Physiological responses to upwelling-induced hypoxia in epipelagic copepods inhabiting the coastal zone in central-southern Chile.
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Date
2024
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Universidad de Concepción
Abstract
Los sistemas de surgencia de borde oriental (EBUS) son regiones marinas del océano mundial de importancia ecológica y económica. En estos sistemas, el zooplancton desempeña un papel clave en la transferencia de energía en las tramas tróficas. Estudios recientes muestran que el calentamiento global está provocando una desoxigenación gradual de los océanos del mundo, mientras que en EBUS una expansión vertical de la zona mínima de oxígeno subsuperficial (OMZ) lo que exacerba aún más las condiciones hipóxicas para el zooplancton que habita en la zona de surgencia costera. La hipoxia puede afectar al zooplancton al alterar sus tasas metabólicas, migración, reproducción y desarrollo. Sin embargo, estos efectos dependen de algunas adaptaciones específicas de los organismos que han evolucionado en hábitats, permanente o episódicamente, sujetos a aguas con poco oxígeno.
En el capítulo 1 se analizó las respuestas diferenciales en las tasas metabólicas de tres especies de copépodos, Calanoides patagoniensis, Paracalanus cf. indicus y Acartia tonsa expuestos a condiciones experimentales de hipoxia. Estas condiciones de bajo oxígeno, fueron asociadas a dos periodos del año: surgencia activa (primavera-verano) y no surgencia (otoño-invierno). Los resultados muestran que Calanoides patagoniensis duplicó su tasa metabólica durante la temporada de surgencia, indicando que aprovecha mejor la floración de fitoplancton de primavera-verano para alimentarse y reproducirse, manteniendo su presión parcial de oxígeno crítica sin cambios entre estaciones. Por el contrario, Paracalanus cf. indicus y Acartia tonsa, mantuvieron sus tasas metabólicas a lo largo de las estaciones, pero aumentaron significativamente su presión parcial crítica de oxígeno durante el período de surgencia activa, volviéndose menos tolerantes a la hipoxia en primavera-verano. Al contrastar estos hallazgos con observaciones de series de tiempo, podemos ver que los niveles de oxígeno igual o inferior a la presión parcial crítica de oxígeno es una condición común (aproximadamente el 70% de la probabilidad de ocurrencia) para los copépodos durante un ciclo anual mientras habitan la capa superior de los 50 m. Estos resultados sugieren la existencia de un balance dependiente de la especie entre la tasa metabólica y la presión parcial crítica de oxígeno. Estas respuestas adaptativas dependientes de las especies, sugieren que la hipoxia exacerbada, impulsada por la desoxigenación del océano y el aumento de la surgencia, conducirá a un cambio en la distribución vertical de los copépodos como consecuencia de una compresión del hábitat, y aumentando su mortalidad, con consecuencias potencialmente drásticas para las tramas tróficas marinas.
En el capítulo 2 se realizó una síntesis bibliográfica de las respuestas adaptativas del zooplancton para resistir a la hipoxia leve o grave y el eventual estrés oxidativo derivado de condiciones de oxígeno altamente fluctuantes, en sistemas de surgencia de borde oriental (EBUS). Estudios recientes dan cuenta de una expansión vertical de la zona de mínimo oxígeno junto con una intensificación de la surgencia costera impulsada por el viento, exacerbando las condiciones hipóxicas para el zooplancton que habita la zona de surgencia costera. La presencia o ausencia de respuestas adaptativas puede desempeñar un papel crucial en la dinámica del zooplancton en EBUS con importantes consecuencias para su red alimentaria y su productividad biológica.
Eastern boundary upwelling systems (EBUS) are marine regions of the global ocean of ecological and economical importance. In these systems, zooplankton play a key role in the energy transfer through the food webs. Recent studies show that global warming is causing a gradual deoxygenation of the world's oceans, while in EBUS a vertical expansion of the subsurface oxygen minimum zone (OMZ) which further exacerbates hypoxic conditions for zooplankton living in the coastal upwelling zone. Hypoxia can affect zooplankton by altering their metabolic rates, migration, reproduction and development. However, these effects depend on some specific adaptations of organisms that have evolved in habitats, permanently or episodically, subjected to low-oxygen waters. In chapter 1, the differential responses in the metabolic rates of three species of copepods, Calanoides patagoniensis, Paracalanus cf. indicus and Acartia tonsa exposed to hypoxic experimental conditions area assessed. These low oxygen conditions were associated with two periods of the year: active upwelling (spring-summer) and nonupwelling (autumn-winter). The results show that Calanoides patagoniensis doubled its metabolic rate during the upwelling season, indicating that it better takes advantage of the spring-summer phytoplankton bloom to feed and reproduce, maintaining its critical oxygen partial pressure unchanged between seasons. On the contrary, Paracalanus cf. indicus and Acartia tonsa, maintained their metabolic rates throughout the seasons, but significantly increased their critical partial pressure of oxygen during the period of active upwelling, becoming less tolerant to hypoxia in spring-summer. By contrasting these findings with time series observations, we found that oxygen levels equal to or less than the critical partial pressure of oxygen is a common condition (approximately 70% probability of occurrence) for copepods during an annual cycle, while they inhabit the upper layer of 50 m. These results suggest the existence of a species-dependent balance between metabolic rate and critical oxygen partial pressure. These species-dependent adaptive responses, under oxygen levels ≤ the critical partial pressure of oxygen, suggest that exacerbated hypoxia, driven by ocean deoxygenation and increased upwelling, will lead to a change in the vertical distribution of copepods, as a consequence of habitat compression, and increasing their mortality, with potentially drastic consequences for marine food webs. In chapter 2, a bibliographic synthesis of the adaptive responses of zooplankton to resist mild or severe hypoxia and the eventual oxidative stress derived from highly fluctuating oxygen conditions, in eastern edge upwelling systems (EBUS), was carried out. EBUS systems are of great ecological and economic importance, where zooplankton plays a fundamental role in carbon transfer in food webs. Recent studies show a vertical expansion of the oxygen minimum zone along with an intensification of wind-driven coastal upwelling as a result of climate change, further exacerbating hypoxic conditions for zooplankton inhabiting the coastal upwelling zone. The presence or absence of adaptive responses may play a crucial role in zooplankton dynamics in EBUS with important consequences for its food web and biological productivity.
Eastern boundary upwelling systems (EBUS) are marine regions of the global ocean of ecological and economical importance. In these systems, zooplankton play a key role in the energy transfer through the food webs. Recent studies show that global warming is causing a gradual deoxygenation of the world's oceans, while in EBUS a vertical expansion of the subsurface oxygen minimum zone (OMZ) which further exacerbates hypoxic conditions for zooplankton living in the coastal upwelling zone. Hypoxia can affect zooplankton by altering their metabolic rates, migration, reproduction and development. However, these effects depend on some specific adaptations of organisms that have evolved in habitats, permanently or episodically, subjected to low-oxygen waters. In chapter 1, the differential responses in the metabolic rates of three species of copepods, Calanoides patagoniensis, Paracalanus cf. indicus and Acartia tonsa exposed to hypoxic experimental conditions area assessed. These low oxygen conditions were associated with two periods of the year: active upwelling (spring-summer) and nonupwelling (autumn-winter). The results show that Calanoides patagoniensis doubled its metabolic rate during the upwelling season, indicating that it better takes advantage of the spring-summer phytoplankton bloom to feed and reproduce, maintaining its critical oxygen partial pressure unchanged between seasons. On the contrary, Paracalanus cf. indicus and Acartia tonsa, maintained their metabolic rates throughout the seasons, but significantly increased their critical partial pressure of oxygen during the period of active upwelling, becoming less tolerant to hypoxia in spring-summer. By contrasting these findings with time series observations, we found that oxygen levels equal to or less than the critical partial pressure of oxygen is a common condition (approximately 70% probability of occurrence) for copepods during an annual cycle, while they inhabit the upper layer of 50 m. These results suggest the existence of a species-dependent balance between metabolic rate and critical oxygen partial pressure. These species-dependent adaptive responses, under oxygen levels ≤ the critical partial pressure of oxygen, suggest that exacerbated hypoxia, driven by ocean deoxygenation and increased upwelling, will lead to a change in the vertical distribution of copepods, as a consequence of habitat compression, and increasing their mortality, with potentially drastic consequences for marine food webs. In chapter 2, a bibliographic synthesis of the adaptive responses of zooplankton to resist mild or severe hypoxia and the eventual oxidative stress derived from highly fluctuating oxygen conditions, in eastern edge upwelling systems (EBUS), was carried out. EBUS systems are of great ecological and economic importance, where zooplankton plays a fundamental role in carbon transfer in food webs. Recent studies show a vertical expansion of the oxygen minimum zone along with an intensification of wind-driven coastal upwelling as a result of climate change, further exacerbating hypoxic conditions for zooplankton inhabiting the coastal upwelling zone. The presence or absence of adaptive responses may play a crucial role in zooplankton dynamics in EBUS with important consequences for its food web and biological productivity.
Description
Tesis presentada para optar al grado de Doctora en Oceanografía
Keywords
Copépodos, Adaptación (Biología), Manejo de ecosistema marino