The National Science FoundationÆs (NSF) Program of Biological Oceanography supported our proposal "Fecal Pellets of Doliolids and Copepods: Two Different Microworlds?" from January 2011 to December 2014 (Grant 1031263). The goal of our study was to compare early decomposition rates of fecal pellets of doliolids with those of calanoid copepods, and their relation to abundances, sizes and processes of heterotrophic prokaryotes. It had been known that zooplankton fecal pellets, mainly produced by copepods, contribute significantly to the oceanÆs carbon cycle. Our findings showed that pellets produced by doliolids (Tunicata, Thaliacea) on the U.S. southeastern subtropical continental shelf differed from those of the mostly studied planktonic copepods: They are produced at a far higher rate, contain far higher amounts of carbon and nitrogen, and can be readily accessed by prokaryotes. As doliolids occur abundantly to being temporarily dominant on numerous continental shelves (e.g. Agulhas Bank, Ivory Coast, Southeastern Australia, most of the Brazilian Coast, coastal regions of Japan, the Gulf of Mexico, the U.S. west coast and the U.S. southeastern shelf), they contribute significantly to the carbon production and cycle in subtropical Ocean Margins as they are producing organic matter via extraordinary asexual production rates as well as pellet production rates. Our findings from the 4-year study contributed the following: Doliolids pellets sink at a lower rate than copepod pellets of similar carbon content, are faster colonized by prokaryotes than copepod pellets, and serve as food for heterotrophic dinoflagellates, copepods and thaliacea. In essence, such pelletsÆ extended residence time in the water column implies that they will hardly reach the sea floor. We also found that such doliolids readily ingested dispersed oil globules (several microns diameter, Fig.1 and Fig.2) in the presence of environmental amounts of phytoplankton without disturbing the feeders. That process leads to a prolonged stay of such oil globules in the water column as such pellets sink only very slowly. Similar to the U.S. southeastern shelf, doliolids can occur intermittently in large numbers in the Gulf of Mexico. Our findings reveal that fecal pellets of doliolids and planktonic copepods indeed represent different environments for microbes i.e. are indeed Different Microworlds. Our results represent not only an initial contribution towards understanding the ecological significance of fecal pellets of vastly different zooplankton taxa but also on the existence and persistence of their producers, the doliolids. Last Modified: 03/26/2015 Submitted by: Jay Brandes