No abstract

The overall intent of restoration is often not only to restore the habitat per se, but to restore the ecosystem services it supplies, and particularly to encourage the return of fauna. Seagrass meadows act as habitat for some of the most diverse and abundant animal life, and as the global loss of seagrass continues, managers have sought to restore lost meadows. We tested how quickly the epifaunal richness, abundances and community composition of experimental restoration plots recovered to that in an adjacent natural seagrass meadow relative to the recovery of seagrass per se. Seagrass structure in the restoration plots took three years to become similar to a nearby natural meadow. The recovery of epifaunal richness and total abundance, however, occurred within one year. These results suggest that although recovering habitats may not be structurally similar to undisturbed habitats, they can support similar richness and abundances of epifauna, and thus have greater economic and social value than otherwise might have been expected. Nevertheless, whilst epifaunal richness and total abundance recovered prior to the recovery of seagrass structure, full recovery of seagrass was required before the composition and relative abundances of the epifaunal community matched that of the natural seagrass meadow.

The capacity of natural systems to resist environmental change underpins ecosystem stability, e.g. the persistence of kelp-dominated states which are sometimes displaced by subordinates or weedy species (i.e. algal turfs). Perturbation by resource enhancement at global (e.g. CO2 emissions) through local scales (e.g. nutrient pollution) increases the probability of turf domination, yet these same resources stimulate an increase in per capita consumption of turfs by herbivores. We test whether such resource perturbation can stimulate herbivores to absorb the additional productivity of turfs that cause kelp displacement. We tested the hypotheses that (1) elevated nitrogen (N) and carbon dioxide (CO2) not only stimulate an increase in consumptive rates, but also stimulate an increase in underlying metabolic rates of gastropod herbivores, so that (2) enhanced primary productivity is countered by herbivory. We reveal that elevated nitrogen and CO2 stimulated an elevation in rates of consumption in proportion to an increase in metabolic rate of grazers. Subsequently, grazers consumed proportionately greater cover of turfs to counter turf expansion. Resource enrichment, therefore, can stimulate metabolic and consumptive activity of herbivores to absorb the additional productivity of opportunistic species. Hence, the competitive potential of subordinates to displace community dominants may be checked by the very resources that otherwise drive instability.

Seagrass meadows are habitat for an abundance and diversity of animal life, and their continuing global loss has focused effort on their restoration. This restoration not only aims to re‐establish the structure of the seagrass, but also to restore its function, particularly as habitat. The success of seagrass restoration is typically measured by the recovery of aboveground structure, but this ignores the important role of the belowground component of seagrass ecosystems, which may not recover at the same rate, and is equally important for faunal communities. We quantify infaunal communities (abundance, richness, and composition) within expanding plots of restored seagrass, and relate their change to the recovery of belowground seagrass biomass and sediment properties. We found that infaunal abundance and composition converged on that found in natural seagrass within 2 years, while the overall infaunal richness was not affected by habitat. The carbon content of surface sediments also recovered within 2 years, although recovery of belowground biomass and sediment grain size took 4 to 6 years. These results suggest that the structure of recovering seagrass habitats may not need to attain that of natural meadows before they support infauna that is comparable to natural communities. This pace and effectiveness of recovery provides some optimism for future seagrass restoration.