RNA:DNA ratios of the hydrothermal-vent vestimentiferans Ridgeia piscesae and R. phaeophiale indicate variations in growth rates over small spatial scales

The ratio of RNA to DNA (RNA:DNA) was used to assess the relative growth rates of the hydrothermal vent vestimentiferans Ridgeia piscesae Jones and R. phaeophiale Jones. This biochemical indicator of growth is especially valuable when actual growth rates are difficult to measure. Tubeworms were collected from five hydrothermally active sites along the Juan de Fuca Ridge, in the Northeast Pacific Ocean in the summers of 1984 and 1986. We found significant variation in RNA:DNA among Ridgeia spp. from the five sites which was not due to size of the tubeworms or to a species-specific difference. Instead, differences in RNA:DNA were related to site of collection. Mean RNA:DNAs of 2.1 and 3.9 for R. piscesae from two sites were significantly different from each other, but not from that of tubeworms from a third site (mean=2.9). Similarly, mean RNA:DNAs of 2.3 and 4.5 for R. phaeophiale from two sites were significantly different. These patterns in RNA:DNA may reflect differences in growth rates arising from variation in environmental factors over spatial scales as small as 2 m.