Observations at the CASM vent site

August 1, 2016

45o 59.4′ N 130o 1.5′ W

Our dive today started with biology collections at the CASM (an acronym for Canadian American Seamount) vent site on the northern caldera floor at Axial. Then we headed north up the caldera wall and crossed several old, heavily sedimented flows, and ended with geology collections on two flows that formed as part of the April 2015 eruption and that we discovered when we compared AUV bathymetry collected before and after the eruption. We found two areas of low-temperature venting with one measured at 32Celsius and lots of orange mat there but no megafauna.

—Jenny Paduan

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A mixed community of organisms thrives in the sulfide-rich waters of this diffuse hydrothermal vent.

The vent field at CASM is very compact, and we were able to explore most of the chimneys in about 30 minutes. Working in the deep sea is incredibly expensive, and we try to pack as much into each dive as possible. Since CASM was a smaller site, we took the opportunity to stop and look around carefully. At sites with more diffuse venting, we saw an abundance of palm worms, Paralvinella, millions of limpets, Lepetodrilus fucensis, provannid snails, scale worms, and munidopsid crabs.

—Shannon Johnson

The margins of the 2015 flows are thin and have lots of lava lobes extending across the underlying sheet flows in complex patterns. The second flow has lovely channels, pillars, and lineated sheet flows—all quite spectacular. These are strange flows! There are hundreds of exploded pillows, including one that is probably a shatter ring that looks like a 15-meter-wide low cone in the bathymetry. The exploded pillows have very thin crusts, and many small pillows are hollow with thin rinds only. The lava samples have a lot of gas vesicles in them. It was a very gassy magma, and high gas content might help account for the fluidity of the flows.

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The rind from a drained lobate pillow from the 2015 eruption, pictured with the inner surface facing up. It has a thin, dense glass rind on the upper surface, about a centimeter of more crystalline lava with many short pipe vesicles perpendicular to the outer rind, and then a thin glass inner rind with large bubbles (one to rear of photo has broken). This was a very gassy lava. (Squares in the background are 2.54 centimers on a side for scale.)


Sample being collected from a drained lobate pillow in one of the flows of the 2015 eruption.

Sample being collected from a drained lobate pillow in one of the flows of the 2015 eruption.


Narrow lava pillars miraculously support the thin roof of a drained lobate sheet flow near the fissure for this flow of the 2015 eruption. The lava channel for the flow (under the ROV) carried the lava down slope and out from under this roof, leaving the hollows we see and drainback veneers (the horizontal lines) on the lava pillars.

Narrow lava pillars miraculously support the thin roof of a drained lobate sheet flow near the fissure for this flow of the 2015 eruption. The lava channel for the flow (under the ROV) carried the lava down slope and out from under this roof, leaving the hollows we see and drain-back veneers (the horizontal lines) on the lava pillars.

—Dave Clague

At the CASM vent field we came across one large chimney absolutely covered by tubeworms, Ridgeia piscesae, of the “short and fat” morphotype. The short and fat morphotypes live in high-sulfide environments characterized by vigorous hydrothermal flows and higher temperatures. They have a high reproductive output compared to the “long and skinny” worms and tend to have shorter lifespans. The long and skinny worms reside in areas of lower sulfide and tend to live longer, but have much lower reproductive output. The red plumes of the two morphotypes are visibly different, and it was once thought that these were two different species.

This large chimney is densely populated with the short, fat morphotype of Ridgeia piscesae, a few of which the manipulator arm is about to collect.

This large chimney is densely populated with the “short and fat” morphotype of Ridgeia piscesae, a few of which the manipulator arm is about to collect.


A cluster of the long, skinny morphotype of Ridgeia piscesae growing on the faulted wall at CASM.

A cluster of the “long and skinny” morphotype of Ridgeia piscesae growing on the faulted wall at CASM.


Close-up of the long, skinny morphotype of Ridgeia piscesae.

Close-up of the “long and skinny” morphotype of Ridgeia piscesae.

Similarities in gene sequences have confirmed that the two morphotypes are, in fact, a single species that exhibit extreme morphological plasticity (variability within a species). Although population genetic data tell us that the morphotypes are a single species, studying how genes are programmed to be “on” or “off” between the morphotypes can help us to understand the genetic factors producing this extreme morphological plasticity. Epigenetics is what we call the study of the various mechanisms that control this genetic programming. We collected the different morphotypes from two locations using the temperature probe to record the temperature of the vent fluid around the collection sites. The pilots used the robotic manipulator arm to collect and place the tubeworms into the biobox.

The temperature of the fluid emanating from this vent is being measured; it was 26oC.

The temperature of the fluid emanating from this vent is being measured; it was 26oC.

Similar to the manner in which the tubeworms respond to the temperature gradients around hydrothermal vents, two sister species of palm worms, Paralvinella palmiformis and P. sulfincola, inhabit different thermal regimes. They exhibit differences in how they regulate the constellation of proteins involved in dealing with thermal stress. We, again, used the temperature probe to gather contextual data from the environment before we collected the worms. We used the suction sampler to collect the palm worms into one of several rotating canisters.

The suction sampler of the ROV <em srcset=

Doc Ricketts.” width=”500″ height=”282″ /> The suction sampler of the ROV Doc Ricketts.

Using the same genetic methods that we use for R. piscesae, we will probe the two species of palm worms in an effort to understand whether similar genetic mechanisms are responsible for the extreme morphological plasticity within R. piscesae and the difference in the upper temperature limit between the two species of palm worms. Studying these worm taxa in extreme environments will help us to understand how genetic programming is encoded in the genome that produces morphological plasticity and how environmental niches contribute to the formation of species.

—Rob Young