Mapping the Future: Launching Our Indian River Bay SAV Pilot Project

Written by DNREC Aquatic Habitat Monitoring & Restoration Scientist, Abigail Young

If you take a look at a map of southern Delaware, tucked right between the bustling shores of Rehoboth and Bethany Beach, you’ll find Indian River Bay. As a core part of Delaware's inland bay system, it's fed by the Indian River at its western end and connected directly to the Atlantic Ocean via the Indian River Inlet.

But if you were to dive down and look at the bay’s floor right now, you’d find something missing: our beloved SAV.

Currently, large stretches of this underwater landscape are relatively barren. But it wasn't always this way. Historically, a tough combination of intense coastal storms, shoreline erosion, and disease outbreaks (like the infamous wasting disease) wiped out the lush Zostera marina (eelgrass) meadows that once thrived here.

Fun fact: A lot can change in 70 years! On the left, an aerial shot from July 1954 shows thriving underwater meadows along the western shore between the Inlet and Pasture Point. On the right, today's modern satellite view shows just how barren that same area has become. Crazy comparison!

Without these plants, the seafloor is vulnerable. By planting SAV back into this region, we aren’t just putting greenery in the water; we are stabilizing sediment, helping to reduce shoreline erosion, and creating critical nursery habitats for Delaware's marine life.

This spring, the DeSSAV crew officially launched an ambitious piloting project to bring these vital underwater habitats back to Indian River Bay. Here is a look at what we’ve been up to over the last few months!

Quick Recap: our initial fieldwork began in early April. As spring temperatures started to warm up, our crew launched into Indian River Bay to conduct bathymetry surveys and deploy our monitoring equipment.

With Indian River Bay’s shallow coves, this area is a prime candidate for piloted restoration, but we needed to know exactly what the underwater terrain looked like first. We navigated our boat in precise grids, surveying depths and contours using a high-resolution sonar system. By emitting sonar signals that measure the distance from the boat to the bay floor, we collected real-time data to build a highly accurate, 3D model of our restoration site.

Hand-in-hand with mapping, we installed a comprehensive water monitoring station. We need to keep a close eye on the water column to ensure the environmental conditions meet the survival needs of the SAV species we want to introduce. Our station includes three powerhouse sensors:

• A Water Level Logger: To track tidal fluctuations and depth changes, ensuring our plants won't be left high and dry or buried too deep.

• Conductivity, Temperature, and Total Dissolved Solids (TDS) Sensors: To monitor salinity levels and water clarity, which tells us how much ambient runoff or environmental stress the plants are enduring.

• A Light/PAR (Photosynthetically Active Radiation) Sensor: To measure the specific spectrum of solar energy reaching the bay floor. Because at the end of the day, these plants need to photosynthesize to survive!

  
  

You might be wondering… why does all this meticulous measuring matter? It helps us determine whether the environment can support our long-term dream: deploying Zostera marina (eelgrass) back into Indian River Bay.

Right now, our state is essentially devoid of naturally occurring, healthy eelgrass beds. But we know Delaware possesses the water quality conditions to support it. To prepare for the future, we spent the previous month harvesting healthy eelgrass seeds from neighboring beds in Maryland, Virginia, and New Jersey.

Fun Fact: Why are we trying so hard with eelgrass? Zostera marina is considered a foundation species. It has an incredibly robust, complex root system that acts like an underwater forest, locking down sediments better than almost any other regional SAV while providing a massive canopy for marine biodiversity.

Since collecting them, we’ve been processing and storing the seeds at our facility, carefully monitoring their health and viability. But before we dropped our precious eelgrass seeds into the wild, we needed a trial run.

Before committing to eelgrass seeding, we needed to test the habitat's suitability. Enter Ruppia maritima (Widgeon grass). Ruppia is famously resilient and highly adaptable to fluctuating salinity and temperatures, making it the perfect pioneer species for Indian River Bay.

In late May, we took 16 young adulting Ruppia plants, which we had successfully grown from our own germination trials at the DNREC SAV facility, and transplanted them into the bay. Their strong, healthy root systems gave them the best possible head start against the bay's currents. 

While in the water, we also performed a seining survey to gather a snapshot of the local community. The waterfront was absolutely buzzing! With it being peak horseshoe crab season, and Delaware being the largest hotspot in the world for spawning, we ran into a massive population of horseshoe crabs, along with other little critters like Atlantic silversides, mummichogs, and blue crabs. It was a beautiful reminder of exactly who we are building this underwater neighborhood for. 

That brings us to now, the last week of June. It has been about a month since our initial Ruppia planting, and a recent site visit brought some unexpected news. As it turns out, our new underwater neighborhood was a bit too popular!

When we waded out to check on the progress, we couldn't find any of our transplanted Ruppia. Our prime suspects? The local horseshoe crab population. Young SAV plants need time to quietly push their roots into the sandy substrate to anchor themselves.

Unfortunately, our planting timeline lined up perfectly with peak spawning season, and the sheer volume of horseshoe crabs shuffling through the area likely uprooted or snacked on our trial plants before they could take hold. While the transplant wasn't as successful as we had hoped, look at the bright side: at least we know the locals approved of the new greenery! It wasn't the exact trade-off we were looking for, but it’s a classic lesson in field biology.

So, where exactly do we go from here?

With this proof-of-concept under our belts, our next step is to pivot and try planting Ruppia seeds in the area. Testing how well the seeds germinate and take root directly in the wild will give us the final piece of the puzzle. If the seeds can successfully hunker down in the sediment and survive the local wildlife, it will pave the way for us to confidently introduce our harvested eelgrass seeds in the near future.

We are one step closer to turning a barren seafloor back into a thriving, green ecosystem. Thank you for following along on this journey with us, and we can’t wait to share how the new seeds take to their new home!

And as always... Stay Grassy!