Seasonal Fluctuations in the Abundance of Marine Tardigrades (Heterotardigrada: Echiniscoides sigismundi, Styraconyx haploceros) Inhabiting Fistulobalanus albicostatus, an Intertidal Barnacle on the West Coast of Korea

The purpose of this study was to further clarify marine tardigrade ecology; in particular, the monthly density fluctuations of Echiniscoides sigismundi and Styraconyx haploceros inhabiting the barnacle Fistulobalanus albicostatus in the intertidal zone. Both species were observed in all months, and the monthly body length distributions did not show a clear pattern, indicating these species breed throughout the year. However, the density of both species was higher in fall/winter than in spring/summer. The two species showed different prevalence and density distributions in the upper and lower parts of a barnacle bedrock in the intertidal zone. S. haploceros was found only in the lower part, where it dominated over E. sigismundi in most months. E. sigismundi was found in both parts, but its occurrence rate and density were higher in the lower part of the intertidal zone. The density of both species was significantly higher on the external surface of the barnacles than internally. No significant differences in tardigrade density were detected among different sizes of barnacles, living or dead, except for a significant difference in the density of E. sigismundi between dead and large live barnacles. Our findings suggest that E. sigismundi and S. haploceros are well adapted to inhabiting intertidal barnacles, and the fall/winter season is more favorable than spring/summer for marine tardigrades in temperate regions. E. sigismundi appears to tolerate the upper part of the barnacle bedrock in the intertidal zone, which may be an extremely harsh environment, better than S. haploceros .