March 27, 2010

Something Old, Something New

When we first met the shrimp of NW Rota in 2004 we wondered what makes them so special that they can thrive in such a volatile environment. Last year both species, Opaepele loihi and an undescribed Alvinocaris species, had expanded their distributions and seemed to be doing quite well for themselves. Hydrothermal vents with bacterial mats were plentiful and there were plenty of shrimp around to take advantage of the favourable conditions. There , were a large number of adults of both species and where one species was found, the other was almost surely there. Alas all good things must come to an end, or in the case of NW Rota a new beginning.
Figure 1- A steep cliff face covered with Opaepele loihi shrimp.
The major landslide that occurred at Rota has given us some excellent clues as to how a major disturbance affects a community dominated by mobile vent organisms and how new habitats on an erupting volcano are colonized by shrimp. There are few remaining habitats from last year and the newly disturbed parts of the volcano have already been colonized by vast numbers of new recruits. The extent of this colonization in less than a year is astounding with thousands of juvenile shrimp in areas newly exposed by the slide.
Even more surprising is that this new crop of shrimp appears to contain just a single shrimp species, Opaepele loihi. This “volcano specialist” is well adapted to living on erupting submarine volcanoes, found at 4 thus far, but we still know nothing about how it survives the harsh conditions or how it finds and colonizes new habitats. By comparing the new populations at NW Rota with populations from previous years and by collecting shrimp larvae in plankton hauls around the seamount we hope to uncover how these shrimp recruit to NW Rota. The Alvinocaris shrimp are notably absent in the slide-affected region yet they remain a part of the vent community in unaffected habitats.
Figure 2- An adult Alvinocaris shrimp stands proud among the smaller “loihi” shrimp.
Both species of shrimp feed by grazing on bacterial mat throughout some or all of their post-larval life. The “loihi” shrimp have specialized claws like garden shears for clipping bacterial mat which allows them to do so very efficiently while the Alvinocaris shrimp also graze mat but transition into scavengers and predators as they get larger. One of our goals this year is to compare bacterial mat samples from areas with and without shrimp. By finding out what they like to eat and comparing this with where they are and the fluid chemistry at different vents we can better understand what makes a suitable habitat for these amazing shrimp.

John Sherrin
University of Victoria