Temporal variations in fatty acid composition of deep-sea holothurians: evidence of bentho-pelagic coupling

Fatty acid biomarkers were used to examine the diet of deep-sea holothurians. We collected 3 species from the Porcupine Seabight and Porcupine Abyssal Plain, NE Atlantic, between 800 and 4850 m in August 2001 (summer), March 2002 (pre-spring bloom), and October 2002 (autumn). Of these, 2 species, the abyssal Amperima rosea and the bathyal Bathyplotes natans, showed significant variations in fatty acid compositions. These are likely to be seasonal. Polyunsaturated fatty acids (PUFAs) were dominant within muscle tissue of both species during August 2001 and October 2002, in particular 20:4 (n-6), 20:5 (n-3) and 22:6 (n-3). During March 2002, prior to the spring bloom, there were substantially lower proportions of PUFAs in both species, and increased amounts of mono-unsaturated fatty acids (monoenes), particularly the bacterially-derived biomarkers 18:1 (n-7) and non-methyl uninterrupted dienes (NMIDs). In contrast, the fatty acid composition of the third species, the abyssal Deima validum, remained relatively stable, with muscle tissue containing a high proportion of PUFAs during pre- and post-spring-bloom periods. A further 6 species were sampled in March 2002 and October 2002. Across all these species, 3 patterns of fatty composition were evident: (1) Laetmogone violacea had higher proportions of PUFAs in October than in March; (2) Psychropotes longicauda and Benthogone rosea had lower proportions of PUFAs in October than in March; (3) Deima validum, Oneirophanta mutabilis, Paroriza pallens and P. prouhoi had unchanged fatty acid compositions during these contrasting periods. These differences may be related to the varying reproductive strategies of the species. The implications of changes in fatty acids for reproductive processes, and how these could be factors determining allocation of lipid resources in gonads, is discussed.