Diversity and taxonomy of intertidal Bryozoa (Cheilostomata) at Akkeshi Bay, Hokkaido, Japan

Abstract

We found 39 cheilostome species among more than 7000 specimens collected at 10 intertidal sites in rocky habitats along the shore of Akkeshi Bay, eastern Hokkaido Island, Japan. These species are herein described in detail and illustrated by scanning electron microscopy. Nine species (23% of total) are described as new (Electra asiatica, Callopora sarae, Conopeum nakanosum, Cauloramphus cryptoarmatus, Cauloramphus multispinosus, Cauloramphus niger, Stomachetosella decorata, Microporella luellae, and Celleporina minima), and 21 species (54%) are reported for the first time from Japan. Species richness ranged from eight to 29 species per study site. A TWINSPAN analysis showed the species fell into nine groups defined by the local pattern of distribution. A cluster analysis of study sites based on similarity of species composition showed three faunistic groups distributed geographically: in Akkeshi Lake, along the eastern‐central shore of the bay, and at the mouth of the bay. Species richness in estuarine Akkeshi Lake was low, with a species composition very different from the outer bay. Most cheilostomes were found on rock and shell substrata, but uncommonly occurred on concrete walls, algae, hydroids, tubes of polychaetes, other bryozoans, and anthropogenic debris. Of the 39 species found, 33 (85%) contained embryos during the collecting periods, 2–7 June and 3–6 July 2004. The biogeographical composition of intertidal cheilostomes at Akkeshi Bay included species with Arctic‐Boreal (28%), Boreal (59%), and Boreal‐Subtropical (13%) distributions. The overall species richness of intertidal cheilostomes was two‐thirds that documented intertidally in a comparable study at Kodiak, Alaska, a locality 15° higher in latitude. We attribute the lower richness at Akkeshi to differences in the nearshore marine environment between the two localities.

Keywords:

• Biodiversity
• biogeography
• Bryozoa
• Cheilostomata
• intertidal
• new species
• species richness
• taxonomy

Acknowledgements

We thank Dr Nina V. Denisenko, Zoological Institution of the Russian Academy of Science, St Petersburg, and Karin Sindemark of the Swedish Museum of Natural History for loans of type specimens for comparison; Dr Yoshinobu Nodasaka of the Hokkaido University School of Dentistry for tireless assistance with SEM; Mary Spencer Jones of The Natural History Museum, London, for accession of a large collection of voucher specimens; the staff of the Akkeshi Marine Biological Station for their support of our collecting efforts; and Luella M. Taranto and Sarah F. Taranto, who greatly helped with collecting during July 2004. This study was supported in part by the Twenty‐first Century COE Program on “Neo‐Science of Natural History” (Program Leader: Dr Hisatake Okada), financed by the Ministry of Education, Culture, Sports, Science, and Technology, Japan.