Protozoan Epibionts on the Prop Roots of the Red Mangrove Tree, Rhizaphora mangle

Despite the importance of understanding carbon flow in mangrove systems, relatively little research has focused on the grazing protozoan populations inhabiting these sensitive areas. A conspicuous feature of the mangrove tree is the array of emergent aerial roots that are covered in epibiont film. This study is the first to consider the numbers of protozoa inhabiting this dense surface film layer. No obvious temporal pattern was detected throughout a one year sampling program; numbers of protozoa were variable between sampling events but always abundant. Heterotrophic flagellates averaged 2.7 x 10^3 g^- 1 dry film, amoebae were the next most abundant group at 7.7 x 10^3 g^- 1 dry wt and ciliates averaged 4.8 x 10^3 g^- 1 dry wt. In this non -limited substrate environment, bacteria were numerous averaging 6.9 x 10^9 cells g^ -1 dry wt as were the other possible prey items, the cyanobacteria (9.8 x 10^6 cells g^- 1 dry wt) and pennate diatoms ( 2.4 x 10^6 cells g ^-1 dry wt). It was estimated that the combined protozoan population was only removing about 3% of bacteria carbon d 1, suggesting that micrograzers are not major regulators of bacterial carbon in this specialized habitat. Some preliminary trials comparing the growth of protozoa (as generation time) on tightly and loosely associated bacteria suggest that amoebae are more capable of removing tightly-associated bacteria than the other micrograzers. Since these attached bacteria are likely to be involved in the degradation of mangrove carbon, this observation suggests a possible important ecological role for amoebae in the film community.