Seasonal variation in the white muscle biochemical composition of deep-sea macrourids in the North-east Atlantic
The foremost temporal signal to the deep benthos, where temperature and light conditions are relatively constant, is a seasonal pulse of organic carbon sinking from the photic layer. In the Porcupine Seabight region of the NE Atlantic this flux begins during late spring and early summer, although the timing and intensity of the peak varies annually. A rapid response to this nutrient input is most apparent amongst bacteria and benthic meiofauna which can directly utilize the carbon. The question remains as to whether the seasonal influx of carbon to the deep Atlantic may affect, and possibly entrain, aspects of the life cycles of generalist scavengers near the top of the trophic hierarchy, such as macrourid fish. Biochemical analyses of the white muscle of three macrourid species indicate a slight seasonal effect. White muscle protein content in Coryphaenoides rupestris is twofold higher in autumn than spring, RNA content and RNA to protein ratio increased in C. guentheri in autumn, and protein, RNA, and RNA to protein ratio all are higher during autumn than spring in shallow living C. armatus (2,500 m). Changes in RNA to protein ratio in the white muscle of C. armatus, relative to depth of capture, appear to reflect expected patterns in specific growth rate. Significantly higher RNA to protein ratios are apparent in shallow than deep living C. armatus in both seasons. There is no significant decline in white muscle protein content with depth of capture in these three taxonomically related species. Data were collected over several successive years and the possibility of interannual variability complicates the interpretation of seasonal patterns. Despite these limitations this study does indicate a slight seasonal difference in the growth rate of C. rupestris, C. guentheri and C. armatus in the deep Northeast Atlantic.