ALBERT

Description: English:Recent calls for a more holistic approach to fisheries management have motivated developmentof trophic mass-balance models of ecosystems that underlie fisheries production. We developeda model hypothesis of the pelagic ecosystem in the eastern tropical Pacific Ocean (ETP) togain insight into the relationships among the various species in the system and to explore the ecologicalimplications of alternative methods of harvesting tunas. We represented the biomasses ofand fluxes between the principal elements in the ecosystem with Ecopath, and examined theecosystem's dynamic, time-series behavior with Ecosim. We parameterized the model for 38species or groups of species, and described the sources, justifications, assumptions, and revisionsof our estimates of the various parameters, diet relations, fisheries landings, and fisheries discardsin the model. We conducted sensitivity analyses with an intermediate version of the model,for both the Ecopath mass-balance and the dynamic trajectories predicted by Ecosim. The analysisshowed that changes in the basic parameters for two components at middle trophic levels,Cephalopods and Auxis spp., exert the greatest influence on the system. When the CephalopodQ/B and Auxis spp. P/B were altered from their initial values and the model was rebalanced, thetrends of the biomass trajectories predicted by Ecosim were not sensitive, but the scaling was sensitivefor several components. We described the review process the model was subjected to, whichincluded reviews by the IATTC Purse-seine Bycatch Working Group and by a working group supportedby the National Center for Ecological Analysis and Synthesis. We fitted the model to historicaltime series of catches per unit of effort and mortality rates for yellowfin and bigeye tunasin simulations that incorporated historical fishing effort and a climate driver to represent theeffect of El Niño-Southern Oscillation-scale variation on the system. The model was designed toevaluate the possible ecological implications of fishing for tunas in various ways. We recognizethat a model cannot possibly represent all the complexity of a pelagic ocean ecosystem, but webelieve that the ETP model provides insight into the structure and function of the pelagic ETP.Spanish:Llamamientos recientes hacia un enfoque más holístico al ordenamiento de la pesca hanmotivado el desarrollo de modelos tróficos de balance de masas de los ecosistemas que sostienenla producción pesquera. Desarrollamos una hipótesis modelo del ecosistema pelágico en el OcéanoPacífico oriental tropical (POT) con miras a mejorar los conocimientos de las relaciones entre lasdistintas especies en el sistema y explorar las implicaciones ecológicas de métodos alternativos decapturar atunes. Con Ecopath representamos las biomasas de los elementos principales en el ecosistema,y los flujos entre los mismos, y con Ecosim examinamos el comportamiento dinámico delecosistema con el tiempo. Parametrizamos el modelo para 38 especies o grupos de especies(denominados “componentes” del modelo), y describimos las fuentes, justificaciones, supuestos, yrevisiones de nuestras estimaciones de los distintos parámetros, relaciones basadas en dieta, capturasretenidas de las pesquerías, y descartes de las mismas en el modelo. Realizamos análisis desensibilidad con una versión intermedia del modelo, para el balance de masas de Ecopath y lastrayectorias dinámicas predichas por Ecosim también. El análisis demostró que cambios en losparámetros básicos para dos componentes en niveles tróficos medianos, Cefalópodos y Auxis spp.,ejercieron la mayor influencia sobre el sistema. Cuando se alteraron el Q/B de los Cefalópodos yel P/B de los Auxis spp. de sus valores iniciales y se balanceó el modelo de nuevo, las tendenciasde las trayectorias de la biomasa predichas por Ecosim no fueron sensibles, pero la escala fue sensiblepara varios componentes. Describimos el proceso de revisión al que fue sujeto el modelo,inclusive revisiones por el Grupo de Trabajo sobre Captura Incidental de la CIAT y un grupo detrabajo apoyado por el Centro Nacional para Síntesis y Análisis Ecológicos. Ajustamos el modeloa series de tiempo históricas de capturas por unidad de esfuerzo y tasas de mortalidad de atunesaleta amarilla y patudo en simulaciones que incorporaron esfuerzo de pesca histórico e impulsosclimáticos para representar el efecto de variaciones a escala de El Niño-Oscilación del Sur sobreel sistema. El modelo fue diseñado para evaluar las posibles implicaciones ecológicas de la pescaatunera de varias formas. Reconocemos la imposibilidad de que el modelo represente toda la complejidadde un ecosistema oceánico pelágico, pero creemos que el modelo del POT mejora losconocimientos de la estructura y función del POT pelágico.

Description: This article is bilingual and contains both English and Spanish translations.

Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in BMC Evolutionary Biology 12 (2012): 209, doi:10.1186/1471-2148-12-209.

Description: Marine phytoplankton drift passively with currents, have high dispersal potentials and can be comprised of morphologically cryptic species. To examine molecular subdivision in the marine diatom Thalassiosira rotula, variations in rDNA sequence, genome size, and growth rate were examined among isolates collected from the Atlantic and Pacific Ocean basins. Analyses of rDNA included T. gravida because morphological studies have argued that T. rotula and T. gravida are conspecific. Culture collection isolates of T. gravida and T. rotula diverged by 7.0 ± 0.3% at the ITS1 and by 0.8 ± 0.03% at the 28S. Within T. rotula, field and culture collection isolates were subdivided into three lineages that diverged by 0.6 ± 0.3% at the ITS1 and 0% at the 28S. The predicted ITS1 secondary structure revealed no compensatory base pair changes among lineages. Differences in genome size were observed among isolates, but were not correlated with ITS1 lineages. Maximum acclimated growth rates of isolates revealed genotype by environment effects, but these were also not correlated with ITS1 lineages. In contrast, intra-individual variation in the multi-copy ITS1 revealed no evidence of recombination amongst lineages, and molecular clock estimates indicated that lineages diverged 0.68 Mya. The three lineages exhibited different geographic distributions and, with one exception, each field sample was dominated by a single lineage. The degree of inter- and intra-specific divergence between T. gravida and T. rotula suggests they should continue to be treated as separate species. The phylogenetic distinction of the three closely-related T. rotula lineages was unclear. On the one hand, the lineages showed no physiological differences, no consistent genome size differences and no significant changes in the ITS1 secondary structure, suggesting there are no barriers to interbreeding among lineages. In contrast, analysis of intra-individual variation in the multicopy ITS1 as well as molecular clock estimates of divergence suggest these lineages have not interbred for significant periods of time. Given the current data, these lineages should be considered a single species. Furthermore, these T. rotula lineages may be ecologically relevant, given their differential abundance over large spatial scales.

Description: This research was supported by National Science Foundation grants, NSF 0727227 (to TAR) and NSF SBE0245039 (to URI, TAR). Part of the research was conducted using instrumentation supported by NSF-EPSCoR grants 0554548 and 1004057.