Major and comparable roles for free-living and attached bacteria in the degradation of Phaeocystis-derived organic matter in Belgian coastal waters of the North Sea

Microbial degradation of Phaeocystls globosa colonies and their denved organic matter by free-living and attached bactena was investigated in Belg~an coastal waters dunng the s p n n g development of diatom-Phaeocystls colonies in 1994 Results obtained show concomitant evolution of hydrol y t ~c ectoprotease and P-ectoglucosidase ectoenzymatic activities with respect to the phytoplankton bloom, suggesting that the low biodegradability of Phaeocystls colonies leading to transient accumulations of Phaeocystls-denved material in the coastal North Sea was not due to a lag phase required for the induction of P-ectoglucosidase Up to 66',) of total bacterial b~omass was found attached to particles larger than 10 pm While occurring always In low abundance compared to free-living bactena both the average specific biomass and growth rate of particle-attached bactena were very high, i e 60 fg C cell ' and 0 28 h-', respectively Similarly s p e c ~f ~c ectoen7ymatic activities of particle-attached bactena were on average about 5 times higher than those charactensing free-living bactena Budget calculations show a 53 % contnbution of Phaeocystls-attached bactena to the mineralisation of Phaeocyst~s-associated production, i e a 53 47 % role for attached and free-living bacteria, respectively KEY WORDS. Phaeocystls degradation . Free-living and