In my last post I described some of the techniques used in salt marsh and barrier island restoration, a pretty important topic here in Louisiana where we wait for the wave of each new storm to break, but it’s also important in many other areas around the world, especially since a large percentage of the global population lives in coastal areas. We need salt marshes and barrier islands to protect us from wave and storm energy, provide nursery habitats for many of the seafood stocks we utilize, provide nesting habitat for wetland birds, and filter a variety of things out of the water cycle. And we can try to restore these areas through adding sediment, restoring tidal and river flow, and building new marsh platforms- but do these methods work? To a certain extent, the answer is yes, and no.
Heron on a breakwater
When we talk about the success of a restoration project, what exactly are we measuring? Well, scientists and the public aren’t always looking at the same characteristics, and that can make this process really complicated. First of all, there is the physical structure of the area- we can see when sediment is added to a beach to combat erosion or when a terrace of rocks and sediment is constructed to create new habitat for marsh grass. Based on that criterion, as long as the beach or new platform is still there, the project has been a success. But there is so much more to restoring an ecosystem- which plants colonize the area, and which animals? How do they interact? Have any invasive species appeared? Is the beach or marsh platform fulfilling its ecological roles? Will it be able to do so into the future? So measuring the true success of a restoration project requires patience, because you will be waiting years (and even decades) to really understand if it worked. Why is this important? Well, maybe you haven’t noticed, but humans aren’t always good at waiting for things- we want results and we wanted them yesterday. Convincing people to give a restoration project the time and attention it needs to go through the full cycle of succession can be a tough sell.
What do we know about the chronology of salt marsh restoration? Scientists have undertaken several long-term studies to better understand how nature gets involved once the digging/construction/etc. is complete. In southern California, Janousek et al. (2007) saw diatoms and cyanobacteria within 2 months of restoration, but it took considerably longer for invertebrate consumers to appear. Once invertebrates do appear, the first colonizer species tend to be opportunists, those that can tolerate a wide variety of conditions and quickly exploit new food sources. In a North Carolina created marsh, after 2 years molluscs and fabricinid polychaetes had become common, but the large burrowing oligochaetes were not (Levin et al. 1996). Those larger burrowing animals are important because they help develop sub-surface structure- they are also more typical of mature marsh systems, so, if they aren’t present, the marsh still has a ways to go. After 3 or 4 years, the plant community in a restored marsh may look like natural marsh, but that’s just the outside- at that point the faunal communities are not complete. To investigate the point at which larger animals (and especially predators) became established in restored marsh communities, Huspeni & Lafferty (2004) looked at trematodes that are snail parasites. The reasoning here was that, since these trematodes need a snail host, a vertebrate host such as fish, and then ingestion by a larger predator such as herons, if the parasite could complete its life cycle in the restored marsh, that must indicate that the faunal community was pretty diverse (and I think this is a brilliant study- the idea that the life cycle of one species can tell you so much about marsh fauna is fantastic!). They found that it took 6 years before trematode species richness had significantly increased over pre-restoration levels. The problem here is that some people might assume, once the fish and birds are back, the marsh is good, but that’s not actually the case. Rozas & Minello (2001) found that created marshes, although supporting more abundant crustaceans and fish than open ponds, were not the functional equivalents of natural marsh 9 years on. And Stagg & Mendelssohn (2010) found that restored marshes were still not functionally equivalent to natural marshes 19 years after sediment had been added. Does that mean these projects aren’t working? Absolutely not- restored areas tend to have more native species and more similar species richness to natural areas than degraded areas do, but it’s a long process and we have to recognize that the restored marsh can’t be treated as natural marsh for quite some time- it may be more sensitive to environmental changes.
What about land-based animals? Well, breeding seabirds certainly appreciate more space, and a study in the Netherlands found that barnacle geese could help disperse the seeds of early successional plants (Chang et al. 2005). European brown hares could be even more effective at dispersing the seeds of mid-successional plants (although seed dispersal by water still takes the cake). And while some restoration projects could help salt marsh animals indirectly (such as increased tidal action which leads to fewer voles which leads to better success for salt marsh harvest mice (Bias & Morrison 2006)), some are specifically focused on the animals themselves- there have been successful translocation efforts for the endangered Lower Keys marsh rabbit (Faulhaber et al. 2006).
So there has been success, but it’s not immediate and we may never get back exactly what we have lost- but at least it’s progress and we are working to restore as much ecosystem function as possible. Although these projects tend to be large, I’m curious to see how individuals can get involved, so that’s what I’ll look into for next time.
Works cited:
Bias, MA and ML Morrison. 2006. Habitat selection of the salt marsh harvest mouse and sympatric rodent species. The Journal of Wildlife Management 70: 732-742.
Chang, ER, Zozaya, EL, Kuijper, DPJ, and JP Bakker. 2005. Seed dispersal by small herbivores and tidal water: are they important filters in the assembly of salt-marsh communities? Functional Ecology 19: 665-673.
Faulhaber, CA, Perry, ND, Silvy, NJ, Lopez, RR, Frank, PA, and MJ Peterson. 2006. Reintroduction of Lower Keys marsh rabbits. Wildlife Society Bulletin 34: 1198-1202.
Huspeni, TC and KD Lafferty. Using larval trematodes that parasitize snails to evaluate a saltmarsh restoration project. Ecological Applications 14: 795-804.
Janousek, CN, Currin, CA, and LA Levin. 2007. Succession of microphytobenthos in a restored coastal wetland. Estuaries and Coasts 30: 265-276.
Levin, LA, Talley, D, and G Thayer. 1996. Succession of macrobenthos in a created salt marsh. Marine Ecology Progress Series 141: 67-82.
Rozas, LP and TJ Minello. 2001. Marsh terracing as a wetland restoration tool for creating fishery habitat. Wetlands 21: 327-341.
Stagg, CL and IA Mendelssohn. 2010. Restoring ecological function to a submerged salt marsh. Restoration Ecology 18: 10-17.