Evaluation of excess ²³⁴Th activity in sediments as an indicator of food quality for deep-sea deposit feeders

Authors: Demopoulos A.W.J.; Smith C.R.; Demaster D.J.; Fornes W.L.

Source: Journal of Marine Research, Volume 61, Number 2, 1 March 2003 , pp. 267-284(18)

Publisher: Sears Foundation for Marine Research

Abstract:

Deep-sea deposit feeders selectively ingest large volumes of sediment. Knowledge of the nature of this selectivity will help to elucidate the limiting nutritional requirements and geochemical impacts of these abundant animals. Shallow-water and theoretical studies suggest that deep-sea deposit feeders should select particles rich in protein, bacterial biomass, and/or chloropigment concentrations. Recent studies indicate that deep-sea megafaunal deposit feeders exhibit strong gut enrichment of excess (xs) ²³⁴Th activity, even though ²³⁴Th_xs lacks nutritional value. To explore the significance of selective ingestion of ²³⁴Th_xs activity, we evaluated the correlations between ²³⁴Th_xs activity and three potential tracers of deposit feeder food quality: chlorophyll a (chl a), enzymatically hydrolyzable amino acids (EHAA), and adenosine triphosphate (ATP). Surface sediments from three quiescent bathyal basins off Southern California (San Nicolas, Santa Catalina, and San Clemente) were collected by a multiple corer and analyzed for 234Th_xs activity, chl a, EHAA, ATP, and total organic carbon and nitrogen. ²³⁴Th_xs activity was positively correlated with chl a and phaeopigment concentrations and negatively correlated with EHAA concentrations. Excess ²³⁴Th was not linearly correlated with concentrations of ATP, organic carbon, or total nitrogen. The results suggest that deep-sea deposit feeders select sediments with high ²³⁴Th_xs activity because it is associated with recently settled phytodetrital material. There is no evidence that this ²³⁴Th_xs-rich material has particularly high concentrations of labile amino acids or microbial biomass. Phytodetrital material may be an important source of some other limiting nutrient to deep-sea deposit feeders, e.g., polyunsaturated fatty acids, labile organic carbon and/or vitamins.

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Document Type: Research article

DOI: http://dx.doi.org/10.1357/002224003322005096

Publication date: 2003-03-01

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