Coastal communities typically exhibit pronounced zonation in composition across the marine-terrestrial transition. With rising seas and intensified storm surges, species that are ecologically “locked” in rigid zones may be at a disadvantage if “unlocking” is required before they can move to more suitable inland habitat. In contrast, species that span several zones, as adults and/or propagules in the soil, should be quicker to respond to chronic and acute saline intrusions. We hypothesized that the latter pattern is more common than previously thought because organisms may be inconspicuous outside of their dominant zone. The objective of this study was to determine the degree of zone rigidity vs. fluidity for bacteria, mycorrhizae, vascular plants, and fiddler crabs, a dominant consumer in Gulf Coast ecosystems. We sampled these four groups in plots established along transects that were arrayed perpendicular to the coast. Bacteria and mycorrhizae were sampled using soil cores that were then subjected to molecular techniques to identify them to operational taxonomic units (OTUs). Plants were visually identified to species and their cover estimated in 1m2 quadrats. Fiddler crabs were sampled from replicate 4m2 enclosures established in each zone.
Results/Conclusions
Based on a cadre of multivariate analyses, we found significant overlap between zones for all organism types. Despite exhibiting dominance in a particular zone, all groups had relatively low zone fidelity and spanned more zones than expected, particularly when the “hidden flora and fauna” were accounted for in the datasets. Even the relatively large adult fiddler crabs were found in unexpected areas. These charismatic and flamboyant consumers were often obscured in the taller vegetation in upslope fresh marsh, a zone that had been overlooked in the literature as fiddler crab habitat. We conclude that these coastal zones are less rigid than they appear at first glance. Results bode well for species at the sea-land interface in that they appear to have a “jump start” on the rising tides.