Video plankton recorder reveals high abundances of colonial Radiolaria in surface waters of the central North Pacific

Polycystine Radiolaria are one of the most conspicuous zooplankton taxa inhabiting the oceanic waters of the tropics and subtropics. Radiolaria are single-celled, eukaryotic organisms that are exclusively marine and, almost exclusively oceanic in their distributions. The unique morphologies and complex life histories of these organisms have captured the attention and imagination of biologists and micropaleontologists for more than 150 years (Ehrenberg, 1847; Haeckel, 1887). Radiolaria exist as single cells ranging in size from less than 30 μm to more than 1 mm. Each cell possesses a segregated central capsule that contains the nucleus, mitochondria and other cellular organelles, and a large pseudopodial network (Anderson, 1983). In addition some, but not all, Radiolaria produce silica skeletal structures of considerable paleontological significance (Casey, 1971; Kling, 1978). Radiolaria are morphologically and trophically complex (Anderson, 1983; Swanberg, 1983; Caron and Swanberg, 1990; Angel, 1991; Swanberg and Caron, 1991). The pseudopodial net produced by these species can be extensive, and is used to ensnare and phagocytose a wide variety of prey ranging from bacteria to relatively large zooplankton. In addition, many surface-dwelling species of Radiolaria possess symbiotic algae, predominantly dinoflagellates, within the outer pseudopodial network that are photosynthetically active and which contribute significantly to the nutrition of the host (Caron et al., 1995). Although Radiolaria are capable of existence as single cells, numerous species (largely within the Order Spumellaria) form colonies of individuals by extending their