PRIMARY PRODUCTIVITY BY SYMBIONT-BEARING PLANKTONIC SARCODINES (ACANTHARIA, RADIOLARIA, FORAMINIFERA) IN SURFACE WATERS NEAR BERMUDA

Rates of primary productivity by the symbiotic algae of a variety of planktonic sarcodines (Acantharia, Radiolaria, Foraminifera) were measured at two limes of the year in 1991 from surface waters of the Sargasso Sea near Bermuda. Rates of symbiont production (expressed on a 'per host' basis) were not significantly different for the two seasons, but measurements for individual sarcodine species varied by more than four orders of magnitude and were roughly correlated with sarcodine size (and thereby with the biomass of the protozoan host). Overall, Acantharia had the lowest production rates per host, while solitary and colonial Radiolaria displayed the highest rates. Symbiont-bearing planktonic sarcodines were always microenvironments of highly concentrated primary production in this oligotrophic oceanic environment. Rates of primary production within the volumes defined by the extension of the cytoplasmic networks of the sarcodines generally exceeded rates of primary production in equivalent volumes of the seawater surrounding these associations by more than four orders of magnitude and showed no clear differences among the sarcodine groups. Total symbiont production, however, contributed a small fraction (generally <1%) of the total primary production in surface waters because of relatively low sarcodine abundances (compared to other primary producers) and because of high total primary production in surface waters. Combining the production rates measured in this study with seasonal abundances of Acantharia and Foraminifera, however, indicates that these assemblages may have contributed an average of similar to 5% to total annual primary production. Moreover, production within these symbioses constituted a significant fraction of the primary production by organisms greater than or equal to 70 mu m (8-67%) and dominated total production in the immediate vicinity of the sarcodine (centimeter to decimeter range). Primary production by the endosymbionts was also a significant contribution to the: carbon budgets of the sarcodine-symbiont associations. Hourly carbon fixation rates by the symbionts of the major sarcodine taxa ranged from 0.0076 to 0.070 mg C [mg C](-1) h(-1), which may have constituted up to similar to 80% of the carbon budgets of the host-symbiont complexes daily.