2002) of a dominant macrophyte, Spartina alterniflora, are tightly linked to tidal amplitude and inundation period, which dictate the biotic and abiotic constraints for this habitat-forming plant. Moreover, empirical data from saltmarshes show that the vertical range (Redfield 1972) and productivity (Morris et al. In coastal saltmarshes, for instance, competition and disturbance also regulate the vertical (upper) limits of species’ distributions (reviewed in Bertness & Silliman 2014), with species-specific patterns of plant biomass also affected by consumer pressure and interspecific facilitation (Gittman & Keller 2013). While these findings have not been directly applied to guide the restoration of intertidal habitats such as mangroves, seagrasses or shellfish reefs, there is evidence that these paradigms regulate community structure across diverse taxa and habitat types. Thus, many species are restricted to discrete zones of the intertidal based on their respective abilities to withstand abiotic stresses associated with aerial exposure better than their ‘enemies’ (Wethey 1984).
For example, classical experimental work along rocky shores has shown that interacting forces such as competition (Connell 1961), predation (Paine 1966) and disturbance (Dayton 1971) set the lower vertical distribution limit for many species and also maintain overall diversity patterns across depths. Within littoral systems, a number of fundamental ecological principles related to the vertical zonation of species could be tested as guides for biogenic habitat restoration. Our developing model proscribes a vertical ‘hot spot’ for restoration efforts to maximize biogenic reef fitness and production. As with Spartina saltmarsh, accumulation of oyster biomass was greatest at an intermediate vertical position relative to mean sea level (i.e. Below this depth, experimentally restored reefs failed completely. smothering) interactions, with a threshold depth at c. 5% daily aerial exposure.
As with rocky shores, the lower vertical limit of adult oyster distribution in our study system was most likely driven by predatory and competitive (i.e. In particular, our results demonstrate that paradigms of vertical zonation learned from the rocky intertidal and saltmarshes also describe the fate of restored shellfish reefs. mangrove, seagrass) or biogenic reef habitats. In littoral systems, vertical gradients in predation, competition and disturbance can be exploited to guide restoration of vegetated (e.g. The success of restoration initiatives involving habitat-forming species can be enhanced by accounting for the biotic interactions that regulate population fitness. stone crabs, gastropods) on deeper reefs where aerial exposure was <5% of the monthly tidal cycle. These patterns are likely to have developed from greater levels of biofouling and predator abundance (e.g. This reversal was due to (i) significantly elevated survivorship on intertidal reefs and (ii) larger surviving oysters on intertidal reefs. We recorded nearly an order-of-magnitude higher oyster settlement on the deepest (subtidal) reefs, but within a year abundance patterns reversed, and oyster densities were ultimately highest on the shallowest (intertidal) reefs by over an order-of-magnitude. We restored oyster reefs across an aerial exposure gradient (shallow-subtidal-to-mid-intertidal) to explore how vertical gradients in natural settlement, growth and interspecific interactions affected the trajectory of man-made shellfish reefs. Gradients in competition and predation that regulate communities should guide biogenic habitat restoration, while restoration ecology provides opportunities to address fundamental questions regarding food web dynamics via large-scale field manipulations.
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