Science Deconstructed: Shoreline Armoring
I’m trying out a new idea! I’m going to steer us away from big National headline science towards recently-published great papers that provide fun insight and/or big implications for the world at large. This will be an exercise for me to communicate science effectively while providing a deeper experience of something new and exciting going on in the world. Thanks in advance for reading, and clap or comment if you liked this type of article and want to see more. The papers selected will be available to all, open source. But unlike snappy science articles,
we’re gonna dive in to really explore what’s going on, piece by piece.
Let’s do this.
Above the paper we’ll look at. There’s several immediately cool things to mention. First it reads well; you don’t need much help from some scientific jargon decoder to figure out what’s going on. It’s approachable. Second if you live in the Pacific Northwest you likely know exactly what they’re talking about. The researchers study iconic spots like Olympic Sculpture Park, a gorgeous property on the N. tip of Bainbridge island, a beach right near Deception State Pass, and two sites in Burien (Figure 1).
The last cool thing to be known before beginning are the incredible researchers behind it. Megan Dethier is a respected, hugely talented marine ecologist, who I once had the privilege of having as my adviser for a quarter at the UW Friday Harbor Labs. Other researchers on the project are also well respected in their field and very active in marine science and policy in the Puget Sound region. The work they have produced together has been a long time coming and is sorely needed.
What you’re about to read will undoubtedly shape the future of our beaches in the Puget Sound region and far beyond.
Introduction:
You’re taking a nice walk along the beach, maybe hopping across big boulders, or strolling by a concrete or wooden barrier. Like these researchers maybe you wonder,
how have these human changes shaped the ecological community of the beach you so love and why are they important?
Lots of people move to coastal areas and other important stuff is put there like shipping and recreation. People like the coast a lot, but coastal areas come with dangers (think sea level rise, Haiti, New Orleans, etc.) so naturally people want to protect themselves. This leads to lots of big rocks, jetties, concrete or wooden man made structures being built in a process known as shoreline armoring.
From the paper: In the United States alone, about 14% of the lower 48 states’ shorelines are armored, and 64% of these armored shorelines are adjacent to estuaries and coastal rivers (Gittman et al., 2015).
If you think about the tens of thousands of miles of coastline we have that’s incredibly high. When humans change the shoreline like this it often leads to unintended consequences. The paper points out that we already know armored shorelines can cause problems like more erosion, worse ecosystem health, and habitat destruction. We also know that it doesn’t always have to be this way, there are other methods for naturally protecting our coasts while restoring shorelines to support healthy ecosystems.
What is not known is whether restoring previously armored shore actually improves things, that’s what this paper is all about.
The paper asks if spending all this effort and money to restore a beach really make things better for the animals and ecological community? Closing this knowledge gap is essential for driving policy to remake our coasts, turning giant, ugly piles of rock into stretches of lovely beach. I’ll let the paper summarize itself:
From the paper: Here we present an analysis of the effects of shoreline restoration, with the objective to determine how coastal biota respond when shoreline armor is removed, sediments nourished, and native vegetation planted. We assess responses across (a) study sites, (b) coastal biota type, © shoreline elevations, and (d) trajectories in time.
Materials and Methods: where, what’d we do, math stuff
The research project was carried out in the Puget Sound, WA, USA (See figure 1). Each shoreline was studied individually during separate projects, but now the scientists are putting it all together with new mathy analyses. Here’s some before and after shots.
Listen up Puget Sounders:
From the paper: More than a quarter of the 4,000 km of shorelines in Puget Sound are armored (Puget Sound Partnership, 2016).
So this is important. I look at figure 2 and it’s very easy to decide which beaches I would prefer, leading me to conclude restoration was quite effective. These scientists do a bit more work than that:
Five ecosystem metrics were monitored before and after restoration, with one site monitored up to 10 years after restoration (Table 1). Survey data varied by site due to goals and characteristics of each restoration site, and included counts and richness (number of individual taxa) of macroinvertebrates for both terrestrial and aquatic groups, wrack % cover, number of logs (which have both biotic and physical attributes), and saltmarsh % cover. Three sites were also monitored at two different shoreline elevations (Table 1).
All of these things are helpful metrics, that are easy to make strong assumptions about. More macroinvertebrates is a direct observation that shows there’s more spineless animals, but macroinvertebrates also provide food for most vertebrates at some point. Beach wrack can be habitat and food source for tons of critters too like crabs and snails. Logs also provide habitat and nutrients to beaches, and salt marshes bring their own ecosystem services, including potential habitat for migratory birds.
The methods vary slightly between different sites but basically they go out along a 50m stretch on the shore and count how much seaweed is lying around, how many logs are present, what critters are on the seaweed and how many, and what critters are in the sediment at different . They do this about 3-10 times per beach, once before then once after, sampling locations in the intertidal and high up on, or out of the intertidal.
Quantitative analysis
And now for the math:
To measure the effectiveness of shoreline restoration on coastal biota, we used Cohen’s D Effect Size (Cohen, 1992).
D=(μA−μB)σD=(μA−μB)σ
Or in other words:
Size of the restoration effect=(variable like number of invertebrates-same variable before restoration) *square root((standard deviation A-standard deviation B)/2)
The standard deviation can be used to generalize the differences within the population from the populations mean and is related to variation. Pooling the two samples (before and after) assumes that the their standard deviation can be considered of the same population (i.e. the beach). Here’s what they say about D.
as a general guideline, when D is less than 0.2, the restoration is considered to have had no effect, while 0.2–0.8 indicate moderate effect, and 0.8 or greater indicates substantial effect (Rosnow, Rosenthal & Rubin, 2000).
They calculate D for a bunch of different comparisons groups like each beach, each variable and different locations (by armor, below armor). Finally they ran t-tests when possible to see if the measured values could be considered significantly different from the pre-restoration values. T-tests are simple but useful math tools designed to measure how likely it is that there was no effect, given your treatment (restoration) and observations (pre vs. post).
Results!
So easy it hardly needs explaining.
All six sites demonstrated positive responses with the mean effect size varying between 1.07 and 1.79 (Fig. 3). Four of the six sites had statistically significant responses (Fig. 3).
Considering the 5 separate metrics mentioned earlier all together, every site improved and 4/6 were statistically significant (The other two seemed to have too few samples to say if they were significant) Among the variables measured, macroinvertebrate abundance and diversity strongly and significantly improved. (See below). So more crawly critters at restored beaches. Finally researchers saw a positive effect even after one year post restoration and that effect moderately increased with time.
Discussion
So now we know not just do the beaches look nicer, they also have more animal life and probably more woody and plant debris too. The environment positively changed quickly and restoration appeared quite effective across many sites.
They point out that this is pretty much what they expected and what other science work supports when looking at similar efforts. Natural shorelines=good for nature.
The researchers would like you to know that logs, salt marshes, and beach wrack also increased on restored beaches, but they only collected a few observations for these features so couldn’t say anything definitive. But let it be known logs, salt marshes, and beach wrack are good for biodiversity and they have citations to back that up. They also emphasize that while the observed positive change were fast other research shows it can sometimes take longer so don’t just expect miraculous recoveries all the time.
There’re things that this study didn’t consider like other variables and stuff. Beach size, sediment, freak weather, whatever. Things can happen. However, they did a good job and they feel they proved what they set out to test.
Conclusion
It worked! Removing armor on shores and replacing that with more natural defenses makes the beach a better place to live for macroinvertebrates and probably lots of other critters too (for all, I might suggest). But the fight is just beginning so tell people this works and support such restoration efforts if you ever get the chance. Basically, policy should recognize that changes be made to shoreline armoring and empower citizens to make those changes on their property and on public beaches.
So, many years from now when you’re walking on a beautiful gradually sloping beach, full of shells and marine life that once was just a walled, rocky waste, you’ll know this research helped proved why that was a really good idea.
