Colonization of marine snow aggregates by invertebrate zooplankton: Abundance, scaling, and possible role

I compiled literature observations of abundances of invertebrate zooplankters associated with marine snow aggregates in the euphotic zone. Abundances, normalized with ambient concentrations of colonizers, scale with equivalent aggregate radius raised to power 2.27. Different taxonomic groups showed different affinities for aggregates and copepods and crustacean nauplii were the dominant groups on aggregates. The encounter volumes (volume searched to find one aggregate) are substantial, e.g., >1 liter for a l-cm aggregate, suggesting that some zooplankters actively search for aggregates. The scaling of the enrichment of invertebrates in aggregates over ambient water with aggregate radius (r) was significantly different from that of bacteria, proportional to r(-0.73) and proportional to r(-2.25) respectively, and for aggregates larger than 0.1 cm radius, invertebrates were one to several orders of magnitude more enriched than bacteria. Tentative estimates of the remineralization and degradation rates of aggregates due to the activity of invertebrate colonizers suggest that aggregate carbon is turned over within one to a few days. This is similar to or faster than turnover rates due to microorganisms. It is also estimated that between 20 and 70% of aggregate carbon is degraded by invertebrate colonizers before a sinking aggregate leaves a 50-m-deep euphotic zone. Thus, the majority of aggregated material may be degraded within the euphotic zone due to the combined activity of colonizing invertebrates, other grazers, and microorganisms.