Trophic Ecology of Atlantic Bluefin Tuna (Thunnus thynnus) Larvae from the Gulf of Mexico and NW Mediterranean Spawning Grounds: A Comparative Stable Isotope Study

The present study uses stable isotopes of nitrogen and carbon (δ15Nandδ13C) as trophic indicators for Atlantic bluefin tuna larvae (BFT) (6–10mm standard length) in the highly contrasting environmental conditions of the Gulf of Mexico (GOM) and the Balearic Sea (MED). These regions are differentiated by their temperature regime and relative productivity, with the GOM being significantly warmer and more productive. MED BFT larvae showed the highest δ15N signatures, implying an elevated trophic position above the underlyingmicrozooplankton baseline. Ontogenetic dietary shifts were observed in the BFT larvae from the GOM and MED which indicates early life trophodynamics differences between these spawning habitats. Significant trophic differences between the GOM and MED larvae were observed in relation to δ15N signatures in favour of the MED larvae, which may have important implications in their growth during their early life stages. These low δ15N levels in the zooplankton from the GOM may be an indication of a shifting isotopic baseline in pelagic food webs due to diatrophic inputs by cyanobacteria. Lack of enrichment for δ15N in BFT larvae compared to zooplankton implies an alternative grazing pathway from the traditional food chain of phytoplankton— zooplankton—larval fish. Results provide insight for a comparative characterization of the trophic pathways variability of the two main spawning grounds for BFT larvaeVersión del editor4,411

Molecular Identification of Atlantic Bluefin Tuna (Thunnus thynnus, Scombridae) Larvae and Development of a DNA Character-Based Identification Key for Mediterranean Scombrids

The Atlantic bluefin tuna, Thunnus thynnus, is a commercially important species that has been severely over-exploited in the recent past. Although the eastern Atlantic and Mediterranean stock is now showing signs of recovery, its current status remains very uncertain and as a consequence their recovery is dependent upon severe management informed by rigorous scientific research. Monitoring of early life history stages can inform decision makers about the health of the species based upon recruitment and survival rates. Misidentification of fish larvae and eggs can lead to inaccurate estimates of stock biomass and productivity which can trigger demands for increased quotas and unsound management conclusions. Herein we used a molecular approach employing mitochondrial and nuclear genes (CO1 and ITS1, respectively) to identify larvae (n = 188) collected from three spawning areas in the Mediterranean Sea by different institutions working with a regional fisheries management organization. Several techniques were used to analyze the genetic sequences (sequence alignments using search algorithms, neighbour joining trees, and a genetic character-based identification key) and an extensive comparison of the results is presented. During this process various inaccuracies in related publications and online databases were uncovered. Our results reveal important differences in the accuracy of the taxonomic identifications carried out by different ichthyoplanktologists following morphology- based methods. While less than half of larvae provided were bluefin tuna, other dominant taxa were bullet tuna (Auxis rochei), albacore (Thunnus alalunga) and little tunny (Euthynnus alletteratus). We advocate an expansion of expertise for a new generation of morphology-based taxonomists, increased dialogue between morphology-based and molecular taxonomists and increased scrutiny of public sequence databases.Versión del editor4,411

Observational evidence for atmospheric modulation of the Loop Current migrations

Recent modeling studies on the shedding of Loop Current rings suggest that the intensification of the dominant zonal wind field delays the detachment of rings and affects the Loop Current migrations. The atmospheric modulation of the Loop Current migrations is analyzed here using reanalysis winds and altimetry-derived observations. A newly developed methodology is applied to locate the Loop Current front, and a wavelet-based semblance analysis is used to explore correlations with atmospheric forcing. The results show that weakening (intensification) of the zonal wind stress in the eastern Gulf of Mexico is related with the Loop Current excursions to the north (south). Semblance analyses confirm negative correlations between the zonal wind stress and the Loop Current migrations during the past 20 years. The intrusions of the Loop Current might involve an increase of the Yucatan Transport, which would balance the westward Rossby wave speed of a growing loop and delay the ring shedding. The results of this study have consequences for the interpretation of the chaotic processes of ring detachment and Loop Current intrusions, which might be modulated by wind stress.69068380,76Q4SCI

Description of surface transport in the region of the Belizean Barrier Reef based on observations and alternative high-resolution models

•An ocean–atmosphere model is prescribed for the Belizean Barrier Reef.•Alternative models with various resolutions are implemented.•The performance of the alternative models is assessed using observations.•The highest-resolution model with tides accurately predicts surface transport.•Resolving tidal flows and looping trajectories is important to improve predictions. The gains from implementing high-resolution versus less costly low-resolution models to describe coastal circulation are not always clear, often lacking statistical evaluation. Here we construct a hierarchy of ocean–atmosphere models operating at multiple scales within a 1 × 1° domain of the Belizean Barrier Reef (BBR). The various components of the atmosphere–ocean models are evaluated with in situ observations of surface drifters, wind and sea surface temperature. First, we compare the dispersion and velocity of 55 surface drifters released in the field in summer 2013 to the dispersion and velocity of simulated drifters under alternative model configurations. Increasing the resolution of the ocean model (from 1/12° to 1/100°, from 1 day to 1h) and atmosphere model forcing (from 1/2° to 1/100°, from 6h to 1h), and incorporating tidal forcing incrementally reduces discrepancy between simulated and observed velocities and dispersion. Next, in trying to understand why the high-resolution models improve prediction, we find that resolving both the diurnal sea-breeze and semi-diurnal tides is key to improving the Lagrangian statistics and transport predictions along the BBR. Notably, the model with the highest ocean–atmosphere resolution and with tidal forcing generates a higher number of looping trajectories and sub-mesoscale coherent structures that are otherwise unresolved. Finally, simulations conducted with this model from June to August of 2013 show an intensification of the velocity fields throughout the summer and reveal a mesoscale anticyclonic circulation around Glovers Reef, and sub-mesoscale cyclonic eddies formed in the vicinity of Columbus Island. This study provides a general framework to assess the best surface transport prediction from alternative ocean–atmosphere models using metrics derived from high frequency drifters’ data and meteorological stations

Varying Mesoscale Structures Influence Larval Fish Distribution in the Northern Gulf of Mexico

The variability of mesoscale circulation structures in the Gulf of Mexico (GOM) was examined using satellite altimeter data collected between 1992 and 2008, and linkages between ocean circulation and the spatial distribution of larval fish were assessed. The abundance and distribution of the larvae of 5 pelagic fish taxa (Auxis spp., Euthynnus alleteratus, Thunnus thynnus, other Thunnus spp., and Coryphaena spp.) were estimated from surveys conducted by the National Oceanic and Atmospheric Administration National Marine Fisheries Service each spring between 1993 and 2007. We observed a tendency for higher northward extension of the Loop Current (LC) during spring each year, with maximum northern penetration in summer, although the exact location of the LC varied from year to year. Generally, higher total larval abundances occurred during years of high northward penetration in a region that was crossed by the LC during its excursions. However, the interannual variability of the LC was not mirrored in a general increase or decrease of larval fish densities in the water masses out of the LC front. Further, the results show that larvae of T. thynnus and Auxis spp. were more abundant within the boundaries of anticyclonic features (usually between 148 to 158 cm of sea surface height) and within GOM common waters, defined as the background waters in between the boundaries of mesoscale features. Our findings suggest that the position and strength of anticyclone mesoscale features in the GOM define a favorable spawning habitat for the species examined

Simulating the effects of droplet size, high-pressure biodegradation, and variable flow rate on the subsea evolution of deep plumes from the Macondo blowout

The relative effects of hydrodynamic, thermodynamic, and geochemical factors on the fate and transport of oil in the subsea are not well understood to date. This glaring lack of knowledge in deep-sea spill studies precludes the parameterization of blowout far-field models. Here we use observations from the Macondo blowout to evaluate the importance of input variables in a numerical model of oil transport and fate. We adapt a multi-hydrocarbon fraction module to oil dissolution and run sensitivity analyses under various parameterization scenarios. We find that the inclusion of oil droplet atomization, variable flow rates (VFR), high-pressure biodegradation (HPB), and vertical currents' velocities (VV) affects significantly the subsea oil mass distribution in the water column as well as the evolution of deep plumes. In particular, droplets up to 50 μm are neutrally buoyant and moved by deep currents predominantly driven by the topography, while the depth of the deep plume is very sensitive to the VV of the hydrodynamic model. We find good agreement between CTD cast observations and modeled mean depth of the oil mass, whereby HPB provide increased accuracy of predictions with time. The model suggests that VFR and HPB are mechanisms for the persistence of the southwestern deep plume observed at 1100 m by increasing the residence time of the oil in the water column. Modeled oil concentrations range from 5 to 500 ppb and present the highest values in the western and deepest locations of the subsea plume, which corroborate with field observations. We hypothesize that a substantial amount of subsea oil mass might have interacted with the bottom of the Mississippi Canyon

Effect of mesoscale eddies and chlorophyll on larval fish assemblages in the Gulf of Mexico: implications for atlantic bluefin tuna (Thunnus thynnus)

2012 Ocean Sciences Meeting, 20-24 February 2012, Salt Lake City, Utah, USAIt is widely known that eddies and their attendant fronts play an important role in oceanic biological processes and may constitute a unique pelagic habitat for larvae. Previous studies that we conducted in the Gulf of Mexico (GOM) region showed that the variability in the Loop Current and anticyclonic ring field was reflected on the larval fish distribution of some species, likely associated to the boundaries of the latter features. To date, however, there has been only very limited studies in the region using satellite data to assess the influence of smaller mesoscale features on larvae assemblages. Our primary goal in this study is to explore the effect of the divergence and convergence associated to cyclonic and anticyclonic eddies on the complex variability of larval fish assemblages in the northern GOM. To complement visual eddy detection techniques, we use the footprint that cyclonic and anticyclonic eddies leave in sea surface height, temperature, and chlorophyll a, basically by analyzing satellite altimetry fields and applying the Okubo-Weiss parameterPeer reviewe