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Cambalik, JJ, Checkley DM, Kamykowski D.  1998.  A new method to measure the terminal velocity of small particles: A demonstration using ascending eggs of the Atlantic menhaden (Brevoortia tyrannus). Limnology and Oceanography. 43:1722-1727. AbstractWebsite

A new method, incorporating video, motion analysis, and a novel experimental apparatus, was used to measure the terminal velocity of particles. The method facilitated the investigation of treatment effects and maximized the number of measurements for each replicate, thus improving the statistics for a population of particles. The eggs of the Atlantic menhaden (Brevoortia tyrannus) were used to demonstrate the method by investigating the effects of salinity and stage of development on their ascent rate. Egg ascent rate was greatest at intermediate salinity (36.5 parts per thousand) and decreased in the late stage of embryonic development. We estimate eggs at oceanic salinities (>35.5 parts per thousand) in nature to ascend at 0.19-0.25 cm s(-1).

Checkley, DM, Miller CA.  1989.  Nitrogen isotope fractionation by oceanic zooplankton. Deep-Sea Research Part a-Oceanographic Research Papers. 36:1449-1456.   10.1016/0198-0149(89)90050-2   AbstractWebsite

The ratio of 15N:14N for particulate matter suspended in oceanic, surface waters is high after recent nitrate depletion and low in the stable, oligotrophic ocean. We hypothesize that zooplankters and other pelagic heterotrophs produce 15N-depleted ammonium and 15N-enriched particulate matter that are, respectively, recycled in and exported from the euphotic zone and thus cause the low values of 15N:14N in oligotrophic seas. Heretofore, this pattern was attributed to nitrogen-fixation by the phytoplankton.We measured the ratio of 15N:14N in the bodies and excreted ammonium of zooplankters from the northwest Pacific Ocean and compared these values to the ratio of 15N:14N for subeuphotic, dissolved nitrate. We report that oceanic zooplankton excrete ammonium that is isotopically light relative to their bodies and subeuphotic nitrate. These results are consistent with our hypothesis and the view that the phytoplankton of oligotrophic seas is nourished primarily by nitrogen recycled within the euphotic zone. Nitrate injected into the euphotic zone may be manifest and hence detected by an increase of the ratio 15N:14N for the particulate matter suspended therein.

Checkley Jr., DM.  1985.  Nitrogen limitation of zooplankton production and its effect on the marine nitrogen cycle. Archiv fuer Hydrobiologie - Beiheft Ergebnisse der Limnologie. 21:103-113. Abstract
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