Vertical Flux of Biogenic Carbon in the Ocean: Is There Food Web Control?

Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions.

Use of Inorganic Membrane Filters (Anopore) for Epifluorescence and Scanning Electron Microscopy of Nanoplankton and Picoplankton

Inorganic membrane filters (Anopore) were examined qualitatively by epifluorescence and scanning electron microscopy to determine their suitability for the study of nanoplankton and picoplankton. Compared with filters currently used, the Anopore filters allowed for increased resolution of the specimen with epifluorescence microscopy because of filter flatness and increased illumination caused by the large number of pores cm -2 . The inorganic filters had a lower filtration rate than polycarbonate filters. For scanning electron microscopy, the metal oxide (Anopore) filters were efficient support for the plankton, with little charging of cells or background.

Visualization of the Transparent, Gelatinous House of the Pelagic Tunicate Oikopleura vanhoeffeni Using Sepia Ink

Appendicularian tunicates of the genus Oikopleura feed using an external, acellular, transparent structure known as the house. Previously, dilute particulate dyes have been used to visualize the internal structure of this house. However, because of toxicity, large particle size, and flocculation, many of these dyes have been of limited practical and scientific use. We report on a new marker, the ink from the cephalopod Sepia officinalis, that solves many of these problems. Specimens of Oikopleura vanhoeffeni relished Sepia ink, having dark black stomachs and producing many dark fecal pellets over several days. When O. vanhoeffeni expanded houses in dilute ink, the internal walls, septae, and filters were shown in great detail, whereas high concentrations of ink showed delicate patterns of lines on the internal walls. We present documentary photographs of previously unillustrated or undescribed morphologies: the escape slot; the incurrent funnels; two dimples caused by insertion of suspensory filaments on the upper wall of the posterior chamber, a large, posterior keel; both the open and closed positions of the exit valve; and the complex pattern of lines on the inner walls. However, the external walls of the house had no affinity for the dye and could only be seen by dark field illumination. We believe that Sepia ink can be used to visualize functionally important transparent structures of other gelatinous zooplankton and can be a colloidal marker in feeding experiments of a wide range of filter feeders.

Temperature Regulation of Bacterial Activity During the Spring Bloom in Newfoundland Coastal Waters

While the spring phytoplankton bloom in Newfoundland coastal waters is in progress during April and May, at water temperatures between -1 degrees and +2 degrees C, bacterial growth and respiratory rates remain low. Microbial community respiration is not measurable at -0.2 degrees C. Particulate materials that would be utilized by microorganisms in 2 to 3 days at 20 degrees to 25 degrees C require 11 days at 4 degrees C and 18 days at -0.2 degrees C. Thus, photosynthesis is active but microbial utilization of the products is suppressed. High secondary production in cold water may result from the low rate of microbial decomposition, enabling herbivores to utilize much of the primary production.