We aimed to clarify and quantify the abundance of palynomorphs of tropical coastal marine shallow-water sediments collected from Oman, Malaysia, Okinawa and also the Sanriku region of Japan for making a comparison with temperate areas. Palynomorphs in these samples contained phototrophic and heterotrophic dinoflagellate cysts, acritarchs, resting cells of Prasinophyceae and Chrysophyceae, tintinnomorphs, microforaminiferal linings, testate amoebae and resting eggs and body fragments of copepods. The sediment samples from Malaysia, Oman, and Okinawa were characterized by dominance of heterotrophic marine palynomorphs, in particular microforaminiferal linings and heterotrophic dinoflagellate cysts, while the samples from Sanriku were different and dominated by phototrophic and heterotrophic dinoflagellate cysts. In addition subtropical-tropical assemblages were characterized by low cell/grain concentrations, especially phototrophic dinoflagellate cysts. These characteristics of marine palynomorphs in tropical shallow-water sediments may reflect lower production of phytoplankton in water column as well as high sedimentation rates. Also, high densities of heterotrophic palynomorphs consisting of microforaminiferal linings, tintinnomorphs, crustacean remains and other elements are other characteristics for tropical coastal shallow-water marine sediments. It is difficult to explain the abundant occurrences of heterotrophic dinoflagellate cysts based on the grazing food web against the fact of low phytoplankton production.
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Vol. 21 • No. 1