Figure 1.
Sampling occasions in relation bloom.
Cyanobacteria bloom development in 2009 and 2010 at stn B1 (near sampling stations Håldämman and Uttervik), dotted line, and stn H3 (close to stn Mörkö), solid line. The X-axis is scaled for Julian days and benthos sampling dates are indicated by arrows. See text for the description of bloom composition. In 2010, stn Mörkö was sampled only in late June and September.
Figure 2.
Change in faunal isotope and elemental composition during summer.
Temporal trends in δ15N, δ13C, C:N ratio and individual weight (top to bottom panels) for each species and station (solid line = stn Uttervik, broken line = stn Mörkö and dotted = stn Håldämman). The peak of the bloom is indicated by the grey bar. The pre-bloom samples were taken 7 and 1 weeks before the peak of the bloom and the post-bloom samples were taken 6 and 11 weeks after the bloom. Data are transformed to z-scores and pooled for 2009 and 2010. Error bars are 95% CI (n∼20 for each sampling occasion; see also Table 1).
Table 1.
Number of individuals for each species (Mac = Macoma balthica, Mz = Marenzelleria arctia, Mon = Monoporeia affinis and Pon = Pontoporeia femorata), station and year, used for stable isotope analysis.
Table 2.
Sediment element composition and isotope ratio before (B) and after (A) the bloom.
Figure 3.
Carbon and nitrogen content pre- and post-bloom.
Carbon and nitrogen (%) in the test species (left to right: Mac - M. balthica, Mz - M. arctia, Mon - M. affinis and Pon - P. femorata) before (white) and after (grey) the bloom. Values are median with 25 and 75% percentiles as well as 95% CI (n = 6 for Mac and Mz, n = 5 for Mon and n = 3 for Pon).
Figure 4.
Isotopic niche for each species and the entire community pre- and post-bloom.
Stable isotope bi-plots illustrating the isotopic niche of the four species, M. affinis (black), M. arctia (red), M. balthica (green), P. femorata (blue) at three study sites (top stn Håldämman, mid stn Uttervik and bottom stn Mörkö) before and after the bloom, for both years (2009, left panels, and 2010, right panel). The dotted lines enclose convex hull area for each species and solid line shows the standard ellipse area, SEAc, for the entire community. Note the presence of M. affinis post-bloom at stn Mörkö 2009 inflates the niche area, since it was not found pre-bloom. Excluding M. affinis at this station in 2009 results in a reduced niche area (as in Fig 5, top panel).
Table 3.
GLM results for δ15N and δ13C for all species.
Figure 5.
Relationship between bloom intensity and bloom induced change in C:N and isotopic niche.
Concurrent changes (post-bloom/pre-bloom) in C:N ratio and SEAc in relation to the bloom intensity (area under curve; top and mid panels) and to each other (bottom panel). Each data point represents one species, station and year.
Figure 6.
Cross-species overlap in isotopic niche pre- and post-bloom.
Isotopic niche overlap defined as an area common for the two populations in relation to the total isotopic space occupied by these populations (proportion; left y-axis) and total community niche (arbitrary units; right y-axis) calculated using pre-bloom and post-bloom datasets for each station and year (see also Fig. 4 for raw data). The grey bars show the overlap estimate for each pair of species whose niches were found to overlap, white bars are the total community niche, and pie charts on the top of the gray bars show overlapping proportions of the isotopic niche for each population in question. Datasets that have no overlap during the study period are not included.