The Importance of Feeding in Two Species of Soritid Foraminifera with Algal Symbionts

The carbon budgets and rates of calcification of Archaias angulatus and Sorites marginalis, two species of symbiont-containing soritid foraminifera, were studied in situ in Key Largo Sound, Florida. Respirometric and radionuclide techniques were used to measure mid-day primary production, calcification, and feeding rates. The algae used in the tracerfeeding studies were prominent species from the local Thalassia community and species which are excellent food sources for other species of littoral benthic foraminifera. Tracer feeding studies clearly indicated that feeding was the more important process at midday; the ratio of carbon gain in both foraminifera-symbiont systems by feeding to primary production was ≥ 10:1. The rate of primary production was generally greater in A. angulatus than in S. marginalis. The diets of the two species of foraminifera were relatively non-overlapping. Under the experimental conditions both species deposited ∼ 4% of dry weight in additional calcium per day. Small specimens of A. angulatus deposited ∼ 1.8 × more calcium than did larger specimens. Under the experimental conditions, light did not enhance the rate of calcification.