Biomass distribution and physiological capabilities of bacteria in the water column above a sea grass system.

The distribution pattern of bacteria in the water column above and within a Posidonia oceanica bed near Ischia (off the Gulf of Naples) was investigated and correlated with DOC and POM data for autumn and winter. Data from samples of 5 stations along a transect from shallow to deep showed rather low bacterial densities (10 super(4).ml super(-1)) for both seasons. The number of attached bacteria was higher in late winter as compared to autumn when the leaves are shed from the stands. Except for occasional peaks DOC ranged between 1.5 and 4.5 mg C/1 while POM concentrations ranged form 4 to 14 mg AFDW.1 super(-1). Hydrolytic capabilities of isolated bacterial colonies showed that more carbohydrate substrates could be fermented in winter as compared to autumn. This is correlated with an input of POM into the system due to the leaf fall of the seagrass which takes place in late autumn. The problem of structural carbohydrate breakdown is discussed.