1. BACTERIOPLANKTON DYNAMICS DURING A MESOCOSM-SIMULATED OIL SPILL Eva Teira 1, JM Gasol 2, I Lekunberri 2, XAG Morán 3, E Fernández 1, XA Álvarez-Salgado 4, F.G. Figueiras 4 1 Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, 36310-Vigo 2 Departament de Biología Marina i Oceanografia, Institut de Ciències del Mar- CMIMA, CSIC, Pg.Marítim de la Barceloneta 37-49, 08003, Barcelona 3 Instituto Español de Oceanografía-Xixón, Camín de l’Arbeyal s/n, 33212, Xixón 4 Instituto de Investigaciones Marinas-IIM, CSIC, Eduardo Cabello 6, 36208, Vigo

2. IMPRESIÓN (VEM2003-20021) “Impacto del vertido de hidrocarburos del PREStige sobre la red trófica microbiana planctÓNica”. Work programme 4: Impact on biologic systems. Impact assessment on biodiversity: population and communities distribution and abundance. Ecosystem restoration monitoring. Pelagic system.

3. Polycyclic Aromatic hydrocarbons (PAHs) LMW (2-3 days) HMW (9 days)

4. marine hydrocarbonoclastic bacteria Alcanivorax Cycloclasticus Oleiphilus Oleispira “professionals” Marine bacteria degrading petroleum hydrocarbons  -Proteobacteria Planococcus G+ bacteria LMW PAHs: Naphthalene Phenanthrene Anthracene

5. Mesocosm experiment-IMPRESIÓN-1: Ría de Vigo, March 2005 Water filtered through 200  m Temperature 10 ºC Chlorophyll-a ≈ 5  g/l

6. 1L11L1 2C22C2 platform Bouzas bay 1.5m 3H23H2 4C14C1 5H15H1 6L26L2 empty C-Control L-Low PAHs concentration (  6  g/L) H-High PAHs concentration (  15  g/L) Mesocosm experiment-IMPRESIÓN-1: Ría de Vigo, March 2005 The experiment lasted 9 days

7. Methods -Bacterial abundance: Direct microscopy on polycarbonate filters (DAPI-staining) -Bacterial production: Rates of protein synthesis with 3 H-Leucine -Bacterial community composition: Fluorescent In Situ Hybridization  -Proteobacteria (Alfa)  -Proteobacteria (Gamma) Cytophaga-Flexibacter-Bacteroidetes (CTB) Cycloclasticus spp. (Cypu)

8. Fluorescence In Situ Hybridization (FISH): fluorescence-labeled oligonucleotide probes targeting the small subunit rRNA of specific prokaryotic groups. target probe 10  m

9. Lauderia annulata Development and decay of a diatom bloom PAHs addition

10. Day 1-3: bacterial abundance decrease in all the mesocosms Day 3: bacterial production is higher in H than in C Day 4-8: bacterial abundance and production is lower in H than in C Bacterial abundance and production

11. -No significant differences in bacterial composition between C and H mesocosms -CTB and  -proteobacteria dominate the bacterial community -Cycloclasticus spp is undetectable. Bacterial composition-Day 0 Alfa (20%) CTB (35%) Gamma (10%) Cypu (<1%) 10  m Control

12. -Total detection is low in both C and L mesocosms (<50%) -Cycloclasticus spp comprise 7% of the total bacterial community in H mesocosms Bacterial composition-Day 4 Alfa (10%) CTB (20%) Gamma (20%) Cypu (7%) 10  m High * *

13. Control High CTB and Alfa Dominate in C Bacterial composition-Day 8 Alfa (30%) CTB (60%) Gamma (15%) Cypu (n.d.) Alfa (15%) CTB (50%) Gamma (30%) Cypu (1%) 10  m CTB and Gamma Dominate in H *

14. PAHs concentration and Cycloclasticus abundance PAHs addition Day 1-4: PAHs concentration rapidly decrease, and Cycloclasticus abundance increase Day 4-8: PAHs concentration drop to the levels in C, and Cycloclasticus abundance decrease

15. Summary -Most of the PAHs disappeared within 3 days after the fuel addition. -Cycloclasticus abundance rapidly increased after the PAHs addition, reaching its maximum 3 days after the oil addition. -Cycloclasticus growth appears to be related to LMW PAHs degradation. -The bacterial community composition significantly changed 8 days after the oil addition: the  -Proteobacteria subclass predominate over  -Proteobacteria subclass.