Each year thousands of massive ships pass over the murky bottom of the Delaware Bay, where the Delaware River meets the Atlantic Ocean.
Despite the traffic, little is known about what lies at the depths of this well-worn waterway.
Health and science reporter Kerry Grens joined some scientists on a mapping expedition, and filed this report.
See what the scientists found at the bottom of the bay:
With just a single metal clip, a small motor boat – a zodiak – dangles from a crane overhead, blocking out the mid-day sun. The crane is mounted to a 146-foot research vessel, idling in the Delaware Bay, near Cape May. University of Delaware professor Art Trembanis is a little bit nervous.
Trembanis: Half million dollar robot is sitting up in the air. It’s fine in the water, it’s not meant to be in the air.
The crane’s arm swings around and lowers the boat into the water. Inside is a bronze, nine-foot long, topedo-looking robot called the Gavia. It’s an AUV — or autonomous underwater vehicle. Trembanis: We’re going to use the AUV as our eyes and ears into the environment and really kinda get in and explore the way fish do and be able to swim near the bottom and take high resolution images of the seabed.
Trembanis and the other scientists are looking for unusual places in the bottom of the Bay that defy the stereotype of a continuous bowl of muck. Doug Miller is another UD professor leading the study.
Miller: Most of the bay is mud and sand. We call those soft bottoms because they’re squishy and wouldn’t support your weight. But there are places in the bay that are actually what we call hard bottom communities. They might be worm tube and reefs, they might be sponges.
Hard bottoms attract fish, conch, crabs, and other animals, some of which are harvested by commercial fisheries. Miller says the hard bottoms may be important to the health of those populations – and the industries as well. Yet Miller says very little is known about these habitats– where they are, why they appear in certain places, and whether they are sensitive to fishing or dredging.
The team on the zodiak radios in to prepare the AUV’s launch. It will spend an hour and a half taking images of the seafloor. Miller keeps vigil from the main vessel’s cabin.
Miller: I have absolutely no idea what we’re going to find.
Miller and Trembanis are not the first to map the bay’s floor – they are just doing it with more scrutiny and exploring less known areas, like the New Jersey side. The state of Delaware is wrapping up a six year project to broadly scan 80 percent of that state’s portion of the Bay and River. Bart Wilson is an environmental scientist with that program.
Wilson: Before the survey that we conducted there wasn’t really much out there. It was kind of piecemeal. The corps had done some surveys in select sites.
One of the prized finds of their survey was habitat hosting a reef building worm called Sabellaria vulgaris. The worm is a key component of hard bottoms. They make lava-rock-looking sand structures that create the nooks and crannies fish like to hang around.
Wilson: We really documented how we can locate the habitat of Sabellaria vulgaris. Not that we can find it in particular, but we know where the habitat looks like.
Wilson says the data are important for guiding the state in work like beach replenishment – and choosing sites to collect sand where there are no hard bottoms to potentially destroy. He says the AUV’s analysis will help provide useful information on the importance of hard bottoms to the ecosystem of the bay as a whole.
After hours of bobbing in seaspray and chop on the zodiak, the team returns with the AUV safely retrieved. Graduate student Nicole Raineault — shivering and wet — is eager to get to her data.
Raineault: I was really excited. Because we were sitting in the little boat and radioing up to the guys that were controling the Gavia from the big boat in the tower and they were already processing the logs.
It’s sundown by the time the images show up on Raineault’s computer. Page after page of the scans show essentially the same thing — an even, flat bottom. Raineault and Doug Miller stare at the screen until they notice something different.
Miller: Definitely not a smooth bottom. That that’s something interesting over there.
A subtle chunkiness appears in the otherwise uniform scan.
Miller: I can’t tell you what it is, but I tell you I’m interested in it.
They instruct the captain to move the boat over to the spot. The crew drops overboard a rusty metal claw with a mesh basket. By now, the moon is out, the crew is exhausted. But the dredge gives Miller a second wind.
Miller: This is a male horseshoe crab. Lots of horseshoe crabs…There’s a hermit crab in here…This is an egg case…
The claw dumps a cornucopia of sea critters on the deck. Conch. Flounder. Hair-like hydra.
Miller: This is what I came out here to find. A conch shell covered in Sabellaria.
One of them being Sabellaria vulgaris. It could be mistaken for a chunk of porous rock the size of a fist, but the nodule is actually a tiny worm city they’ve built out of sand — the pores their houses. Miller brings his treasure to the team.
Nicole: So exciting. We haven’t seen these at any of the sites we’ve looked at so far.
Raineault says the find confirms that there are hard bottoms in this region of the bay.
Nicole: They’re normally found off shore in courser sediments. So it’s exciting to see these habitats.
Raineault says it gives her reason to come back and do more studies on this area. How extensive is the hard bottom, who else is living there, and do they matter to the health of the fish populations in the Bay? But at midnight on this trip, the boat heads back to Lewes, Delaware. The scientists’ questions will have to wait till tomorrow, when they return to the sea.