Mapping South Texas Banks: DAY FIVE (9/21/12)

To core or not to core? That was the question of the day as the ROV explored Aransas Bank this morning. Scientists jumped to their feet in the labs cheering throughout the vessel when ROV pilot returned the first successful push core safely to its holder full of a muddy sediment sample. Whooping and hollering from the science control room could be heard across the Gulf (well, at least throughout the R/V Falkor). One small tap from a hydraulic robotic arm, one giant push for benthic ecology at Aransas Bank.

ROV hydraulic arm returning core with sediment to the holder.

Image credit: Harriet Nash; Deep Sea Systems International; Schmidt Ocean Institute

After a couple of successful push cores on the landward side of the bank, we did a video transect to the peak. The ROV followed the same procedure of core sampling and video transect from the seaward side as well. Visibility on the landward side of Aransas Bank was quite murky, but visibility on the seaward side was much better and similar to that at Baker Bank. In general, we observed similar biota at Aransas Bank when compared to what we saw at Baker Bank. Several species were common at both sites—Atlantic thorny oyster, long sea whip, tattler basslet, reef butterfly fish, blue angelfish, French angelfish, sponges, and wire coral. Notable differences between sites include no sea cucumbers; fewer Hypnogorgia white sea fans; many more red snapper; and more depressions, ledges, and burrows than at Baker Bank. Aransas Bank is home to more short bigeyes, which darted into burrows when the ROV approached. We also saw a few interesting species on Aransas Bank that we did not see at Baker Bank. They included silky shark, scrawled cowfish, spotfin hogfish, serpent star, a huge hermit crab, jackknife fish, and giant basket stars.

After spending quite a bit of time collecting samples of sponges, rocks, and sea fans, the ROV returned to the mother ship. The crew fixed the ROV in its place on the aft deck, and almost immediately a sponge brittlestar frantically scurried from the ROV across the deck trying to get back to its home. A scientist quickly scooped it up for the collection.

We unloaded the completely full sample box and the sediment cores. Once the samples reached the wet lab, the scientists entered a frenzied state of chaotic excitement while sorting and processing samples. The sediment samples were very watery and loose so only a few survived and were stored for later analysis by benthic ecologists and geologists. Living inside sponges and rocks were polychaete worms, tiny shrimps, squat lobsters, juvenile crabs, brachiopods, and white tangled bryozoans. The scientists turned in for the night quite pleased with the high biodiversity represented in their samples.