Sunday, September 23, 2012

DAY SEVEN (9/23/12)

Today our exploration centered on Dream Bank.  Similar to Aransas Bank, the landward side was murkier with suspended muddy sediment in the water column while the seaward side of the bank was quite clear.  Dream Bank has quite a few crevices and some burrows, which serve as refugia for fish escaping the frightening ROV.  The fish assemblage at Dream Bank is similar to that of Aransas Bank.  In addition, we spotted a sea robin, which looks like a winged fish flying near the sea bottom, and a few schools of amberjack.  Other exciting sights were sea stars, a flame box crab, a cleaning station with a fish and a couple of cleaner shrimp, an arrow crab, and several sea serpents and basket stars.
Large female basket star with smaller male basket star attached in center
Image credit:  Harriet Nash

While attempting to collect rocks for the geologists, we came upon a fishing weight that was mistaken by one of the rather nerdy scientists in the group as a mermaid’s tassel.  We quickly moved on to collect some soft corals.  As Wes Tunnell put it, collecting soft corals with the ROV’s hydraulic arm is “like collecting a flower with a bulldozer.”  However, we still managed to bring a fine specimen of black coral safely to the lab for analysis.  We also collected a soft coral with basket stars.  A full set of sediment cores was collected for analysis.

The biologists AND geologists all became giddy when the ROV approached a mound of rubble that resembled staghorn coral (Acropora cervicornis).  A mound of dead A. cervicornis would provide strong support for the theory that Dream Bank is an ancient drowned reef and could also be carbon dated.  After looking at a piece of the rubble sample, Wes Tunnell and Tom Shirley determined that the rubble was composed of staghorn bryozoans, which are filter-feeding invertebrates that live in colonies but are not related to corals.  We have not seen any living staghorn bryozoans so the feature could be a mound of fossils.  Another unanswered question:  how did the staghorn bryozoans end up in a mound formation?

Staghorn bryozoans
Image credit:  Harriet Nash

Not far from the mound there was a large crater, which could be the result of groupers digging a large hole or a geophysical phenomenon such as a “mud volcano” or methane geyser producing a hole in the sea floor with steep walls.  The cause of the crater is not certain. 

The mound of ancient A. cervicornis was a dream that did not come true, but don’t fret because science never sleeps.  Dream on, dream on…

Day 7 Sunset
Image credit:  Harriet Nash

Written by Harriet Nash for HRI at TAMU-CC.

No comments:

Post a Comment