Seasonal changes of the biochemical composition of marine particulate matter with special reference to fatty acids and sterols

Abstract

Seasonal changes in particulate size spectra, biochemical con~position, fatty acid and sterol content were followed from winter to fall in a small north Atlantic coastal basin. Strong seasonality, related to both spnng-bloom and summer biological production, was recorded for most chemical and biochemical descriptors. Size spectra were generally characterized by donunance of small particles in the size range 6.35-25.4 pm equivalent diameter, except in early summer when an additional component in the 32.0-64.0 pm size range became important. Changes in either C:N ratio or carbohydrate:protein ratio indicated physiological changes which could be related to nutrient limitation or senescence The fatty a c ~d and sterol composition of the lipid fraction displayed major seasonal changes which reflected: (1) the seasonal heterogeneity of the taxonomic composition of the particles; (2) the physiological changes w t h i n each group of organism; and (3) the various penods of low production or bloom decay. Spring bloom production of small to medium size particles (12.7-50.8 pm) was associated with C16 polyunsaturated acid, 20:5w3, 24 methylene-cholesterol and desmosterol. Summer production of small particles (2.0-6.4 pm) was associated w t h C18 polyunsaturated acids, 2 2 : 6 ~3 , nor-24-cholesterol and isofucosterol, while the late winter-early spring period displayed close relationships between some saturates as well as monoenes (18.0, 18-lw9, 20:lw9, 2 2 . 1 ~9 ) and cholesterol Post-bloom decay associated another group of saturates and monoenes (14.0, 20:0, 22:0, 16 lw9, 16:ltA3) and p-sitosterol. Overall particulate biochemical dynamics is discussed in terms of both phytoplankton metabolism and trophic influence for the zooplankton consumers.