Month: May 2011

Longshore Drift and Pufferfish

A groin strains to hold back the longshore drift. It is, as always, only partially successful.

It was about 1.5 kilometers from the Research Lab to the estuary where we spent our first morning sampling (overview of the trip is here).

Elevated beach house.

Walking along the beach to get there, we could see the beach houses to the right of us, across the narrow road of East Beach Drive, standing tall on columns to keep them above the reach of the storms. According to Stephanie, our guide, the storm surge from Hurricane Katrina in 2005, reached awfully close to the tops of the columns. The research lab, which is not elevated, lost an entire building to that hurricane. Indeed, much of the coast is still recovering from Katrina’s damage.

The white sandy beach, on the other hand, looked beautiful, which was a bit odd. After all, how did it survive the storm? Furthermore, when you think about it, this beach is located behind a string of barrier islands, which protect the coast from the full force of the waves coming out of the Gulf of Mexico, so how come there is enough wave energy to maintain a sandy beach. The relatively calm waters should allow finer grained sediment, like clay and silt, to settle out, and this area really should be a marsh. The answer, it seems, is that this is an artificial beach. Every few years, thousands of tons of sand are dumped along the coast to “replenish” the beachs.

Without beach replenishment the beaches would revert to salt marshes like this one.

This coastline really should be a tidal marsh, like the one we found when we got to the estuary. These Gulf-coast salt-marshes are fronted by a relatively short version of smooth cordgrass (spartina alterniflora), backed up by the taller, and more common black needlerush (Juncus roemerianus Scheele) .

Longshore Drift

Now, if this is a low-energy environment that allows silt and clay can settle out of the water column, where does the sand go so that it has to be replenished every so often? It is gradually moved along the coast by longshore drift.

Longshore drift moves sand along the coast in the direction of the wind. Image via the USGS.

Waves hit the beach at an angle. As they break, the turbulent swash pushes sand up the beach at the same angle as the movement of the waves. As the wave retreats, the backwash, drawn by gravity, pulls sand perpendicularly down towards the water. The net effect, is that sand gradually moves down the coastline with each swash and backwash of the waves.

Since dumping tons of sand is expensive, engineers try other things to prevent the sand from running off down the beach. Someone, a very long time ago, had the great idea to build a wall sticking out from the beach to impede the sand in its unwanted migration. This type of wall is called a groin (or sometimes a groyne in polite company), and it does stop the sand. In fact, the sand builds up on the upwind side of the groin. Unfortunately, it does not stop the longshore drift on the downwind side, and that results in the erosion of a bay on that side.

A groin impedes longshore drift. Note that the waves approach the beach at an oblique angle.

Pufferfish

Beaches are also great places to find random things washing up. We lucked upon an unusually large pufferfish (family: tetraodontidae). It was quite puffed up. It was also quite dead.

Pufferfish.

Pufferfish are famous for being extremely poisonous. According to the National Geographic page on pufferfish, their tetrodotoxin over a thousand times more poisonous than cyanide, and there is no known antidote.

Seining in the Sound

Setting up the seine.

After surface sampling with the dip nets, and subsurface sampling with the little corers, we tried sampling the water column using a small seine.

Seining requires teamwork, and I was pleased to see everyone working well together, focused on the job at hand.

Working together to bring in the catch.

Hauling on the nets, with the smell of salt in the air, resurrected long neglected memories of fishermen at work on tropical, Atlantic beaches. Back then they were going after fish for the market, here, with our much finer meshed net, we were looking for anything interesting in the water column.

Examining the catch.

Everyone got touch a ctenophore (comb jelly), which I will note is not a jellyfish, and is also not poisonous.

If you look carefully you can just make out a comb jelly in the jar.

Students also had a chance to hold a croaker (a fish of the family Sciaenidae), and feel it croak.

Feeling the croak.

Our guide was great. She was quite knowledgeable about the fauna we ran into, and very good at sharing information.

Stephanie T. pointing out the finer points of piscine morphology.

Interestingly, we were not the only ones out seining that morning. There was a small group from the research lab looking for skates for a research project. I think they said that this was their third time out looking, but like us, they did not find any elasmobranchs (not counting the one dead specimen we ran into while dip netting).

Remains of a skate, lying in the grass at the edge of the beach.

Dip Nets in the Estuary

Dip nets in action.
Sampling in the estuary.

Doing the “sting ray shuffle” through the shallow waters of the estuary of a small stream and the Mississippi Sound, we used dip nets to collect organisms from the sediment-water interface.

We found mostly invertebrates. There were lots of small white crabs. Most, but not all, were too small to pinch.

We also grabbed quite a number of translucent shrimp.

You can very clearly see the entire gastro-intestinal system of this small shrimp.

And there were a lot of hermit crabs.

An understandably shy hermit crab.

A couple students also picked up some small snakes, but they quickly slipped through the dip net’s mesh and escaped.

Simple and effective, dip netting was a nice way to start the Coastal Sciences Camp.

Moving on

Break, break, break,
On thy cold gray stones, O Sea!
And I would that my tongue could utter
The thoughts that arise in me.

–Tennyson (1842): Break, Break, Break via the Poetry Foundation.

I feel as if I’ve been posting more poetry than normal. I know I’ve been reading a lot more. It’s a habit I fall back into at major transitions. I’m leaving Lamplighter Montessori in Memphis and instead of doing everything in the Middle School, I will be taking a more Math and Science oriented position at the Fulton School at St. Albans near St. Louis. I’ve really enjoyed being the Middle School teacher at Lamplighter, so it is hard to leave, but the hardest part of moving on is that, in my multi-age, single-teacher classroom, there are seventh graders who I won’t be able to take through the full cycle.

It’s particularly hard because I’m leaving behind an exceptional group of students that any teacher would love to have in their classroom. They’re kids who love to learn, are serious about their work, and are well-balanced, “normalized” Montessori students; the epitome of constructivist education. For this reason, I know they’ll do well, which is some consolation (I also have a lot of confidence in their new teacher), but I will miss not being able to work with them.

Saying goodbye to the graduating students was also more difficult than I expected. There’s always some sadness in seeing them move on, but it is part of the normal progression of things, so it is a sweet sorrow. Now, however, my moving to another city introduces another element to a naturally traumatic change, especially for the kid who have had a harder time making the transition. Part of the safe anchor back to middle school, which some students need during that first year of high school, has become untethered.

At least, with the blog and email it is harder to loose all contact, but electronic communications cannot always satisfy the need to know that there is something, somewhere, safe behind you, somewhere that will provide a little unconditional positive regard we all need sometimes. Admittedly, this is often an illusion, institutions evolve, but I think it is a useful fiction we all need sometimes.

There is a lot to commend my new position, which I will undoubtedly be writing a lot about over the summer as I prepare classes, but after talking to my students individually today, I feel like I need to take a moment to reflect on what has been a few, wonderful years. Hence my need to resort to poetry.

Coastal Science Camp at the Gulf Coast Research Lab

Dip netting in a small estuary.

As you may have guessed from the previous posts about waterspouts and the dolphin, we’ve been on the Gulf coast for the last few days. Specifically, we were visiting the Gulf Coast Research Lab‘s Marine Education Center for two days for our end-of-year trip.

It was excellent. The weather was perfect; sunny with lots of cumuliform clouds for shade but little rain. However, the what really made the trip work was that we had a good, interesting, and varied program, directed by an excellent instructor, Stephanie T..

Stephanie T. pointing out the finer points of piscine morphology.

For reference (to link all posts about the Coastal Science Camp):


View Coastal Sciences Camp, Gulf Coast Research Lab in a larger map

Dolphin

Dolphin in the boat's wake.

We weren’t looking for them at the time, and later when we were looking for them we didn’t find them, but on our trip back to the GCRL-MEC a dolphin decided it wanted to play in our boat’s wake.

It would jump through the face of the bow wave. Usually horizontally, but vertically once or twice.

Playing.

Dolphins usually travel in pods of up to a dozen or so individuals. This one, however, was alone. We’d seen it earlier, while we were walking on the beach and picking up trash. The dolphin may have been playing or eating, but it was certainly scaring the small fish. A couple birds took advantage of this to make their own catches, with near vertical dives into the gently rolling waters of the sound.

It was wonderful to observe.

Bird caught in the middle of a dive, just before it splashed into the water.

Waterspouts

Two waterspouts seen over Ocean Springs.

As we waded through the Mississippi Sound, doing the Sting Ray Shuffle, sampling for benthic fauna, we came across these two waterspouts. Our guide, Stephanie, from the Gulf Coast Research Lab’s Marine Education Center, said they’re not that common.

Subtly sinuous.

They’re quite elegant.

In the distance.

Fortunately, they were very far away.

Fascinating.