par- 2 février 2009
lundi 2 février à 13h30
Counter-intuitive particle behavior. effect of age on discarded appendicularians houses : shrinking but sinking faster
Fabien Lombard (LOV) présentera un séminaire le lundi 2 février à 13h30 en salle de réunion du COM à Luminy :
Appendicularian are zooplanktic tunicate filter feeders. Because their feeding strategy implies to use external mucous structures named “house”, they are major contributors to the production of fast sinking aggregates in the water column. We have studied the normal behaviour of appendicularian houses from the discarding to six days afterward in absence of detritivorous organisms. After discarding, appendicularian houses deflate quickly, resulting in a 65% loss in diameter (92% in volume) within one hour and this deflation continues afterward until six days. Despite this loss in size, the sinking velocity increase in a very counterintuitive way. This deflation process can be separated in two steps. A first step during the first hour, with intense deflation, leading to a major weigh loss of the house that leak some of it particle content in a visible trail. A second step, with a less intense deflation process, a low decrease in weight that leads to increase the density of the particle and then it sedimentation rate. This behaviour suggest that 20-60% of appendicularian houses particles content is released quickly after discarding due to a physical deflation process only. Moreover, the trail released by the house can be used by detritivorous zooplankton to locate these sinking particles.