El destino de huevos y larvas de tres especies pelágicas caballa, (Scomber scombrus), jurel (Trachurus trachurus) y sardina (Sardina pilchardus) en relación a las corrientes prevalentes en el área del Golfo de Vizcaya. ¿Podrían afectar a la supervivencia larvaria?

The spatial distribution of eggs and larvae of three pelagic species, mackerel, horse mackerel and sardine, in the Bay of Biscay was studied in 1998, 2001 and 2004. The spatial distribution was clearly different between the years studied and corresponds quite precisely to different water circulation regimes. Mackerel and horse mackerel larvae are more affected by the prevailing currents than sardine, as their spawning grounds are located offshore, far from the shelf break where the current velocities are higher. Survival rates for mackerel and horse mackerel were higher in 2001, when the offshore larval transport was stronger. However, for sardine, the mortality rate hardly varied between years. The abundance of 25-day-old larvae, considered as an index of the survival rate, appears to be a good recruitment indicator, at least for 1998, 2001 and 2004. Our results did not support the hypothesis of Bakun (1996), which states that dispersion of early life stages towards open ocean waters should cause high larval mortality. At least under the conditions observed for the years studied, the retention of larvae offshore appears to have a positive effect on larval growth and/or survival.La distribución espacial de los huevos y larvas de tres especies pelágicas, caballa, jurel y sardina en el Golfo de Vizcaya fue estudiada en 1998, 2001 y 2004. Esta distribución espacial fue claramente diferente entre los años estudiados y se ajustan, bastante bien a los diferentes regímenes de circulación. Las larvas de caballa y jurel resultaron más directamente afectadas por estas corrientes prevalentes que las larvas de sardina. Esto se explica porque las sardinas desovan en la plataforma, relativamente alejadas del cantil, donde las velocidades de las corrientes son más altas. Las tasas de supervivencia larvaria de caballa y jurel fueron superiores en 2001, cuando el transporte de larvas offshore era más importante. Para las larvas de sardina, sin embargo, la tasa de mortalidad apenas varió entre años. La abundancia de larvas mayores de 25 días, considerada aquí como un índice de la tasa de supervivencia larvaria, resultó ser un buen indicador del reclutamiento por lo menos para los años estudiados. Nuestros resultados contradicen la teoría de Bakun (1996), que afirma que la dispersión de las etapas de vida temprana hacia las aguas del océano abierto causa una alta mortalidad larvaria. Por lo menos bajo la condición que se observó durante estos años (temperatura y abundancia de alimento), la retención de larvas en mar abierto parece tener un efecto positivo en el crecimiento larvario y/o supervivencia

Connectivity between coastal lagoons and sea: asymmetrical effects on assemblages' and populations' structure

Connectivity among marine populations plays a fundamental role in the dynamic of metapopulations and communities. Moreover, genetic connectivity is important for the evolutionary history and adaptive capability of species while demographic connectivity is essential to maintain ecological processes. In coastal lagoons, isolation degree or confinement is considered the main factor structuring biological assemblages. These environments also function as nursery areas for many marine species that colonize the lagoons as larvae or juveniles, returning to the sea for reproduction. It is therefore essential to know the connectivity between lagoons and sea for the management of biodiversity and the exploitation of coastal living resources. This work anases the role that connectivity between coastal lagoons and sea plays in the assemblages and subpopulations structure of the first. To this purpose, a finite element hydrodynamic model was used coupled with a lagrangian module to simulate the potential exchange of organisms between Mar Menor lagoon (Western Mediterranean) and the adjacent sea. Connectivity parameters from 40 stations, located inside and outside the Mar Menor, have been estimated. The outcomes of the eight simulations carried out were compared with field data, including ichthyoplankton species composition and genetic fluxes in 6 species with different life stories. The results suggest that pelagic larval phases are longer than expected or the species can extend PLD within certain limits if the conditions for the settlement are not adequate. Repetition can improve the chance of self-recruitment, coupling larval duration, competency period and finding the adequate location for settlement. The results also show that connectivity between all lagoon and Mediterranean stations is very low and is independent of geographical distance. There is a strong asymmetry in the probability of receiving particles, being lower the probability of colonization of the lagoon stations from the sea than vice versa. Despite its low values, connectivity can explain up to 65% of the similarities in species composition of the ichthyoplankton and between 30 and 96% of the variance in genetic differentiation of the studied species. The low value of connectivity and colonization rates is enough, however, to maintain the genetic fluxes between populations and, at the same time, restricted connectivity can play an important role in maintaining high diversity and heterogeneous assemblage structure

Connectivity of coastal and neritic fish larvae to the deep waters

Four ichthyoplankton cruises and backward tracking experiments were conducted to study the connectivity of coastal and neritic fish larvae over the continental slope and to the oceanic deep-water region of the western Gulf of Mexico. Distribution patterns of larval abundance at oceanic stations showed higher abundance and the presence of larvae at oceanic stations during two cruises. Larval transport was simulated using outputs of a data assimilation model that represented the flow conditions during each cruise. Higher abundances of larvae of coastal and neritic species at oceanic stations agreed with offshore transport inferred from numerical experiments seeding particles over different spatial scales (stations vs. transects). Satellite images of surface chlorophyll were consistent with the circulation patterns indicated by the model, indicating filaments of shelf waters were transported toward the transects with higher larval abundances. Particle tracking experiments indicated that the northwestern shelf provinces of Perdido, Tamaulipas, and Texas were the main source of propagules to the oceanic region, while shelf provinces of northern Veracruz, Campeche, Yucatan, Louisiana, and Mississippi-Alabama contributed much less. The length and intensity of the shelf front limited ichthyoplankton cross-shelf exchange during some cruises, and mesoscale anticyclonic and cyclonic eddies advected larvae to the deep-water region during others. The agreement between the spatial distribution of fish larvae and the simulated larval transport confirm that circulation models are a valuable tool for examining potential dispersal pathways of neritic species, as long as similar spatial and temporal scales as the ones used in this study are considered.Fil: Cano Compaire, Jesus. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Pérez Brunius, Paula. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Jiménez Rosenberg, Sylvia Patricia Adelheid. Instituto Politécnico Nacional. Centro Interdisciplinario de Ciencias Marinas; MéxicoFil: Rodríguez Outerelo, Javier. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Echeverri García, Laura del Pilar. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; MéxicoFil: Herzka, Sharon Z.. Consejo Nacional de Ciencia y Tecnología de México. Centro de Investigación Científica y de Educación Superior de Ensenada Baja California; Méxic

Modelling the effects of spatio-temporal spawning variability on the transport and retention success of sardine (Sardinops sagax) eggs and larvae around South Africa

The transport and retention of sardine (Sardinops sagax) eggs on the west and south coasts of South Africa were investigated using a Lagrangrian, particle tracking, individual-based model (IBM), coupled with two 3-D hydrodynamic Regional Ocean Modeling System (ROMS) model configurations of different generations. The same IBM is coupled with PLUME, an older ROMS model configuration used in a previous sardine IBM for the southern Benguela, as well as BENGSAFE, a more recent, better resolved ROMS model configuration. Results from the two runs were compared to see if and how the underlying ocean model affects modelled retention and transport. An updated IBM, extended spatially and temporally to better represent sardine spawning and recruitment, was then coupled with the BENGSAFE model configuration, and assessed. The effects of spawning area, and month, year and depth of particle release, were investigated for each coupled 3D-IBM simulation using linear models. The portion of particles transported from the south coast to the west coast was a focus throughout, as this is of great importance to the management of the sardine fishery. In all simulations, three main systems were identified depending on where particles were released and recruited. Two of these systems were retention-based: particles released on the west coast and retained in the west coast recruitment area (WC-WC), and particles released on the south coast and retained in the south coast recruitment area (SC-SC). The other system is transport-based and represents particles released on the south coast and transported by ocean dynamics to recruit in the west coast recruitment area. Results were similar for the west coast when either hydro- dynamic model configuration was used; depth of release proved to be important in this system with its effect varying depending where on the west coast particles were released. Differences occurred on the south coast, with more transport to the west coast and more offshore loss in the higher resolved BENGSAFE IBM than the PLUME IBM. The difference was attributed to the positioning of the PLUME model's boundary in close proximity to the Agulhas Current, and the conditions at this boundary not properly resolving the current. The initial BENGSAFE IBM was spatially restricted to match the PLUME IBM, and therefore south coast spawning and recruitment was not fully represented. Therefore, the BENGSAFE IBM was spatially extended on the south coast and run for a longer time period. Similar results were obtained in the extended BENGSAFE IBM and the initial BENGSAFE IBM. However south coast retention increased and the average percentage of particles transported to the west coast decreased slightly. Spawning area proved to be an important determinant of retention and transport success in all recruitment systems, and the further east a particle was spawned the less likely it was to be transported to the west coast, and the more likely it was to be retained on the south coast. Transport to the west coast was most successful in late winter; a significant monthly effect on transport success was present. Correlations between standardised anomalies for stock assessment model estimated recruitment and IBM modelled retention/transport for the west and south coast were not significant, highlighting that retention and transport are not the only determinants of recruitment success. The extended BENGSAFE IBM can act as a base level to which extra layers of biological complexities can be added, such as horizontal and vertical egg distribution matching observations, incorporating gonadosomatic index (GSI) values, diurnal vertical migration and buoyancy

The reduction of plankton biomass induced by mesoscale stirring: a modeling study in the Benguela upwelling

Recent studies, both based on remote sensed data and coupled models, showed a reduction of biological productivity due to vigorous horizontal stirring in upwelling areas. In order to better understand this phenomenon, we consider a system of oceanic flow from the Benguela area coupled with a simple biogeochemical model of Nutrient-Phyto-Zooplankton (NPZ) type. For the flow three different surface velocity fields are considered: one derived from satellite altimetry data, and the other two from a regional numerical model at two different spatial resolutions. We compute horizontal particle dispersion in terms of Lyapunov Exponents, and analyzed their correlations with phytoplankton concentrations. Our modelling approach confirms that in the south Benguela there is a reduction of biological activity when stirring is increased. Two-dimensional offshore advection and latitudinal difference in Primary Production, also mediated by the flow, seem to be the dominant processes involved. We estimate that mesoscale processes are responsible for 30 to 50% of the offshore fluxes of biological tracers. In the northern area, other factors not taken into account in our simulation are influencing the ecosystem. We suggest explanations for these results in the context of studies performed in other eastern boundary upwelling areas

MOHID as a tool to evaluate the impact of water discharge from dams on the advection of estuarine fish larval stages

The impoundment of rivers by dams is the biggest direct anthropogenic impact on the hydrological cycle. The utility of dams, as providers of water for human consumption, irrigation and electrical production, is undeniable. However, the price to pay, weighting benefits versus ecological impacts caused by dams, is enormous and often questionable. The deleterious ecological impacts caused by dams are detected at the dam’s site are and at hundreds of kilometers downstream from dams, even in estuaries and coastal areas. The uncontrolled water discharge from dams, both high volumes of water and inappropriate timing, compromise fish recruitment because eggs are flushed from estuarine spawning and nursery areas. Thus, our goal was to develop an hydrodynamic modelling approach that evaluates the impact of water discharge from dams on the advection of fish larval stages off estuaries and into coastal areas. This goal was accomplished by merging the abundance of anchovy eggs along the Guadiana estuary in MOHID

Spreading of Lagrangian Particles in the Black Sea: A Comparison between Drifters and a High-Resolution Ocean Model

The Lagrangian dispersion statistics of the Black Sea are estimated using satellite-tracked drifters, satellite altimeter data and a high-resolution ocean model. Comparison between the in-situ measurements and the model reveals good agreement in terms of the surface dispersion. The mean sub-basin coherent structures and currents of the Black Sea are well reproduced by the model. Seasonal variability of the dispersion in the upper (15 m), intermediate (150 m) and deep (750 m) layers are discussed with a special focus of the role of sub-basin scale structures and currents on the turbulent dispersion regimes. In terms of the surface relative dispersion, the results show the presence of the three known turbulent exponential, Richardson and diffusive-like regimes. The non-local exponential regime is only detected by the model for scales <10 km, while the local Richardson regime occurs between 10 and 100 km in all cases due to the presence of an inverse energy cascade range, and the diffusive-like regime is well detected for the largest distance by drifters (100–300 km) in winter/spring. Regarding the surface absolute dispersion, it reflects the occurrence of both quasi-ballistic and random-walk regimes at small and large times, respectively, while the two anomalous hyperbolic (5/4) and elliptic (5/3) regimes, which are related to the topology of the Black Sea, are detected at intermediate times. At depth, the signatures of the relative and absolute dispersion regimes shown in the surface layer are still valid in most cases. The absolute dispersion is anisotropic; the zonal component grows faster than the meridional component in any scenario

The role of short-term atmospheric variability in shaping Lagrangian transport in the Southern Benguela

This work studies the links between the Lagrangian transport in the Southern Benguela upwelling system and the ocean circulation through modelling experimentation. More specifically, it intends to show that the wind-induced circulation at short-time scales impacts the drift of Lagrangian particles released in the model. Three ocean model (ROMS) simulations are set-up. Simulation A is forced with a6 hourly atmospheric forcing (surface heat and fresh-water fluxes and wind stress). In simulation B and C, the atmospheric forcing is low-pass filtered with 5 days and 30 days cut-off periods. The ocean model outputs are averaged and saved at deferent temporal frequency: frequencies of 6 hours and 3 days. Particles released in the Lagrangian tracking tool are transported by the velocity vectors produced by the ocean model into the nursery area located at Saint Helena Bay. The presence of short-term fluctuations result in higher inner shelf transport and amore elongated plume dispersion pattern with much refine spatial scales. This finding contrasts with previous studies where the inner shelf transport success was always low compared to the outer shelf nursery. When the high frequency signal is filtered out, the inner shelf transport is greatly reduced especially during the upwelling season. The archiving frequency of the ROMS output is shown to impact Lagrangian studies, especially when the atmospheric forcing has variability at short time scales (less than 5 days).Monthly mean forcing results in dynamics variable with periods of not less than a month and 5 daily averaged forcing with sub-weekly dynamics. Therefore, in simulations B and C the less than 3 days archiving of the model outputs is not necessary, because their forcing does not generate dynamics with such periods. The latter must be adapted so that it does not filter out the ocean response to the high frequency atmospheric forcing. To explain the Lagrangian transports, as a first approach, the transport success was linked to the variability of the ocean circulation

Use of Lagrangian simulations to hindcast the geographical position of propagule release zones in a Mediterranean coastal fish

The study of organism dispersal is fundamental for elucidating patterns of connectivity between populations, thus crucial for the design of effective protection and management strategies. This is especially challenging in the case of coastal fish, for which information on egg release zones (i.e. spawning grounds) is often lacking. Here we assessed the putative location of egg release zones of the saddled sea bream (Oblada melanura) along the south-eastern coast of Spain in 2013. To this aim, we hindcasted propagule (egg and larva) dispersal using Lagrangian simulations, fed with species-specific information on early life history traits (ELTs), with two approaches: 1) back-tracking and 2) comparing settler distribution obtained from simulations to the analogous distribution resulting from otolith chemical analysis. Simulations were also used to assess which factors contributed the most to dispersal distances. Back-tracking simulations indicated that both the northern sector of the Murcia region and some traits of the North-African coast were hydrodynamically suitable to generate and drive the supply of larvae recorded along the coast of Murcia in 2013. With the second approach, based on the correlation between simulation outputs and field results (otolith chemical analysis), we found that the oceanographic characteristics of the study area could have determined the pattern of settler distribution recorded with otolith analysis in 2013 and inferred the geographical position of main O. melanura spawning grounds along the coast. Dispersal distance was found to be significantly affected by the geographical position of propagule release zones. The combination of methods used was the first attempt to assess the geographical position of propagule release zones in the Mediterranean Sea for O. melanura, and can represent a valuable approach for elucidating dispersal and connectivity patterns in other coastal species

Modeling Iberian sardine Early Life Stages dynamics

The Iberian sardine (Sardina pilchardus) constitutes a traditional target species in western Iberia that remains to be economically important in Portugal and, to a lesser extent, in Galicia (NW Spain). The time series of recruitment shows ups and downs in the last decades. According to the ICES Advice 2013 for regions VIII and IXa, the biomass of age 1 sardine and older has decreased since 2006 and recruitment has been below the long term average since 2005. In order to understand these fluctuations, a Lagrangian model to simulate sardine Early Life Stages (ELS), this is, egg and larvae stages, has been set up. The results of a high resolution hydrodynamic model for North and Northwest Iberia have been used as an input of the Lagrangian model Ichthyop (Lett et al., (2008)) to simulate ELS advection and dispersion. Ichthyop has been adapted to sardine by including some biological behavior. A biogeochemical model coupled to the hydrodynamic model was also used to get some insight on recruitment for years 2006 2007