Macroaggregates and their phytoplanktonic components in the Southern California Bight

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Abstract
The abundances of phytoplankton associated with scuba-collected, visible macroaggregates (i e. ‘marine Snow’) from various euphotic zone depths of several nearshore and offshore sites sampled in late winter/early spring and summer were determined by microscopic study. Such phytoplankters have a different potential for predator/prey interactions than they would as separate individuals. Mean macroaggregate concentrations of 1.7–7 6 1−1 and mean individual macroaggregate sizes of 27–175 mm3 were observed at the different sites. Phytoplankters associated with the macroaggregates were generally a few percent or less of the total phytoplankton (range for numbers. 0.2–2.5%. range for carbon, 0.2–7.1%. n = 11). Of the taxonomic groups, pennate diatoms in general showed high relative association with macroaggregates. Compared to the mean abundance of phytoplankton in an equivalent volume of surrounding water, macroaggregates were algal-enriched by factors ranging from 6.2–1300 (median, 65) for numbers and 6.3–2500 (median. 110) for carbon (n = 11). ATP and chlorophyll a showed degrees of association with, and enrichment in. macroaggregates similar to that of phytoplankton carbon. Before assessing the overall importance of phytoplanktonic associations with aggregates in terms of pelagic food web consequences, the abundances and algal composition of the smaller microaggregates must also be known

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