Confirmation of a new food chain utilizing geothermal energy: Unusual fatty acids of a deep-sea bivalve, Calyptogena phaseoliformis
Limnol. Oceanogr., 52(5), 2007, 1910-1918 | DOI: 10.4319/lo.2007.52.5.1910
ABSTRACT: Neutral and polar lipids of the cold-seep clam Calyptogena phaseoliformis were determined to assess the trophic relationship at hydrothermal vents. The clam obtained many of its lipids from the chemosynthetic microorganisms within the bacteriocytes on its gill filaments. The major fatty acids in the triacylglycerols and phospholipids in the clam consisted only of the n-4 family polyunsaturated fatty acids (PUFA) plus saturated and n-7 monounsaturated fatty acids and were completely lacking n-3 PUFA, such as docosahexaenoic acid (22:6n-3) and icosapentaenoic acid (20:5n-3). Such unique fatty acid composition markedly differs from those reported for other marine animals, which depend on organic matter derived from surface-layer phytoplankton. The relationship between C. phaseoliformis and its symbiotic bacteria is documented and revealed a closed novel food chain, independent of the photosynthetic food chain. The fluidity of the fatty acids in the animals membrane are maintained by adaptation of the exogenous n-4 family PUFA. These unusual but dominant fatty acids are assimilated from the symbiotic chemosynthetic bacteria, which use only geothermal energy and minerals from the cold-seep vents.