Preliminary study on micro-endolithic organisms in seafloor near the Dokdo island, Korea

Abstract

In order to identify modern endolithic organisms, first in Korea, diverse carbonate shells were collected from the seafloor of Dokdo island, Korea. Shells of different organismal groups including gastropods, bivalves and bryozoans were collected because endoliths tend to penetrate in different ways according to the different shell structures. To understand the penetrating system of endoliths depending on the absence and/or presence of periostracum layers, both living (with periostracum layer) and abandoned (without periostracum layer) skeletons of bivalve shells were also obtained. A systematic collection at every 20 meters below the sea surfaces was also conducted due to difference of light availability according to different organisms (e.g., phototrohic cyanobacteria and heterotrophic fungi). Investigation of shell surfaces under SEM (scanning electron microscope) after resin embedding with alcohol and vacuum series revealed that most of Dokdo shells are densely penetrated by diverse endolithic groups, including cyanobacteria, green algae, fungi and unidentified heterotrophic bacteria. They are all characterized by tiny spherical holes in surfaces, but differ each other in internal structures such as size of cells, branching, and networking of whole colonies. Identification of species level, difference of penetration mechanisms of different endolithic groups, and difference of organism groups dependillected because endoliths tend to penetrate in different ways according to the different shell structures. To understand the penetrating system of endoliths depending on the absence and/or presence of periostracum layers, both living (with periostracum layer) and abandoned (without periostracum layer) skeletons of bivalve shells were also obtained. A systematic collection at every 20 meters below the sea surfaces was also conducted due to difference of light availability according to different organisms (e.g., phototrohic cyanobacteria and heterotrophic fungi). Investigation of shell surfaces under SEM (scanning electron microscope) after resin embedding with alcohol and vacuum series revealed that most of Dokdo shells are densely penetrated by diverse endolithic groups, including cyanobacteria, green algae, fungi and unidentified heterotrophic bacteria. They are all characterized by tiny spherical holes in surfaces, but differ each other in internal structures such as size of cells, branching, and networking of whole colonies. Identification of species level, difference of penetration mechanisms of different endolithic groups, and difference of organism groups dependi