Functional recovery of an epifaunal invertebrate community associated with a restored eelgrass bed
Biodiversity has long been implicated in the functioning of ecosystems, and as such has often been used to gauge the success of ecological restoration. Indices like species richness, however, ignore redundancy among species, potentially overestimating functional recovery if richness is high but resident species are ecologically similar. In contrast, indices based on functional traits can be used to directly quantify the degree of redundancy among species based on their morphological, and ecological characteristics, and thus directly inform the functional recovery of restored ecosystems. Here, we apply a functional approach to understand how the recovery of a critical coastal ecosystem, eelgrass (Zostera marina L.), in Virginia’s coastal bay, influenced the recruitment of a diverse assemblage of associated epifaunal invertebrates. Since 1999, over 4,500 acres of eelgrass has recovered from an initial 400 acres of seeding. We conducted an observational survey from 2001-2013 to characterize the changes in the epifaunal community alongside restoration of the eelgrass habitat. Concurrently, we surveyed a mature bed to serve as a baseline for recovery, and drift macroalgae to determine possible sources of epifaunal recruitment. We supplemented these survey data with data from the literature on functional traits relating to body size, diet, and life histories.
Over the 12 years of the survey, we observed an increase in the total abundance, species, and functional diversity of the restored eelgrass bed. These properties remained relatively consistent in the natural bed. By 2013, the mature and restored beds converged on similar values of diversity, although the restored bed exhibited higher evenness. There were also significant shifts in community composition during this period, with both bays later dominated by the gastropod, Bittiolum varium. Recruitment of this species did not appear to be facilitated by drift macroalgae, as B. varium was all but absent in algal samples collected in the restored bed. Both bays also exhibited an increase in the grazing amphipods Dulichiella appendiculata and Elasmopus levis, suggesting a degree of regional control over community composition. The restored bed, however, exhibited greater functional variation among the remaining abundant invertebrates, with the grazing amphipods Cymadusa compta, and Batea catharensis and particularly the grazing gastropod Mitrella lunata comprising a much larger proportion of community abundance in the restored but not the mature bed. Overall, the application of functional traits revealed diversification of the epifaunal community as the restored bed matured, particularly when considering relative abundances of functionally-distinct species.