Species diversity patterns of choanoflagellates in the Pettaquamscutt River Estuary, Rhode Island, USA

Abstract

Choanoflagellates are a large group of heterotrophic protists that play an important role in carbon transfer through the microbial loop, as they consume bacterioplankton and have also been found to be a major food source for macrozooplankton. Although many choanoflagellate species are cosmopolitan, species diversity of the acanthoecid choanoflagellates has been shown to vary substantially between study areas around the globe. A seasonal investigation of acanthoecid species diversity was conducted along the salinity gradient in the Pettaquamscutt River Estuary (PRE), Rhode Island, USA. The taxonomy of the Acanthoecidae is based upon the morphology of a complex basket‐like lorica that surrounds the protoplast. Only one previously published study has investigated the diversity of this choanoflagellate family in the western North Atlantic, specifically in the coastal waters of Newfoundland. The Rhode Island survey found that maximum species richness occurred between July and October, and some species exhibited a salinity preference in their distributions, while others had a seasonal shift in occurrence. Acanthocorbis apoda (Leadbeater) Hara and Takahashi, 1984 occurred most consistently throughout the study (55% of samples), while Diaphanoeca grandis Ellis, 1930, Diplotheca costata Valkanov, 1970, Savillea micropora (Norris) Leadbeater, 1975, Stephanoeca cupula (Leadbeater) Thomsen 1988, and Stephanoeca supracostata Hara 1996 were each present in 36‐45% of samples. The PRE survey found a four‐fold increase in species richness of acanthoecid choanoflagellates over the Canadian study, providing further evidence of the large regional variability in choanoflagellate distributions.