Shrimp on the Rim

Living on the Edge…of an Active Volcano

Verena Tunnicliffe
University of Victoria

Dense colonies of shrimp near the summit of the volcano. (click images for full size)

NW Rota does not seem to be the best habitat for animals and yet there is a hive of activity buzzing around the summit. Most of these animals are dependent upon the diffuse hydrothermal venting that provides the basic food source: bacteria in the form of filaments on the rocks. Upon our return, my main question was whether there would be any changes in the simple community that we encountered in 2004 and 2006. There is. The major difference is the extent of the animal populations; it appears that the diffuse venting has spread and, with it, the vent animals.

Close-up view of both species of shrimp.

There is now a very large biomass of shrimp on the volcano. Two species are able to cope with the volcano conditions. The “loihi” shrimp has adapted to grazing bacterial filaments with tiny claws like garden shears. The second shrimp is a new species; it also grazes bacteria after the juveniles settle to the volcano. But, as they grow to the adult stage, their front claws enlarge and they become predators. While the second species is able to evade Jason’s suction sampler, we took advantage of its scavenging habits: a trap baited with Spam came back with 4 dozen shrimp.

Limpets and their eggs collected from the rim.

Another new species we found in 2004 is a limpet that was restricted to one small vent. But now it has spread to many different sites on the volcano. How does a limpet “spread”? This animal glues egg cases to the rock where the embryos develop; then, the larvae hatch and swim to a new site. Another surprise is the presence of a barnacle that we never saw before – in fact, I am not sure it is a known species. It is intriguing that NW Rota is attracting more animals even though the volcano went through a very intense eruption cycle. It is impressive that, for some species, the highly unpredictable nature of this site is balanced by conditions that enhance population survival. It remains to be seen whether the next more violent phase of the volcano will eradicate much of the new colonization.

An interesting question to solve at NW Rota is how the shrimp recruit to the seamount. We are collecting samples to examine them in several ways. First, collections can determine the proportion of the populations that are reproductive; there appear to be a lot of juveniles and few adults. Second, plankton tows are searching for the dispersing juvenile phases in the water column. Third, we can examine gene flow with the loihi shrimp we collected at two other seamounts on the Arc and on Loihi Seamount off Hawai’i…a long trek for a shrimp juvenile!

A rocky outcrop on a ridge of the volcano provides habitat for two species of shrimp adapted to live at hydrothermal vents. (no audio)

The smaller shrimp species is a grazer while the larger one is a carnivore. The smaller grazers get out of the way as a larger carnivore walks through a crowd. The carnivore species uses its large claws in aggressive displays. (no audio)
All video copyright by Advanced Imaging and Visualization Lab WHOI