Mk. Zdanowski et Fg. Figueiras, RELATIONSHIPS BETWEEN THE ABUNDANCE OF BACTERIA AND OTHER BIOTA AND THE HYDROGRAPHIC VARIABILITY IN THE RIA DE VIGO, SPAIN, Marine ecology. Progress series, 147(1-3), 1997, pp. 257-267
Hydrographic variability driven by changes in wind speed and direction
and by meteorological parameters, such as incoming solar radiation, f
luvial discharges, and temperature, affects biological standing stocks
(e.g. of bacteria) in the marine environment. We studied the effects
of such parameters in the Ria de Vigo (Galicia, Spain), between Octobe
r 1990 and August 1991, where downwelling in winter results from predo
minantly poleward winds, whilst in summer upwelling is driven by winds
travelling towards the equator. Total bacterial abundance was strongl
y affected by physical factors in the Ria de Vigo. Almost 60% of the v
ariance in bacterial abundance in the surface layer could be explained
by an equation relating logTC [log(total count of heterotrophic bacte
rioplankton)] to incoming solar radiation, water temperature, run-off
and coastal upwelling, where solar radiation, water temperature and mo
derate upwelling are all positive terms, while run-off and strong upwe
lling act negatively. Consideration of biological variables such chlor
ophyll, ciliates and heterotrophic flagellates did not further explain
the variance. Physical factors, however, only accounted for 40% of th
e total variance in bacterial abundance at the bottom of the photic la
yer. The inclusion of biological variables in the regression equations
increased the explained variance to 55%; chlorophyll was the most imp
ortant of these variables and was positively related to logTC. This in
dicates that bacterial populations in the surface layer are mainly con
trolled by physical factors with a weak phytoplankton influence; howev
er, a stronger coupling between primary production and bacterial growt
h must exist at the bottom of the photic layer. Physical variables als
o explained 60 to 65% of the variance in cultivable spore-forming sapr
ophytic bacteria, but, in contrast to effects on total bacterial numbe
rs, run-off had a positive effect while moderate upwelling had a negat
ive influence on spore-forming numbers. This suggests that terrestrial
run-off has some ecological importance through the enrichment of near
shore bacterial populations with cells of terrestrial origin.