Slow growth rate of a deep-sea clam determined by 228Ra chronology.

Abstract

The age of a deep-sea clam, Tindaria caifisti-formis, from 3800 m depth has been determined by MRa (6.7 year half-life) chronology of separated size fractions of a captured population. A length of 8.4 mm is attained in about 100 years. Shells of this size fraction show about 100 regularly spaced bands, indicating that the growth feature may be an annual one.There are several reports indicating that the rate of metabolism on the deep ocean floor is extremely slow-generally one to two orders of magnitude slower than the rate for comparable organisms in shallow water systems (1-4). From small brood size and the high proportion of adult size classes observed for deep ocean benthos Grassle and Sanders (5) have postulated life histories with low rates of reproduction, growth, and mortality. The deep sea is an environment devoid of light, virtually invariant in ambient high pressure and low temperature, and probably subject to a slow food supply rate. These facts provide the basis for expectation of slow metabolic rates at depth but they also make the interpretation of growth features in the hard parts of deep-sea organisms difficult.The aim of our study was to explore the possibility of radiometrically determining the rates of growth of deep-sea benthic organisms that secrete a hard mineral shell. Our initial effort reported here is on a deep-sea clam, Tindaria callistiformis, an exclusively deep-sea species with regular growth bands. Our technique is to use the 228Ra (half-life = 6.7 years) concentrations in a number of growth stages and to infer from these data the growth rate of the organism.Radium-228 is produced from the decay of long-lived 232Th, which is found ubiquitously in clay-rich sediments at a concentration of about 10 parts per million although virtually absent in sea water. The 228Ra produced by a-decay is subject to release from sediments by diffusion or physical transport via the pore waters of the sediment into the overlying water. The distribution of 228Ra in the ocean after the initial study by Moore (6, 7) has been the subject of several intensive investigations (8, 9). Fig. 1 shows a profile from Trier et al. (9) for a North Atlantic Ocean station in the general vicinity of the site from which the clams used in this study were recovered.Radium-228 in surface waters of the deep ocean is derived from the sediment-water interactions in shallow coastal regions, especially where physical mixing knd bioturbation rates are high. Using 228Ra concentrations found in different layers of coral, Dodge and coworkers (10, 11) were able to date corals and determine that for several species the growth bands were indeed annual. Furthermore, by comparing the 228Ra/Ca ratio with 210Pb dating, they were able to demonstrate that this ratio was sensibly invariant in the surface ocean over at least 30 years.The 228Ra concentration at the water-sediment interface of the deep ocean floor is also high. Its concentration there is expected to be stabilized as well or better than in the surface waters. Thus the ...

Adult somatic progenitor cells and hematopoiesis in oyster

“…The longest living animals belong to the Bivalvia (Bureau et al, 2002;Peck and Bullough, 1993;Turekian et al, 1975;Ziuganov et al, 2000;Wanamaker et al, 2008;Butler et al, 2013), a main class in the phylum Mollusca. Long-lived animals have been defined as non-senescing species (Finch and Austad, 2001) because they do not show any observable age-related decline in physiological capacity or disease resistance.…”

Bomb-produced radiocarbon in the shell of the chambered nautilus: rate of growth and age at maturity

“…An alternative approach involves the use of chronometers incorporated into the shell during growth. Naturally occurring radionuclides of the uranium and thorium decay series have been used to determine the growth rates of a variety of marine organisms [6][7][8][9][10][11][12][13][14][15][16]. In particular, the radionuclides 228Ra (half-life=5.75 y) and 21°Pb (half-life=22 y) present in sea water are incorporated into the shells of marine organisms where they undergo radioactive decay to 228Th (half-life = 1.9 y) and 2a°Po (half-fife= 138 days), respectively.…”

THREADS: A Life in Geochemistry

“…Further work on profiles in the Atlantic Ocean, as part of the GEOSECS campaign at Lamont under Wally Broecker, affirmed the high concentration of 228 Ra in the ocean bottom, and other studies indicated high values in deep-sea sediment pore waters (Trier et al 1972). So, brashly, we determined the growth rate of Tindaria using the bands and the 228 Ra-based age (Turekian et al 1975). The largest clam (8 mm) was about 100 years old and, on the basis of comparison with shallow water clams, probably reached puberty at about 40 years.…”