Browsing by Author "Navarrete, SA"

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    Alongshore and temporal variability in chlorophyll a concentration in Chilean nearshore waters
    (2003) Wieters, EA; Kaplan, DM; Navarrete, SA; Sotomayor, A; Largier, J; Nielsen, KJ; Véliz, F
    Phytoplankton and particulate organic matter constitute the primary food source for adult filter-feeders, as well as for larval stages of many benthic and pelagic organisms. The structure and dynamics of nearshore benthic communities may be associated with variation in nearshore primary production. However, we know little about the scales of variability in phytoplankton in nearshore waters along open coasts, or about their causes. To characterize spatial and temporal patterns of chl a concentration, we conducted 2.5 yr of daily, shore-based monitoring at 3 sites separated by 10s of km within an upwelling region in central Chile. We found that: (1) peaks in chl a concentration were typically short-lived, persisting no longer than 4 d, (2) blooms occurred in spring to early summer months at all sites, but also during autumn months at 1 site (Las Cruces), and (3) the intensity and frequency of blooms were consistently different among sites; highest concentrations were at Las Cruces, lower at El Quisco, and the lowest at Quintay. Analyses of wind data and surface temperature, and inspection of Advanced Very High Resolution Radiometer (AVHRR) satellite images, suggested that among-site differences were due, at least in part, to alongshore variation in upwelling intensity and the formation of warm-water pockets or upwelling shadows in sections of the coast, such as Las Cruces. In contrast to the spatial pattern described offshore and over larger spatial scales, chl a concentrations were significantly lower at the coldest site, Quintay, located at the core of an upwelling center (Pta. Curaumilla), than at the warmer site of Las Cruces, which lies downstream from upwelling. Day-to-day variation in chl a levels during spring at Las Cruces seems related to the alongshore intrusion of waters upwelled upstream. Overall, the pattern observed at our 3 sites, together with previous studies at other upwelling systems, suggests that sections of the coast around 15 to 20 km downstream (equatorward) from upwelling centers could exhibit consistently higher phytoplankton concentrations than sites located in front of upwelling centers, generating a source-sink type of geographic pattern of nearshore nutrients and phytoplankton along the coast.
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    Avoiding offshore transport of competent larvae during upwelling events
    (2002) Poulin, E; Palma, AT; Leiva, G; Narvaez, D; Pacheco, R; Navarrete, SA; Castilla, JC
    The coast of central Chile is characterized by the occurrence of coastal upwelling during the austral spring and summer seasons, which probably has important consequences for the cross-shelf transport of larval stages of many species. Three cruises were conducted off the locality of El Quisco during upwelling-favorable wind periods to determine the surface distribution of epineustonic competent larvae of the gastropod Concholepas concholepas during such events. Contrary to the predictions of a traditional model, where neustonic-type larvae are transported offshore under such conditions, competent larvae of this species were exclusively found in the area between the shore and the upwelling front. Two additional cruises were conducted during calm periods to determine diel variation in the vertical distribution of C. concholepas competent larvae. The absence of competent larvae at the surface during early night hours suggests a reverse vertical migration. Thus, the retention of C. concholepos competent larvae in the upwelled waters could be the result of the interaction between their reverse diel vertical migration and the typical two-layer upwelling dynamics.
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    Feeding by larvae of intertidal invertebrates
    (2006) Vargas, CA; Manríquez, PH; Navarrete, SA
    One of the leading determinants of the structure and dynamics of marine populations is the rate of arrival of new individuals to local sites. While physical transport processes play major roles in delivering larvae to the shore, these processes become most important after larvae have survived the perils of life in the plankton, where they usually suffer great mortality. The lack of information regarding larval feeding makes it difficult to assess the effects of food supply on larval survival, or the role larvae may play in nearshore food webs. Here, we examine the spectrum of food sizes and food types consumed by the larvae of two intertidal barnacle species and of the predatory gastropod Concholepas concholepas. We conducted replicated experiments in which larvae were exposed to the food size spectrum (phytoplankton, microprotozoan and autotrophic picoplankton) found in nearshore waters in central Chile. Results show that barnacle nauplii and gastropod veligers are omnivorous grazers, incorporating significant fractions of heterotrophs in their diets. In accordance with their feeding mechanisms and body size, barnacle nauplii were able to feed on autotrophic picoplankton (< 5 mu m) and did not consume the largest phytoplankton cells, which made the bulk of phytoplankton biomass in spring-summer blooms. Balanoid nauplii exhibited higher ingestion rates than the smaller-bodied chthamaloid larvae. Newly hatched C. concholepas larvae also consumed picoplankton cells, while competent larvae of this species ingested mostly the largest phytoplankton cells and heterotrophic protozoans. Results suggest that persistent changes in the structure of pelagic food webs can have important effects on the species-specific food availability for invertebrate larvae, which can result in large-scale differences in recruitment rates of a given species, and in the relative recruitment success of the different species that make up benthic communities.
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    Internal tidal bore warm fronts and settlement of invertebrates in central Chile
    (2004) Vargas, CA; Narváez, DA; Piñones, A; Venegas, RM; Navarrete, SA
    We studied the occurrence of large high frequency temperature fluctuations and their potential association with settlement of intertidal invertebrates during the spring/summer period 1999/2000 at Las Cruces, on the coast of central Chile. Our results showed the existence of internal tidal bores, characterized by sharp drops in water temperature at the surface and near the bottom, and subsequent temperature increases, which occurred with a semidiurnal periodicity. Measured currents support the hypothesis of alternating onshore and offshore movement of warm-water fronts. The frequency of the events varied through the summer and their amplitude seems to be modulated by onshore winds. The strongest events were observed when strong onshore winds occurred in late afternoon hours and the entire water column showed a semidiurnal temperature signal. Highest values of chlorophyll concentration in the intertidal zone and daily settlement of bivalves, gastropods and crustaceans were observed at times when conditions were favorable for occurrence of internal tidal bores. Results suggest that internal tidal bore warm fronts could play an important role in the transport of neustonic larval invertebrates and the delivery of phytoplankton to at least some intertidal sites along the coast of Chile. (C) 2004 Elsevier Ltd. All rights reserved.
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    Larval development of the intertidal barnacles Jehlius cirratus and Notochthamalus scabrosus (Cirripedia: Chthamalidae) under laboratory conditions
    (2000) Venegas, RM; Ortíz, V; Olguín, A; Navarrete, SA
    Larvae of the common intertidal chthamalid barnacles Jehlius cirratus and Notochthamalus scabrosus were obtained from mature adults collected in central and northern Chile and cultivated in the laboratory at temperatures typical of the conditions encountered by larvae in these regions. Morphological and developmental descriptions of the six naupliar stages and the cyprid stage of both species are given. Both species clearly present the general pattern of development for chthamalids, in which the structural characters of the cephalic shield and abdominal process, in conjunction with the utilization of the alphabetical setation formula for antennae, facilitate the identification and differentiation between larval stages. The average time of naupliar larval development of J. cirratus and N. scabrosus in sea-water temperature ranging 15-18 degrees C was 31 and 37 days, while larvae cultivated in temperatures ranging 18-20 degrees C completed naupliar development after 13 and 20.2 days, respectively. This represents a 58% and 45.5% reduction in naupliar development time with a three-degree increase in mean sea water temperature for J. cirratus and N. scabrosus, respectively. The development time from cyprid until settlement and metamorphosis of N. scabrosus lasted between 9 and 11 days, depending on the temperature, while cyprid development for J. cirratus lasted 8 days at 18-20 degrees C. The average sizes of the naupliar and cyprid stages were similar between the species at both temperature ranges. Although the increased temperature reduced the time of larval development, it did not significantly affect larval sizes.
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    Latitudinal trends of species diversity in rocky intertidal herbivore assemblages
    (2002) Rivadeneira, MM; Fernández, M; Navarrete, SA
    In this study we assessed the impact of the spatial scale of analysis on patterns of latitudinal diversity of rocky intertidal invertebrates and on the relationship between local and regional species richness. Fifty-three wave-exposed sites were sampled along the coast of Chile between 18degrees40'S and 42degrees35'S, covering a range of over 2600 km and 25degrees of latitude. Three spatial scales were defined to analyze latitudinal trends of diversity: (1) regional, based on species range limits across the entire region (100s of km), (2) site, corresponding to hundreds of square meters sampled at each location, (3) sampling unit scale, corresponding roughly with a square meter of rocky shore. The analysis showed that spatial patterns of species richness and species turnover varied according to the scale used. At a regional scale, species richness showed a mid-latitudinal peak (i.e. around 30 to 32degreesS), decreasing toward northern and southern latitudes. No clear latitudinal trends in diversity were detected at site and especially at sampling unit scales. Despite the fact that at regional scale species turnover was low and geographically uniform, at the site scale beta diversity showed the existence of 2 zones of higher species turnover (19 to 20degreesS and 30 to 32 S), which may be attributed to changes in ecological and oceanographical regimes. The relationship between regional and local species richness changed depending on the 'local' scale used; unsaturated patterns (linear positive relationship between local and regional diversity) were evident at site scale, whereas saturated patterns (quadratic trend between local and regional diversity) were observed when the local scale was defined in terms of the sampling unit. We suggest that different regulating processes, operating at different spatial scales, may explain the latitudinal trends in diversity at site and sampling unit scales. While regional processes may set an upper limit in species richness at site scale, species interactions (e.g. competition) may control species richness at sampling unit scales. These findings question the current idea of the disproportionate prevalence of regional factors over local ones in determining diversity of local assemblages. They also suggest that regulation of local diversity results from the interplay of regional and local processes.
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    Scales of benthic-pelagic and the intensity of species interactions: From recruitment limitation to top-down control
    (2005) Navarrete, SA; Wieters, EA; Broitman, BR; Castilla, JC
    Large and usually unpredictable variation in species interaction strength has been a major roadblock to applying local experimental results to large-scale management and conservation issues. Recent studies explicitly considering benthic-pelagic coupling are starting to shed light on,and find regularities in, the causes of such large-scale variation in coastal ecosystems. Here, we evaluate the effects of variation in wind-driven upwelling on community regulation along 900 km of coastline of the southeastern Pacific, between 29 degrees S and 35 degrees S during 72 months. Variability in the intensity of upwelling occurring over tens of km produced predictable variation in recruitment of intertidal mussels, but not barnacles, and did not affect patterns of community structure. In contrast, sharp discontinuities in upwelling regimes produced abrupt and persistent breaks in the dynamics of benthic and pelagic communities over hundreds of km (regional) scales. Rates of mussel and barnacle recruitment changed sharply at approximate to 32 degrees-33 degrees S, determining a geographic break in adult abundance of these competitively dominant species. Analysis of satellite images demonstrates that regional-scale discontinuities in oceanographic regimes can couple benthic and pelagic systems, as evidenced by coincident breaks in dynamics and concentration of offshore surface chlorophyll-a. Field experiments showed that the paradigm of top-down control of intertidal benthic communities holds only south of the discontinuity. To the north, populations seem recruitment-limited, and predators have negligible effects, despite attaining similarly high abundances and potential predation effects across the region. Thus, geographically discontinuous oceanographic regimes set bounds to the strength of species interactions and define distinct regions for the design and implementation of sustainable management and conservation policies.
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    Settlement of the gastropod Concholepas concholepas on shells of conspecific adults
    (2004) Manríquez, PH; Navarrete, SA; Rosson, A; Castilla, JC
    Competent larvae of the commercially important marine gastropod Concholepas concholepas (Gastropoda: Muricidae) 'loco', were collected in the field and exposed in the laboratory to adult conspecific shells with and without barnacle epibionts. Settlement and metamorphosis was induced by the presence of barnacles on shells of live or dead conspecifics, but not by C concholepas shells without barnacles. Results from laboratory experiments agreed well with field surveys showing the presence of recruits on conspecific shells overgrown with barnacles in shallow subtidal habitats (similar to3-30 m deep), suggesting the potential importance of barnacles inin inducing settlement and metamorphosis of locos under natural conditions. Most loco recruits were found below the C. concholepas shell apex, feeding on barnacles, inhabiting crevices among them, and inside dead barnacles. The mean size of recruits on locos' shells increased over four months from the beginning of the settlement season and no individual larger than 1.5 cm was observed, suggesting that they abandon adult loco shells at this size, roughly 5-6 months after settlement.
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    Species interactions in intertidal food webs: Prey or predation regulation of intermediate predators?
    (2000) Navarrete, SA; Menge, BA; Daley, BA
    Most natural food webs have more than one predator species, and many have trophic interactions among these predators. When a top predator feeds on an intermediate predator and they both feed on a shared basal resource, a phenomenon labeled intraguild predation (IGP), the potential exists for complex food web dynamics due to predation and competitive effects. Here we investigate the relative importance of direct predation vs. competition by a top predator on an intermediate predator.
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    Temporal and spatial variation in settlement of the gastropod Concholepas concholepas in natural and artificial substrata
    (2002) Martínez, P; Navarrete, SA
    Settlement of concholepas concholepas (Gastropoda: Muricidae) on natural and artificial substrata was studied between April 1999 and March 2001 at two sites in central Chile; the Las Cruces Marine Reserve and El Quisco Management and Exploited Area. Four different artificial materials were tested in the low intertidal zone during 1999 settlement season to determine their properties as settlement and microhabitat substrata for competent Concholepas larvae. Globular pads made of plastic filaments were identified as the best artificial collectors, exhibiting overall higher settlement rates than rock plots and lower variability among replicates within a given site. Thus, subsequent monitoring of settlement used only these globular pads that were replaced twice monthly, The temporal pattern of settlement was remarkably similar from year to year, starting at the end of austral winter (August-September) and ending in summer (December-January), defining a temporally restricted settlement season. Settlement at two sites within the Marine Reserve of Las Cruces was significantly higher than at sites in El Quisco. However, during the second settlement season, an additional site at El Quisco exhibited settlement rates comparable to those observed at Las Cruces. The results show that Concholepas settlement varies significantly over scales of several hundreds of metres as well as tens of kilometres, probably due to differences in coastal oceanographic conditions.
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    Temporal and spatial variation in the distribution of epineustonic competent larvae of Concholepas concholepas along the central coast of Chile
    (2002) Poulin, E; Palma, AT; Leiva, G; Hernández, E; Martínez, P; Navarrete, SA; Castilla, JC
    The abundance of competent epineustonic larvae of the gastropod Concholepas concholepas (Gastropoda: Muricidae) in nearshore waters at 2 sites along the central coast of Chile was examined through monthly plankton tows from July 1999 to June 2000, Larvae were found in plankton collections from July 1999 to February 2000 with maximum abundance in September and October. Settlement in artificial collectors deployed onshore on the lower intertidal zone showed the same unimodal pattern with a settlement peak during October and November. Variation in larval distribution among sampling dates was related to the occurrence of north-south winds. We found that C, concholepas larvae were more abundant closer to shore after moderate southerly wind periods than on calm days, probably because of the shoreward advection of the upper sea surface layer. While sampling during a strong coastal upwelling event (produced by strong southwesterly winds), C. concholepas larvae were only found in the upwelled waters between the front and the coast. This unusual pattern contrasts with what would be expected for typical epineustonic larvae, suggesting the existence of a mechanism of transport or retention by which C. concholepas larvae stay near coastal settling areas, thus avoiding offshore dispersion.