Distribution of zooxanthellate zoanthid species (Zoantharia: Anthozoa: Hexacorallia) in southern Japan limited by cold temperatures

The distribution of several zooxanthellate zoanthid species (Hexacorallia: Anthozoa) from the genera Palythoa, Zoanthus, and Isaurus in the oceans surrounding Japan are generally now well documented, but no examination of potential environmental factors limiting their distribution has been conducted until now. Here, using distribution data from previous works as well as ocean and air temperature data, we examined the minimum ocean temperature threshold for these zoanthid species' existence, as well as what winter air temperatures limit intertidal distribution of zoanthids. Our results show that in the Japan region zooxanthellate zoanthids are limited to oceans with winter temperatures above approximately 16°C. Additionally, intertidal colonies of zooxanthellate zoanthids were not found in locations where air temperatures dropped below 8°C. Thus, as with zooxanthellate scleractinian corals, zooxanthellate zoanthid species ranges are strictly limited by minimum ocean (overall range) and air (intertidal distribution) temperatures. Utilizing these threshold data, an examination of the potential ranges of Palythoa, Zoanthus and Isaurus on a global scale shows that it is very likely Atlantic and Indo-Pacific species are isolated from each other, as previously seen with zooxanthellate corals. Additionally, the documented northern Japanese ranges of intertidal occurrences as well as overall distribution northern limits will provide valuable baseline data for future surveys to help ascertain whether tropical and sub-tropical marine species are “invading” northwards in Japan due to global warming.