Guillermo Boyra

Bio: Guillermo Boyra is an academic researcher. The author has contributed to research in topics: Anchovy & Tuna. The author has an hindex of 14, co-authored 32 publications receiving 2967 citations.

Large mesopelagic fishes biomass and trophic efficiency in the open ocean

Abstract: With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters. Mesopelagic fishes dominate the global fishes biomass, yet there exist major uncertainties regarding their global biomass. Irigoien et al.analyse acoustic data collected during a circumglobal cruise and show that biomass estimates should be raised by an order of magnitude.

Buoyancy measurements and vertical distribution of eggs of sardine ( Sardina pilchardus ) and anchovy ( Engraulis encrasicolus )

Abstract: Measurements were made of the density and settling velocity of eggs of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus), using a density-gradient column. These results were related to observed vertical distributions of eggs obtained from stratified vertical distribution sampling in the Bay of Biscay. Eggs of both species had slightly positive buoyancy in local seawater throughout most of their development until near hatching, when there was a marked increase in density and they became negatively buoyant. The settling velocity of anchovy eggs, which are shaped as prolate ellipsoids, was close to predictions for spherical particles of equivalent volume. An improved model was developed for prediction of the settling velocity of sardine eggs, which are spherical with a relatively large perivitelline volume; this incorporated permeability of the chorion and adjustment of the density of the perivitelline fluid to ambient seawater. Eggs of both species were located mostly in the top 20 m of the water column, in increasing abundance towards the surface. A sub-surface peak of egg abundance was sometimes observed at the pycnocline, particularly where this was pronounced and associated with a low-salinity surface layer. There was a progressive deepening of the depth distributions for successive stages of egg development. Results from this study can be applied for improved plankton sampling of sardine and anchovy eggs and in modelling studies of their vertical distribution.

Optimizing the number of classes in automated zooplankton classification

Abstract: Zooplankton biomass and abundance estimation, based on surveys or time-series, is carried out routinely. Automated or semi-automated image analysis processes, combined with machine-learning techniques for the identification of plankton, have been proposed to assist in sample analysis. A difficulty in automated plankton recognition and classification systems is the selection of the number of classes. This selection can be formulated as a balance between the number of classes identified (zooplankton taxa) and performance (accuracy; correctly classified individuals). Here, a method is proposed to evaluate the impact of the number of selected classes, in terms of classification performance. On the basis of a data set of classified zooplankton images, a machine-learning method suggests groupings that improve the performance of the automated classification. The end-user can accept or reject these mergers, depending on their ecological value and the objectives of the research. This method permits both objectives to be equally balanced: (i) maximization of the number of classes and (ii) performance, guided by the end-user.

Plastic debris in the open ocean

Abstract: There is a rising concern regarding the accumulation of floating plastic debris in the open ocean. However, the magnitude and the fate of this pollution are still open questions. Using data from the Malaspina 2010 circumnavigation, regional surveys, and previously published reports, we show a worldwide distribution of plastic on the surface of the open ocean, mostly accumulating in the convergence zones of each of the five subtropical gyres with comparable density. However, the global load of plastic on the open ocean surface was estimated to be on the order of tens of thousands of tons, far less than expected. Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered. Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean.

The biomass distribution on Earth

Abstract: A census of the biomass on Earth is key for understanding the structure and dynamics of the biosphere. However, a global, quantitative view of how the biomass of different taxa compare with one another is still lacking. Here, we assemble the overall biomass composition of the biosphere, establishing a census of the ≈550 gigatons of carbon (Gt C) of biomass distributed among all of the kingdoms of life. We find that the kingdoms of life concentrate at different locations on the planet; plants (≈450 Gt C, the dominant kingdom) are primarily terrestrial, whereas animals (≈2 Gt C) are mainly marine, and bacteria (≈70 Gt C) and archaea (≈7 Gt C) are predominantly located in deep subsurface environments. We show that terrestrial biomass is about two orders of magnitude higher than marine biomass and estimate a total of ≈6 Gt C of marine biota, doubling the previous estimated quantity. Our analysis reveals that the global marine biomass pyramid contains more consumers than producers, thus increasing the scope of previous observations on inverse food pyramids. Finally, we highlight that the mass of humans is an order of magnitude higher than that of all wild mammals combined and report the historical impact of humanity on the global biomass of prominent taxa, including mammals, fish, and plants.

Computation And Interpretation Of Biological Statistics Of Fish Populations

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