Participant Perspective - July 18, 2001

Interview with Ana Metaxas
Biological Oceanographer

Jeff: What are you studying at Axial Volcano?

Anna: I'm interested in the period between when larvae are released into the water column and when they are recruited back to the benthic population. Also, I'm interested in why they settle in a particular location. The site may have other adults, the right chemistry or substrate texture. I want to put down larval traps to look at larval abundance in the water column and an array to see where they actually settle at different sites at Axial. We're not looking for a specific type of larvae. Last year we got a lot of limpets and some polycheate worms. We're probably going to get gastropods and we should get tube worms if it's in the right area.

Jeff: How do your larval traps work?

Anna: I have two types. One is a passive larval trap. They are basically tubes filled with formalin (a poison) and as water moves over the top of the cylinder it forms a small eddy that traps things and transports them into the cylinder. They hit the poison and fall to the bottom. The traps give us an idea of what type of larvae are transported near the bottom. We also have settlement array instruments. They are basically soap dishes with substrates that are supposed to mimic the bottom and attract the larvae so they stick on them and stay there. We
have two kinds of substrates. One is basalt because that's the type of rock at Axial. The other are Scotch Brights (scrubbies). The reason the scrubbies are so successful is that they have a lot of structure to them. Anything that comes to settle wants to stay away from currents in little holes and cracks so things can't eat them. We'll leave the traps down for 10 days and the arrays we'll leave down for one and two years.

Jeff: Is vent larval dispersal one of the hardest things to study at vent areas?

Anna: Yes. A study on tube worm larvae dispersal based on respiration rates at
the East Pacific Rise suggests that they don't feed, so whatever energy they
have has come from the egg. They estimated that they can live up to 36 days. They calculated, based on currents, how far the larvae can be transported in 36 days. The farthest they could get is 105 km, although most of them can get about< 50 to 60 km which would barely get them to the next vent. So, they can't go very< far. It also suggests, because currents rotate, that a lot of the larvae get transported off axis and presumably they are lost. That could be 40 - 70 % of larvae just disappearing off axis, given the current. It's not very easy to get from vent to vent.

Jeff: What about larval dispersal in hydrothermal vent plumes?

Anna: I have a hard time believing that theory now that water column samples have been taken and large larvae densities haven't shown up in the plume. We're talking 1 to 2 individuals per m3 or 10 m3. If they can only get to the next vent, I don't know if that could work. Larval dispersal is the hardest problem to work with because we don't know that much about dispersal mechanisms. It has been suggested that larvae get released from a vent area and entrained into a plume. They rise to where the plume becomes neutrally buoyant then, as the plume is traveling up and down the ridge, little plumes with concentrated larvae get separated from the large plume and those larvae move onto the next vent and then drop. I don't know if I believe that.

Jeff: What do you find most fascinating about studying larvae dispersal?

Anna: I think that larvae actually have behaviors, show behaviors and show some responses to their environment which I don't think people think about that much. If you think of really big scales, larvae are just particles that are transported in currents. I think when we get to smaller scales larvae actually show behavioral responses to their environment and I think that is really neat. I've done lab experiments that show that larvae respond to food patches. They will stop and feed at a food patch. When larvae settle we know they respond to chemicals, to conspecifics. Despite their simple structures, they do have behaviors that suggest they sense their environment and that increases their chances of survival and that's really neat. We don't think about them. They are just particles in the water column. I don't think they are just little particles, they do things (laughter).