Fig 1.
Experimental timeline and setup.
Timeline (top) and experimental setup (bottom). Northern Macoma balthica samples were taken from the northern Stockholm archipelago, while southern samples were taken from the southern Stockholm archipelago. Each regional group was fed either the cyanobacteria Nodularia spumigena (brown) or the diatom Skeletonema marinoi (green), to create four treatments, and allowed to feed for 24 hours before the food source was removed. Samples were taken every 24 hours for one week, and either dissected and frozen immediately (left samples, represented by scalpel and tube) or allowed to empty their guts for 24 hours in freshwater before dissection and freezing (right; see S1 File for more information). All clams were kept in their original sediment without feeding for at least six months at the time of experiment start.
Fig 2.
Phytoplankton consumed by Macoma balthica determined by qPCR assays.
Phytoplankton consumption by M. balthica, determined by qPCR and reported in number of copies μL-1 (16S rRNA gene for Nodularia spumigena and 18S rRNA gene for Skeletonema marinoi). Panel A represents consumption of the diatom S. marinoi (green), while B represents the cyanobacteria N. spumigena (brown). Squares and solid lines represent the northern Stockholm archipelago clams, and circles and dotted lines represent the southern Stockholm archipelago clams. Error bars represent standard error.
Table 1.
Differences in phytoplankton detection in Macoma balthica by qPCR.
Table 2.
Multiple linear regression of phytoplankton detection in Macoma balthica by qPCR over time.
Fig 3.
Phytoplankton consumption by Macoma balthica.
The main orders of phytoplankton detected in the digestive tract of M. balthica, from selected samples sequenced after 23S rRNA gene metabarcoding, divided by phytoplankton fed (A; cyanobacteria Nodularia spumigena (brown), diatom Skeletonema marinoi (green), or not fed (gray)) and region (B; northern (red) and southern (blue) Stockholm archipelago). The size of the colored lines denotes the relative abundance (%) of the various taxa detected in the digestive tract of M. balthica.
Fig 4.
Phytoplankton community consumed by Macoma balthica ordination.
Non-metric multidimensional (NMDS) scaling based on the Bray-Curtis dissimilarity index of DNA 23S rRNA gene metabarcoding communities in guts of M. balthica found by phytoplankton fed (cyanobacteria Nodularia spumigena on top, diatom Skeletonema marinoi on bottom), with shapes showing region (circle southern Stockholm archipelago, square northern Stockholm archipelago), and sampling time point (stress = 0.16). For full NMDS see S3 Fig.