Award: OCE-1031718

his project was focused on understanding the ecological role of a ubiquitous put poorly known group of algae, the cryptomonads, and a widespread and important marine ciliate, Mesodinium rubrum, in Chesapeake Bay. Cryptomonad algae are an abundant flagellate that is consumed by numerous predators within the microbial food web. In Chesapeake Bay, cryptophyte algae can be associated with blooms of mixotrophic dinoflagellates, some of which are toxic. However, little is known regarding their genetic diversity in natural ecosystems, and how it is distributed in relation to environmental gradients (e.g. temperature or salinity) and other factors (e.g. predators). M. rubrum is known throughout much of the world for forming non-toxic red-tides. The ciliate is unique in that it steals numerous intracellular components of cryptophyte algal prey, including chloroplasts and the nucleus, which it uses symbiotically in its cell. We investigated the genetic diversity of both cryptophyte algae and Mesodinium spp. ciliates in the Chesapeake Bay ecosystem, during spring and fall. A high degree of genetic diversity was found for cryptophyte algae throughout Chesapeake Bay, with no strong patterns for species distribution with season or with the estuarine salinity gradient. However, within-species (i.e. strain) distribution did show strong patterns of both seasonality and salinity preference. Genetic diversity of M. rubrum throughout much of Chesapeake Bay was dominated by a novel subspecies of the ciliate, with diversity increasing near the mouth of Chesapeake Bay (i.e. with salinity). We also investigated grazing pressure on cryptophyte algae by microzooplankton, including M. rubrum and mixotrophic dinoflagellates. Cryptophyte algae in the bay experience high grazing pressure, but also were found to have high growth rates. M. rubrum were found to harbor chloroplasts from only one species of cryptophyte algae, but were found to consume several other species by tracking fluorescently labeled cryptophyte prey. These results underscore the dynamic and important role of cryptophyte algae in Chesapeake Bay, and that while M. rubrum specializes in forming a "symbiosis" with a small component of their diversity, it a general grazer on this diverse population of flagellates. During this project we trained an undergraduate participating in NSFÆs Research Experience for Undergraduates (REU) program in PI JohnsonÆs lab at Woods Hole Oceanographic Institution. We also provided research cruise experiences for graduate students from Woods Hole Oceanographic Institution, University of Maryland, and the University of Delaware. Results from this project were presented at scientific meetings and workshops, and this research will result in several research articles. Last Modified: 11/27/2013 Submitted by: Matthew D Johnson