Mapping the South Texas Banks

The Rise of the Rubble

Mark Schrope
Sep. 23 2012
A pair of basket stars collected at Dream Bank. The red striped male is smaller and spends its life latched onto the much larger and more intricately patterned female.
A pair of basket stars collected at Dream Bank. The red striped male is smaller and spends its life latched onto the much larger and more intricately patterned female.Mark Schrope

Yesterday I joked about a mystery at Mysterious Bank, but today we came on something of a real mystery. It happened about midway through an 8-hour ROV dive at a spot called Dream Bank.

An unusual arch at Dream Bank.
An unusual arch at Dream Bank.Schmidt Ocean Institute/Deep Sea Systems International

The views were a little dull at the base of the bank, but as we made our way up, the slope became increasingly picturesque with scenes reminiscent of shallow water reefs including bright splotches of sponge, large white sea fans, and more red snapper.

But it was geology that grabbed the most attention. One especially striking feature was a large arch, perhaps 8 feet across, that looked like a miniature version of something at a national park. Like most of the structure on the banks, it’s probably the remnants of some ancient ice age coral.

I’ve been doing this for a lot of years and I’ve never seen that. – Wes Tunnell

Prehistoric Realm

David Hicks examining a sample.
David Hicks examining a sample.Mark Schrope

Seeing these features, you can’t help but wonder what it would have been like snorkeling through this place 12,000 years ago or so when it was shallow reef close to the beach, instead of 50 miles offshore and nearly 200 feet down. You can imagine something like this arch covered in even brighter corals and sponges, and all manner of prehistoric beasties swimming about.

But the most intriguing find was the mysterious one. As I’ve mentioned in previous dispatches, geologist Andre Droxler is looking for pieces of ancient coral that he can date to get a better understanding of the banks’ history. So he was quite pleased when the ROV came upon something we hadn’t seen yet—a pile of what looked to be the rubble of shallow water hard corals. “I thought, ‘This is it,’” says Droxler.

The bryozoan rubble pile.
The bryozoan rubble pile.Schmidt Ocean Institute/Deep Sea Systems International

The ROV crew started grabbing pieces. But this afternoon, when the scientists began scrutinizing these pieces, they realized they had something very different from what they expected. Though it looked like coral on first glance, closer examination along with a bit of digging through books and internet photos revealed that what the ROV retrieved was instead the remains of something called a bryozoan.

These simple animals are ubiquitous and come in various forms. Most are soft and look more like algae. But a rare few look very much like coral and build similar hard calcium carbonate skeletons that form reefs. But they are still genetically and physiologically quite different from corals.

Surprise Conclusion

The staghorn bryozoan rubble pieces.
The staghorn bryozoan rubble pieces.Mark Schrope

The best current guess is that the rubble is from something called a staghorn bryozoan, but we don’t know exactly what that means yet. “I’ve been doing this for a lot of years and I’ve never seen that,” says Wes Tunnel, “so I’ve got a feeling it doesn’t even live here anymore.” It’s quite possible that the species is now extinct in the Gulf. It could be ancient, but it might be newer. We’ll be able to tell based on the same dating techniques you’d use with coral.

But if it is something quite old this begs the question of how in the world it got into the form we found it–in large piles. It’s hard to figure how something that’s been around for 1,000 years, much less 10,000 years, could end up like that.

The team will be consulting with a bryozoan expert and Droxler has a colleague ready to run the dating once he ships off some samples. So they’ll start there and see where it all leads.

Meanwhile, the exploration continues. Tomorrow we’ll be mapping more of the banks to the south, as we make our way down to the level of the Mexican border. Then we’ll plan to run two more full days with the ROV on Tuesday and Thursday. Thankfully, the weather reports are still looking good, so there should be plenty more good finds to come.

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