MICROBIAL PLANKTON COMMUNITY
RESPONSES TO NUTRIENT AND B12-VITAMIN
ADDITIONS
Recen s udies in coas al wa e s sugges ha phy oplank on is e en ually limi ed o colimi ed by some me aboli es de i ed
om bac e ial ac i i y. The majo i y o phy oplank on species equi e an exogenous sou ce o B12 i amin o g ow h. As
only selec ed p oka yo es a e able o syn hesize B12, hey mus be he ul ima e sou ce o B12 o auxo ophic
phy oplank on. We conduc ed 3 mic ocosm expe imen s o assess he esponse o mic obial plank on o B12- i amin
amendmen in he coas al-ocean ansi ion zone o NW Spain. Su ace seawa e was mixed wi h ino ganic nu ien s, B12-
i amin o a combina ion o bo h and incuba ed du ing 72h, unde in si u empe a u e and ligh condi ions. Size- ac iona ed
(20, 3 and 0.2 µm) chlo ophyll-a concen a ion and picoplank on abundance we e moni o ed e e y 24h and changes in he
size- ac iona ed euka yo ic and p oka yo ic communi y s uc u e we e assessed by ARISA (au oma ic RNA in e genic
space analysis) a he end o he expe imen s. We obse ed ha phy oplank on esponded o B12- i amin (alone o in
combina ion) in 2 expe imen s. Nanophy oplank on was he mos esponsi e ac ion in e ms o biomass, whe eas
changes in communi y s uc u e associa ed o B12- i amin addi ion we e mainly obse ed o la ge euka yo es.