Juan Hofer | Pontificia Universidad Catolica de Valparaiso (original) (raw)

Papers by Juan Hofer

The Chilean fjord region includes many remote and poorly known areas where management plans for t... more The Chilean fjord region includes many remote and poorly known areas where management plans for the marine living resources and conservation strategies are urgently needed. Few data are available about the spatial distribution of its marine invertebrate fauna, prevalently influenced by complex interactions between biotic and abiotic factors, animal behavior and human activities. Patagonian fjords are a hotspot for finfish aquaculture, elevating Chile to the world's second producer of farmed salmon, after Norway, a condition that emphasizes the necessity to develop strategies for a sustainable aquaculture management. The present study focuses on the emblematic cold-water coral Desmophyllum dianthus, dwelling the Comau Fjord from shallow to deep waters, with the aim to illustrate population structure, demography and adaptation of the species and its potential use for the development of a sustainable conservation and management plan for human activities. The analyses of microsatellite loci of D. dianthus individuals from four sampling localities along horizontal and vertical gradients of Comau Fjord, lead to identify them as panmictic population. The results also contributed to consider a careful examination the synchrony between the temporal and spatial variations of environmental factors and biological cycle of the species as key role player in the inference of autecology of the species. This study also highlights the importance of oceanographic data in the entire process of the genetic analyses and interpretation of results. The discussion stresses the importance of molecular analyses as extremely helpful tools for studies focussing on remote areas and non-model organisms, where logistic difficulties and limited scientific knowledge hamper a better management and conservation of marine resources, and in particular the relevance of multidisciplinary approaches to reduce the extensive knowledge gap on the remote fjord ecosystems of Patagonia.

AGU Fall Meeting Abstracts, Dec 1, 2020

Frontiers in Ecology and Evolution, May 17, 2021

Within the framework of the Marine Ecosystem Assessment for the Southern Ocean (MEASO), this pape... more Within the framework of the Marine Ecosystem Assessment for the Southern Ocean (MEASO), this paper brings together analyses of recent trends in phytoplankton biomass, primary production and irradiance at the base of the mixed layer in the Southern Ocean and summarises future projections. Satellite observations suggest that phytoplankton biomass in the mixed-layer has increased over the last 20 years in most (but not all) parts of the Southern Ocean, whereas primary production at the base of the mixed-layer has likely decreased over the same period. Different satellite models of primary production (Vertically Generalised versus Carbon Based Production Models) give different patterns and directions of recent change in net primary production (NPP). At present, the satellite record is not long enough to distinguish between trends and climate-related cycles in primary production. Over the next 100 years, Earth system models project increasing NPP in the water column in the MEASO northern and Antarctic zones but decreases in the Subantarctic zone. Low confidence in these projections arises from: (1) the difficulty in mapping supply mechanisms for key nutrients (silicate, iron); and (2) understanding the effects of multiple stressors (including irradiance, nutrients, temperature, pCO 2 , pH, grazing) on different species of Antarctic phytoplankton. Notwithstanding these uncertainties, there are likely to be changes to the seasonal patterns of production and the microbial community present over the next 50-100 years and these changes will have ecological consequences across Southern Ocean food-webs, especially on key species such as Antarctic krill and silverfish.

AGU Fall Meeting Abstracts, Dec 1, 2019

This study is the first integrated assessment of the main oceanographic features of the Beagle Ch... more This study is the first integrated assessment of the main oceanographic features of the Beagle Channel, using data from several oceanographic cruises conducted between 19-25 October 2016, 19-26 July 2017 and 18-23 July 2018 by the IDEAL center (Research Center: Dynamics of High Latitude Marine Ecosystems). During 2016 transects were done between the NW entrance of the Beagle Channel up to Yendegaia bay (mid of the channel). In winter 2017, simultaneous to the IDEAL transect, a full oceanographic survey onboard M/O Bernardo Houssay (PNA, Argentina) by researchers of CADIC (Austral Center for Scientific Research in Ushuaia) was conducted from nearby Yendegaia bay to the eastern limit of the Beagle Channel (27-30 August 2017), thus closing for the first time a full, high resolution, hydrographic section along the entire Channel. During 18-23 July 2018 the NW branch and the SW branch of the Beagle Channel was surveyed.The study was funded by the IDEAL center (https://www.centroideal.cl/, award: FONDAP 15150003).

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Dec 8, 2017

Estudios en un fiordo chileno con un fuerte gradiente de pH ̶ ̶ regulación del pH interno por el ... more Estudios en un fiordo chileno con un fuerte gradiente de pH ̶ ̶ regulación del pH interno por el coral de aguas frias Desmophyllum dianthus Max Planck Institute for Marine Microbiology El fiordo Comau en la Patagonia chilena norte se caracteriza por presentar un marcado gradiente de pH, de 7.4 a 8.1. En él, Desmphyllum dianthus promueve la aparición de un ecosistema bentónico con una alta diversidad estructural y funcional (Fig. 1). Sorprendentemente, D. dianthus crece en aguas de alto (sobresaturadas de aragonita) y bajo pH (insaturadas de aragonita), así como en aguas someras y profundas (desde aprox. 15 m hasta más de 400 m). Esto indica que el coral es capaz de regular y controlar su calcificación. Medidas de

Seasonal, diel and vertical distribution of mesozooplankton was described over the entire water c... more Seasonal, diel and vertical distribution of mesozooplankton was described over the entire water column of Comau Fjord, northern Chilean Patagonia. Stratified vertical hauls we taken with a Nansen net (100 μm mesh) between the surface and the bottom (0-50-100-200-300-400-450 m) in spring, summer, autumn and winter. Samples were scanned with a ZooScan, and abundance, biovolume and biomass were determined for 41 taxa identified on the web-based platform EcoTaxa 2.0. This dataset was generated in the frame of the co-operation between the Universidad Austral de Chile (https://www.uach.cl), the Huinay Scientific Field Station (http://www.huinay.cl) and the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (http://www.awi.de) in the frame of the project PACOC Plankton- And cold-water COral ecology in Comau Fjord, Chile. The study was also embedded in activities of the Research Center Dynamics of High Latitude Marine Ecosystems (IDEAL) (http://www.centroideal.cl/eng/)

&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp... more &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;In our collective endeavour towards global sustainability, there is now a broad appreciation that producing scientifically robust knowledge requires new forms of engagement between scientists, stakeholders and society. But what is the role of Early Career Scientists (ECS) in these processes that are closing the gap between science and policy? Because opportunities to interact with more experienced peers through science refereeing are scarce, the role of ECS in the peer-review process remains minor despite ECS possessing strong academic credentials. Such engagement in the peer-review process represents a valuable opportunity for ECS and the scientific community as a whole. This opportunity provides a robust platform for ECS to understand the overall review process and editorial activities related to high-credibility publications such as those conducted by the Intergovernmental Panel on Climate Change (IPCC). During May/November 2018, 174 ECS on behalf of the Association of Polar Early Career Scientists (APECS) reviewed the first and second-order drafts of the IPCC &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8220;Special Report on Ocean and Cryosphere and in a Changing Climate (SROCC)&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#8221;. Here, we present the methodology, results, and lessons learned from these group reviews. Altogether, data from participant surveys on their experience and their comments catalog illustrate ECS as competent reviewers, comparable to more experienced researchers. The diverse disciplines and geographic perspectives, fostered through APECS and its partners, are currently being mobilized in the First Order Draft of the Working Groups I and II of the Assessment Report 6 of the IPCC, and will continue during the second round of reviews of these reports in early 2020. Information gathered during these ongoing reviews will add to the findings obtained during the review of the SROCC.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;

The primary objective for this krill research activity was twofold 1) to conduct a survey that pr... more The primary objective for this krill research activity was twofold 1) to conduct a survey that provides updated estimates of the biomass and distribution of krill which are used in models to estimate sustainable yield in CCAMLR Area 48 and 2) to develop knowledge on the marine environment essential for the implementation of a FeedBack Management (FBM) system. The survey follows a similar design as a survey initiated by CCAMLR in year 2000 for comparative purposes, but in addition focuses on high krill-density areas, contains state-of-the art methods and employs modern technology for the research topics currently in focus. In terms of FBM, Marine Protected Area (MPA) development in CCAMLR Planning Domain 1 encompasses the major krill fishing grounds. Thus, data supporting FBM are critical if the fishery is to be managed by an empirical understanding of krill density, distribution, availability and predator needs as opposed to purely conservation-based measures. A future developed FBM system, requires acoustic data to be collected, processed and reported continuously during the fishing season as a measure of the available prey field. This information can be integrated with finer-scale knowledge of krill predator feeding strategies and updated through specific scientific studies at regular (multiyear) intervals. The survey and coupled FBM process studies took place during the Austral summer 2018-2019. The work was coordinated by Norway and involved collaborative international efforts as well as vessels from Norway, Association of Responsible Krill fishing companies (ARK) and the Norwegian fishing company Aker BioMarine AS, China, Korea, Ukraine and United Kingdom. This report presents preliminary results from the survey performed with the Norwegian RV Kronprins Haakon during 08th January-24th February 2019 and the land-based predator research carried out between 21st November 2018 and 20th February 2019. Content 1 Background 2 Krill Acoustics 3 Plankton, nutrients and environment 4 FlowCam studies 5 Fish and Cephalopods 6 Marine mammals and birds 7 Thermosalinograph and ADCP data 8 CTD data 9 Chemical indicators to monitor Ocean Acidification 10 Dissolved Oxygen 11 Sailbuoy with acoustics 12 LADCP measurements 13 Krill sound speed and density contrast 14 Acoustic backscatter of krill measured with lowered transducer 15 Echosounder moorings 16 Environmental toxicology 17 Metabolism balance in krill 18 Microbial communities 19 Trophic interactions 20 Land based predator research in support of adaptive management of the krill fishery 21 Acknowledgements 22 References 23 Appendix 1. Harstad-trawl rigging and procedures 24 Appendix 2. Scientific personell 25 Appendix 3. Crewlist KPH

<p>Despite being major players on the global biogeochemical cycles, microorganisms are gene... more <p>Despite being major players on the global biogeochemical cycles, microorganisms are generally not included in holistic views of Earth’s system. The Microbial Conveyor Belt is a conceptual framework that represents a recurrent and cyclical flux of microorganisms across the globe, connecting distant ecosystems and Earth compartments. This long-range dispersion of microorganisms directly influences the microbial biogeography, the global cycling of inorganic and organic matter, and thus the Earth system’s functioning and long-term resilience. Planetary-scale human impacts disrupting the natural flux of microorganisms pose a major threat to the Microbial Conveyor Belt, thus compromising microbial ecosystem services. Perturbations that modify the natural dispersion of microorganisms are, for example, the modification of the intensity/direction of air fluxes and ocean currents due to climate change, the vanishing of certain dispersion vectors (e.g., species extinction or drying rivers) or the introduction of new ones (e.g., microplastics, wildfires). Transdisciplinary approaches are needed to disentangle the Microbial Conveyor Belt, its major threats and their consequences for Earth´s system resilience.</p>

PLOS ONE, Jul 23, 2013

Dilution experiments were performed to estimate phytoplankton growth and microzooplankton grazing... more Dilution experiments were performed to estimate phytoplankton growth and microzooplankton grazing rates during two Lagrangian surveys in inner and eastern locations of the Eastern North Atlantic Subtropical Gyre province (NAST-E). Our design included two phytoplankton size fractions (0.2-5 mm and .5 mm) and five depths, allowing us to characterize differences in growth and grazing rates between size fractions and depths, as well as to estimate vertically integrated measurements. Phytoplankton growth rates were high (0.11-1.60 d 21), especially in the case of the large fraction. Grazing rates were also high (0.15-1.29 d 21), suggesting high turnover rates within the phytoplankton community. The integrated balances between phytoplankton growth and grazing losses were close to zero, although deviations were detected at several depths. Also, O 2 supersaturation was observed up to 110 m depth during both Lagrangian surveys. These results add up to increased evidence indicating an autotrophic metabolic balance in oceanic subtropical gyres.

Frontiers in Ecology and Evolution, Jun 17, 2022

In the Southern Ocean, several zooplankton taxonomic groups, euphausiids, copepods, salps and pte... more In the Southern Ocean, several zooplankton taxonomic groups, euphausiids, copepods, salps and pteropods, are notable because of their biomass and abundance and their roles in maintaining food webs and ecosystem structure and function, including the provision of globally important ecosystem services. These groups are consumers of microbes, primary and secondary producers, and are prey for fishes, cephalopods, seabirds, and marine mammals. In providing the link between microbes, primary production, and higher trophic levels these taxa influence energy flows, biological production and biomass, biogeochemical cycles, carbon flux and food web interactions thereby modulating the structure and functioning of ecosystems. Additionally, Antarctic krill (Euphausia superba) and various fish species are harvested by international fisheries. Global and local drivers of change are expected to affect the dynamics of key zooplankton species, which may have potentially profound and wide-ranging implications for Southern Ocean ecosystems and the services they provide. Here

Science of The Total Environment