Parasites indicate trophic complexity and faunal succession in restored oyster reefs over a 22-year period.

Foundation species like the eastern oyster (Crassostrea virginica) create complex habitats for organisms across multiple trophic levels. Historic declines in oyster abundance have prompted decades of restoration efforts. However, it remains unclear how long it takes for restored reefs to resemble the trophic complexity of natural reefs. We used a space-for-time approach to examine community succession of restored reefs ranging in age from 3 to 22 years old in coastal North Carolina, surveying both free-living taxa and parasite communities and comparing them to natural reefs that are decades old. Trophically transmitted parasites can serve as valuable biodiversity surrogates, sometimes providing greater information about a system or question than their free-living counterparts. We found that the diversity of free-living taxa was highly variable and did not differ among new (<10 years), old (20 years), and natural reefs. Conversely, parasite diversity increased with elapsed time after restoration, and parasite communities in older restored reefs resembled those found in natural reefs. Our study also revealed that oyster toadfish (Opsanus tau) act as a key host species capable of facilitating parasite transmission and trophic ascent in oyster reef food webs. Overall, our results suggest that trophic complexity in restored oyster reefs requires at least 8 years to resemble that found in natural reefs. This work adds to a growing body of evidence demonstrating how parasites can serve as biodiversity surrogates, proxies for the presence of additional taxa that are often difficult or impractical to sample. Given the multiplicity of links formed with their hosts, parasites offer a powerful tool for quantifying diversity and trophic complexity in environmental monitoring studies.

Reef design and site hydrodynamics mediate oyster restoration and marsh stabilization outcomes.

The detrimental ecological impacts of engineered shoreline protection methods (e.g., seawalls) and the need to protect the coastal zone have prompted calls for greater use of natural and nature-based infrastructure (NNBI). To balance competing needs of structural stability and ecological functioning, managers require assessments of NNBI designs and materials for differing environmental settings (e.g., among wave-energy regimes). To examine the effects of setting and oyster-based NNBI design on the provision of shoreline protection, we constructed reefs from two substrates: a novel, biodegradable material (Oyster Catcher, OC) and traditional oyster shell bags (SB) on low- and high-energy eroding salt marsh shorelines, designated based on fetch and boat wake exposure. Both reef types buffered marsh elevation change on the high-energy shoreline relative to unaltered controls, but only SB reefs were able to do so on the low-energy shoreline. Additionally, both shorelines experienced high ambient rates of retreat and declines in marsh vegetation shoot density. Although constructed reefs did not mitigate marsh retreat on the low-energy shoreline, novel OC reefs significantly reduced retreat relative to SB reefs and control sites (no reefs) on the high-energy shoreline. Those SB reefs were severely damaged by storm events, increasing their areal footprints at the expense of vertical relief. Conversely, OC reefs on both shorelines exhibited steady oyster recruitment and growth and hosted higher densities of larger oysters. To successfully provide shoreline stabilization benefits, oyster-based NNBI must be structurally stable and able to promote sustained oyster recruitment and growth. Our results indicate that deliberate decisions regarding NNBI substrate, siting, and configuration can produce resilient reefs, which reduce rates of erosion and, in some cases, enhance vertical accretion along salt marsh edges. The growth trajectory, structural stability, and co-benefit provisioning of OC reefs demonstrate the potential of alternative restoration substrates to provide valuable oyster habitat along threatened marsh shorelines.

Competitive and agonistic interactions between the invasive Asian shore crab and juvenile American lobster.

Invasive species can have profound ecological and evolutionary impacts on native fauna, particularly those from overlapping guilds. Intraguild predation and competition often occur simultaneously, and ontogenetic shifts in competitive strength can dictate the magnitude and direction of species interactions. The recent introduction of the Asian shore crab Hemigrapsus sanguineus to the Atlantic coast of North America has resulted in the potential for considerable intraguild interactions with juvenile American lobsters Homarus americanus, with which it now co-occupies rocky intertidal and shallow subtidal habitats. We present data from 5 yr of monthly (May-October) field sampling revealing a significant decline in lobster density as H. sanguineus density increased in the low intertidal. To investigate potential mechanisms behind this pattern, we conducted three mesocosm experiments designed to examine whether competitive interactions between H. americanus and H. sanguineus are size- or density-dependent. Larger early benthic phase lobsters (16-34 mm CL) outcompeted H. sanguineus for both food and shelter resources. These lobsters fed faster and more in the presence of H. sanguineus, effectively defended shelter, were responsible for the majority of agonistic interactions, and, in multiple instances, killed and consumed H. sanguineus. Effects on sheltering and agonstic interactions by these lobsters were independent of H. sanguineus density; however, prior shelter residency increased lobster agonistic behavior towards crabs. In contrast, H. sanguineus outcompeted smaller, early benthic phase lobsters (7.2-11.2 mm CL) for shelter, and these interactions were density dependent. Displacement of lobsters from shelter by crabs and cumulative agonistic interactions instigated by crabs towards lobsters scaled positively with H. sanguineus density. Given the similarity of the invasion documented here and others occurring globally, these experiments demonstrate the importance of considering how factors such as ontogeny, density-dependence, and primacy influence the outcomes of interactions between intraguild predators. Disentangling how these factors structure intraguild interactions between invasive and endemic species will both advance our fundamental understanding of community ecology and enhance efforts to conserve and manage natural resources.

Social Factors Key to Landscape-Scale Coastal Restoration: Lessons Learned from Three U.S. Case Studies.

In the United States, extensive investments have been made to restore the ecological function and services of coastal marine habitats. Despite a growing body of science supporting coastal restoration, few studies have addressed the suite of societally enabling conditions that helped facilitate successful restoration and recovery efforts that occurred at meaningful ecological (i.e., ecosystem) scales, and where restoration efforts were sustained for longer (i.e., several years to decades) periods. Here, we examined three case studies involving large-scale and long-term restoration efforts including the seagrass restoration effort in Tampa Bay, Florida, the oyster restoration effort in the Chesapeake Bay in Maryland and Virginia, and the tidal marsh restoration effort in San Francisco Bay, California. The ecological systems and the specifics of the ecological restoration were not the focus of our study. Rather, we focused on the underlying social and political contexts of each case study and found common themes of the factors of restoration which appear to be important for maintaining support for large-scale restoration efforts. Four critical elements for sustaining public and/or political support for large-scale restoration include: (1) resources should be invested in building public support prior to significant investments into ecological restoration; (2) building political support provides a level of significance to the recovery planning efforts and creates motivation to set and achieve meaningful recovery goals; (3) recovery plans need to be science-based with clear, measurable goals that resonate with the public; and (4) the accountability of progress toward reaching goals needs to be communicated frequently and in a way that the general public comprehends. These conclusions may help other communities move away from repetitive, single, and seemingly unconnected restoration projects towards more large-scale, bigger impact, and coordinated restoration efforts.

Voluntary Restoration: Mitigation's Silent Partner in the Quest to Reverse Coastal Wetland Loss in the USA.

Coastal ecosystems are under pressure from a vast array of anthropogenic stressors, including development and climate change, resulting in significant habitat losses globally Conservation policies are often implemented with the intent of reducing habitat loss. However, losses already incurred will require restoration if ecosystem functions and services are to be recovered. The United States has a long history of wetland loss and recognizes that averting loss requires a multi-pronged approach including mitigation for regulated activities and non-mitigation (voluntary herein) restoration. The 1989 "No Net Loss" (NNL) policy stated the Federal government's intent that losses of wetlands would be offset by at least as many gains of wetlands. However, coastal wetlands losses result from both regulated and non-regulated activities. We examined the effectiveness of Federally funded, voluntary restoration efforts in helping avert losses of coastal wetlands by assessing: (1) What are the current and past trends in coastal wetland change in the U.S.?; and (2) How much and where are voluntary restoration efforts occurring? First, we calculated palustrine and estuarine wetland change in U.S. coastal shoreline counties using data from NOAA's Coastal Change Analysis Program, which integrates both types of potential losses and gains. We then synthesized available data on Federally funded, voluntary restoration of coastal wetlands. We found that from 1996 to 2010, the U.S. lost 139,552 acres (~565 km2) of estuarine wetlands (2.5% of 1996 area) and 336,922 acres (~1,363 km2) of palustrine wetlands (1.4%). From 2006 to 2015, restoration of 145,442 acres (~589 km2) of estuarine wetlands and 154,772 acres (~626 km2) of palustrine wetlands occurred. Further, wetland losses and restoration were not always geographically aligned, resulting in local and regional "winners" and "losers." While these restoration efforts have been considerable, restoration and mitigation collectively have not been able to keep pace with wetland losses; thus, reversing this trend will likely require greater investment in coastal habitat conservation and restoration efforts. We further conclude that "area restored," the most prevalent metric used to assess progress, is inadequate, as it does not necessarily equate to restoration of functions. Assessing the effectiveness of wetland restoration not just in the U.S., but globally, will require allocation of sufficient funding for long-term monitoring of restored wetland functions, as well as implementation of standardized methods for monitoring data collection, synthesis, interpretation, and application.