Abstract
Many marine protists form resting stages that can remain viable in coastal sediments for several decades. Their long‐term survival offers the possibility to explore the impact of changes in environmental conditions on population dynamics over multidecadal time scales. Resting stages of the phototrophic dinoflagellate Pentapharsodinium dalei were isolated and germinated from five layers in dated sediment cores from Koljö fjord, Sweden, spanning ca. 1910–2006. This fjord has, during the last century, experienced environmental fluctuations linked to hydrographic variability mainly driven by the North Atlantic Oscillation. Population genetic analyses based on six microsatellite markers revealed high genetic diversity and suggested that samples belonged to two clusters of subpopulations that have persisted for nearly a century. We observed subpopulation shifts coinciding with changes in hydrographic conditions. The large degree of genetic diversity and the potential for both fluctuation and recovery over longer time scales documented here, may help to explain the long‐term success of aquatic protists that form resting stages.
Highlights
Population genetic analyses based on six microsatellite markers revealed high genetic diversity and suggested that samples belonged to two clusters of subpopulations that have persisted for nearly a century
The clustering was compared to abundances of P. dalei cysts in Koljö Fjord and indices of winter North Atlantic Oscillation (NAO) over the same time period based on results from Harland et al (2004a) and Jones and Mann (2004) (Figure 3)
The sediment record that served as basis for this study has a robust age control, clear indication of undisturbed sediment deposition, and yielded a large number of well-preserved viable resting stages of several protist species (Lundholm et al, 2011)
Summary
KEYWORDS dinoflagellate, environmental change, microsatellites, phytoplankton resting stage, population genetic structure, sediment core 1 | INTRODUCTION We revived P. dalei resting cysts from dated sediment layers spanning nearly a century, established cultures of vegetative cells (Lundholm et al, 2011), amplified species-specific microsatellite markers (Lundholm, Nielsen, Ribeiro, & Ellegaard, 2014), and explored the data for estimating protist effective populations sizes (Watts et al, 2013).
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