The dynamics and formation mechanisms of marine snow aggregates from a
bandoned larvacean houses were examined by laboratory experiments and
field sampling during a spring diatom bloom in a shallow fjord on the
west coast of the USA. Intact aggregates were sampled both from sedime
nt traps and directly from the water column by divers. ALI aggregates
were composed of 1 abandoned house of the larvacean Oikopleura dioica
to which numerous diatoms, fecal pellets, ciliales, and amorphous detr
itus were attached. High vertical flux rates (20000 to 120000 houses m
(-2) d(-1)) and settling velocities (average 120 m d(-1)) imply a rapi
d turnover of suspended larvacean houses, and concentrations of diatom
s and fecal pellets in the aggregates exceeding ambient concentrations
by 3 to 5 orders of magnitude suggest their potential importance in d
riving the vertical flux of particles. Identical particle assemblages
were observed in aggregates collected in the water column and in sedim
ent traps. Most of the fecal pellets found in the houses were most Lik
ely produced by the larvaceans themselves. Numbers of diatoms per hous
e corresponded with the diatom concentrations in the ambient water and
, on average, each aggregate contained diatoms in abundances correspon
ding to those found in 4.5 ml of ambient water. Laboratory measurement
s showed that larvacean houses scavenge diatoms and fecal pellets whil
e sinking, and observed scavenging rates were similar to those predict
ed from theory. However, both predicted and observed scavenging rates
in experiments were orders of magnitude too low to account for the par
ticle content observed on aggregates from the water column. Based on m
odels, shear coagulation was also assessed to be insignificant in form
ing aggregates. It is concluded that most of the particles become atta
ched to the incurrent filters of the larvacean house while it is still
inhabited, and that shear and sinking insignificantly contribute to p
article collisions and adhesions on the abandoned house.