Mesozooplankton associations with medium to large marine snow aggregates in the northern Gulf of Mexico

Large and diverse mesozooplankton communities were observed on marine snow particles collected in coastal and oceanic waters of the northern Gulf of Mexico. Mesozooplankton were collected from seven phyla, including ostracods, cladocerans, pelecypods and ascidian larvae not previ ously recorded as being associated with marine snow. Copepod nauplii were the most common, sometimes at concentrations >100 per aggregate. Oncaea spp., Oithona spp. and Microsetella norvegica were the most common copepod species. Total mesozooplankton abundance ranged between 2 and 278 organisms per aggregate. Organisms varied markedly in their distribution across the aggregate surface and in their behaviour towards the snow matrix. Comparison of snow communities with zoo-plankton abundance determined from net tows suggests that some species are concentrated on snow particles. Snow particles and their associated microbial communities may be a significant source of nutrition for these mesozooplankton. Mesozooplankton may contribute significantly to the degra dation and decomposition of large snow particles as they sink through the upper water column.