Phycologia (2011 ) Volume 50 (6), 629 640 Published 10 November 2011 Buried alive - germination of up to a century-old marine protist resting stages NINA LUNDHOLM'*, SOFIA RiBEiRO^f, THORBJORN J. ANDERSEN\ TRINE KOCH", ANNA GODHE", FLEMMING EKELUND' AND MARIANNE ELLEGAARD^ ^Natural History Mu.seum of Denmark, University of Copenhagen. Sohgade 83S, DK-1307 Copenhagen K, Denmark -Marine Biological Section. Department of Biology, Uniyersity of Copenhagen, 0ster Farimagsgade 2D, DK-1353 Copenhagen K, Denmark ''Department of Geography and Geology. University of Copenhagen. 0ster Voklgade 10. 1350 Copenhagen K. Denmark '*Department of Marine Ecology, University of Gothenburg. Box 461, SE 405 30 Göteborg. Sweden ^ of Terrestrial Ecology, Department of Biology. University of Copenhagen. 0ster Farimagsgade 2D. DK-1353 Copenhagen K, Denmark LtJNDHOLM N., RujEiRO S., ANDRRSEN T.J., KOCH T., GODHE A., EKELUND F. AND ELLEGAARD M . 2011. Buried alive- germination of up to a century-old marine protist resting stages. Phycologia 50: 629-640. DOI: 10.2216/11-16.1 We report on the survival and germination of up to a century-old marine protist resting stages naturally preserved in sediments from Koljö Fjord on the west coast of Sweden. This work has focused on germination of dinoOagellate cysts, but diatom resting stages were also observed. We record the longest known survival of dormant dinollagellate cells. We individually isolated more than 1200 cysts ofthe three most abundant dinollagellate taxa: Pentapharsodinium dalei. Lingulodinium polycdriim and Scrippsiella spp. Germination success decreased with core depth, and all successful germinations took place within the first 2 wk of incubation. Pentaphar.sodinium dalei had the highest germination success rate, with a maximum of up to 80% in 28-yr-old sediment, and could successfully germinate from core sediments dated to 1920 ± 12. Scrippsiella spp. cysts with cell contents occurred down to c. 90-yr-old sediment and could germinate from down to ca. 40-yr-old sediments, with a maximum germination rate of 50-6070 in recent sediments. Cysts of L polycdrum germinated frequently down to 20 yr and rarely to <. 80 yr, with a maximum of 20-50'M, germination success in recent sediments. Cyst isolation under cooled conditions rather than at room temperature resulted in a significantly higher germination success in P. dctlci. while no elïect was observed for L. polycdrum. The time elapsed since slicing of the core affected survival of L. polycdrum cysts negatively, most likely due to the effect of oxygen. The long-term survival potential of benthic resting stages that we report here has important implications, as viable resting stages accumulated in bottom sediments can be transported back to the water column by, for example, bioturbation and human-mediated sediment dredging. Hence, the sediment may to a higher degree than previously considered play a role as seed bank. This is important in a changing climate and might have particularly severe impacts in the case of harmful species. INTRODUCTION Resting stages are part of the life cycle of many planktonic organisms (Marcus & Boero 1998; von Dassow & Montresor 2011 ), notably resting cysts of dinofiagellates (Dale 1983) and spores or resting cells of diatoms (McQuoid & Hobson 1996). For dinofiagellates, resting stages are most often a result of sexual reproduction; whilst, for diatoms they result from vegetative division. These two major marine algal groups make up an important part of the base of food webs, responsible for a large part of the primary productivity of aquatic ecosystems. Once present, the fate of testing stages is determined by physical, biological and sedimentological processes, such as degradation, prédation, bioturbation and burial (Keafer et al 1992; Kremp et al 2003; Persson & Rosenberg 2003). Resting stages of dinofiagellates and diatoms are non- motile and are often protected by highly resistant material; * Corresponding author (nlundholm(ii!snm.ku.dk). t Present address: Marine Geology and Glaciology Department, Geological Survey of Denmark and Greenland, 0ster Voldgade 10, 1350 Copenhagen K, Denmark, thus, they sink and accumulate in bottom sediments (Dale 1983), This leads to the formation of 'seed banks', comparable to those found in terrestrial ecosystems, which may comprise a higher diversity than the pool of physiologically active cells at any particular time (Boero (7 al. 1996). A benthic life cycle stage serves as an 'anchor' in time and space and can provide survival advantages in unstable pelagic environtnents. The occurrence of phyto- plankton species in the water column is often discontinuous and/or ephemeral, with high numbers of individuals being present during short periods (sometimes forming blooms) and then decreasing in abundance or even completely disappearing from the plankton community. In fact, many species spend a greater part of their life resting in the sediment than as metabolically active organisms in the water column (Wyatt & Jenkinson 1997). Resting stages also aid dispersal and constitute a reservoir of genetic diversity, which increases the survival potential of the populations (Jones & Lennon 2010). Thus, dinofiagellate cysts and diatom spores accumulated in coastal sediments have great ecological importance. Knowledge of the factors that promote germination of resting stages may allow strategic monitoring to predict plankton dynamics; this could include blooms of hatmful algae (Genovesi-Giunti 629