Myrionecta rubra (Mesodinium rubrum; Family Mesodiniidae) is a non-toxic red-tide forming ciliate in coastal and estuarine waters of the world. M. rubra possesses symbiotic organelles derived from cryptophyte algae, a ubiquitous group of algae in aquatic ecosystems. Because ciliates are usually considered protozoa, unicellular eukaryotes that have animal rather than plant-like qualities, M. rubra was long considered an enigma. Studies of phytoplankton ecology have frequently overlooked M. rubra, instead considering it part of the microzooplankton. In the last decade great progress has been made in understanding how the ciliate functions, largely due to the establishment of cultures. Recent studies have shown that one strain of M. rubra steal organelles (chloroplasts, mitochondria, and a nucleus) from cryptophyte prey, while another possesses stable (permanent) cryptophyte organelles. All strains of the ciliate, however, must feed on cryptophyte algae, either for acquiring organelles or growth factors. While we now have a greater understanding of the physiology of M. rubra, almost nothing is known regarding its ecological interactions with cryptophyte algae, bacteria, and potential predators in aquatic ecosystems.
Cryptophyte algae are one of the major phytoplankton groups in Chesapeake Bay, contributing to primary production and acting as a major food item for a variety of organisms. M. rubra is widespread and seasonally abundant in Chesapeake Bay and its tributaries, and can reach red-tide concentrations in the spring and fall. Little is known regarding the genetic diversity of cryptophyte or M. rubra populations in Chesapeake Bay or other ecosystems.
The objectives of this study are to determine the physical and chemical factors and biological interactions that regulate production of M. rubra and cryptophytes, and to characterize the range and seasonal patterns of genetic diversity of these organisms in Chesapeake Bay. Another goal is to determine the role of cryptophyte genetic diversity in the production of Myrionecta ciliates. Using oceanographic, physiological, and molecular approaches, the team of investigators proposes to execute the first large scale ecological studies of this unique and ecologically important ciliate, in order to understand its role in marine microbial food webs and to better predict its abundance and distribution. The Project is important for two reasons, 1) M. rubra can be a dominant member of the plankton in nearly all coastal ecosystems, yet its trophic role remains enigmatic and 2) cryptophyte algae play a pivotal role in the ecology of most estuarine and coastal ecosystems, yet they remain a "black box" of poorly characterized flagellates. Despite numerous reports of M. rubra red tides, we still have a rudimentary understanding of its mixotrophic role, as both alga and grazer, and how these strategies are balanced in natural food webs. The production of M. rubra, like many other mixotrophs in Chesapeake Bay and other coastal ecosystems, is linked to cryptophyte algal production. However, we are currently unable to predict ecosystem dynamics of M. rubra, due largely to our lack of knowledge of their cryptophyte prey selection, the spatial and temporal dynamics of cryptophyte production, and the effects of grazing pressure on bloom formation and termination. The Chesapeake Bay is an ideal location to perform this research because both M. rubra and cryptophytes are extremely abundant, their productivity is seasonally predictable in its timing and location, and sampling sites are easily accessible.
This activity will be used to advance Ocean Science Literacy by educating the public about microbial diversity and microbial food web interactions. Results from this project will be broadly disseminated through scientific papers, workshop presentations, conferences, seminars, contributions to existing and new web sites, and discussions with the media. Undergraduates will participate in this project through the WHOI winter and summer research program. This proposal will also contribute to the professional development a young scientist.
Normal 0 false false false EN-US X-NONE X-NONE This 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. M. rubrum is important in some ecosystems as both a primary producer and as prey for larger zooplankton. 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 NSF’s Research Experience for Undergraduates (REU) program in PI Johnson’s lab at Woods Hole Oceanographic Institution. We also provided research cruise experiences for graduate students from the 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
