The rate of proteolysis of armno acids was used to assess the nutntional labihty of vanous materials making up estuanne seston in 3 Maine, USA, estuanes Physical separations of subcellular fractions of phytoplankton cells led to higher proteolysis rate constants for the cytoplasmic fractlon ( > l 2 h-') than for the membrane fraction (0 2 to 1 h-') Whole cells, copepod fecal pellets, bottom sedi m e n t ~, a n d estuarine seston had overlapping ranges of rate constants of 0 17 to 1 3 h-', which were indistinguishable from one another Protein pools in the seston of these estuaries throughout the seasons were dominated by phytoplankton production and its fresh detrital products Inverse relationships between proteolysis rate constants for estuarine seston and the ratios of pheopigments to chlorophyll indicates that the average l a b h t y of seston decreases with the disappearance of cytoplasmic matenal in suspension This k i n e t ~c approach to the quality of food resources implies the existence of different pools of digestible protein for estuarine heterotrophs with different gut residence times Preferential ennchment of membrane components in sestonlc detntus may result from the differential lability of proteins in cytoplasm versus membrane components of cells
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Laursen et al. (1996) studied this question.