Temporal modification in cardiac rhythmicity of <i>Nephrops norvegicus</i> (Crustacea: Decapoda) in relation to trawl capture stress

Abstract

SUMMARY: The effects of trawling on cardiac rhythmicity of Nephrops norvegicus (L.) are still mostly unknown. Ultradian rhythms reported in previous studies may result from trawling capture stress, thus disappearing following acclimatisation to laboratory conditions. To test this hypothesis, 34 time series of cardiac activity data recorded in constant darkness were studied by Fourier analysis. Spectral decomposition of time series was obtained by defining the fundamental or circadian harmonic (CH) in 24-h together with 9 submultiples of this period. The power content (PC) of each harmonic was estimated in data segments of 24-h duration (days), giving graphic matrices of PC values over consecutive days. Values of PC for 9 submultiples were summed and studied in a block named ultradian band (UB). The modification in the PC of the CH and of the UB was evaluated during laboratory acclimatisation. A significant increase in the PC of the circadian harmonic component (CH) over consecutive days of testing was observed. These findings suggest that, rather than being a product of dim light environmental fluctuations experienced by the animals from the deep waters of the continental slope, ultradian periodicity could well be caused by the stress of capture.Keywords: Nephrops norvegicus, stress, cardiac rhythms, constant darkness, Fourier analysis, circadian and ultradian rhythms. RESUMEN: MODIFICACIÓN TEMPORAL DE LA RITMICIDAD CARDÍACA DE NEPHROPS NORVEGICUS EN RELACIÓN AL ESTRÉS DE CAP-TURA POR ARRASTRE. -Los efectos de la pesca de arrastre sobre la ritmicidad cardíaca de Nephrops norvegicus (L.) son aún desconocidos y los ritmos ultradianos descritos en estudios previos podrían ser consecuencia del estrés de captura por el arte de pesca de arrastre, desapareciendo éstos al continuar la aclimatación en el laboratorio. Para probar esta hipótesis, 34 series temporales de datos de actividad cardíaca registrados en oscuridad constante fueron estudiadas mediante análisis de Fourier. Se obtuvo la descomposición espectral de las series definiendo el armónico fundamental o armónico circadiano (CH) en 24 h junto con 9 submúltiplos de este período. Se estimó el contenido de potencia (PC) de cada armónico en segmentos de datos de 24 h de duración (días) obteniéndose matrices gráficas de valores del PC en días consecutivos. Los valores del PC de los 9 submúltiplos fueron sumados y estudiados en un bloque llamado banda ultradiana (UB). Fue evaluada la modificación diaria del PC del CH y de la UB durante la aclimatación en el laboratorio. Se observó un incremento significativo en el PC del componente armónico circadiario (CH) durante los días consecutivos. Estos hallazgos sugieren que la periodicidad ultradiana no sería producida por las fluctuaciones ambientales de luz ténue experimentadas por el animal en aguas profundas del talud continental, sino que estarían provocadas probablemente por el estrés de captura.Palabras clave: Nephrops norvegicus, estrés, ritmos cardíacos, oscuridad constante, análisis de Fourier, ritmos circadianos y...

A new tracking system for the measurement of diel locomotor rhythms in the Norway lobster, Nephrops norvegicus (L.)

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