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 p lanktonic sarcodines (Acantharia, Radiolaria, Foraminifera) were measu red at two limes of the year in 1991 from surface waters of the Sargas so Sea near Bermuda. Rates of symbiont production (expressed on a 'per host' basis) were not significantly different for the two seasons, bu t measurements for individual sarcodine species varied by more than fo ur orders of magnitude and were roughly correlated with sarcodine size (and thereby with the biomass of the protozoan host). Overall, Acanth aria had the lowest production rates per host, while solitary and colo nial Radiolaria displayed the highest rates. Symbiont-bearing plankton ic sarcodines were always microenvironments of highly concentrated pri mary production in this oligotrophic oceanic environment. Rates of pri mary production within the volumes defined by the extension of the cyt oplasmic networks of the sarcodines generally exceeded rates of primar y production in equivalent volumes of the seawater surrounding these a ssociations by more than four orders of magnitude and showed no clear differences among the sarcodine groups. Total symbiont production, how ever, contributed a small fraction (generally <1%) of the total primar y production in surface waters because of relatively low sarcodine abu ndances (compared to other primary producers) and because of high tota l primary production in surface waters. Combining the production rates measured in this study with seasonal abundances of Acantharia and For aminifera, however, indicates that these assemblages may have contribu ted an average of similar to 5% to total annual primary production. Mo reover, production within these symbioses constituted a significant fr action of the primary production by organisms greater than or equal to 70 mu m (8-67%) and dominated total production in the immediate vicin ity of the sarcodine (centimeter to decimeter range). Primary producti on by the endosymbionts was also a significant contribution to the: ca rbon budgets of the sarcodine-symbiont associations. Hourly carbon fix ation 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 d aily.