Seasonal and spatial variations in the RNA:DNA ratio and its relation to growth in sub-Arctic scallops

Abstract

We examined the RNA and DNA concentration of field-caught scallops Chlamys islandica, maintained in suspended cultures at 15 and 30 m depth, and scallops from a wild population at 50 to 60 m in Kobbefjord, southwest Greenland. General relations between RNA and DNA concentrations and individual shell height were established, and we found that the RNA:DNA ratio (RD) worked well as a standardisation of the RNA concentration independent of size and sex. During an experimental period of 14 mo, we observed a pronounced seasonal pattern in RD and mass growth, and differences between depths. Even though the period with high levels of RD reflected the growth season relatively well, RD was a poor predictor of individual mass growth rates of C. islandica. However, we found a non-linear response in RD to increased food concentrations resulting in RD being up-and down-regulated at the beginning and end of the productive summer season, respectively. These results indicate that short-term dynamics in the actual mass growth rate might be controlled through regulation of ribosome activity rather than ribosome number (RNA concentration). This adaption would allow scallops to up-regulate protein synthesis more rapidly, thereby ensuring efficient utilisation of the intense peaks in food availability in coastal areas in the Arctic. Therefore, we suggest that RD in C. islandica reflects the growth potential rather than the actual growth rate. Still, the amount of unexplained variance in RD is considerable and not independent over time, suggesting the existence of unresolved mechanisms or relationships.KEY WORDS: Macrobenthos · Bivalve · Pectinid · Chlamys islandica · Greenland · Biomarker · Food availability Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 407: [87][88][89][90][91][92][93][94][95][96][97][98] 2010 with a pronounced seasonal sea ice cover. Consequently, little is known about the spatial or the temporal dynamics in the marine environment off Greenland. This is in strong contrast to the need for knowledge about the ecological relationships in the marine environment in the Arctic (ACIA 2005). Therefore, the validation of an easily obtained proxy for the growth rate of Arctic marine fauna would be of great value in studies of population dynamics. It would provide the opportunity to study growth dynamics at a multitude of locations with contrasting habitat characteristics, potentially revealing causal relationships between environment and biota. The RNA:DNA ratio (RD) of animal tissue is a measure of the capacity for protein synthesis (Wright & Hetzel 1985, Dahlhoff 2004. RD has been widely used in studies of fish larvae, where it has been validated as a proxy for the mass growth rate or the physiological condition (Buckley 1984, Clemmesen & Doan 1996, Grønkjaer et al. 1997, Caldarone et al. 2003, Buckley et al. 2008. In studies of invertebrate taxa, it has been suggested that variations in nucleic acid ratios (RD, RNA:protein, or total RNA concentration) relate t...