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Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼  30° S) based on a high-resolution atmospheric regional model

Autores:

Bravo, L., Ramos, M., Astudillo, O., Dewitte, B., & Goubanova, K.

Resumen:

Two physical mechanisms can contribute to coastal upwelling in eastern boundary current systems: offshore Ekman transport due to the predominant alongshore wind stress and Ekman pumping due to the cyclonic wind stress curl, mainly caused by the abrupt decrease in wind stress (drop-off) in a cross-shore band of 100 km. This wind drop-off is thought to be an ubiquitous feature in coastal upwelling systems and to regulate the relative contribution of both mechanisms. It has been poorly studied along the central-northern Chile region because of the lack in wind measurements along the shoreline and of the relatively low resolution of the available atmospheric reanalysis. Here, the seasonal variability in Ekman transport, Ekman pumping and their relative contribution to total upwelling along the central-northern Chile region (∼  30° S) is evaluated from a high-resolution atmospheric model simulation. As a first step, the simulation is validated from satellite observations, which indicates a realistic representation of the spatial and temporal variability of the wind along the coast by the model. The model outputs are then used to document the fine-scale structures in the wind stress and wind curl in relation to the topographic features along the coast (headlands and embayments). Both wind stress and wind curl had a clear seasonal variability with annual and semiannual components. Alongshore wind stress maximum peak occurred in spring, second increase was in fall and minimum in winter. When a threshold of −3  ×  10−5 s−1 for the across-shore gradient of alongshore wind was considered to define the region from which the winds decrease toward the coast, the wind drop-off length scale varied between 8 and 45 km. The relative contribution of the coastal divergence and Ekman pumping to the vertical transport along the coast, considering the estimated wind drop-off length, indicated meridional alternation between both mechanisms, modulated by orography and the intricate coastline. Roughly, coastal divergence predominated in areas with low orography and headlands. Ekman pumping was higher in regions with high orography and the presence of embayments along the coast. In the study region, the vertical transport induced by coastal divergence and Ekman pumping represented 60 and 40 % of the total upwelling transport, respectively. The potential role of Ekman pumping on the spatial structure of sea surface temperature is also discussed.

Año: 2016

Palabras claves:

Referencia APA: Bravo, L., Ramos, M., Astudillo, O., Dewitte, B., & Goubanova, K. (2016). Seasonal variability of the Ekman transport and pumping in the upwelling system off central-northern Chile (∼  30° S) based on a high-resolution atmospheric regional model (WRF). Ocean Science, 12(5), 1049-1065. http://dx.doi.org/10.5194/os-12-1049-2016

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

Autores:

Vergara, O., Dewitte, B., Montes, I., Garçon, V., Ramos, M., Paulmier, A., & Pizarro, O.

Resumen:

In addition to being one of the most productive upwelling systems, the oceanic region off Peru is embedded in one of the most extensive oxygen minimum zones (OMZs) of the world ocean. The dynamics of the OMZ off Peru remain uncertain, partly due to the scarcity of data and to the ubiquitous role of mesoscale activity on the circulation and biogeochemistry. Here we use a high-resolution coupled physical/biogeochemical model simulation to investigate the seasonal variability of the OMZ off Peru. The focus is on characterizing the seasonal cycle in dissolved O2 (DO) eddy flux at the OMZ boundaries, including the coastal domain, viewed here as the eastern boundary of the OMZ, considering that the mean DO eddy flux in these zones has a significant contribution to the total DO flux. The results indicate that the seasonal variations of the OMZ can be interpreted as resulting from the seasonal modulation of the mesoscale activity. Along the coast, despite the increased seasonal low DO water upwelling, the DO peaks homogeneously over the water column and within the Peru Undercurrent (PUC) in austral winter, which results from mixing associated with the increase in both the intraseasonal wind variability and baroclinic instability of the PUC. The coastal ocean acts therefore as a source of DO in austral winter for the OMZ core, through eddy-induced offshore transport that is also shown to peak in austral winter. In the open ocean, the OMZ can be divided vertically into two zones: an upper zone above 400 m, where the mean DO eddy flux is larger on average than the mean seasonal DO flux and varies seasonally, and a lower part, where the mean seasonal DO flux exhibits vertical–zonal propagating features that share similar characteristics than those of the energy flux associated with the annual extratropical Rossby waves. At the OMZ meridional boundaries where the mean DO eddy flux is large, the DO eddy flux has also a marked seasonal cycle that peaks in austral winter (spring) at the northern (southern) boundary. In the model, the amplitude of the seasonal cycle is 70 % larger at the southern boundary than at the northern boundary. Our results suggest the existence of distinct seasonal regimes for the ventilation of the OMZ by eddies at its boundaries. Implications for understanding the OMZ variability at longer timescales are discussed.

Año: 2016

Palabras claves:

Referencia APA: Vergara, O., Dewitte, B., Montes, I., Garçon, V., Ramos, M., Paulmier, A., & Pizarro, O. (2016). Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model. Biogeosciences, 13(15), 4389-4410. http://dx.doi.org/10.5194/bg-13-4389-2016

The OMZ and nutrient features as a signature of interannual and low-frequency variability in the Peruvian upwelling system

Autores:

Graco, M., Purca, S., Dewitte, B., Castro, C., Morón, O., Ledesma, J., Flores, G., & Gutiérrez, D.

Resumen:

Over the last decades, the Humboldt Current upwelling ecosystem, particularly the northern component off the coast of Peru, has drawn the interest of the scientific community because of its unique characteristics: it is the upwelling system with the biggest catch productivity despite the fact it is embedded in a shallow and intense oxygen minimum zone (OMZ). It is also an area of intense nitrogen loss and anammox activity and experiences large interannual variability associated with the equatorial remote forcing. In this context, we examined the oceanographic and biogeochemical variability associated with the OMZ off central Peru from a monthly time series (1996–2011) recorded off the coast of Callao (12° 02′ S, 77° 29′ W). The data reveal a rich spectrum of variability in the OMZ that includes frequencies ranging from seasonal to interannual scales. Due to the efficient oceanic teleconnection off Peru, the observed variability is interpreted in the light of an estimate of the equatorial Kelvin wave contribution to sea level anomalies considering the peculiarities of its vertical structure (i.e., the first two baroclinic modes). The span of the data set allows us to contrast two OMZ regimes. The strong regime is associated with the strong 1997–1998 equatorial Pacific El Niño, during which the OMZ adjusted to Kelvin-wave-induced downwelling conditions that switched off the upwelling and drastically reduced nutrient availability. The weak regime corresponds to the post-2000 period associated with the occurrence of moderate central Pacific El Niño events and enhanced equatorial Kelvin wave activity, in which mean upwelling conditions are maintained. It is shown that the characteristics of the coupling between physics and biogeochemistry is distinct between the two regimes with the weak regime being associated with a larger explained variance in biogeochemical properties not linearly related to the ENSO oceanic teleconnection. The data also reveal a long-term trend from 1999 corresponding to a deepening of the oxygen-deficient waters and warming. The implications of our results for understanding the OMZ dynamics off Peru are discussed.

Año: 2017

Palabras claves:

Referencia APA: Graco, M., Purca, S., Dewitte, B., Castro, C., Morón, O., Ledesma, J., Flores, G., & Gutiérrez, D. (2017). The OMZ and nutrient features as a signature of interannual and low-frequency variability in the Peruvian upwelling system. Biogeosciences, 14(20), 4601-4617. http://dx.doi.org/10.5194/bg-14-4601-2017

Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific

Autores:

Vergara, O., Dewitte, B., Ramos, M., & Pizarro, O.

Resumen:

The question of how energy is redistributed in the ocean has renewed the interest for the processes leading to midlatitude subthermocline variability at low frequency. Here we investigate a process that has been disregarded although potentially relevant for climatic studies dealing with the planetary energy budget. The focus is on the Southeastern Pacific where an efficient oceanic teleconnection takes place, linking the remote surface equatorial momentum forcing with the subthermocline through the vertical propagation of low‐frequency long‐wavelength extratropical Rossby waves (ETRW). A high‐resolution model is used to document the vertical energy flux associated with ETRW at interannual to decadal time scales. The analysis of a long‐term (1958–2008) simulation reveals that the vertical energy flux can be interpreted to a large extent as resulting from the coastally forced ETRW as far south as 35°S, so that heat content variability can be predicted along theoretical trajectories originating from the coast below the thermocline. It is shown that the vertical energy flux associated with the El Niño Southern Oscillation forms beams below the thermocline that account for a large fraction of the total vertical energy flux at interannual time scales. Extreme El Niño events are the dominant contributor to this flux, which is hardly impacted by mesoscale activity. The energy beams experience a dissipation processes in the ocean below 1000 m that is interpreted as resulting from vertical turbulent diffusion. Our results suggest that the ETRW at ENSO time scales are strongly dissipated at the surface but still can modulate the heat content in the deep ocean of the Southeastern Pacific.

Año: 2017

Palabras claves: Extratropical Rossby wave, Energy flux, El Niño, Humboldt currents system

Referencia APA: Vergara, O., Dewitte, B., Ramos, M., & Pizarro, O. (2017). Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific. Journal Of Geophysical Research: Oceans, 122(7), 6011-6038. http://dx.doi.org/10.1002/2016jc012614

First Deployment and Validation of in Situ Silicate Electrochemical Sensor in Seawater

Autores:

Barus, C., Chen Legrand, D., Striebig, N., Jugeau, B., David, A., & Valladares, M., Munoz Parra, P., Ramos, M.E., Dewitte, B., & Garçon, V.

Resumen:

An electrochemical sensor is proposed to measure silicate concentration, in situ, in the ocean without any addition of liquid reagent. From the analytical principle to the laboratory prototype toward the first in situ, immersible sensor, the evolution of the mechanical design is presented and discussed. The developed in situ electronics were compared to the commercial potentiostat and gave promising results to detect low silicate signals with a limit of quantification of 1 μmol L−1.The flow rate of the pump appeared to be a crucial parameter in order to transfer the silicomolybdic complex formed from the “complexation cell” to the “detection cell” without dilution as well as to fill and rinse the whole circuit. The study of temperature effect revealed no influence on the electrochemical signal between ~7° and ~21°C. Finally the sensor was successfully deployed for the very first time on a mooring off Coquimbo, Chile and also integrated onto a PROVOR profiling float in the Mediterranean Sea off Villefranche-sur-Mer, France. The data collected and/or sent through satellite were in good agreement with the 2 reference samples and previously published values illustrating the great potential of this electrochemical sensor. A 7 days silicate time series from the mooring deployment off Chile is also presented.

Año: 2018

Palabras claves: Autonomous sensor, Reagentless electrochemical detection, Silicate, Seawater, Mooring and float deployments

Referencia APA: Barus, C., Chen Legrand, D., Striebig, N., Jugeau, B., David, A., & Valladares, M., Munoz Parra, P., Ramos, M.E., Dewitte, B., & Garçon, V. (2018). First Deployment and Validation of in Situ Silicate Electrochemical Sensor in Seawater. Frontiers In Marine Science, 5. doi: 10.3389/fmars.2018.00060

Tangled and drowned: a global review of penguin bycatch in fisheries

Autores:

Crawford, R., Ellenberg, U., Frere, E., Hagen, C., Baird, K., Brewin, P., Crofts, S., Galss, J., Mattern, T., Pompert, J., Ross, K., Kemper, J., Ludynia, K., Asherley, R., Steinfurth, A., Suazo, C., Yorio, P., Tamini, L., Mangel, J., Bugoni, L., Jiménez Uzcategui, G., Simeone, A., Luna-Jorquera, G., Gandini, P., Woehler, E., Putz, K., Dann, P., Chiaradia, A., & Samll, C.

Resumen:

Penguins are the most threatened group of seabirds after albatrosses. Although penguins are regularly captured in fishing gear, the threat to penguins as a group has not yet been assessed. We reviewed both published and grey literature to identify the fishing gear types that penguins are most frequently recorded in, the most impacted species and, for these susceptible species, the relative importance of bycatch compared to other threats. While quantitative estimates of overall bycatch levels are difficult to obtain, this review highlights that, of the world’s 18 species of penguins, 14 have been recorded as bycatch in fishing gear and that gillnets, and to a lesser extent trawls, are the gear types that pose the greatest threats to penguins. Bycatch is currently of greatest concern for yellow-eyed Megadyptes antipodes (Endangered), Humboldt Spheniscus humboldti (Vulnerable) and Magellanic Spheniscus magellanicus penguins (Near Threatened). Penguins face many threats; reducing bycatch mortality in fishing gear will greatly enhance the resilience of penguin populations to threats from habitat loss and climate change that are more difficult to address in the short term. Additional data are required to quantify the true extent of penguin bycatch, particularly for the most susceptible species. In the meantime, it is crucially important to manage the fisheries operating within known penguin foraging areas to reduce the risks to this already threatened group of seabirds.

Año: 2017

Palabras claves: Fishery, Gillnet, Seabird, Trawl, Conservation, Direct mortality

Referencia APA: Crawford, R., Ellenberg, U., Frere, E., Hagen, C., Baird, K., Brewin, P., Crofts, S., Galss, J., Mattern, T., Pompert, J., Ross, K., Kemper, J., Ludynia, K., Asherley, R., Steinfurth, A., Suazo, C., Yorio, P., Tamini, L., Mangel, J., Bugoni, L., Jiménez Uzcategui, G., Simeone, A., Luna-Jorquera, G., Gandini, P., Woehler, E., Putz, K., Dann, P., Chiaradia, A., & Samll, C. (2017). Tangled and drowned: a global review of penguin bycatch in fisheries. Endangered Species Research, 34, 373-396. http://dx.doi.org/10.3354/esr00869

Microplastic sampling with the AVANI trawl compared to two neuston trawls in the Bay of Bengal and South Pacific

Autores:

Eriksen, M., Liboiron, M., Kiessling, T., Charron, L., Alling, A., Lebreton, L., Richards, H., Roth, B., Ory, N.C., Hidalgo-Ruz, V., Meerhoff, E., Box, C., Cummins, A., & Thiel, M.

Resumen:

Many typical neuston trawls can only be used during relatively calm sea states and slow tow speeds. During two expeditions to the Bay of Bengal and the eastern South Pacific we investigated whether the new, high-speed AVANI trawl (All-purpose Velocity Accelerated Net Instrument) collects similar amounts and types of microplastics as two established scientific trawl designs, the manta trawl and the DiSalvo neuston net. Using a 335 μm net, the AVANI trawl can collect microplastics from the sea surface at speeds up to 8 knots as it “skis” across the surface, whereas the manta and DiSalvo neuston trawls must be towed slowly in a less turbulent sea state and often represent shorter tow lengths. Generally, the AVANI trawl collected a greater numerical abundance and weight of plastic particles in most size classes and debris types than the manta trawl and DiSalvo neuston net, likely because these trawls only skim the surface layer while the AVANI trawl, moving vertically in a random fashion, collects a “deeper” sample, capturing the few plastics that float slightly lower in the water column. However, the samples did not differ enough that results were significantly affected, suggesting that studies done with these different trawls are comparable. The advantage of the AVANI trawl over traditional research trawls is that it allows for collection on vessels underway at high speeds and during long transits, allowing for a nearly continuous sampling effort over long distances. As local surface currents make sea surface abundance widely heterogeneous, widely spaced short-tow trawls, such as the manta and DiSalvo trawls, can catch or miss hotspots or meso-scale variability of microplastic accumulations, whereas the AVANI trawl, if utilized for back-to-back tows of intermediate distances (5–10 km), can bridge variable wind conditions and debris concentrations potentially reducing variance and provide a greater resolution of spatial distribution.

Año: 2018

Palabras claves: Plastic pollution, Marine debris, Microplastics, Bay of Bengal, South Pacific Gyre, Trawl comparison, Validation, Neuston trawls, AVANI trawl

Referencia APA: Eriksen, M., Liboiron, M., Kiessling, T., Charron, L., Alling, A., Lebreton, L., Richards, H., Roth, B., Ory, N.C., Hidalgo-Ruz, V., Meerhoff, E., Box, C., Cummins, A., & Thiel, M. (2017). Microplastic sampling with the AVANI trawl compared to two neuston trawls in the Bay of Bengal and South Pacific. Environmental Pollution, 232, 430-439. https://doi.org/10.1016/j.envpol.2017.09.058

Seasonal variation of carrageenans from Chondracanthus chamissoi with a review of variation in the carrageenan contents produced by Gigartinales

Autores:

Véliz, K., Chandía, N., Rivadeneira, M., & Thiel, M.

Resumen:

Seasonal and geographic variations in carrageenan biosynthesis influence the commercial value and industrial applications of these phycocolloids due to the variation in yield and quality. This study examined the effects of season and seaweed origin on the carrageenans produced by the isomorphic phases of the red alga Chondracanthus chamissoi collected during winter and summer from two localities in the SE Pacific Ocean (northern-central Chile). Results were compared with those from other carrageenan-producing seaweeds, and a random forest analysis was carried out with the carrageenan contents reported for Gigartinales in order to determine the principal variables influencing carrageenan yields. The mean carrageenan contents of C. chamissoi ranged from 15.2 to 42.1% DW. Higher yields were observed in gametophytes than in tetrasporophytes, and in samples collected in summer than in winter. Seaweeds from the site close to a local upwelling center had more carrageenans than those from a more distant site. The chemical composition of the carrageenans of C. chamissoi varied only between phases. Carrageenan contents reported for Gigartinales vary from 5.4 to 75.5% DW. The random forest model showed a large accuracy explaining variation in carrageenan yields (pseudo-r 2 = 0.63), where genus was ranked as the most important factor, followed by biogeographical origin, solar radiation, nitrate concentrations, and temperature. Considering that the understanding of the genetic basis of carrageenan biosynthesis is limited, our analysis highlights the need for experimental studies examining the effects of taxon and geographical origin in these polysaccharides as a strategy for improving both carrageenan quality and quantity through strain selection.

Año: 2017

Palabras claves: Carrageenans, Gigartinales, Chondracanthus chamissoi, Chile

Referencia APA: Véliz, K., Chandía, N., Rivadeneira, M., & Thiel, M. (2017). Seasonal variation of carrageenans from Chondracanthus chamissoi with a review of variation in the carrageenan contents produced by Gigartinales. Journal of Applied Phycology, 29(6), 3139-3150. http://dx.doi.org/10.1007/s10811-017-1203-6

DOI:

Genotype by environment interactions, heritabilities and genetic correlations for productive traits of Haliotis rufescens

Autores:

Farías, W. J., Winkler, F. M., & Brokordt, K. B.

Resumen:

A critical aspect of a selective breeding program is whether responses of traits of interest are similar in different environments. The magnitude of the genotype by environment interaction (GEI) together with heritability (h2) accounts for this aspect. Despite the economic significance of abalones and the interest in genetic improvement programs for their cultivation, only one previous study has reported GEI estimations for this group of mollusks. The objective of the present study was to estimate h2 and the existence of GEI for growth traits of Haliotis rufescens cultivated in Chilean farms with different environmental and management conditions. A total of 2 cohorts (2007 and 2009) of 50 and 42 families of full sibs (FS), respectively, were used. Replicates of each FS family of the 2007 cohort were distributed in two farms in the northern region of the country and were evaluated after 1 and 2 years of cultivation. For the 2009 cohort, replicates of each family were distributed in a farm in the northern region and a farm in the southern region of the country. The estimated h2 values were significant for all traits, with the length and width of the shell and total weight varying primarily by cohort between 0.22–0.62, 0.16–0.58 and 0.40–0.53, respectively. The genetic correlations (rG) between traits were all higher than 0.82. The expected correlated responses for improving the total weight using the shell length as a selection criterion predict a selection gain (14–51%) similar to what would be obtained by selecting directly for weight (16–51%) in all environments examined. Thus, indirect selection by shell length and the direct use of total weight as a selection criterion would yield similar effects in terms of the increase in weight. High rG, not significantly different from 1, were observed for the analyzed traits between replicates of the families in any of the farms compared, both within the northern region and between the northern and southern regions of the country. These high rG were indicative of non-significant GEI for the analyzed traits. Therefore, results suggest that one selective breeding program could provide improved red abalone for the industry in Chile with consistent results between farms located in different environments.

Statement of relevance

Abalones are one of the most important mollusks in aquaculture due to their commercial value in international markets, especially in Asia; as such there are several efforts to develop abalone breeding programs in different countries. In this work we addressed a critical aspect for a selective breeding program, which is to know whether responses of productive traits are similar in different environments. Considering that the magnitude of the genotype by environment interaction (GEI) together with heritability (h2) accounts for this aspect, we estimated these genetic quantitative parameters for growth traits (total mass, shell length and width) in two cohorts of the red abalone, Haliotis rufescens, cultivated throughout Chile. Results indicated that the application of selection by the shell length at age of harvest has the greatest potential for improving the production of H. rufescens. These improvements are practical (ease and accuracy in measurement), have indirect effects on the objective trait of selection (weight), and consist of a trait that is not significantly affected by genotype-environment interactions. In addition, the results obtained suggest that a single selective breeding program would be sufficient for the red abalone industry in Chile, as the response to selection of traits associated with growth would be similar in different environments. Red abalone is naturally distributed in California and Baja California coasts, and this information can be especially useful in planning breeding programs also in the west coast of USA and México.

Año: 2017

Palabras claves: Abalone, Aquaculture, Breeding, Heritability, Genetic correlation, Genotype by environment interaction

Referencia APA: Farías, W. J., Winkler, F. M., & Brokordt, K. B. (2017). Genotype by environment interactions, heritabilities and genetic correlations for productive traits of Haliotis rufescens. Aquaculture, 473, 407-416. https://doi.org/10.1016/j.aquaculture.2017.02.030

First assessment of MODIS satellite ocean color products (OC3 and nFLH) in the inner Sea of Chiloé, northern Patagonia

Autores:

Lara, C., Saldías, G. S., Westberry, T. K., Behrenfeld, M. J., & Broitman, B. R.

Resumen:

The use of remote sensing has allowed enormous progress in our understanding of biophysical processes worldwide. Despite their importance, the use of satellite bio-optical products is still limited due to optical complexity. In this study we assess the performance of the Moderate Resolution Imaging Spectroradiometer algorithm for chlorophyll-a (MODIS-OC3) and of normalized Fluorescence Line Height (nFLH), in inner waters of northern Chilean Patagonia (41°-45ºS). Satellite data were evaluated using a compilation of in situ chlorophyll-a data collected by the CIMAR-FIORDOS program during 2003-2012.

During austral spring MODIS-OC3 showed a significant relationship with in situ measurements (R2 = 0.2, P = 0.03, F = 5.33) in comparison with winter when the relationship was non-significant. In contrast, nFLH explained a significant fraction of observed variance of Chl-a during austral winter (R2 = 0.54, P = <0.01, F = 10.68) and this relationship was not significant in spring. Our preliminary results offer an excellent chance to understand patterns of variability of the autotrophic biomass and physiological status in optically complex interior marine ecosystems.

Año: 2017

Palabras claves: Satellite validation, MODIS, fluorescence, chlorophyll-a, optical complex, northern Patagonia

Referencia APA: Lara, C., Saldías, G. S., Westberry, T. K., Behrenfeld, M. J., & Broitman, B. R. (2017). First assessment of MODIS satellite ocean color products (OC3 and nFLH) in the inner Sea of Chiloé, northern Patagonia. Latin American Journal of Aquatic Research, 45(4), 822-827. http://dx.doi.org/10.3856/vol45-issue4-fulltext-18

Seasonal variation in epifaunal communities associated with giant kelp (Macrocystis pyrifera) at an upwelling‐dominated site

Autores:

Winkler, N. S., Pérez‐Matus, A., Villena, Á. A., & Thiel, M.

Resumen:

Kelp forests are highly productive and species‐rich benthic ecosystems in temperate regions that provide biogenic habitat for numerous associated species. Diverse epifaunal communities inhabit kelp sporophytes and are subject to variations in the physical environment and to changes experienced by the kelp habitat itself. We assessed seasonal variations in epifaunal invertebrate communities inhabiting giant kelps, Macrocystis pyrifera, and their effects on this seaweed. Six seasonal samplings were conducted over a year at an upwelling‐dominated site in northern‐central Chile where physical conditions are known to fluctuate temporally. More than 30 taxa were identified, among which peracarid crustaceans stood out in both diversity and abundance. Species richness and abundance differed among sporophyte sections (holdfast and fronds) and throughout the year. The frond community was dominated by two grazers (the amphipod Peramphithoe femorata and the isopod Amphoroidea typa), while suspension feeders, grazers, and omnivores (the amphipod Aora typica, the isopod Limnoria quadripunctata, and polychaetes) dominated the holdfasts. Abundances of the dominant species fluctuated throughout the year but patterns of variation differed among species. The most abundant grazer (P. femorata) had highest densities in summer, while the less abundant grazer (A. typa) reached its peak densities in winter. Interestingly, the area of kelp damaged by grazers was highest in autumn and early winter, suggesting that grazing impacts accumulate during periods of low kelp growth, which can thus be considered as ‘vestiges of herbivory past.’ Among the factors determining the observed seasonal patterns, strong variability of environmental conditions, reproductive cycles of associated fauna, and predation by fishes vary in importance. Our results suggest that during spring and early summer, bottom‐up processes shape the community structure of organisms inhabiting large perennial seaweeds, whereas during late summer and autumn, top‐down processes are more important.

Año: 2017

Palabras claves: Associated epifauna, Kelp, Macrocystis pyrifera, Seasonal fluctuations, Temperate regions

Referencia APA: Winkler, N. S., Pérez‐Matus, A., Villena, Á. A., & Thiel, M. (2017). Seasonal variation in epifaunal communities associated with giant kelp (Macrocystis pyrifera) at an upwelling‐dominated site. Austral Ecology, 42(2), 132-144. http://dx.doi.org/10.1111/aec.12407

The variable routes of rafting: stranding dynamics of floating bull kelp Durvillea antartica (Fucales, Phaeophyceae) on beaches in the Pacific

Autores:

Lopez, B. A., Macaya, E. C., Tala, F., Tellier, F., & Thiel, M.

Resumen:

Dispersal on floating seaweeds depends on availability, viability, and trajectories of the rafts. In the southern hemisphere, the bull kelp Durvillaea antarctica is one of the most common floating seaweeds, but phylogeographic studies had shown low connectivity between populations from continental Chile, which could be due to limitations in local supply and dispersal of floating kelps. To test this hypothesis, the spatiotemporal dynamics of kelp strandings were examined in four biogeographic districts along the Chilean coast (28°–42°S). We determined the biomass and demography of stranded individuals on 33 beaches for three subsequent years (2013, 2014, 2015) to examine whether rafting is restricted to certain districts and seasons (winter or summer). Stranded kelps were found on all beaches. Most kelps had only one stipe (one individual), although we also frequently found coalesced holdfasts with mature males and females, which would facilitate successful rafting dispersal, gamete release, and reproduction upon arrival. High biomasses of stranded kelps occurred in the northern‐central (30°S–33°S) and southernmost districts (37°S–42°S), and lower biomasses in the northernmost (28°S–30°S) and southern‐central districts (33°S–37°S). The highest percentages and sizes of epibionts (Lepas spp.), indicative of prolonged floating periods, were found on stranded kelps in the northernmost and southernmost districts. Based on these results, we conclude that rafting dispersal can vary regionally, being more common in the northernmost and southernmost districts, depending on intrinsic (seaweed biology) and extrinsic factors (shore morphology and oceanography) that affect local supply of kelps and regional hydrodynamics.

Año: 2017

Palabras claves: Floating kelps, Marine biogeography, Rafting, Stalked barnacles, Strandings

Referencia APA: Lopez, B. A., Macaya, E. C., Tala, F., Tellier, F., & Thiel, M. (2017). The variable routes of rafting: stranding dynamics of floating bull kelp Durvillea antartica (Fucales, Phaeophyceae) on beaches in the Pacific. J. Phycol, 53, 70-84. http://dx.doi.org/10.1111/jpy.12479