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Rocky shore microbial diversity presents an excellent system to test for microbial habitat specificity or generality, enabling us to decipher how common macrobiota shape microbial community structure. At two coastal locations in the northeast Pacific Ocean, we show that microbial composition was significantly different between inert surfaces, the biogenic surfaces that included rocky shore animals and an alga, and the water column plankton. While all sampled entities had a core of common OTUs, rare OTUs drove differences among biotic and abiotic substrates. For the mussel Mytilus californianus, the shell surface harbored greater alpha diversity compared to internal tissues of the gill and siphon. Strikingly, a 7-year experimental removal of this mussel from tidepools did not significantly alter the microbial community structure of microbes associated with inert surfaces when compared with unmanipulated tidepools. However, bacterial taxa associated with nitrate reduction had greater relative abundance with mussels present, suggesting an impact of increased animal-derived nitrogen on a subset of microbial metabolism. Because the presence of mussels did not affect the structure and diversity of the microbial community on adjacent inert substrates, microbes in this rocky shore environment may be predominantly affected through direct physical association with macrobiota.
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A Principal Component Analysis of the environmental parameters measured in the experimental tidepools at Second Beach, WA
Supplementary Figure 1. A Principal Component Analysis of the environmental parameters (seawater pH, oxygen, and nutrient concentrations), as well as the ammonium regeneration and removal rates (from Pather et al., 2014) measured in the experimental tidepools at Second Beach (Table S1). The first principal component explained 81.7% of the variance and differed among mussel controls (filled symbols) versus removals (open symbols, p=0.049).
The environmental parameters of experimental tidepools at Second Beach
The environmental parameters of tidepools at Second Beach where mussels were either removed or remained shown as means (se). All values were the maximum measured in each tidepool (see Pather et al., 2014). The Principal Components Analysis based on these environmental parameters is shown in Supplementary Figure 1. The last column represents environmental parameters for seawater surrounding Tatoosh Island (see Wootton and Pfister, 2012) encompassing the period that artificial substrates were deployed and rock and biogenic substrates collected (10 Jun to 6 Aug 2009).