Exceptional species richness of ciliated Protozoa in pristine intertidal rock pools

Abstract

Marine intertidal rock pools can be found almost worldwide but little is known about the microscopic life forms they support, or the significance of regular tidal inundation. With regard to ciliated Protozoa in rock pools, little progress has been achieved since 1948, when the question was first posed as to how a community of ciliates can remain relatively constant in a rock pool that is flushed twice a day. Here we show that local ciliate species richness is very high and that it may persist over time. This elevated species richness can be attributed to ciliate immigration with the incoming tide, and also to the resident ciliate community that withstands tidal flushing. A 15 cm deep intertidal rock-pool no bigger than 1 m2 on the island of St. Agnes (Scilly Islands, UK) contained at least 85 ciliate species, while a 20 cm-deep rock pool with roughly the same area on Bryher (also in the Scilly Islands) yielded 75 species. More than 20% of the global number of described marine interstitial ciliate species was recorded from these rock pools. We explore the paradox of a persisting community assembly living in an ecosystem that is physically highly dynamic. © Inter-Research 2007.