; (2) for most of the species, the abundance of megalopae and YOY was highly seasonal, with peaks during the austral spring and summer months; and (3) for at least 2 of the 4 species considered in the southernmost peninsula, the abundance of YOY and > 1 yr individuals exhibited higher abundance at the protected site. In spite of our efforts, we failed to find significant correlation between local abundance of settlers on artificial collectors and YOY individuals that settled in nursery habitats directly below. Post-settlement mortality, operating very soon after settlement, is a likely explanation for this finding. Our study highlights the importance of considering factors such as coastal morphology together with the occurrence of post-settlement processes when studying coastal organisms with complex life cycles.
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    Crypsis in Paraxanthus barbiger (Decapoda: Brachyura)
    (2008) Manriquez, Karen C.; Pardo, Luis M.; Wells, R. J. David; Palma, Alvaro T.
    Marine organisms have evolved a suite of responses to minimize the exposure to predators. Visual crypsis is one such strategy to avoid predation. Paraxanthus barbiger (Poeppig, 1836) is a species that exhibits different color morphotypes over heterogeneous substrates as a means of protection against visual predators. Our main objectives were to quantify the occurrence of color morphotypes over a three-year period and to investigate, via an experimental approach, on the possible mechanisms involved that would provide crypsis to this species. Field surveys occurred over a three-year period at two,nearby sites on the central Chilean coast. Initial observations indicated that small juvenile P. barbiger exhibited higher degrees of color polymorphism than larger (> 20 mm carapace width) conspecifics. Furthermore, survival rates of small (< 10 mm carapace width) P. barbiger exposed to predators increased on heterogeneous substrata under both natural and laboratory conditions. Laboratory experiments further demonstrated that newly settled P. barbiger actively select heterogeneous substrata. Hence, cryptic responses of this species might reduce predation-mediated mortality through color pattern disruption of individuals with respect to their environment.
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    Effect of prolonged exposition to pulp mill effluents on the invasive aquaticplant Egeria densa and other primary producers
    (2008) Palma, Alvaro T.; Silva, Marcelo G.; Munoz, Carlos A.; Cartes, Carolina; Jaksic, Fabian M.
    The recent disappearance of the aquatic plant Egeria densa, a Brazilian native invasive species, from a wetland in southern Chile prompted several efforts to unveil the origin of this phenomenon. Because these changes occurred by the time a newly built pulp mill started its operations in the area, a reasonable doubt for a cause-effect relationship is plausible. We implemented a mesocosm approach to directly evaluate the effect of treated pulp mill effluents (PMEs) on several growth-related parameters of E. densa as well as other primary producers. We hypothesize that effluent, at a dilution similar to that detected in the zone of the wetland where the negative environmental impacts were evident, has a significant negative effect on this aquatic plant as well as on other primary producers inside a mesocosm system. After a prolonged (months) exposure to both 0% PME with pure river water and a 4 to 5% (v/v) dilution of treated PME, no effect on E. densa was measured. Furthermore, plants exposed to effluent exhibited a significantly greater general growth rate. Coincidently, chlorophyll a concentration in the water column and periphyton biomass also changed over time, but without any pattern attributable to the effluent. Values of the autotrophic index obtained from the periphyton growth pattern did not suggest enrichment of the system with organic matter. Our results only refer to the direct effect of mill effluents on several biotic responses, but they represent an important advance toward generation of the scientific knowledge necessary to understand how the ecosystem functions while receiving this and other unquantified sources of water.
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    Experimental Evidence of the Tolerance to Chlorate of the Aquatic Macrophyte Egeria densa in a Ramsar Wetland in Southern Chile
    (2013) Palma, Alvaro T.; Schwarz, Alex O.; Farina, Jose M.
    In 2004, a massive die-off of the aquatic macrophyte Egeria densa occurred in a Ramsar wetland in southern Chile. In 2004, a pulp mill started its operations upstream from the wetland. Chlorate, a chemical compound found in pulp mill effluent, was one of the suspected causes of the observed ecosystem-level changes. The hypothesis was that high concentrations of chlorate in the wetland caused a massive die-off of the large populations of Egeria densa in this ecosystem. In this study several experimental efforts were aimed to understanding the potential effect of chlorate on E. densa. Plants were exposed to different doses of chlorate for variable periods in a large mesocosm array and several morphometric endpoints were quantified. Additionally, an ecotoxicological assay was implemented providing the first insight into the tolerance to chlorate of this aquatic plant. Both mesocosm and ecotoxicological evidences suggest that E. densa is tolerant to fairly high levels of chlorate (i.e. EC50 in the order of 1000 mg/L), at least three orders of magnitude larger than the highest concentration recorded in the wetland. Our results provide evidence that should guide the efforts of understanding the real causes of this environmental change.
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    Near-shore distribution of phyllosomas of the two only lobster species (Decapoda: Achelata) present in Robinson Crusoe Island and endemic to the Juan Fernandez archipelago
    (SOC BIOLGIA CHILE, 2011) Palma, Alvaro T.; Caceres Montenegro, Ismael; Bennett, Richard S.; Magnolfi, Spartaco; Henriquez, Luis A.; Guerra, Jorge F.; Manriquez, Karen; Palma, R. Eduardo
    Two lobster species coexist in the southeast Pacific Juan Fernandez archipelago, Jasus frontalis (Milne-Edwards, 1837) and Acantharctus delfini (Bouvier, 1909). Like most lobster species they undergo a prolonged larval period, which is particularly long for J. frontalis (> 16 months). Though typical of Palinurids, this long larval duration is usually not thought to be conducive to local recruitment. While it is known that settlement is confined to the three islands of the archipelago (Robinson Crusoe, Alejandro Selkirk and Santa Clara) and Desventuradas Islands (aprox. 800 km to the north), it remains poorly understood how local larval supply allows such distribution pattern. The goal of this study is twofold. Firstly, we aimed to characterize the distribution and abundance of the larvae of these two species around Robinson Crusoe Island using plankton tows and systematic hydrographic records between October 2008 to March of 2011, thus providing the first systematic and prolonged coupled biophysical observations in the nearshore of the archipelago. We hypothesize that spatial and temporal larval distribution patterns are associated to their retention around the archipelago, thus contributing to our knowledge of the physical and biological processes maintaining their extreme isolation. Secondly, using molecular genetics, we confirm a simple taxonomic criteria to distinguish the larvae of the two species, thus aiding future studies of larval dynamics. Throughout phyllosomas of A. delfini were more abundant than that of J. frontalis. Both species were more abundant on the northern shores of Robinson Crusoe Island and generally associated with warmer and saltier waters and mostly present in the samples collected during spring and summer months. Phyllosomas of both species were more abundant during night-time tows in the upper layer of the water column surveyed suggesting a diurnal vertical migration behavior which, for coastal dwelling meroplanktonic species, can be related to a nearshore larval retention mechanism. These preliminary results represent a pioneering effort to understand the mechanisms driving the endemism and extreme isolation of the two study species.
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    Phytoplanktonic primary production modulated by coastal geomorphology in a highly dynamic environment of central Chile
    (2009) Palma, Alvaro T.; Henriquez, Luis A.; Patricio Ojeda, F.
    Coastal upwelling circulation has a regional fertilizing effect upon phytoplanktonic communities (i.e. enhancement of photosynthetic rates, increased biomass), but its influence at smaller spatial and temporal scales is less clear. At local scale (100's m) and under upwelling-favorable conditions, retention zones with higher primary production (PP) levels tend to occur at the lee or protected side of small headlands induced by the orientation, geometry, size and general geomorphology of these coastal formations. Here we quantified net and gross primary production (NPP and GPP), community respiration (CR) and biomass (Chl-a) of natural phytoplankton assemblages in coastal environments of central Chile. The main goal was to determine short-term patterns in PP and CR around two small peninsulas in central Chile where measurable differences in several environmental variables can be expected, and we hypothesize that differences will no longer occur under non-upwelling/relaxation conditions. Results indicate that NPP GPP and CR differ at local scale, and contrary to previous findings we found that weakening of upwelling-favorable winds can generate an opposite pattern to that observed under active upwelling periods, whereas the exposed site retains higher biomass and exhibits higher PP levels compared to the protected site. Our results highlight the importance of short-term variability in PP, CR and their coupling with the distribution and abundance of the quick-responding phytoplankton at local spatial scale.
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    Restricted geographic distribution and low genetic diversity of the brooding sea urchin Abatus agassizii (Spatangoidea: Schizasteridae) in the South Shetland Islands: A bridgehead population before the spread to the northern Antarctic Peninsula?
    (2012) Diaz, Angie; Alejandro Gonzalez-Wevar, Claudio; Maturana, Claudia S.; Palma, Alvaro T.; Poulin, Elie; Gerard, Karin
    The glacial cycles of the Pleistocene have promoted the principal climatic changes of the Southern Ocean, and motivated scientific interest regarding the strategies developed by marine benthic invertebrates to tolerate and overcome the extension and contraction of the ice sheet on the Antarctic continental platform. A recent study of the bathymetric zonation and distribution of macro-invertebrates in a shallow subtidal area of Fildes Bay (King George Island, South Shetlands Islands, Antarctica) highlighted the presence of a large aggregation of the brooding sea urchin Abatus agassizii, whose geographic distribution is known only for localities south of the Antarctic convergence (Antarctic Peninsula and South Shetland and South Georgia Islands in the Scotia Arc). Its presence is atypical, given that these shallow populations should have been erased from the vicinity of the Antarctic Peninsula by the advances and retreats of the ice sheet, and the absence of a larval stage associated with brooding should limit re-colonization from northern Subantarctic areas. The aim of the study was to evaluate whether A. agassizii may have survived the glaciations in its narrow bathymetric range in the South Shetland Islands, or whether this population corresponds to a newcomer that re-colonized the area despite its low dispersal capacities. For this, we combined multidisciplinary approaches based on the geographical distribution of A. agassizii, its genetic diversity and its phylogenetic relationships with other species of the genus. In spite of an intensive sampling effort, the low occurrence of A. agassizii indicated that its distribution is very scarce along the Shetlands Islands and the Antarctic Peninsula, and seems to be restricted to protected and ice-free areas of Fildes Bay in King George Island. Moreover, this population presented very low genetic diversity associated with the signal of a recent demographic expansion. Finally, the reconstruction of the phylogenetic relationships among species of Abates using mitochondrial COI sequences established the affinity of the Antarctic A. agassizii with Subantarctic species. Based on these results we consider that the presence of this species in the Shetland Islands more likely corresponds to a recent re-colonization from Antarctic Islands located further north.
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    Seasonal dynamics of zooplankton in a northern Chile bay exposed to upwelling conditions
    (2016) Loreto Torreblanca, M.; Perez-Santos, Ivan; San Martin, Bruno; Varas, Eduardo; Zilleruelo, Rodrigo; Riquelme-Bugueno, Ramiro; Palma, Alvaro T.
    Due to the ever-increasing use of the coastline for industrial purposes, particularly by those activities that take up great amounts of sea water, it is fundamental to understand the composition of the planktonic fauna and its natural spatial and temporal variability in relation to hydrographic variables, in order to understand the potential impact of such undertakings. Totoralillo Norte (similar to 30 degrees S) is an embayment located within a well-known area of recurring upwelling events, as well as a zone with projection for industrial development. Here we performed seasonal surveys (several days sampling within each season) during 2013 and 2014 recognizing an abundant zooplanktonic community with a good representation of the main taxa comprised by at least 166 species. In terms of numbers, copepods dominated the holoplankton (91.7%), whereas meroplankton was mainly composed of larval stages of barnacles, mollusks, decapods, bryozoans and fish. In spite this being a coastal zone normally affected by upwelling events, zooplankton abundance was high throughout the year, even during periods dominated by weak winds and downwelling conditions. Studies such as this can help unveil relevant ecological patterns and their related processes; vital information that must be considered during an environmental impact assessments.