Abstract
Two crawling medusae, Staurocladia oahuensis (Edmondson, 1930) and S. bilateralis (Edmondson, 1930) were found to be abundant in intertidal rock pools in Kominato from late summer until early winter. The two species were found to rarely share the same individual alga, and sometimes showed exclusive occupancy of pools at higher intertidal levels. The abundance of the two species of medusae fluctuated widely over time with both species showing similar population structures during their period of occurrence. The asexual reproduction of the medusae was considered to be a cause of the distributional pattern and the fluctuation in abundance. An experiment was conducted to evaluate the rate of asexual reproduction under different conditions. At 12°C neither species performed asexual reproduction, while at 17°C and higher temperatures both species reproduced asexually at a high rate. The number of each population was found to nearly double in about a week. The coexistence of the two species of medusae in tidepools is discussed in relation to the habitat characteristics. S. oahuensis and S. bilateralis were not known previously from Japan; this constitutes a new record of both species from Japanese waters. We also found both species in several other warm water locations in Japan.
Highlights
Crawling medusae are small benthic medusae that live on algae and seagrasses
We found that two species of crawling medusae were common in Kominato and they often occurred in abundance in intertidal rock pools from late summer to early winter
Staurocladia bilateralis was very abundant in late August, 1995, when nearly 500 medusae were collected from about 40g of Ulva conglobata, and 150 medusae from about 100 g of Sargassum thunbergii
Summary
Most of them are known to reproduce asexually either by budding or fission including schizogony (Bouillon, 1978); all are hydrozoans They are primarily non-swimmers and move by crawling or creeping on the substrate by means of walking tentacles, swimming behavior has been observed in a few species (Browne, 1910; Brinckmann, 1964). Because of this they are confined to coastal waters, and are sometimes common along shorelines (Gilchrist, 1919; Edmondson, 1930; Millard, 1975). The two species were identified as Staurocladia oahuensis (Edmondson, 1930) and S. bilateralis
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