(POM) amounting to 15% of the yearly production, resulting in extensive wrack beds on
the shore as well as along the edges and within the stands. During a one year study to
quantify seasonal variations of bacterial density in the water around a seagrass meadow
( Velimirov, in prep.), the bacteria from November samples and those from February (the
begin of the main growing season) were correlated to DOC and POM values and were
also tested for their fermentation capabilities. Since most of the wrack beds are progressively reduced in size until spring it is of interest to investigate whether the bacterial
population exhibits different hydrolytic properties in late autumn as compared to early
spring.
MATERIAL AND METHODS
The study area was located at the north coast of the island Ischia (Lacco Ameno), off the
Gulf of Naples in southern Italy. One liter water samples were taken with a PVC-syringe
from 5 stations along a line transect through a Posidonia meadow extending from 0.5 to
33 m depth. Station 1 to station 4 covered a range from 0 to 20 m depth in 5 m intervals,
station 5 was situated at 30 m depth. At all stations samples were taken from the water
surface as well as within and above the meadow at the proximity of the leaf tips. At
stations 2 to 5 additional samples were taken from the water column.
Total bacterial counts and cell volumes were determined using the method of Hobbie et
al. (1977). Additionally, subsamples of 150 ml were filtered through 0.2 µm nuclepore
polycarbonate filters for SEM observation of suspended particles and associated microbes. For the isolation of bacterial strains, two water samples were taken from 5 and 15 m
depth including suspended particulate matter. The samples were pooled in a sterile glass
bottle and kept dark at 6°C during transport. Plate cultures were prepared on ZoBell
Agar at 20°C and incubated for 72 hours. Only the colonies appearing within this time
were isolated and used for the inoculation of the specific media to perform routine
morphological and physiological tests. Working from the perimeter of the plate in a spiral
to the center, approximately 15% of the colonies were isolated and restreaked to purity.
Oxidative utilization of carbohydrates was indicated by acid formation under aerobic
conditions using a carbohydrate nutrient broth (modified after Hallmann and Burkhardt,
1974), containing phenol red as indicator.
To estimate the POM load of the same water samples 800 ml were filtered through
preashed (480°C) Watman GF/F filters (nominal pore size 0.7 µm) and then trough 0.2
µm Sartorius filters, dried to constant weight at 70°C and ashed at 480°C for 6 hours. 15
ml of the 0.2 µm filtered water were acidified with 2% HCl, sparged with synthetic CO2
free air for 10 to 15 minutes and injected into a total organic carbon analyser (Beckman
Tocamaster, Model 915-B) fitted with IR detector and calibrated with anhydrous potassium biphtalate in carbon free double distilled water. Dissolved free carbohydrates in the
same samples were determined according to Dawson and Liebezeit (1983).
RESULTS
The distribution pattern of DOC, POM and bacteria in November are shown in Figure 1.
Only slight variations occur in DOC, ranging from 1.5 to 3.2 mg/1, exept for station 4
where a peak of 31.3 mg/1 was recorded in the water column at 15 m. The samples taken
just above and within the meadow show that the water body between sediment bottom
and the leaf tip niveau is homogenous. A similar distribution pattern is noticed for POM,
which varies from 8 to 14 mg AFDW/1 over the entire depth range. A different situation is
evident in the case of the bacterial distribution. Densities vary from 0.5 x 10 4 to 4 x 104
130
the shore as well as along the edges and within the stands. During a one year study to
quantify seasonal variations of bacterial density in the water around a seagrass meadow
( Velimirov, in prep.), the bacteria from November samples and those from February (the
begin of the main growing season) were correlated to DOC and POM values and were
also tested for their fermentation capabilities. Since most of the wrack beds are progressively reduced in size until spring it is of interest to investigate whether the bacterial
population exhibits different hydrolytic properties in late autumn as compared to early
spring.
MATERIAL AND METHODS
The study area was located at the north coast of the island Ischia (Lacco Ameno), off the
Gulf of Naples in southern Italy. One liter water samples were taken with a PVC-syringe
from 5 stations along a line transect through a Posidonia meadow extending from 0.5 to
33 m depth. Station 1 to station 4 covered a range from 0 to 20 m depth in 5 m intervals,
station 5 was situated at 30 m depth. At all stations samples were taken from the water
surface as well as within and above the meadow at the proximity of the leaf tips. At
stations 2 to 5 additional samples were taken from the water column.
Total bacterial counts and cell volumes were determined using the method of Hobbie et
al. (1977). Additionally, subsamples of 150 ml were filtered through 0.2 µm nuclepore
polycarbonate filters for SEM observation of suspended particles and associated microbes. For the isolation of bacterial strains, two water samples were taken from 5 and 15 m
depth including suspended particulate matter. The samples were pooled in a sterile glass
bottle and kept dark at 6°C during transport. Plate cultures were prepared on ZoBell
Agar at 20°C and incubated for 72 hours. Only the colonies appearing within this time
were isolated and used for the inoculation of the specific media to perform routine
morphological and physiological tests. Working from the perimeter of the plate in a spiral
to the center, approximately 15% of the colonies were isolated and restreaked to purity.
Oxidative utilization of carbohydrates was indicated by acid formation under aerobic
conditions using a carbohydrate nutrient broth (modified after Hallmann and Burkhardt,
1974), containing phenol red as indicator.
To estimate the POM load of the same water samples 800 ml were filtered through
preashed (480°C) Watman GF/F filters (nominal pore size 0.7 µm) and then trough 0.2
µm Sartorius filters, dried to constant weight at 70°C and ashed at 480°C for 6 hours. 15
ml of the 0.2 µm filtered water were acidified with 2% HCl, sparged with synthetic CO2
free air for 10 to 15 minutes and injected into a total organic carbon analyser (Beckman
Tocamaster, Model 915-B) fitted with IR detector and calibrated with anhydrous potassium biphtalate in carbon free double distilled water. Dissolved free carbohydrates in the
same samples were determined according to Dawson and Liebezeit (1983).
RESULTS
The distribution pattern of DOC, POM and bacteria in November are shown in Figure 1.
Only slight variations occur in DOC, ranging from 1.5 to 3.2 mg/1, exept for station 4
where a peak of 31.3 mg/1 was recorded in the water column at 15 m. The samples taken
just above and within the meadow show that the water body between sediment bottom
and the leaf tip niveau is homogenous. A similar distribution pattern is noticed for POM,
which varies from 8 to 14 mg AFDW/1 over the entire depth range. A different situation is
evident in the case of the bacterial distribution. Densities vary from 0.5 x 10 4 to 4 x 104
130