The relative contribution of marine snow of different origins to biological processes in coastal waters

Abstract

While a disproportionate quantity of photosynthetic and hetrotrophic microbial activity can occur on marine snow in surface waters, the significance of these macroscopic aggregates as sites for the transformation of matter in the euphotic zone appears to be highly variable. We investigated the hypothesis that this variability results from differences in aggregate origin by comparing the properties of marine snow at 13 stations in the Southern California Bight and California Current. Four types of marine snow were encountered including larvacean houses, diatom flocs, fecal aggregates and aggregates composed primarily of miscellaneous debris and detritus. More than 95% of the aggregates observed at any one station were of the same type. Bacteria grew 3 fold faster and phaeopigments were significantly concentrated on marine snow of all types. However, an insignificant fraction (<1%) of total bacterial abundance, bacterial production, primary production, Chl a and nutrients occurred in association with marine snow of larvacean, fecal or miscellaneous origin. Marine snow formed from the coagulation of living diatom cells contributed more than 5% to these parameters, but only when the aggregates were large, abundant and recently formed. Our results indicate that only marine snow of direct phytoplankton origin contributes significantly to primary production in surface waters, and that a significant fraction of total photosynthetic and heterotrophic microbial activity is likely to occur on marine snow only episodically when aggregates are newly formed.