Biogeographic and diversity patterns of pelagic copepods in the South Pacific Ocean
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Date
2024
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Universidad de Concepción
Abstract
El zooplancton es un componente clave del ecosistema marino, principalmente por su papel como parte de la base de la vida en el océano, actuando como enlace trófico entre los productores primarios y otros niveles tróficos superiores, así como un componente del anillo microbiano y ejerciendo una función esencial en los ciclos biogeoquímicos. Además, debido a sus ciclos de vida relativamente cortos, responde rápidamente a las variaciones oceanográficas y ambientales asociadas con el cambio climático-oceanográfico. En general, el zooplancton ha sido ampliamente estudiado, especialmente los copépodos, que muestran una fuerte dependencia de sus tasas vitales con la temperatura y otros factores ambientales relacionados con el clima. En cuanto al impacto ambiental sobre el zooplancton, en el Océano Pacífico Sur existe una amplia variabilidad de la productividad superficial-oceánica y los regímenes físico-oceanográficos que dan forma a diferentes ambientes y condiciones tróficas dentro del océano costero y abierto; por lo tanto, estudiar los forzantes de la diversidad de especies de copépodos en esta región es útil para dilucidar cómo el zooplancton puede responder a un océano cambiante. El presente trabajo de tesis evaluó la diversidad del zooplancton en relación con la variación oceanográfica a gran escala en el Pacífico Sur.
En el primer capítulo, se utilizó una base de datos de 27 años (1993-2019) de ocurrencia de especies de copépodos planctónicos en el Océano Pacífico Sur, junto con variables oceanográficas asociadas, para evaluar los patrones espaciales de biodiversidad en los 200 m superiores del océano. El objetivo de este estudio fue identificar las regiones ecológicas y los predictores ambientales que explican dichos patrones. Se encontró que los puntos calientes y fríos de diversidad y los conjuntos de especies distintivos se encuentran vinculados a las principales corrientes oceánicas y grandes regiones sobre la cuenca, con una creciente riqueza de especies en las áreas subtropicales de los lados este y oeste del Pacífico Sur. Los modelos espaciales señalan que los mejores predictores ambientales que contribuyen a la varianza de la diversidad y la composición de especies son la temperatura, la salinidad, la concentración de clorofila-a, la concentración de oxígeno y la autocorrelación residual. No obstante, se encontró que los patrones espaciales observados y los efectos ambientales derivados estaban fuertemente influenciados por la cobertura de muestreo en el espacio y el tiempo, lo que revela una cuenca altamente sub-muestreada.
En el segundo capítulo, demostramos la hipótesis de que la estabilidad ambiental es el mecanismo modulador clave de los patrones de diversidad de copépodos en el Sistema de la Corriente de Humboldt (SCH), utilizando una base de datos de 17 años (1995-2011) de ocurrencia de especies y datos ambientales en los 500 m superiores (divididos en cinco estratos verticales) para la zona de surgencia frente a Chile, distinguiendo dos regiones (norte y sur) con diferentes regímenes estacionales de surgencia impulsada por el viento. Estimamos índices de diversidad de copépodos y su distribución, segregados por regiones y estratos de profundidad. Los índices fueron asociados con variables oceanográficas forzadas por la intensidad de surgencia, junto con una estimación de la energía cinética turbulenta (EKE), como un proxy de la estabilidad ambiental. En la comunidad, encontramos 18 especies dominantes ampliamente distribuidas en el área de estudio. Algunas corresponden a especies exclusivas para el estrato de profundidad superior con diferencias en el número de especies exclusivas por región y profundidad. Los modelos lineales mixtos revelaron que los índices de diversidad diferían significativamente entre regiones y estratos, y su varianza se explicaba principalmente por la temperatura, la salinidad, la concentración de oxígeno, la estabilidad de la temperatura y la energía cinética turbulenta (EKE). Tanto la estabilidad de la temperatura como la EKE fueron los predictores más eficientes de la diversidad de copépodos, lo que sugiere que la estabilidad climática-oceanográfica, forzada por la intensidad de surgencia, es el impulsor clave para promover y mantener la diversidad de copépodos en el SCH.
La tesis en su conjunto entrega resultados que permiten apoyar la hipótesis principal, concluyendo que la estructuración de comunidades de copépodos a una escala espacial extensa en el Pacífico Sur está fuertemente asociada a una zonación significativa sobre los ejes horizontales y verticales en los cuales la estabilidad (varianza) de parámetros ambientales, tales como la temperatura y energía cinética aparecen como factores claves en la modulación de estos patrones biogeográficos y de diversidad.
Zooplankton are a key component of the marine ecosystem, mainly due to their role as part of the foundation of life in the ocean acting as the trophic link between primary producers and the other upper-trophic levels, as well as a component of the microbial loop and their function in biogeochemical cycles. Moreover, due to their relatively short life cycles, they are known to rapidly respond to oceanographic and environmental variations associated with climate-oceanographic change. Zooplankton representatives have been widely studied, especially copepods, which exhibit a strong dependence of their vital rates with temperature and other climate-related environmental factors. Regarding environmental impact on zooplankton, in the South Pacific Ocean there is a broad range of surface-ocean productivity and physical-oceanographic regimes that shape different environments and trophic conditions within the coastal and open ocean; therefore, to study the drivers of their species diversity in these areas would be useful to elucidate how zooplankton may respond to a changing ocean. The present thesis work focused on zooplankton diversity in relation to large-scale oceanographic variation in the South Pacific while considering the vertical axis as well. In the first chapter, a 27-years (1993–2019) database on species occurrence of planktonic copepods of the South Pacific Ocean was used, along with associated oceanographic variables, to examine their spatial patterns of biodiversity in the upper 200 m of the ocean. The aim of this study was to identify ecological regions and the environmental predictors explaining such patterns. It was found that hot and cold spots of diversity, and distinctive species assemblages were linked to major ocean currents and large regions over the basin, with increasing species richness over the subtropical areas on the East and West sides of the South Pacific. While applying the spatial models, it was shown that the best environmental predictors for diversity and species composition were temperature, salinity, chlorophyll-a concentration, oxygen concentration, and the residual autocorrelation. Nonetheless, the observed spatial patterns and derived environmental effects were found to be strongly influenced by sampling coverage over space and time, revealing a highly under-sampled basin. In the second chapter, we tested the hypothesis that environmental stability is the key modulating mechanism of copepod diversity patterns in the Humboldt Current System (HCS), by using a 17-years (1995-2011) database on species occurrence of copepods along with environmental data for the upper 500 m of the ocean (divided into five vertical strata) for the upwelling zone off Chile, distinguishing two regions (northern and southern) having different seasonal regimes of wind-driven upwelling. We estimated indices for copepod diversity and their distribution, segregated by regions and depth strata. The indices were then associated with oceanographic variables forced by upwelling intensity, along with an estimate of eddy kinetic energy (EKE), as a proxy of environmental stability. From the entire community, we found 18 dominant species widely distributed in the study area. Some were exclusive species for the upper depth stratum with differences in the number of exclusive species per region and depth. From Linear Mixed Models we found that the diversity indices significantly differed between regions and strata, and their variance was mainly explained by temperature, salinity, oxygen concentration, temperature stability, and eddy kinetic energy (EKE). Both temperature stability and EKE were the best predictors of copepods diversity, suggesting that climate-oceanographic stability, forced by upwelling intensity, is the key driver for promoting and maintaining copepod diversity in the HCS. The thesis provides findings that support the main hypothesis, concluding that the structuring of copepod communities on a large spatial scale in the South Pacific is strongly associated with a significant zonation on the horizontal and vertical axes in which the stability (variance) of environmental parameters, such as temperature and kinetic energy appear as key factors in the modulation of these biogeographic and diversity patterns.
Zooplankton are a key component of the marine ecosystem, mainly due to their role as part of the foundation of life in the ocean acting as the trophic link between primary producers and the other upper-trophic levels, as well as a component of the microbial loop and their function in biogeochemical cycles. Moreover, due to their relatively short life cycles, they are known to rapidly respond to oceanographic and environmental variations associated with climate-oceanographic change. Zooplankton representatives have been widely studied, especially copepods, which exhibit a strong dependence of their vital rates with temperature and other climate-related environmental factors. Regarding environmental impact on zooplankton, in the South Pacific Ocean there is a broad range of surface-ocean productivity and physical-oceanographic regimes that shape different environments and trophic conditions within the coastal and open ocean; therefore, to study the drivers of their species diversity in these areas would be useful to elucidate how zooplankton may respond to a changing ocean. The present thesis work focused on zooplankton diversity in relation to large-scale oceanographic variation in the South Pacific while considering the vertical axis as well. In the first chapter, a 27-years (1993–2019) database on species occurrence of planktonic copepods of the South Pacific Ocean was used, along with associated oceanographic variables, to examine their spatial patterns of biodiversity in the upper 200 m of the ocean. The aim of this study was to identify ecological regions and the environmental predictors explaining such patterns. It was found that hot and cold spots of diversity, and distinctive species assemblages were linked to major ocean currents and large regions over the basin, with increasing species richness over the subtropical areas on the East and West sides of the South Pacific. While applying the spatial models, it was shown that the best environmental predictors for diversity and species composition were temperature, salinity, chlorophyll-a concentration, oxygen concentration, and the residual autocorrelation. Nonetheless, the observed spatial patterns and derived environmental effects were found to be strongly influenced by sampling coverage over space and time, revealing a highly under-sampled basin. In the second chapter, we tested the hypothesis that environmental stability is the key modulating mechanism of copepod diversity patterns in the Humboldt Current System (HCS), by using a 17-years (1995-2011) database on species occurrence of copepods along with environmental data for the upper 500 m of the ocean (divided into five vertical strata) for the upwelling zone off Chile, distinguishing two regions (northern and southern) having different seasonal regimes of wind-driven upwelling. We estimated indices for copepod diversity and their distribution, segregated by regions and depth strata. The indices were then associated with oceanographic variables forced by upwelling intensity, along with an estimate of eddy kinetic energy (EKE), as a proxy of environmental stability. From the entire community, we found 18 dominant species widely distributed in the study area. Some were exclusive species for the upper depth stratum with differences in the number of exclusive species per region and depth. From Linear Mixed Models we found that the diversity indices significantly differed between regions and strata, and their variance was mainly explained by temperature, salinity, oxygen concentration, temperature stability, and eddy kinetic energy (EKE). Both temperature stability and EKE were the best predictors of copepods diversity, suggesting that climate-oceanographic stability, forced by upwelling intensity, is the key driver for promoting and maintaining copepod diversity in the HCS. The thesis provides findings that support the main hypothesis, concluding that the structuring of copepod communities on a large spatial scale in the South Pacific is strongly associated with a significant zonation on the horizontal and vertical axes in which the stability (variance) of environmental parameters, such as temperature and kinetic energy appear as key factors in the modulation of these biogeographic and diversity patterns.
Description
Tesis presentada para optar al grado académico de Doctora en Oceanografía
Keywords
Ecología marina, Zooplancton, Ciclos biogeoquímicos