//
you're reading...

Coastal Management

Rip Rap Sill: The Best of Both Worlds

Original Paper: Richard G. Balouskus & Timothy E. Targett (2016). “Fish and Blue Crab Density along a Riprap-Sill-Hardened Shoreline: Comparisons with Spartina Marsh and Riprap”, Transactions of the American Fisheries Society, 145:4, 766-773 doi: 10.1080/00028487.2016.1172508

Figure 1: A rip rap and salt marsh, two different types of shoreline.

Figure 1: A rip rap and salt marsh, two different types of shoreline.

We humans love to live near the ocean. According to the UN Atlas, 44% of the global population lives within 150 km (93 miles) of the sea shore. So it makes sense that we would want to protect our shorelines from erosion processes caused by storms, tides, waves, wind, etc.

Figure 2: The study area was in the Delaware Coastal Bays.

Figure 2: The study area was in the Delaware Coastal Bays.

Many of the shoreline stabilization methods involve “hardened structures” such as putting up a sea wall or lining the shore with tightly packed rocks, called rip raff (Fig. 1). However, previous studies have noted that removing the natural vegetated habitats and replacing it with concrete and rocks reduces the biodiversity of fish and crabs.

Because of this loss of ecosystem services, a new hybrid shoreline stabilization technique has been gaining popularity with land managers. Rip rap sills combine the stabilizing rocks of rip rap with native vegetation planted just behind and in between the rock line, creating an intertidal-like habitat. The protection of rip raff plus the biotic diversity of a native marsh? Sounds like a win-win!

However, very little work has been done to statistically show if rip rap sills actually provide more fish and crab habitat than the standard rip rap. With that in mind, Balouskus and Targett (2016) set out to test fish and blue crab diversity along a salt marsh, rip rap, and rip rap sill in the Delaware coastal bays (Fig. 2).

The Study Approach

Three nearby shoreline types (a smooth cordgrass salt marsh, rip raff, and a rip rap sill) where sampled weekly from June 18th to September 19th, 2010 in the Indian River, a tributary to Delaware’s coastal bays (Fig. 2). This translated to 16 different sampling efforts for each shoreline type. Sampling occurred during both ebb and flood tide. Ebb tide is the mid-point when the tide is becoming low and flood when tide is coming in.

Figure 3: An example of scientists using a seine net to capture fish.

Figure 3: An example of scientists using a seine net to capture fish.

A seine net was used to sample the fish and blue crabs present at each shoreline type (Fig. 3). Minnow traps were used in locations where seining was not feasible. Two main measurements were tested: the mean density of fish and blue crab (the total number of individuals per cubic meter of water sampled) and the species richness (how many different species were present in each sample). Three different diversity indices were calculated: Margalef’s richness index examines the number of different species by the total abundance of organisms caught, the widely popular Shannon diversity index looks at the evenness of diversity, and Pielou’s evenness index which looks at how, well, even the species richness is at each site (for example, are all species equal in numbers, or is one species much more abundant?).

The Findings

The greatest total abundance of fish, as mean total density, was found in the smooth cordgrass marsh (563.8 individuals per cubic meter), followed by the rip rap sill (255.5 individuals per cubic meter), and then rip rap (176.2 individuals per cubic meter). The high mean density in the marsh was largely due to the high presence of mummichogs (Fig. 4). Blue crabs followed a similar rank by shoreline type, however, the abundance was not statistically different. Additionally, there was no difference found in the tidal cycle (ebb versus flood).

Fig. 4: Mummichogs were found in high abundance.

Fig. 4: Mummichogs were found in high abundance.

Species richness was greatest in the rip rap sill (17 species), followed by the marsh (14 species), and rip rap (12 species). Similarly, the Margalef’s richness index and Shannon diversity index were greatest in the rip rap sill. The Pielou’s evenness index was greatest in the rip rap; this finding was likely due because the rip rap shoreline did not have a single dominant fish species present.

There were some species-specific patterns found between the different shoreline types. Mummichogs, Atlantic silversides, and, striped killifish were most abundant along the marsh, the bay anchovy along the rip rap sill, and Atlantic menhaden (Fig. 5) along the rip rap. The Atlantic silverside and silver perch were significantly more abundant in the marsh and rip rap sill shoreline types than the rip rap. Additionally, the Atlantic silverside, silver perch, and bay anchovy had significantly greater densities in the rip rap sill than the rip rap AND was not significantly different from the marsh shoreline. This suggests that, for these three fish species, the rip rap sill was more appeasing of a habitat than the hardened rip rap.

Figure 5: An Atlantic menhaden.

Figure 5: An Atlantic menhaden.

The Significance

This study suggests that rip rap sill has fish and blue crab abundance and diversity more similar to the native salt marsh habitat than the hardened structure of a rip rap. This is one of the first studies to demonstrate that rip rap sills should be considered by land managers to mitigate erosion and habitat reduction.

The researchers noted that this is just one study in one tributary over one summer, so more comparisons need to be conducted to better understand how shoreline stabilization methods affect fish densities and diversity.  The author of this post (Kari) notes that the rip rap sill method is still so new, that an open source picture was not even available! We have a long way to go, but this study suggests that combining gray and green infrastructures could help protect our shoreline and our fish!

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 6 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 9 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 10 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 11 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com